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Yoseph Imry

Publications and source records attributed to Yoseph Imry.

At least 19 recordsLinked to original sources
arXiv2020

Unconventional four-terminal thermoelectric transport due to inelastic transport: cooling by transverse current, transverse thermoelectric effect and Maxwell demon

We show that in mesoscopic four-terminal thermoelectric devices with two electrodes (the source and the drain) and two heat baths, inelastic scattering processes can lead to unconventional thermoelectric transport. The source (or the drain) can be cooled by passing a thermal current between the two heat baths, with no net heat exchange between the heat baths and the electrodes. This effect, termed as cooling by heat current, is a mesoscopic heat drag effect. In addition, there is a transverse thermoelectric effect where electrical current and power can be generated by a transverse temperature bias (i.e., the temperature bias between the two heat baths). This transverse thermoelectric effect, originates from inelastic scattering processes, may have advantages for improved figures of merit and power factor due to spatial separation of charge and heat transport. We study the Onsager current-affinity relations, the linear-response transport properties, and the transverse thermoelectric figure of merit of the four-terminal thermoelectric devices for various system parameters. In addition, we investigate the efficiency and power of the cooling by transverse current effect in both linear and nonlinear transport regimes. We also demonstrate that by exploiting the inelastic transport in the quantum-dot four-terminal systems, a type of Maxwell's demon can be realized using nonequilibrium heat baths.

cond-mat.mes-hall↗
arXiv2020

The effect of interactions and disorder on the relaxation of two-level systems in amorphous solids

At low temperatures the dynamical degrees of freedom in amorphous solids are tunnelling two-level systems (TLSs). Concentrating on these degrees of freedom, and taking into account disorder and TLS-TLS interactions, we obtain a "TLS-glass", described by the random field Ising model with random $1/r^3$ interactions. In this paper we perform a self consistent mean field calculation, previously used to study the electron-glass (EG) model [A.~Amir {\it et al.}, Phys. Rev. B {\bf 77}, 165207, (2008)]. Similar to the electron-glass, we find $\frac{1}λ$ distribution of relaxation rates $λ$, leading to logarithmic slow relaxation. However, with increased interactions the EG model shows slower dynamics whereas the TLS glass model shows faster dynamics. This suggests that given system specific properties, glass dynamics can be slowed down or sped up by the interactions.

cond-mat.dis-nn↗
arXiv2019

Thermal conductance of one dimensional disordered harmonic chains

We study heat conduction mediated by longitudinal phonons in one dimensional disordered harmonic chains. Using scaling properties of the phonon density of states and localization in disordered systems, we find non-trivial scaling of the thermal conductance with the system size. Our findings are corroborated by extensive numerical analysis. We show that a system with strong disorder, characterized by a `heavy-tailed' probability distribution, and with large impedance mismatch between the bath and the system satisfies Fourier's law. We identify a dimensionless scaling parameter, related to the temperature scale and the localization length of the phonons, through which the thermal conductance for different models of disorder and different temperatures follows a universal behavior.

cond-mat.dis-nn↗
arXiv2018

High Temperature Superconductivity: A Simple Model Exploiting Hydrogen Bonds

Lately, there has been much interest in high temperature superconductors, and more recently hydrogen-based superconductors. This work offers a simple model which explains the behavior of the superconducting gap based on BCS theory, and reproduces most effects seen in experiments, including the isotope effect and T_c enhancement as a function of pressure. We show that this is due to a combination of the factors appearing in the gap equation: the matrix element between the proton states, and the level splitting of the proton.

cond-mat.supr-con↗
arXiv2018

Near-field three-terminal thermoelectric heat engine

We propose a near-field inelastic thermoelectric heat engine where quantum-dots are used to effectively rectify the charge flow of photo-carriers. The device converts near-field heat radiation into useful electrical power. Heat absorption and inelastic transport can be enhanced by introducing two continuous spectra separated by an energy gap. The thermoelectric transport properties of the heat engine are studied in the linear-response regime. Using a small band-gap semiconductor as the absorption material, we show that the device achieves very large thermopower and thermoelectric figure-of-merit, as well as considerable power-factor. By analyzing thermal-photo-carrier generation and conduction, we reveal that the Seebeck coefficient and the figure of merit have oscillatory dependence on the thickness of the vacuum gap. Meanwhile, the power-factor, the charge and thermal conductivity are significantly improved by near-field radiation. Conditions and guiding principles for powerful and efficient thermoelectric heat engines are discussed in details.

cond-mat.mes-hall↗
arXiv2018

Thermal conductivity in 1d: disorder-induced transition from anomalous to normal scaling

