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Prof. Juan Carlos Cuevas  
 

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  • August 2nd, 2019: Our work showing that a protein junction can behave as a current switch has been highlighted in a cover in Angewandte Chemie. This work resulted from a collaboration with David Cahen's group (Weizmann Institute of Science, Israel) and Carlos Romero-Muñiz and Linda Zotti at UAM.
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  • July 26rd, (2019): My comment on the thermal radiation of subwavelength objects has been published in Nature Communications.

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  • December 12th, (2018): Víctor Fernández-Hurtado has been awarded by GEFES with the prize for the Best Theoretical Doctoral Thesis in Condensed Matter Physics 2018. Víctor made his doctoral thesis on "Theoretical description of radiative heat transfer: Exploring the limits of Planck law" under the supervision of Francisco J. Garcia-Vidal and myself. Congratulations Víctor!
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  • November 23rd, (2018): Our popular science book (in Spanish) "Las ideas que cambiaron el mundo" is now available for sale. Find all the details about it in: Las ideas que cambiaron el mundo.


  • October 8th, 2018: Opening of a PhD position in our group. For more info see: Announcement.
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  • September 20th, 2018: Our review on radiative heat transfer is now available in ACS Photonics.
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    Description of the work: Thermal radiation is one of the most universal physical phenomena and its study has played a key role in the history of modern physics. Our understanding of this subject has been traditionally based on Planck law, which in particular sets limits on the amount of thermal radiation that can be emitted or exchanged. However, recent advances in the field of radiative heat transfer have defied these limits and a plethora of novel thermal phenomena have been discovered, which in turn hold the promise to have an impact in technologies that make use of thermal radiation. Here, we review the rapidly growing field of radiative heat transfer paying special attention to the remaining challenges and identifying future research directions. In particular, we focus on the recent work on near-field radiative heat transfer including: (i) experimental advances, (ii) theory proposals to tune, actively control, and manage near-field thermal radiation, and (iii) potential applications. We also review the recent progress in the control of thermal emission of an object, with especial emphasis in its implications for energy applications, and in the understanding of far-field radiative heat transfer. Heat is becoming the new light and its understanding is opening many new research lines with great potential for applications.

  • July 6th, 2018: Our work on the super-Planckian far-field radiative heat transfer between 2D materials has been published today in ACS Photonics. This is a result of a collaboration with our department colleagues Antonio I. Fernández-Domínguez, Johannes Feist, and Francisco J. Garcia-Vidal. This contribution is part of the thesis work of Víctor Fernández-Hurtado.
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    Description of the work: Very recently we have predicted that the far-field radiative heat transfer between two macroscopic systems can largely overcome the limit set by Planck law if one of their dimensions becomes much smaller than the thermal wavelength, which around 10 microns at room temperature. To explore the ultimate limit of the far-field violation of Planck law, we present in this work a theoretical study of the radiative heat transfer between two-dimensional (2D) materials. We show that the far-field thermal radiation exchanged by two coplanar systems with a one-atom-thick geometrical cross section can be more than 7 orders of magnitude larger than the theoretical limit set by Planck law for blackbodies and can be comparable to the heat transfer of two parallel sheets at the same distance. In particular, we illustrate this phenomenon with different materials such as graphene, where the radiation can also be tuned by a external gate, and single-layer black phosphorus. In both cases the far-field radiative heat transfer is dominated by TE-polarized guiding modes, and surface plasmons play no role. Our predictions provide a new insight into the thermal radiation exchange mechanisms between 2D materials.

  • April 30th, 2018: Our work on the electron transport through Azurin monolayers has been published in PNAS.
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    Description of the work: Proteins play a fundamental role in numerous biological energy conversion processes such as photosynthesis, respiration, and a wide variety of enzymatic reactions. In recent years, redox proteins containing transition metal ion centers have been integrated into solid-state electronic junctions. The goal is to shed new light on the electron transfer mechanisms in these biomolecules, but also to investigate the possibility of using proteins as active elements in novel, bio-inspired electronic devices. In this context, recent experiments have shown that the electron transport through proteins can be surprisingly efficient. However, the origin of this efficiency and, in general, the underlying transport mechanisms remain largely unknown.

    We have now shed new light on this fundamental problem in a work published in the Proceedings of the National Academy of Sciences of USA (PNAS) in collaboration with the group of David Cahen (Weizmann Institute of Science, Rehovot, Israel). In this work, we report low-temperature (10 K) electron transport measurements via monolayer junction based on the blue copper protein Azurin that strongly suggest that quantum tunneling is the dominant charge transport mechanism. In particular, we show that weakening the protein-electrode coupling by introducing a spacer, one can switch the electron transport from off-resonant to resonant tunneling, which has never been reported before in protein-based junctions. Moreover, we identified vibronic features of the Cu(II) coordination sphere in the transport characteristics that show directly the active role of the metal ion in the resonant tunneling. These results illustrate how quantum mechanical effects may dominate electron transport via protein-based junctions.

