Theoretical Study of Superconducting Collective Excitations Taking Account of Various Frequency Dependences

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K05183
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Condensed matter physics II
• Research Institution: International Christian University
• Principal Investigator: HIRASHIMA DAI 国際基督教大学, 教養学部, 教授 (20208820)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 超伝導集団励起 / ヒッグスモード / 奇数振動数対 / 流体力学的領域 / 強結合超伝導 / 準1次元超流動 / 位相スリップ

Outline of Final Research Achievements

Superconducting collective modes are studied paying attention to various frequency dependence. First, the stability of odd-frequency pairing states is examined, but no stable bulk solution has been found. The possibility of coupling between the amplitude mode and external probes is studied not only for weak coupling superconducting state but also for strong coupling ones, where the frequency dependece of the orderparameter is important. However, no finite coupling has been found so far. From a general discussion, it is concluded that we should look at non-conserved quantities such as orbital-selective quantities to find a possible coupling of the amplitude mode.
Simulating a hard-core boson system on a quasi-one-dimensional lattice, it is shown that the superfluid density remains finite at finite temperatures even in the strongly one-dimensional limit if the effect of phase slippage is suppressed. This finding is consistent with the one for a classical system.

Free Research Field

物性理論

Academic Significance and Societal Importance of the Research Achievements

超伝導や超流動はきわめて基本的な量子多体現象である。素粒子物理学におけるヒッグス粒子の発見とも深く関連しているように、物理学における基本的な問題として、研究を進める意義の深い問題である。本研究では必ずしも肯定的な成果は十分に得られなかったが、今後の研究の方向について重要な示唆が得られた。今後の基礎学理として超伝導、超流動研究に資するものである。