It is well known that the contribution of harmonic phonons to the thermal conductivity of 1D systems diverges with the harmonic chain length $L$ (explicitly, increases with $L$ as a power-law with a positive power). Furthermore, within various one-dimensional models containing disorder it was shown that this divergence persists, with the thermal conductivity scaling as $\sqrt{L}$ under certain boundary conditions, where $L$ is the length of the harmonic chain. Here we show that when the chain is weakly coupled to the heat reservoirs and there is strong disorder this scaling can be violated. We find a weaker power-law dependence on $L$, and show that for sufficiently strong disorder the thermal conductivity stops being anomalous -- despite both density-of-states and the diverging localization length scaling anomalously. Surprisingly, in this strong disorder regime two anomalously scaling quantities cancel each other to recover Fourier's law of heat transport.

cond-mat.dis-nn↗
arXiv2017

Enhancing Thermoelectric Performance Using Nonlinear Transport Effects

We study nonlinear transport effects on the maximum efficiency and power for both inelastic and elastic thermoelectric generators. The former refers to phonon-assisted hopping in double quantum-dots, while the latter is represented by elastic tunneling through a single quantum-dot. We find that nonlinear thermoelectric transport can lead to enhanced efficiency and power for both types of devices. A comprehensive survey of various quantum-dot energy, temperature, and parasitic heat conduction reveals that the nonlinear transport induced improvements of the maximum efficiency and power are overall much more significant for inelastic devices than the elastic devices, even for temperature biases as small as $T_h=1.2T_c$ ($T_h$ and $T_c$ are the temperatures of the hot and cold reservoirs, respectively). The underlying mechanism is revealed as due to the fact that, unlike the Fermi distribution, the Bose distribution is not bounded when the temperature bias increases. A large flux density of absorbed phonons leads to great enhancement of the electrical current, the output power, and the energy efficiency, dominating over the concurrent increase of the parasitic heat current. Our study reveals that nonlinear transport effects can be a useful tool for improving thermoelectric performance.

cond-mat.mes-hall↗
arXiv2017

Reduction of electron repulsion and enhancement of $T_{c}$ in small diffusive superconducting grains

The superconducting properties of small metallic grains has been a topic of active research for half a century now. Early experiments demonstrated a remarkable rise in the critical temperature, $T_{c}$, with reducing grain size in a variety of materials. In two dimensional diffusive superconductors, $T_{c}$ is decreased due to enhanced Coulomb repulsion. We propose that in finite size grains, the diffusive enhancement of the Coulomb repulsion is weakened and leads ultimately to an increase in $T_{c}$ in isolated, disordered two dimensional grains. Our mechanism is superimposed on the possible enhancement in $T_{c}$ due to the change in the density of states of finite size systems.

cond-mat.supr-con↗
arXiv2016

Linear and Nonlinear Mesoscopic Thermoelectric Transport with Coupling to Heat Baths

Decades of research on thermoelectrics stimulated by the fact that nano- and meso-scale thermoelectric transport could yield higher energy conversion efficiency and output power has recently uncovered a new direction on inelastic thermoelectric effects. We introduce the history, motivation, and perspectives on mesoscopic inelastic thermoelectric effects.

cond-mat.mes-hall↗
arXiv2015

Phonon-thermoelectric transistors and rectifiers

We describe nonlinear phonon-thermoelectric devices where charge current and electronic and phononic heat currents are coupled, driven by voltage and temperature biases, when phonon-assisted inelastic processes dominate the transport. Our thermoelectric transistors and rectifiers can be realized in a gate-tunable double quantum-dot system embedded in a nanowire which is realizable within current technology. The inelastic electron-phonon scattering processes are found to induce pronounced charge, heat, and cross rectification effects, as well as a thermal transistor effect that, remarkably, can appear in the present model even in the linear-response regime without relying on negative differential thermal conductance.

cond-mat.mes-hall↗
arXiv2015

Superconducting fluctuations--Large Diamagnetism of Low $T_c$ Nanoparticles

It is shown that nanoparticles made of low $T_c$ superconductors have large diamagnetic response at temperatures several orders of magnitude above $T_c$. Most features of the recently observed Giant diamagnetism of Au nanorods are explained in terms of superconducting fluctuations, except for the huge magnitude of the effect.

