Vortex Hall effect in the BCS-BEC crossover: Experiment

In some of the recently found low carrier density superconductors, the superconducting temperature T_c is in the order of 10^-1 of the Fermi temperature T_F, which is much higher than that of the superconductors in the Bardeen-Cooper-Schrieffer (BCS) regime, indicating that these new superconductors are in the crossover regime between the BCS limit and the other opposite limit, the Bose-Einstein condensation (BEC). These new systems are perfect candidates to uncover how the transport properties evolve in the largely unexplored BCS-BEC crossover regime. In this work LixZrNCl served as platform for a low carrier density superconductor where the carrier density is systematically controllable over nearly two-orders of magnitude through the amount of intercalated Li [1]. This enabled to navigate the single-crystal ZrNCl within the BCS-BEC crossover in an intercalation-only device structure as previously reported [2]. Several doping levels, i.e., Lithium contents x, were realized and allowed to study how the transport properties evolve in the BCS-BEC crossover regime [3]. In this light, we report a substantial enhancement of the vortex Hall effect by reducing the carrier density towards the crossover regime in this two-dimensional (2D) superconductor. This anomalous behavior in the Hall effect is attributed to vortices, and the time-dependent Ginzburg-Landau (TDGL) theory proves a qualitative scenario enhancement of the vortex Hall effect is caused by the particle-hole asymmetry characteristics in the BCS-BEC crossover. This presentation should be followed by the theory talk by Dr. Adachi.

[1] S. Yamanaka et al, Adv. Mater. 8, 771–774 (1996).

[2] Y. Nakagawa et al., PHYSICAL REVIEW B 98, 064512 (2018)

[3] Y. Nakagawa et al., Science 372, 190 (2021)