  • February 6th, 2018: Our work on Peltier cooling in molecular junctions has been featured in the cover of the February issue of Nature Nanotechnology.
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    Our article was also praised in a nice editorial by the journal: A cool paper.

  • January 14th, 2018: Our work on Anisotropic Thermal Magnetoresistance has been published in ACS Photonics.
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    Description of the work: We predict in this work a huge anisotropic thermal magnetoresistance (ATMR) in the near-field radiative heat transfer between magneto-optical particles when the direction of an external magnetic field is changed with respect to the heat current direction. We illustrate this effect with the case of two InSb spherical particles where we find that the ATMR amplitude can reach values of up to 800% for a magnetic field of 5 T, which is many orders of magnitude larger than its spintronic analogue in electronic devices. This thermomagnetic effect could find broad applications in the fields of ultrafast thermal management as well as magnetic and thermal remote sensing.

  • January 8th, 2018: Our new work on the super-Planckian far-field radiative heat transfer has been published today in Physical Review B. This is a result of a collaboration with our department colleagues Antonio I. Fernández-Domínguez, Johannes Feist, and Francisco J. Garcia-Vidal. This contribution is part of the thesis work of Víctor Fernández-Hurtado.
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    Description of the work: Understanding heat exchange via thermal radiation is key for many areas of science and engineering. Radiative heat transfer between closely placed objects, with separations smaller than the thermal wavelength (around 10 microns at room temperature), is attracting a lot of attention because of the possibility to overcome the classical limit set by Planck law. However, in the far-field regime, when gaps are larger than the thermal wavelength, thermal radiation is supposed to be well understood and no super-Planckian heat transfer has been reported. In this work we present a theoretical analysis that demonstrates that the far-field radiative heat transfer between objects with dimensions smaller than the thermal wavelength can overcome the Planckian limit by orders of magnitude. We illustrate this phenomenon in micron-sized dielectric structures, the so-called suspended pads, that can be readily fabricated and tested with existing technology. Our work shows the dramatic failure of the classical theory to predict the far-field radiative heat transfer between micro- and nano-devices.

  • December 18th, 2017: Our new work on Peltier cooling in molecular junctions was published today in Nature Nanotechnology. This is again a result of our collaboration with Pramod Reddy and Edgar Meyhofer (University of Michigan) and our department colleague Linda A. Zotti.
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    [Image credit: Enrique Sahagún, Scixel]

    Description of the work: Thermoelectric cooling is based on the Peltier effect that consists in the generation of a reversible heat flow in response to the passage of an electrical current. Thus, depending on the direction of the electrical current in a junction, one can cool down an electrode at the expense of heating up the other one. Thermoelectric or Peltier coolers have many applications, especially in electronics, and they possess several advantages over conventional vapor-compression refrigeration systems, although they are typically less efficient than these latter ones. In the context of nanoscale systems, a lot of attention has been devoted to the study of thermoelectricity in molecular junctions with the hope, in particular, to increase the efficiency of Peltier cooling. However, in spite of the fact that a lot of progress has been made in probing related phenomena such as the Seebeck effect (the conversion of a temperature difference into an electrical current), the observation of Peltier cooling in molecular junctions has remained inaccessible thus far.

    We have now resolved this fundamental problem in a work published in Nature Nanotechnology that resulted from a close collaboration with the groups of Pramod Reddy and Edgar Meyhofer (University of Michigan) and with Linda A. Zotti (Department of Theoretical Condensed Matter Physics, Universidad Autónoma de Madrid). In this work, we report for the first time the direct observation of Peltier cooling in molecular junctions. This observation was possible due to the use of a novel experimental platform that combines conducting-probe atomic force microscopy with home-built calorimetric micro-devices with picowatt resolution. This platform, developed by our colleagues in Ann Arbor (Michigan, USA), enables the simultaneous measurement of electrical, thermoelectric and energy dissipation characteristics of molecular junctions. Using this platform, molecular junctions formed with gold electrodes and a variety of organic molecules were investigated. Such studies revealed not only the possibility to achieve molecular-based refrigeration, but they also showed the close relationship between heating or cooling and the transmission characteristics of these junctions. In particular, it was shown that the Peltier cooling can be tuned and optimized by an appropriate choice of the molecular architecture, and all this in exquisite agreement with density-functional-theory-based calculations performed in the framework of the Landauer approach for quantum coherent transport.

