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理論・ナノサイエンス合同セミナー

日程 : 2023年10月31日(火) 15:00 - 17:00 場所 : 物性研究所本館6階 第5セミナー室 (A615) 世話人 : 加藤岳生(63255) / 橋坂昌幸 (63305)講演言語 : 英語

Lecture1 15:00~
Coherent few-electron states in interacting low-dimensional systems

Lecturer : Dr. Flavio Ronetti
Affiliation : Centre de Physique Théorique, CNRS

The on-demand generation of single- and few-electron states in mesoscopic systems has opened the way to the fascinating field of electron quantum optics (EQO), where individual fermionic quantum states are manipulated with methods borrowed from photonic quantum-optical experiments. In this framework, a train of Lorentzian voltage pulses represents one of the most reliable experimental protocol to inject coherent single-electronic states, known as Levitons, into ballistic channels of meso-scale devices. These fascinating results open up the possibility of investigating the dynamics of single-electron states in one-dimensional systems. Indeed, it is well known that, in contrast with photons, electronic systems are drastically affected by electron-electron correlations. In this talk, we will discuss how the propagation of Levitons is affected by the presence of correlations between electrons and how these effects can be exploited in potential applications for quantum electronics and quantum information.

 

Lecture2 15:50~
Andreev-like reflection in the Pfaffian fractional quantum Hall effect

Lecturer : 大橋 良伊 氏
Affiliation : 大阪大学基礎工学研究科

In the edge of a fractional quantum Hall state and an integer quantum Hall state point contact, Andreev-like reflection occurs similar to superconducting Andreev reflection [1]. This reflection scenario is due to a mismatch between fractional charge ve and normal charge e. Recently, Andreev-like reflection has been detected for the Laughlin fractional quantum Hall system [2]. We study tunnel transport between the edge of a Pfaffian fractional quantum Hall state and that of an integer quantum Hall state [3]. Based on the duality argument between strong and weak tunnelings, we find that Andreev-like reflection appears for a strong tunneling regime with fractional charge e/4. We also evaluate charge conductance in the weak and strong tunneling regimes for the low-voltage limit.

[1] N. P. Sandler, C.C. Chamon, and E. Fradkin, Phys. Rev. B 57, 12324 (1998).
[2] M. Hashisaka, T. Jonckheere et al., Nat. Commun. 12, 2794 (2021).
[3] RO, R. Nakai, T. Yokoyama et al., J. Phys. Soc. Jpn. 91, 123703 (2022).

 

Lecture3 16:25~
Pairing symmetry of Josephson current flowing through a spin-polarized quantum anomalous Hall insulator

Lecturer : 仲井 良太 氏
Affiliation : 九州大学理学研究院

Superconducting proximity effect for topological materials works effectively in engineering topological electronic structures [1]. However, this is not the case for quantum (anomalous) Hall insulators as time-reversal partners of the chiral edge modes are absent. In this talk, I will discuss a Josephson junction through a spin-polarized quantum anomalous Hall insulator [2], which is robust against the proximity effect and hence is a highly opaque conductor of spin-singlet Cooper pairs. We showed that supercurrent in this system is carried by Cooper pairs with (i) equal-spin triplet, (ii) a combination of even and odd frequencies, and (iii) a finite momentum (the Fulde-Ferrell state). Experimentally, these features can be examined by the Josephson effect. Specifically, we showed that the triplet spins can be detected by the interface-magnetization dependence of the equilibrium phase difference, and the Cooper-pair momentum can be detected by the width dependence of the critical current.

[1] L. Fu and C. L. Kane, Phys. Rev. Lett. 100, 096407 (2008); A. R. Akhmerov, J. Nilsson, and C. W. J. Beenakker, Phys. Rev. Lett. 102, 216404 (2009).
[2] RN, K. Nomura, and Y. Tanaka, Phys. Rev. B 103, 184509 (2021).


(公開日: 2023年10月13日)