Transient Charge and Energy Flow in the Wide-Band Limit

Abstract

The wide-band limit is a commonly used approximation to analyze transport through nanoscale devices. In this work we investigate its applicability to the study of charge and heat transport through molecular break junctions exposed to voltage biases and temperature gradients. We find by comparative simulations that while the wide-band-limit approximation faithfully describes the long-time charge and heat transport, it fails to characterize the short-time behavior of the junction. In particular, we show that the charge current flowing through the device shows a discontinuity when a temperature gradient is applied, while the energy flow is discontinuous when a voltage bias is switched on and even diverges when the junction is exposed to both a temperature gradient and a voltage bias. We provide an explanation for this pathological behavior and propose two possible solutions to this problem.

Distinguishing Majorana zero modes from impurity states through time-resolved transport

“…The validity of WBA has been discussed in, e.g. [21,[103][104][105], and for the purpose of the present work (weak coupling of the central region to electrodes of large bandwidth), this is a well-justfied approximation. In frequency space the retarded Keldysh component of the embedding self-energy can then be written as…”

“…applying an external perturbation. In contrast, the nonequilibrium problems are often much richer and more interesting than equilibrium properties [20][21][22]. This is especially relevant when nowaday transport measurements are pushing the temporal resolution to sub-picosecond regime [23][24][25][26][27][28][29][30], and these ultrafast processes can be observed in real time.…”

Numerically exact full counting statistics of the energy current in the Kondo regime

“…The level width Γ is taken to be frequency independent, an additional approximation which could be easily removed, but is justified for the band width and shape used here. 47,109 In the presence of the counting field, the transition rates undergo the modification…”

“…In certain specific cases, quantum coherence effects have been shown to increase arXiv:1907.09546v1 [cond-mat.mes-hall] 22 Jul 2019 the thermal efficiency, 41 to exceed the Carnot efficiency and approach a perfect efficiency of 1, 42 to increase the power output 43 and to reduce fluctuations in the power. 44 Whereas it is possible to study nanoscale thermoelectricity within a single-particle approximation with Green's function [45][46][47] or DFT-based [48][49][50] methods, the effect of Kondo physics on the thermoelectric performance of devices is not fully understood beyond linear response. An exception is recent work based on the matrix product states method, which gives access to the current generated by a temperature bias in the Kondo regime.…”

Transient dynamics in interacting nanojunctions within self-consistent perturbation theory

“…On the theoretical side transport transient dynamics has been addressed using different methods valid for different regimes. Thus, the scattering approach or the non-equilibrium Green function formalism have been used for describing the dynamics in the coherent non-interacting regime [19][20][21][22][23][24][25][26][27][28][29][30]. However, the inclusion of interactions is essential to analyze the transport dynamics through localized states, as is the case of molecular junctions or semiconducting quantum dots.…”