    The advances reported in this work are expected to stimulate the exploration of atomic- and molecular-scale thermal transport and the quantification of the thermoelectric figure of merit in a variety of interesting molecules, nanostructures and materials.

    You can also read about this story in Spanish in the press release of the Universidad Autonoma de Madrid.

  • August 1st, 2017: The second edition of our book "Molecular Electronics: An Introduction to Theory and Experiment" is now available. For more information, please visit: Molecular Electronics Book (2nd Edition).
    Molecular Electronic Book
    Second Edition of "Molecular Electronics" (July 2017)

  • May 15th, 2017: Our work on the radiative heat transfer between Si metasurfaces was published today in Physical Review Letters.

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  • March 17th, 2017: A Perspective about our paper on thermal conductance of atomic contacts was published today by Dvira Segal in Science 355, 1125 (2017).

  • February 16th, 2017: Our new work on quantized thermal transport in single-atom junctions was published today in Science. This is the result of my collaboration with Pramod Reddy and Edgar Meyhofer (University of Michigan) and Fabian Pauly and Peter Nielaba (University of Konstanz). This contribution was possible due to the hard work of several brilliant PhD students and post-docs: Longji Cui, Wonho Jeong, and Sunghoon Hur (University of Michigan), and Manuel Matt and Jan Klöckner (University of Konstanz).
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    [Image credit: Enrique Sahagún, Scixel]

    Description of the work: What does determine the heat flow through a single atom? This is the ultimate question in the field of nanoscale energy transport and its answer is crucial to establish the fundamental laws that should describe the thermal transport in a variety of nanoelectronic devices. In the context of electrical circuits, the atomic scale was first reached with the advent of metallic atomic-size contacts and single-molecule junctions in the 1990s. These systems constitute the ultimate limit of miniaturization and have emerged as an ideal playground to investigate quantum effects related to charge and energy transport. Thus for instance, in recent years it has been shown that transport properties of metallic atomic-size contacts such as the electrical conductance, shot noise, thermopower, or Joule heating are completely dominated by quantum effects, even at room temperature. However, the experimental study of thermal conduction in these atomic-scale systems continues to be a formidable challenge and it has remained elusive to date in spite of its fundamental interest.

    This basic open problem has now been resolved in our work published in Science in collaboration with the groups of Pramod Reddy and Edgar Meyhofer (University of Michigan) and Fabian Pauly and Peter Nielaba (University of Konstanz). In this work, our experimental colleagues made use of custom-designed picowatt-resolution calorimetric scanning probes to measure simultaneously the electrical and thermal conductance of gold and platinum atomic contacts all the way down to the single-atom level. The experiments reveal that the thermal conductance of gold single-atom junctions is quantized at room temperature in units of the universal thermal conductance quantum. They also show that the Wiedemann-Franz law relating thermal and electrical conductance is satisfied even in single-atom contacts, irrespective of the metal. On the other hand, we show that all these observations can be quantitatively explained within the Landauer picture for quantum coherent thermal transport. In particular, our calculations indicate that the observations described above are due to the fact that electrons dominate the thermal conductance in these metallic nanowires, and in the gold case electrons proceed ballistically through the contacts via fully open conduction channels.

    The experimental techniques developed by our colleagues in the University of Michigan in this work will enable the study of thermal transport in atomic chains and molecular junctions, which is key to investigating numerous fundamental issues that have remained inaccessible despite great theoretical interest.

    You can see a brief description of our work in the following video:

    You can also read about this story in Spanish in the press release of the Universidad Autonoma de Madrid, in English in the press release of the University of Michigan, and in German in the press release of the University of Konstanz. See also article in nanotechweb.org.


  • February 15th, 2017: Our new work on radiative heat transfer in the extreme near-field regime was published today in Nature Communications. This is again a result of our collaboration with Pramod Reddy and Edgar Meyhofer (University of Michigan) and our department colleagues Johannes Feist and Francisco J. Garcia-Vidal (Nanophotonics Group, UAM). This contribution is part of the thesis work of Víctor Fernández-Hurtado.
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    Description of the work: Radiative heat transfer between closely placed objects is attracting a lot attention for several reasons. First, recent experiments have finally verified the long-standing prediction that radiative heat transfer can be greatly enhanced over the classical far-field limit set by the Stefan-Boltzmann law for blackbodies if the gap between two objects is smaller than the thermal wavelength, which is of the order of 10 microns at room temperature This is possible due to the contribution of the near field in the form of evanescent waves (or photon tunneling). Second, this confirmation has triggered the hope that near-field radiative heat transfer could have an impact in different technologies that make use of thermal radiation such as thermophotovoltaics, thermal management, lithography, data storage, and thermal microscopy.

