Vortex dynamics in the two-dimensional BCS-BEC crossover

Max Heyl; Kyosuke Adachi; Yuki M Itahashi; Yuji Nakagawa; Yuichi Kasahara; Emil J W List-Kratochvil; Yusuke Kato; Yoshihiro Iwasa

doi:10.1038/s41467-022-34756-x

Vortex dynamics in the two-dimensional BCS-BEC crossover

Nat Commun. 2022 Nov 16;13(1):6986. doi: 10.1038/s41467-022-34756-x.

Authors

Max Heyl^#^{1

2}, Kyosuke Adachi^#^{3

4}, Yuki M Itahashi¹, Yuji Nakagawa¹, Yuichi Kasahara⁵, Emil J W List-Kratochvil^{2

6}, Yusuke Kato⁷, Yoshihiro Iwasa^{8

9}

Affiliations

¹ Quantum-Phase Electronics Center and Department of Applied Physics, University of Tokyo, Tokyo, Japan.
² Department of Chemistry, Department of Physics & IRIS Adlershof, Humboldt-Universität zu Berlin, Zum Großen Windkanal 2, Berlin, Germany.
³ Nonequilibrium Physics of Living Matter RIKEN Hakubi Research Team, RIKEN Center for Biosystems Dynamics Research, Kobe, Japan.
⁴ RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program, Wako, Japan.
⁵ Department of Physics, Kyoto University, Kitashirakawa Oiwakecho, Kyoto, Japan.
⁶ Helmholtz-Zentrum für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, Berlin, Germany.
⁷ Department of Basic Science, University of Tokyo, Tokyo, Japan.
⁸ Quantum-Phase Electronics Center and Department of Applied Physics, University of Tokyo, Tokyo, Japan. iwasa@ap.t.u-tokyo.ac.jp.
⁹ RIKEN, Center for Emergent Matter Science, Wako, Japan. iwasa@ap.t.u-tokyo.ac.jp.

^# Contributed equally.

Abstract

The Bardeen-Cooper-Schrieffer (BCS) condensation and Bose-Einstein condensation (BEC) are the two limiting ground states of paired Fermion systems, and the crossover between these two limits has been a source of excitement for both fields of high temperature superconductivity and cold atom superfluidity. For superconductors, ultra-low doping systems like graphene and Li_xZrNCl successfully approached the crossover starting from the BCS-side. These superconductors offer new opportunities to clarify the nature of charged-particles transport towards the BEC regime. Here we report the study of vortex dynamics within the crossover using their Hall effect as a probe in Li_xZrNCl. We observed a systematic enhancement of the Hall angle towards the BCS-BEC crossover, which was qualitatively reproduced by the phenomenological time-dependent Ginzburg-Landau (TDGL) theory. Li_xZrNCl exhibits a band structure free from various electronic instabilities, allowing us to achieve a comprehensive understanding of the vortex Hall effect and thereby propose a global picture of vortex dynamics within the crossover. These results demonstrate that gate-controlled superconductors are ideal platforms towards investigations of unexplored properties in BEC superconductors.