Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC

Palma, Spain

Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC

Palma, Spain

Time filter

Source Type

Zitko R.,Jozef Stefan Institute | Zitko R.,University of Ljubljana | Lim J.S.,Korea Institute for Advanced Study | Lopez R.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

Hybrid semiconductor-superconductor systems are interesting melting pots where various fundamental effects in condensed-matter physics coexist. For example, when a quantum dot is coupled to a superconducting electrode two very distinct phenomena, superconductivity and the Kondo effect, compete. As a result of this competition, the system undergoes a quantum phase transition when the superconducting gap Δ is of the order of the Kondo temperature TK. The underlying physics behind such transition ultimately relies on the physics of the Anderson model where the standard metallic host is replaced by a superconducting one, namely the physics of a (quantum) magnetic impurity in a superconductor. A characteristic feature of this hybrid system is the emergence of subgap bound states, the so-called Yu-Shiba-Rusinov (YSR) states, which cross zero energy across the quantum phase transition, signaling a switching of the fermion parity and spin (doublet or singlet) of the ground state. Interestingly, similar hybrid devices based on semiconducting nanowires with spin-orbit coupling may host exotic zero-energy bound states with Majorana character. Both parity crossings and Majorana bound states (MBSs) are experimentally marked by zero-bias anomalies in transport, which are detected by coupling the hybrid device with an extra normal contact. We here demonstrate theoretically that this extra contact, usually considered as a nonperturbing tunneling weak probe, leads to nontrivial effects. This conclusion is supported by numerical renormalization-group calculations of the phase diagram of an Anderson impurity coupled to both superconducting and normal-state leads. We obtain this phase diagram for an arbitrary ratio ΔTK, which allows us to analyze relevant experimental scenarios, such as parity crossings as well as Kondo features induced by the normal lead, as this ratio changes. Spectral functions at finite temperatures and magnetic fields, which can be directly linked to experimental tunneling transport characteristics, show zero-energy anomalies irrespective of whether the system is in the doublet or singlet regime. We also derive the analytical condition for the occurrence of Zeeman-induced fermion-parity switches in the presence of interactions which bears unexpected similarities with the condition for emergent MBSs in nanowires. ©2015 American Physical Society


Sierra M.A.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC | Saiz-Bretin M.,Complutense University of Madrid | Saiz-Bretin M.,University of Warwick | Dominguez-Adame F.,Complutense University of Madrid | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

We investigate the nonequilibrium transport properties of a double quantum-dot system connected in parallel to two leads, including intradot electron-electron interaction. In the absence of interactions, the system supports a bound state in the continuum. This state is revealed as a Fano antiresonance in the transmission when the energy levels of the dots are detuned. Using the Keldysh nonequilibrium Green's-function formalism, we find that the occurrence of the Fano antiresonance survives in the presence of Coulomb repulsion. We give precise predictions for the experimental detection of bound states in the continuum. First, we calculate the differential conductance as a function of the applied voltage and the dot level detuning and find that crossing points in the diamond structure are revealed as minima due to the transmission antiresonances. Second, we determine the thermoelectric current in response to an applied temperature bias. In the linear regime, quantum interference gives rise to sharp peaks in the thermoelectric conductance. Remarkably, we find interaction-induced strong current nonlinearities for large thermal gradients that may lead to several nontrivial zeros in the thermocurrent. The latter property is especially attractive for thermoelectric applications. © 2016 American Physical Society.


Ludovico M.F.,FCEyN | Lim J.S.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC | Lim J.S.,Korea Institute for Advanced Study | Moskalets M.,Kharkiv Polytechnic Institute | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We analyze the time-dependent energy and heat flows in a resonant level coupled to a fermionic continuum. The level is periodically forced with an external power source that supplies energy into the system. Based on the tunneling Hamiltonian approach and scattering theory, we discuss the different contributions to the total energy flux. We then derive the appropriate expression for the dynamical dissipation, in accordance with the fundamental principles of thermodynamics. Remarkably, we find that the dissipated heat can be expressed as a Joule law with a universal resistance that is constant at all times. © 2014 American Physical Society.


Goncalves B.,Aix - Marseille University | Goncalves B.,University of Toulon | Sanchez D.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC
PLoS ONE | Year: 2014

We perform a large-scale analysis of language diatopic variation using geotagged microblogging datasets. By collecting all Twitter messages written in Spanish over more than two years, we build a corpus from which a carefully selected list of concepts allows us to characterize Spanish varieties on a global scale. A cluster analysis proves the existence of well defined macroregions sharing common lexical properties. Remarkably enough, we find that Spanish language is split into two superdialects, namely, an urban speech used across major American and Spanish citites and a diverse form that encompasses rural areas and small towns. The latter can be further clustered into smaller varieties with a stronger regional character. Copyright: © 2014 Gonçalves, Sanchez.