    In spite of the progress made in recent years in the understanding of thermal radiation at the nanoscale, several recent experiments exploring the radiative thermal transport in nanometric gaps have seriously questioned this understanding. In particular, measurements on two gold-coated surfaces with gap sizes in the range of 0.2-10 nm have suggested an extraordinarily large near-field enhancement more than 3 orders of magnitude larger than the predictions of fluctuational electrodynamics, which is presently the standard theory used for the description of near-field thermal radiation.

    We now propose a possible solution to this puzzle in a work published in Nature Communications in collaboration with the groups of Pramod Reddy and Edgar Meyhofer (University of Michigan) and Víctor Fernández-Hurtado, Johannes Feist, and Francisco J. Garcia-Vidal. In this work, we explore the radiative heat transfer in Ångström- and nanometer-sized gaps between an Au-coated scanning thermal microscopy probe and a planar Au substrate in an ultrahigh vacuum environment. Using the apparent tunneling barrier height as a measure of cleanliness, we found that upon systematically cleaning via plasma-cleaning or locally pushing the tip into the substrate by a few nanometers, the observed radiative conductances decreased from unexpectedly large values to extremely small ones, below the detection limit of the probe, as expected from our computational results obtained within the framework of fluctuational electrodynamics. These results suggest that the huge signal reported in recent experiments might be an artifact due to the presence of contaminants bridging the gap between the tip and the substrate, thus providing an additional path for heat transfer via conduction. Moreover, this work shows that it is possible to avoid the confounding effects of surface contamination and systematically study thermal radiation in Ångström- and nanometer-sized gaps.

  • January 19th, 2017: "The Oxford Handbook of Small Superconductors" was published by Oxford University Press. I have contributed to this monograph with a chapter on Proximity Superconductivity with my colleagues Dimitri Roditchev, Tristan Cren, and Christophe Brun of the Group of Spectroscopy of Novel Quantum States (Institut des Nanosciences de Paris and Universite Pierre et Marie Curie, Paris)
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  • February 12th, 2016: Blanca Caballero successfully defended her thesis on the "Theoretical description of wave propagation in magnetoplasmonic nanostructures". Congratulations Blanca!!

  • January 28th, 2016: A News and Views about our paper on extreme near-field radiative heat transfer [Nature 528, 387 (2015)] has now been published by David Pile in Nature Photonics 10, 79 (2016).
  • January 19th, 2016: Our work on hybrid nanohole arrays as plasmonic sensors with Blanca Caballero and A. García-Martín (IMM-CSIC, Madrid) has been published online in ACS Photonics.

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  • December 7th, 2015: Our work with our colleagues Pramod Reddy and Edgar Meyhofer (University of Michigan) and our department colleagues Johannes Feist and Francisco J. Garcia-Vidal (Nanophotonics Group, UAM) on the radiative heat transfer in the extreme near field has been published in Nature.

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    Description of the work: Radiative heat transfer between objects at different temperatures is of fundamental importance in applications such as energy conversion, thermal management, lithography, data storage, and thermal microscopy. It was predicted long ago that when the separation between objects is smaller than the thermal wavelength, which is of the order of 10 microns at room temperature, the radiative heat transfer could be greatly enhanced over the theoretical limit set by the Stefan-Boltzmann law for blackbodies. This is possible due to the contribution of the near field in the form of evanescent waves (or photon tunneling). In recent years, different experimental studies have confirmed this long-standing theoretical prediction. However, and in spite of this progress, recent experiments exploring the radiative thermal transport in nanometric gaps have seriously questioned our present understanding of thermal radiation at the nanoscale. In particular, these experiments cast some doubt on the validity of fluctuational electrodynamics, which is presently the standard theory for the description of near-field radiative heat transfer (NFRHT).

    This fundamental puzzle has now been resolved in our new work now published in Nature. This work, where Víctor Fernández-Hurtado has been the key person from our side, is the result of a close collaboration with our experimental colleagues in the University of Michigan led by Pramod Reddy and Edgar Meyhofer, with our department colleagues Johannes Feist and Francisco J. Garcia-Vidal (Nanophotonics Group, UAM), and with Homer Reid (MIT). In this work, our colleagues in Ann Arbor used scanning thermal probes with embedded thermocouples to measure the NFRHT between different materials (dielectrics and metals) down to gaps as small as 2 nm. In particular, they showed that heat transfer between silica-silica, silicon nitride-silicon nitride and gold-gold surfaces exhibits a dramatic enhancement as the gap is reduced down to a few nanometers. On the other hand, we performed state-of-the-art simulations using the framework of fluctuational electrodynamics and were able to reproduce all the experimental observations without any adjustable parameters. These results unambiguously demonstrate that fluctuational electrodynamics based on Maxwell equations provides an accurate description of the NFRHT between both metals and dielectrics all the way down to nanometer-size gaps. This work clarifies the fundamental mechanisms that govern the radiative heat transfer at the nanoscale and establishes a firm basis for the future design of novel technologies that make use of nanoscale radiative heat transfer.