cond-mat.mes-hall↗
arXiv2013

Memory Effects in the Electron Glass

We investigate theoretically the slow non-exponential relaxation dynamics of the electron glass out of equilibrium, where a sudden change in carrier density reveals interesting memory effects. The self-consistent model of the dynamics of the occupation numbers in the system successfully recovers the general behavior found in experiments. Our numerical analysis is consistent with both the expected logarithmic relaxation and our understanding of how increasing disorder or interaction slows down the relaxation process, thus yielding a consistent picture of the electron glass. We also present a novel finite size "domino" effect where the connection to the leads affects the relaxation process of the electron glass in mesoscopic systems. This effect speeds up the relaxation process, and even reverses the expected effect of interaction; stronger interaction then leading to a faster relaxation.

cond-mat.dis-nn↗
arXiv2013

Three-terminal semiconductor junction thermoelectric devices: improving performance

A three-terminal thermoelectric device based on a $p$-$i$-$n$ semiconductor junction is proposed, where the intrinsic region is mounted onto a, typically bosonic, thermal terminal. Remarkably, the figure of merit of the device is governed also by the energy distribution of the {\em bosons} participating in the transport processes, in addition to the electronic one. An enhanced figure of merit can be obtained when the relevant distribution is narrow and the electron-boson coupling is strong (such as for optical phonons). We study the conditions for which the figure of merit of the three-terminal junction can be greater than those of the usual thermoelectric devices made of the same material. A possible setup with a high figure of merit, based on Bi$_2$Te$_3$/Si superlattices, is proposed.

cond-mat.mes-hall↗
arXiv2013

Emergent percolation length and localization in random elastic networks

We study, theoretically and numerically, a minimal model for phonons in a disordered system. For sufficient disorder, the vibrational modes of this classical system can become Anderson localized, yet this problem has received significantly less attention than its electronic counterpart. We find rich behavior in the localization properties of the phonons as a function of the density, frequency and the spatial dimension. We use a percolation analysis to argue for a Debye spectrum at low frequencies for dimensions higher than one, and for a localization/delocalization transition (at a critical frequency) above two dimensions. We show that in contrast to the behavior in electronic systems, the transition exists for arbitrarily large disorder, albeit with an exponentially small critical frequency. The structure of the modes reflects a divergent percolation length that arises from the disorder in the springs without being explicitly present in the definition of our model. Within the percolation approach we calculate the speed-of-sound of the delocalized modes (phonons), which we corroborate with numerics. We find the critical frequency of the localization transition at a given density, and find good agreement of these predictions with numerical results using a recursive Green function method adapted for this problem. The connection of our results to recent experiments on amorphous solids are discussed.

cond-mat.dis-nn↗
arXiv2012

Straightforward quantum-mechanical derivation of the Crooks fluctuation theorem and the Jarzynski equality

We obtain the Crooks and the Jarzynski non-equilibrium fluctuation relations using a direct quantum-mechanical approach for a finite system that is either isolated or coupled not too strongly to a heat bath. These results were hitherto derived mostly in the classical limit. The two main ingredients in the picture are the time-reversal symmetry and the application of the first law to the case where an agent performs work on the system. No further assumptions regarding stochastic or Markovian behavior are necessary, neither a master equation or a classical phase-space picture are required. The simplicity and the generality of these non-equilibrium relations are demonstrated, giving very simple insights into the Physics.

cond-mat.stat-mech↗
arXiv2012

Thermoelectric three-terminal hopping transport through one-dimensional nanosystems

A two-site nanostructure (e.g, a "molecule") bridging two conducting leads and connected to a phonon bath is considered. The two relevant levels closest to the Fermi energy are connected each to its lead. The leads have slightly different temperatures and chemical potentials and the nanos- tructure is also coupled to a thermal (third) phonon bath. The 3 x 3 linear transport ("Onsager") matrix is evaluated, along with the ensuing new figure of merit, and found to be very favorable for thermoelectric energy conversion.

cond-mat.mes-hall↗
arXiv2011

On relaxations and aging of various glasses

Slow relaxation occurs in many physical and biological systems. `Creep' is an example from everyday life: when stretching a rubber band, for example, the recovery to its equilibrium length is not, as one might think, exponential: the relaxation is slow, in many cases logarithmic, and can still be observed after many hours. The form of the relaxation also depends on the duration of the stretching, the `waiting-time'. This ubiquitous phenomenon iscalled aging, and is abundant both in natural and technological applications. Here, we suggest a general mechanism for slow relaxations and aging, which predicts logarithmic relaxations, and a particular aging dependence on the waiting-time. We demonstrate the generality of the approach by comparing our predictions to experimental data on a diverse range of physical phenomena, from conductance in granular metals, to disordered insulators, and dirty semiconductors, to the low temperature dielectric properties of glasses.

cond-mat.dis-nn↗