Nonequilibrium Kubo Formula of Finite Conductor Connected to Reservoirs based on Keldysh Formalism

Superconductive proximity effect in interacting disordered conductors

We present a general theory of the superconductive proximity effect in disordered normal--superconducting (N-S) structures, based on the recently developed Keldysh action approach. In the case of the absence of interaction in the normal conductor we reproduce known results for the Andreev conductance G_A at arbitrary relation between the interface resistance R_T and the diffusive resistance R_D. In two-dimensional N-S systems, electron-electron interaction in the Cooper channel of normal conductor is shown to strongly affect the value of G_A as well as its dependence on temperature, voltage an…

Obtaining localization properties efficiently using the Kubo-Greenwood formalism

We establish, through numerical calculations and comparisons with a recursive Green's function based implementation of the Landauer-Büttiker formalism, an efficient method for studying Anderson localization in quasi-one-dimensional and two-dimensional systems using the Kubo-Greenwood formalism. Although the recursive Green's function method can be used to obtain the localization length of a mesoscopic conductor, it is numerically very expensive for systems that contain a large number of atoms transverse to the transport direction. On the other hand, linear-scaling has been achieved with the Ku…

Which Kubo formula gives the exact conductance of a mesoscopic disordered system?

In both research and textbook literature one often finds two ``different'' Kubo formulas for the zero-temperature conductance of a non-interacting Fermi system. They contain a trace of the product of velocity operators and single-particle (retarded and advanced) Green operators: $\text{Tr} (\hat{v}_x \hat{G}^r \hat{v}_x \hat{G}^a)$ or $\text{Tr} (\hat{v}_x \text{Im} \hat{G} \hat{v}_x \text{Im} \hat{G})$. The study investigates the relationship between these expressions, as well as the requirements of current conservation, through exact evaluation of such quantum-mechanical traces for a nanosca…

速度规范Keldysh形式中的二阶直流电导率：非线性Drude、Berry曲率偶极子和量子度规响应的规范不变分解

Second-order dc conductivity in the velocity-gauge Keldysh formalism: gauge-invariant decomposition into nonlinear Drude, Berry-curvature-dipole, and quantum-metric responses

本文在速度规范Keldysh格林函数框架下，推导了多带紧束缚系统中二阶直流非线性电导率的规范不变清洁极限分解，将响应分为非线性Drude项、Berry曲率偶极子项和量子度规偶极子项，并展示了规范不变性。

Detection of finite frequency photo-assisted shot noise with a resonant circuit

Photo-assisted transport through a mesoscopic conductor occurs when an oscillatory (AC) voltage is superposed to the constant (DC) bias which is imposed on this conductor. Of particular interest is the photo assisted shot noise, which has been investigated theoretically and experimentally for several types of samples. For DC biased conductors, a detection scheme for finite frequency noise using a dissipative resonant circuit, which is inductively coupled to the mesoscopic device, was developped recently. We argue that the detection of the finite frequency photo-assisted shot noise can be achie…

Transport theory for interacting electrons connected to reservoirs

We describe microscopic theory for the quantum transport through finite interacting systems connected to noninteracting leads. It can be applied to small systems such as quantum dots, quantum wires, atomic chain, molecule, and so forth. The Keldysh formalism is introduced to study the nonlinear current-voltage characteristics, and general properties of the nonequilibrium Green's functions are provided. We apply the formulated to an out-of-equilibrium Anderson model that has been used widely for the Kondo effect in quantum dots. In the linear-response regime the Kubo formalism still has an adva…

Transport theory for disordered multiple-band systems: Anomalous Hall effect and anisotropic magnetoresistance

We present a study of transport in multiple-band non-interacting Fermi metallic systems based on the Keldysh formalism, taking into account the effects of Berry curvature due to spin-orbit coupling. We apply this formalism to a Rashba 2DEG ferromagnet and calculate the anomalous Hall effect (AHE) and anisotropic magnetoresistance (AMR). The numerical calculations reproduce analytical results in the metallic regime revealing the crossover between the skew scattering mechanism dominating in the clean systems and intrinsic mechanism dominating in the moderately dirty systems. As we increase the d…

拓扑绝缘体与自旋电子边界电磁学用于MRI射频线圈：一种理论框架用于损耗、噪声和互易性

Topological-Insulator and Spintronic Boundary Electrodynamics for MRI RF Coils: A Theoretical Framework for Loss, Noise, and Reciprocity

本文提出了一种理论框架，利用拓扑绝缘体和自旋电子学特性，改进MRI射频线圈的电磁学模型，以减少损耗、改变噪声机制并实现非互易性响应。