    You can read more about our work in phys.org.

    You can also read about this story in Spanish in the press release of the Universidad Autonoma de Madrid.

  • November 3rd, 2015: Our work on the longitudinal MOKE in a 2D magneto-plasmonic crystal with the experimental group of Paolo Vavassori (CIC nanoGUNE, Donostia) has been published in ACS Photonics.

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  • Sept 14th, 2015: Our work on the magnetic field dependence of the near-field radiative heat transfer been published in Physical Review B.

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    Description of the work: Radiative heat transfer is a fundamental problem of great importance in numerous areas of science and engineering. Presently, a great effort is being devoted to the investigation of the radiative heat transfer between closely placed objects. In particular, recent experiments have shown that when objects are separated by a distance smaller than the thermal wavelength (around 10 microns at room temperature), they can exchange a huge amount of heat in the form of evanescent electromagnetic waves overcoming the fundamental limit set by the Stefan-Boltzmann law for black bodies. This fact has triggered the hope that near-field radiative heat transfer could have a great impact in numerous nanotechnologies that make use of heat transfer such as heat-assisted magnetic recording, scanning thermal microscopy or thermophotovoltaics. In this context, one of the main open problems is to figure out how to actively control the near field thermal radiation.

    In this work we report a detailed theoretical study of the effect of an external magnetic field in near field radiative heat transfer. We show that in a wide class of materials, namely polar and non-polar semiconductors, the application of an external field can greatly modify the radiative heat transfer providing a straightforward way to tune and modulate the near-field thermal radiation. More importantly, we show that the presence of a magnetic field radically changes the nature of the radiative heat transfer. In particular, we show that semiconductors under a magnetic field behave as ideal (and highly tuneable) hyperbolic materials. These materials are a special class of highly anisotropic optical materials that exhibit extraordinary properties such as negative refraction or subwavelength focusing and imaging, and their study is presently attracting a huge attention in the communities of metamaterials and photonics. Usually, hyperbolic materials are made of complex hybrid metamaterials whose properties are determined by the geometry and composition of the system. Amazingly, we now predict that bulk semiconductors can behave as hyperbolic materials whose properties can be easily tuned by an external magnetic field. In particular, we show that they constitute the simplest realization of near-field hyperbolic thermal emitters, a new class of emitters that is being intensively investigated from a theoretical point of view, but that it has not been yet realized experimentally. We believe that our work could change this situation.

  • July 2nd, 2015: Our work on single-molecule rectification with the group of Nicolás Agraït's group (Universidad Autónoma de Madrid) been published online in Nanotechnology.

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    Description of the work: Single-molecule rectification lies at the heart of the field of molecular electronics and its experimental realization is quite challenging. In this work, our experimental colleagues at UAM have demostrated large rectification ratios (> 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction. More importantly, by following the variation of the IV characteristics with the separation between the tip and the molecule, we have been able to unambiguously demostrate that rectification is due to asymmetric coupling to the electrodes of a molecule with an asymmetric level structure. In principle, this mechanism can be implemented in other type of molecular junctions using both organic and inorganic molecules and provides a simple strategy for the rational design of molecular diodes.

  • May 25th, 2015: My News and Views on Latha Venkataraman's work on single-molecule rectification has been published online in Nature Nanotechnology.

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  • February 23th, 2015: Our work with my colleagues Dimitri Roditchev, Tristan Cren, Christophe Brun and his coworkers in the Group of Spectroscopy of Novel Quantum States (Institut des Nanosciences de Paris and Universite Pierre et Marie Curie, Paris) has been published in Nature Physics.

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    Description of the work: When a normal metal is brought in contact with a superconductor, Cooper pairs may leak into the metal inducing genuine superconducting properties in it, an effect generically referred to as proximity effect. In particular, if a metal is sandwiched between two superconductors, it can sustain the flow of a dissipationless or Josephson current. When a magnetic is applied to a Josephson junction, the Josephson currents oscillate along the interface splitting up the junction into regions that enclose no net current, which are known as Josepshon vortices. Contrary to Abrikosov vortices in type II superconductors, the Josephson vortices are supposed to lack of a normal core (where the superconductivity is completely suppressed). However, in 2007 Sebastian Bergeret and myself predicted that if the weak link is made of a diffusive metal, the junctions can sustain Josephson vortices with true vortex cores inside the metal. In this work, we report the first direct observation of these proximity Josephson vortices. Our junctions are made of superconducting Pb nanoislands weakly linked by a normal (atomically thin) wetting layer of Pb, which is not superconducting. The Josephson vortices were imaged by means of a low-temperature scanning tunneling microscope, and they were revealed by the spatial modulation of the local density of state in the wetting layer induced by the magnetic field. Our results strongly suggest that it should be possible to induce these proximity vortices in novel quantum devices by purely electrical means. Moreover, we may anticipate the observation of these vortices in other superconducting weak links made of low-dimensional materials such a graphene.

