Density-induced BCS-Bose evolution in gated two-dimensional superconductors: The role of the interaction range in the Berezinskii-Kosterlitz-Thouless transition

¹ Department of Physics, Renmin University of China - Beijing 100872, China
² Beijing Academy of Quantum Information Sciences - Beijing 100193, China
³ Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China - Beijing 100872, China
⁴ School of Physics, Georgia Institute of Technology - Atlanta, GA 30332, USA

^(a) wzhangl@ruc.edu.cn (corresponding author)
^(b) carlos.sademelo@physics.gatech.edu

Received: 30 March 2022
Accepted: 21 June 2022

Abstract

We discuss the evolution from Bardeen-Cooper-Schrieffer (BCS) to Bose superconductivity vs. carrier density n in two-dimensional (2D) gated superconductors and address the fundamental role that the interaction range plays in the Berezinskii-Kosterlitz-Thouless transition. We investigate the density dependence of the critical temperature (T_c), superfluid density, order parameter modulus, chemical potential and pair size. Our most important finding is that it is absolutely essential to include classical and quantum phase fluctuations, as well as finite-ranged interactions to explain the non-monotonic behavior of T_c vs. n and to guarantee that the upper bound on T_c is not exceeded in 2D superconductors, as experimentally observed in (Nakagawa Y. et al., Science, 372 (2021) 190), a lithium-intercalated layered nitride, and in magic-angle twisted trilayer graphene (Park J. M. et al., Nature, 590 (2021) 249). Furthermore, we show that we can extract, from measurements of T_c and the order parameter modulus, the effective mass of charge carriers and their interaction strength and range.