Ludovico M.F.,University of Buenos Aires | Lim J.S.,Korea Institute for Advanced Study | Moskalets M.,Kharkiv Polytechnic Institute | Arrachea L.,University of Buenos Aires | Sanchez D.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC
Journal of Physics: Conference Series | Year: 2014

We study time-dependent heat transport in systems composed of a resonant level periodically forced with an external power source and coupled to a fermionic continuum. This simple model contains the basic ingredients to understand time resolved energy exchange in quantum capacitors that behave as single particle emitters. We analyse the behaviour of the dynamic heat current for driving frequencies within the non-adiabatic regime, showing that it does not obey a Joule dissipation law. © Published under licence by IOP Publishing Ltd.


Sierra M.A.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC | Sanchez D.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC
Materials Today: Proceedings | Year: 2015

We analyze the heat current flowing across interacting quantum dots within the Coulomb blockade regime. Power can be generated by either voltage or temperature biases. In the former case, we find nonlinear contributions to the Peltier effect that are dominated by conventional Joule heating for sufficiently high voltages. In the latter case, the differential thermal conductance shows maxima or minima depending on the energy level position. Furthermore, we discuss departures from the Kelvin-Onsager reciprocity relation beyond linear response. © 2015.


Pilgram S.,Kantonsschule Frauenfeld | Sanchez D.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC | Lopez R.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2016

The efficiency of macroscopic heat engines is restricted by the second law of thermodynamics. They can reach at most the efficiency of a Carnot engine. In contrast, heat currents in mesoscopic heat engines show fluctuations. Thus, there is a small probability that a mesoscopic heat engine exceeds Carnot's maximum value during a short measurement time. We illustrate this effect using a quantum point contact as a heat engine. When a temperature difference is applied to a quantum point contact, the system may be utilized as a source of electrical power under steady state conditions. We first discuss the optimal working point of such a heat engine that maximizes the generated electrical power and subsequently calculate the statistics for deviations of the efficiency from its most likely value. We find that deviations surpassing the Carnot limit are possible, but unlikely. © 2016.


Ludovico M.F.,University of Buenos Aires | Ludovico M.F.,International Center for Advanced Studies | Moskalets M.,Kharkiv Polytechnic Institute | Sanchez D.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

We analyze the time-resolved energy transport and the entropy production in ac-driven quantum coherent electron systems coupled to multiple reservoirs at finite temperature. At slow driving, we formulate the first and second laws of thermodynamics valid at each instant of time. We identify heat fluxes flowing through the different pieces of the device and emphasize the importance of the energy stored in the contact and central regions for the second law of thermodynamics to be instantaneously satisfied. In addition, we discuss conservative and dissipative contributions to the heat flux and to the entropy production as a function of time. We illustrate these ideas with a simple model corresponding to a driven level coupled to two reservoirs with different chemical potentials. © 2016 American Physical Society.


Sierra M.A.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC | Sanchez D.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We investigate the nonlinear regime of charge and energy transport through Coulomb-blockaded quantum dots. We discuss crossed effects that arise when electrons move in response to thermal gradients (Seebeck effect) or energy flows in reaction to voltage differences (Peltier effect). We find that the differential thermoelectric conductance shows a characteristic Coulomb butterfly structure due to charging effects. Importantly, we show that experimentally observed thermovoltage zeros are caused by the activation of Coulomb resonances at large thermal shifts. Furthermore, the power dissipation asymmetry between the two attached electrodes can be manipulated with the applied voltage, which has implications for the efficient design of nanoscale coolers. © 2014 American Physical Society.


Pilgram S.,Kantonsschule Frauenfeld | Sanchez D.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC | Lopez R.,Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2015

The efficiency of macroscopic heat engines is restricted by the second law of thermodynamics. They can reach at most the efficiency of a Carnot engine. In contrast, heat currents in mesoscopic heat engines show fluctuations. Thus, there is a small probability that a mesoscopic heat engine exceeds Carnot's maximum value during a short measurement time. We illustrate this effect using a quantum point contact as a heat engine. When a temperature difference is applied to a quantum point contact, the system may be utilized as a source of electrical power under steady state conditions. We first discuss the optimal working point of such a heat engine that maximizes the generated electrical power and subsequently calculate the statistics for deviations of the efficiency from its most likely value. We find that deviations surpassing the Carnot limit are possible, but unlikely. © 2015 Elsevier B.V. All rights reserved.

Loading Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC collaborators
Loading Institute Fisica Interdisciplinar y Sistemas Complejos IFISC UIB CSIC collaborators