  • February 23th, 2015: Our work with our colleagues Pramod Reddy and Edgar Meyhofer (University of Michigan) and our department colleagues Johannes Feist and Francisco J. Garcia-Vidal (Nanophotonics Group, UAM) on the near field radiative heat transfer in dielectric thin films has been published in Nature Nanotechnology.

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    Description of the work: Thermal radiation plays a major role in energy conversion, thermal management, and data storage. In recent years, several experiments on thermal radiation between bulk materials have demonstrated that radiative heat transfer can be greatly enhanced in nanoscale gaps. However, it was not clear whether such enhancements can be obtained with nanoscale films thinner than the penetration depth of radiation. In this work, our colleagues of the University of Michigan (the groups of Pramod Reddy and Edgar Meyhofer) have conducted near-field radiation experiments using a novel ultrasensitive calorimeter that demonstrate enhancements of several orders of magnitude in radiative heat transfer, even for ultra thin dielectric films (50 nm), at spatial separations comparable to or smaller than the film thickness. In collaboration with our department colleagues Johannes Feist and Francisco J. Garcia-Vidal (Nanophotonics Group, UAM), we explained these striking results making use of the theory of fluctuational electrodynamics. In particular, we showed that the near field radiative heat transfer in polar dielectric thin films is determined by the excitation of cavity surface phonon polaritons. These surface electromagnetic modes have characteristic penetration depths that are on the order the gap separating the receiver from the emitter. In practice, this implies that all the near field thermal radiation emitted by a polar material comes from its surface. Thus, the thermal emission of a polar thin film is independent of its thickness, as long as the gap between materials remains smaller than the film thickness. Our findings have important implications to a variety of future energy conversion and heat transfer nanotechnologies. It is worth stressing that this work has been part of the master thesis of Víctor Fernández-Hurtado, a new talented PhD student in our group.

    See also the accompanying News and Views by Mathieu Francoeur.

    You can also read about this story in Spanish in the press release of the Universidad Autonoma de Madrid.

    Our work has also been highlighted in different Spanish media: ABC, El Confidencial, ELDIA.es, Europapress.es.

  • January 24th, 2015: Our work with Nicolás Agraït's group (Universidad Autónoma de Madrid) and our colleagues Manuel Matt, Fabian Pauly, and Peter Nielaba (University of Konstanz) on the thermopower of metallic atomic-size contacts has been published in Nano Letters.

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    Description of the work: Thermoelectric devices hold the promise for helping to solve key problems related to energy conversion and refrigeration. The discovery that nanostructured materials may enhance their efficiency underlines the need to understand the mechanisms that govern thermoelectricity at the nanoscale. Although notable progress has been made in this respect, there remain basic open problems. Thus for instance, it is still unclear what determines the thermoelectricity in a metallic atomic-size contact, a system that has become a test bed for the fields of nanoelectronics, mesoscopic physics, and molecular electronics. In this work, we present a combined experimental and theoretical study of the room temperature thermopower of metallic atomic-size contacts. In particular, we report conductance and thermopower measurements of gold and platinum atomic contacts using a scanning tunneling microscope (STM). We find that few-atom gold contacts have an average negative thermopower, whereas platinum contacts present a positive thermopower, showing that for both metals, the sign of the thermopower in the nanoscale differs from that of bulk wires. We also find that the magnitude of the thermopower exhibits minima at the maxima of the conductance histogram in the case of gold nanocontacts while for platinum it presents large fluctuations. Making use of tight-binding calculations and Green function techniques, together with molecular dynamics simulations, we show in this work that these observations can be understood in the context of the Landauer-Büttiker picture of coherent transport in atomic-scale wires. In particular, we show that the differences in the thermopower between these two metals are due to the fact that the elastic transport is dominated by the 6s orbitals in the case of gold and by the 5d orbitals in the case of platinum.

  • October 26th, 2014: Our work with, among others, Danny Porath's group (The Hebrew University of Jerusalem) and Alexander Kotlyar's group (Tel Aviv University) on the long-range transport through single G4-DNA molecules has been published in Nature Nanotechnology.

