## ■Theoretical Quantum Physics Laboratory

A. Nishino

###
Akinori Nishino

(Associate Professor)

e-mail: nishino@kanagawa-u.ac.jp

03/2002, D.Sc., Graduate School of Science, The University of Tokyo

#### Research Field

#### Research Overview

#### Research Subjects

1. Scattering theory in open quantum systems.

2. Quantum transport in nanoscale devices.

3. Solvable models in quantum mechanics and statistical mechanics.

#### Introduction:

Nanoscience has attracted much interest in various fields of physics, chemistry, and engineering. In particular, quantum transport in nanoscale devices is a rapidly developing field of condensed matter physics. For devices smaller than the coherent length, quantum effects appear in the electron transport, which cannot be described by classical Ohm’s law. To analyze quantum transport theoretically, we must treat nonequilibrium steady states in open quantum systems. The Landauer formula can be used to calculate electrical conductance with the transmission eigenvalues of the scattering matrix, which implies that the nonequilibrium steady states are scattering eigenstates. However, the formula has been restricted to non-interacting cases.

We study the quantum transport of interacting electrons in open quantum systems. Let us consider the nanoscale device shown in Figure 1. The blue area in Figure 1 is negatively charged, and hence electrons are localized in the small area indicated by the dashed green circle, which is called a quantum dot (QD). We must consider the Coulomb repulsion for the electrons localized in the QD. Recently, we have proposed an extension of the Landauer formula for these QD systems that include interactions. Through constructing exact many-electron scattering eigenstates, we have obtained an analytical form of the average electric current for the interacting resonant-level model under bias voltages. Figure 2 shows the I-V curve of the average electric current. The electric current is suppressed for large bias voltages, which is the negative differential conductance originating from the Coulomb interaction.

##### Publications

- 1) A. Nishino, N. Hatano and G. Ordonez, “Exact scattering eigenstates in double quantum-dot systems with an interdot Coulomb interaction,” Journal of Physics: Conference Series, vol. 670, pp. 012038-1-15 (2016).
- 2) A. Nishino, N. Hatano, and G. Ordonez, “Universal electric current of interacting resonant-level models with asymmetric interactions: An extension of the Landauer formula,” Physical Review B, vol. 91, pp. 045140-1-11 (2015).
- 3) A. Nishino, T. Imamura, and N. Hatano, “Exact many-electron scattering states in a parallel-coupled double quantum-dot system,” Journal of Physics: Conference Series, vol. 343, pp. 012087-1-7 (2012).
- 4) A. Nishino, T. Imamura, and N. Hatano, “I-V characteristics of an open quantum dot with a Coulomb interaction: Extension of the Landauer formula with exact scattering eigenstates,” Physical Review B, vol. 83, pp. 035306-1-17 (2011).

##### Affiliated Academic Organizations

A. Nishino: The Physical Society of Japan.

##### Current members

◯ Associate Professors: 1 | ◯ Undergraduates: 8 |