Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic

Palma, Spain

Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic

Palma, Spain
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Hwang S.-Y.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Sanchez D.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Lopez R.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic
New Journal of Physics | Year: 2016

We propose a highly efficient thermoelectric diode device built from the coupling of a quantum dot with a normal or ferromagnetic electrode and a superconducting reservoir. The current shows a strongly nonlinear behavior in the forward direction (positive thermal gradients) while it almost vanishes in the backward direction (negative thermal gradients). Our discussion is supported by a gauge-invariant current-conserving transport theory accounting for electron-electron interactions inside the dot. We find that the diode behavior is greatly tuned with external gate potentials, Zeeman splittings or lead magnetizations. Our results are thus relevant for the search of novel thermoelectric devices with enhanced functionalities. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Hwang S.-Y.,Pohang University of Science and Technology | Hwang S.-Y.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Soo Lim J.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Soo Lim J.,Korea Institute for Advanced Study | And 5 more authors.
Applied Physics Letters | Year: 2013

We propose a two-terminal spin-orbit interferometer with a hot molecule inserted in one of its arms to generate pure spin currents. Local heating is achieved by coupling the vibrational modes of the molecule to a third (phononic) reservoir. We show that this spin caloritronic effect is due to the combined influence of spin-dependent wave interference and inelastic scattering. Remarkably, the device converts heat flow into spin-polarized current even without applying any voltage or temperature difference to the electronic terminals. © 2013 AIP Publishing LLC.


Hwang S.-Y.,Pohang University of Science and Technology | Hwang S.-Y.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Sanchez D.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Sanchez D.,University of the Balearic Islands | And 3 more authors.
New Journal of Physics | Year: 2013

Nonlinear transport coefficients do not obey, in general, reciprocity relations. We here discuss the magnetic-field asymmetries that arise in thermoelectric and heat transport of mesoscopic systems. Based on a scattering theory of weakly nonlinear transport, we analyze the leading-order symmetry parameters in terms of the screening potential response to either voltage or temperature shifts. We apply our general results to a quantum Hall antidot system. Interestingly, we find that certain symmetry parameters show a dependence on the measurement configuration. © IOP Publishing and Deutsche Physikalische Gesellschaft.


Khim H.,Korea University | Lopez R.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Lim J.S.,Korea Institute for Advanced Study | Lee M.,Kyung Hee University
European Physical Journal B | Year: 2015

We investigate the linear thermoelectric response of an interacting quantum dot side-coupled by one of two Majorana modes hosted by a topological superconducting wire. We employ the numerical renormalization group technique to obtain the thermoelectrical conductance L in the Kondo regime while the background temperature T, the Majorana-dot coupling Γm, and the overlap εm between the two Majorana modes are tuned. We distinguish two transport regimes in which L displays different features: the weak- (ΓmK) and strong-coupling (Γm>TK) regimes, where TK is the Kondo temperature. For an infinitely long nanowire where the Majorana modes do not overlap (εm = 0), the thermoelectrical conductance in the weak-coupling regime exhibits a peak at T ~ ΓmK. This peak is ascribed to the anti-Fano resonance between the asymmetric Kondo resonance and the zero-energy Majorana bound state. In the strong-coupling regime, on the other hand, the Kondo-induced peak in L is affected by the induced Zeeman splitting in the dot. For finite but small overlap (0 <εmm), the interference between the two Majorana modes restores the Kondo effect in a smaller energy scale Γ′m and gives rise to an additional peak in Γ ~ Γ′m, whose sign is opposite to that at T ~ Γm. In the strong-coupling regime this additional peak can cause a non-monotonic behavior of L with respect to the dot gate. Finally, in order to identify the fingerprint of Majorana physics, we compare the Majorana case with its counterpart in which the Majorana bound states are replaced by a (spin-polarized) ordinary bound state and find that the thermoelectric features for finite εm are the genuine effect of the Majorana physics. © 2015, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.


Lim J.S.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Lim J.S.,Korea Institute for Advanced Study | Lopez R.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Lopez R.,University of the Balearic Islands | And 2 more authors.
New Journal of Physics | Year: 2014

We discuss population imbalances between different orbital states due to applied thermal gradients. This purely thermoelectric effect appears quite generically in nanostructures with a pseudospin (orbital) degree of freedom. We define an orbital Seebeck coefficient that characterizes the induced orbital bias generated across a quantum conductor in response to a temperature difference applied to the attached reservoirs. We analyze a two-terminal strongly interacting quantum dot with two orbital states and find that the orbital thermopower acts as an excellent tool to describe the crossover between SU(4) and SU(2) Kondo states. Our conclusions are reinforced with a detailed comparison to the charge thermopower using exact numerical renormalization group calculations. © 2014 IOP Publishing and Deutsche Physikalische Gesellschaft.


Lim J.S.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Sanchez D.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Sanchez D.,University of the Balearic Islands | Lopez R.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Lopez R.,University of the Balearic Islands
AIP Conference Proceedings | Year: 2013

We present fluctuation relations that connect spin-polarized current and noise in mesoscopic conductors. In linear response, these relations are equivalent to the fluctuation-dissipation theorem that relates equilibrium current-current correlations to the linear conductance. More interestingly, in the weakly nonlinear regime of transport, these relations establish a connection between the leading-order rectification spin conductance, the spin noise susceptibility and the third cumulant of spin current fluctuations at equilibrium. Our results are valid even for systems in the presence of magnetic fields and coupled to ferromagnetic electrodes. © 2013 AIP Publishing LLC.


Alomar M.I.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Alomar M.I.,University of the Balearic Islands | Sanchez D.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Sanchez D.,University of the Balearic Islands
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We investigate the transport properties of a graphene layer in the presence of Rashba spin-orbit interaction. Quite generally, spin-orbit interactions induce spin splittings and modifications of the graphene band structure. We calculate within the scattering approach the linear electric and thermoelectric responses of a clean sample when the Rashba coupling is localized around a finite region. We find that the thermoelectric conductance, unlike its electric counterpart, is quite sensitive to external modulations of the Fermi energy. Therefore, our results suggest that thermocurrent measurements may serve as a useful tool to detect nonhomogeneous spin-orbit interactions present in a graphene-based device. Furthermore, we find that the junction thermopower is largely dominated by an intrinsic term independently of the spin-orbit potential scattering. We discuss the possibility of canceling the intrinsic thermopower by resolving the Seebeck coefficient in the subband space. This causes unbalanced populations of electronic modes which can be tuned with external gate voltages or applied temperature biases. © 2014 American Physical Society.


Alomar M.I.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Serra L.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic | Sanchez D.,Institute Of Fisica Interdisciplinaria I Sistemes Complexos Ifisc Uib Csic
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We consider a spin-orbit-coupled two-dimensional electron system under the influence of a thermal gradient externally applied to two attached reservoirs. We discuss the generated voltage bias (charge Seebeck effect), spin bias (spin Seebeck effect), and magnetization-dependent thermopower (magneto-Seebeck effect) in the ballistic regime of transport at linear response. We find that the charge thermopower is an oscillating function of both the spin-orbit strength and the quantum well width. We also observe that it is always negative for normal leads. We carefully compare the exact results for the linear response coefficients and a Sommerfeld approximation. When the contacts are ferromagnetic, we calculate the spin-resolved Seebeck coefficient for parallel and antiparallel magnetization configuration. Remarkably, the thermopower can change its sign by tuning the Fermi energy. This effect disappears when the Rashba coupling is absent. Additionally, we determine the magneto-Seebeck ratio, which shows dramatic changes in the presence of a the Rashba potential. © 2015 American Physical Society.

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