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    Description of the work: Research into the charge transport mechanisms in single DNA molecules and their derivatives has been hindered by the inherent difficulty to form reliable electrical contacts with single molecules as well as by the absence of DNA derivatives that conduct over long distances when adsorbed on a substrate. In this work, we report on detailed and reproducible charge transport in G4-DNA adsorbed on a mica substrate. Making use of a novel benchmark process for testing molecular conductance in single polymer wires, we observed currents of tens to over 100 pA in many G4-DNA molecules over distances ranging from tens to over 100 nm, which we show to be compatible with a hopping mechanism. These results may re-ignite the interest in DNA-based wires and devices towards a practical implementation of DNA-based circuits assembled on a hard substrate.

    See also the accompanying News and Views by Elke Scheer.

    You can read more about our work in the press release of the The Hebrew University of Jerusalem.

    See also releases in phys.org, IEEE Spectrum, Amazing Science, or ScienceDaily.

    You can also read about this story in Spanish in the press release of the Universidad Autonoma de Madrid.

    Our work has also been highlighted in different Spanish media: La Vanguardia, La Razón Digital, elPeriódico, teinteresa.es, Diario Siglo XXI, Tendencias21, ElDía.es , elEconomista.es, El Confidencial, Catalunya Vanguardista, actualidad.es, YAHOO Noticias, SINC, medicinatv.com, etc.

  • March 13th, 2014: Our work with our colleagues of the Group of Spectroscopy of Novel Quantum States (Institut des Nanosciences de Paris and Universite Pierre et Marie Curie, Paris) has been published in Physical Review X.

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    Description of the work: When a metal and a superconductor are interfaced through a good electrical contact, the electronic properties of the metal in the vicinity of the interface are altered. This phenomenon, known as the proximity effect, has been investigated since the early 1960s. What happens when the two materials in electrical contact are both superconductors and the scale of the contact is atomic? This question takes on renewed importance and interest, because of its relevance to a great variety of hybrid electronic systems based on novel low-dimensional or small-scale materials, as well as the much greater technical possibilities of studying such systems. So far, however, experimental studies that address this question have been scarce. In this paper, we report the first demonstration of a proximity effect between two superconductors connected through an atomic-scale junction, which is resolved in real space experimentally by a very-low-temperature scanning tunneling microscope and quantitatively explained theoretically.

    The two superconductors in our system are a submicrometer island of single-crystal Pb and a crystalline monolayer Pb, with the former embedded in the latter. The electrical contact is provided by the atoms on the periphery of the island. Although both can be superconducting, the island becomes so at a much higher temperature than the monolayer, leaving a window of temperature within which the former is already superconducting and the latter still behaves like a normal metal. The density of electronic states in the vicinity of the interface, which we have mapped out with unprecedented 1-nm spatial and 30-meV energy resolutions, reveals a spectacular proximity effect in this temperature range: The region of induced superconductivity in the still metal-like Pb monolayer is many times bigger than what is typically seen in a normal nonsuperconducting metal. All our experimental observations have been quantitatively explained within the framework of the quasiclassical theory of superconductivity in the diffusive limit.

  • September 1st, 2013: Our work with our colleagues in the University of Konstanz (Christian Schirm, Manuel Matt, Fabian Pauly, Peter Nielaba and Elke Scheer) has been published online in Nature Nanotechnology.

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    [Image credit: Enrique Sahagún, Scixel]

    See also the accompanying News and Views by Sense Jan van der Molen.

    See also a nice article about our work from Katia Moskvitch in PhysicsWorld.

    You can also read a popular article about our work in 2physics.com.

    You can read more about this story in Spanish in the press release of the Universidad Autonoma de Madrid or in German in the press release of the University of Konstanz.

  • August 6th, 2013: Our work with the experimental group of Yoram Selzer and coworkers in the University of Tel Aviv and with Marius Buerkle (KIT, Karlsruhe) and Fabian Pauly (University of Konstanz) has been published in The Journal of Physical Chemistry Letters.

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  • June 13th, 2013: Our work with our colleagues in the University of Michigan (Ann Arbor, USA) and in the University of Konstanz (Germany) has been published today in Nature: "Heat dissipation in atomic-scale junctions", W. Lee, K. Kim, W. Jeong, L.A. Zotti, F. Pauly, J.C. Cuevas, and P. Reddy, Nature 498, 209 (2013).

    In this collaboration, we have investigated how the Joule heating takes place in atomic and molecular junctions, a fundamental issue for the fields of molecular electronics and quantum transport. In particular, our colleague Pramod Reddy and his coworkers fabricated novel scanning tunneling probes with integrated nanothermocouples. These ingenious probes allowed them to fabricate single-atom and single-molecule junctions, in the spirit of break-junction techniques, and at the same time to measure the temperature rise in the probe electrode due to the passage of an electrical current through the junctions. Moreover, with the help of the Landauer theory of quantum transport and ab initio calculations, we understood that the heat dissipation in the electrodes of a nanoscale device depends on its transmission characteristics and, in general, this dissipation is asymmetric --that is, unequal between the electrodes-- and also dependent on both the bias polarity and the identity of the majority charge carriers (electrons versus holes). We believe that our work paves the way for the study of the Peltier effect --the electrical cooling of a conductor--- at the atomic scale and it is also the first step towards the study of thermal transport through atomic and molecular junctions, which is presently one of the main challenges in nanoscience.

    You can read more about this story in the following press release of the University of Michigan: University of Michigan press release, or (in Spanish) in the following press release of our university: press release (UAM Gazette). Similar releases can be found in Engineering and Technology Magazine or in Science Daily. An interesting article about our work was written by the scientific journalist Katia Moskvitch and it was published in New Scientist.

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    [Image credit: Enrique Sahagún, Scixel]
  • October 22nd, 2012: Thanks to our course on Molecular Electronics imparted in the University of Konstanz in the winter semester of 2011-2012, Prof. Elke Scheer and myself have been awarded with the first "Tina-Ulmer-Lehrpreis" (Tina Ulmer Prize for Teaching) for our teaching performance. The foundation Science and Society in the University of Konstanz was created by Manfred Ulmer in 1979 and since then it has supported a good number young researchers in the University of Konstanz by means of different grants and prizes. Now, the family that runs the foundation has decided to also distinguish professors of the University of Konstanz for special teaching performance, and Elke Scheer will be the recipient of the first "Tina-Ulmer-Lehrpreis". This prize will be awarded in a special act in Donaueschingen on Friday 16th of November (2012).

    It is certainly a nice reward for our efforts to put forward an innovative and attractive lecture. In this respect, I want to thank here all the students that participated in that lecture for their engagement and enthusiasm. It really was a fun experience for me!!


  • September 12th, 2012: A very kind review of our book on Molecular Electronics written by Prof. Gianaurelio Cuniberti (Technical University of Dresden) has appeared today in Physik Journal. If you understand German, you can read the review in Physik Journal.


  • August 9th, 2012: Our work with our colleagues in Orsay on the magnetic field dependence of the critical current of a diffusive SNS junctions has been published in PRB. The experimental confirmation of a very nice prediction: a sweet moment for a theoretician! You can find the manuscript in Physical Review B.


  • August 7th, 2012: Our work with our colleagues in Uppsala on the influence of the magnetic field on the plasmonic properties of Ni anti-dot arrays has been published in APL. We are progressing quickly in the field of magnetoplasmonics! You can find the manuscript in Applied Physics Letters.


  • June 4th, 2012: Our first work on the propagation of electromagnetic waves in magneto-plasmonic nanostructures has been published in PRB. My first paper without hbar! You can find the paper in Physical Review B.


  • Oct 31st, 2011: Our work on the transport through noble gas atoms has been accepted in PRB (Brief Report). You can find the paper in arXiv 1110.6104.


  • December 14th, 2010: Our work on the transport through single-molecule junctions based on nitrile-terminated biphenyls has been published online in Journal of American Chemical Society.

    abstract-JACS


  • September 19th, 2010: Our paper on optical rectification in plasmonic nanogaps with our colleagues Dan Ward and Douglas Natelson (Rice University) and Falco Hüser and Fabian Pauly (Karlsruhe Institute of Technology) has been published online in Nature Nanotechnology.

    abstract-nnano1 abstract-nnano2


  • September 10th, 2010: Our paper on the theory of supercurrent in microwave-irradiated quantum point contacts with Sebastian Bergeret, Pauli Virtanen and Tero Heikkilä has been published in Physical Review Letters.

    microwave-PC


  • September 1st, 2010: Our book "Molecular Electronics: An Introduction to Theory and Experiment" with Elke Scheer (University of Konstanz) has been published in World Scientific!!

    Molecular Electronics Book


  • June 24th, 2010: Linda's paper on the role of anchoring groups in the electrical conduction through single-molecule junctions with our colleagues Artur Erbe and Elke Scheer (University of Konstanz) has been published in Small.

    abstract-Small


  • June 18th, 2010: Our paper on the theory of microwave-assisted supercurrent in diffusive SNS junctions with Pauli Virtanen, Sebastian Bergeret and Tero Heikkilä has been published in Physical Review Letters.

    microwave-sns