Real-space BCS-BEC crossover in FeSe monolayer

Abstract

The quantum many body states in the BCS-BEC crossover regime are of long-lasting interest. Here we report direct spectroscopic evidence of BCS-BEC crossover in real-space in a FeSe monolayer thin film by using spatially resolved scanning tunneling spectra. The crossover is driven by the shift of band structure relative to the Fermi level. The theoretical calculation based on a two-band model qualitatively reproduces the measured spectra in the whole crossover range. In addition, the Zeeman splitting of the quasi-particle states is found to be consistent with the characteristics of a condensate. Our work paves the way to study the exotic states of BCS-BEC crossover in a two-dimensional crystalline material at the atomic scale.

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Cited by in corpus (7)

• Tunable BCS-BEC crossover, reentrant, and hidden quantum phase transitions in two-band superconductors with tunable valence and conduction bands
• High-$T_c$ Berezinskii-Kosterlitz-Thouless transition in 2D superconducting systems with coupled deep and quasi-flat electronic bands with van Hove singularities
• Lateral quantum confinement effect on monolayer high-Tc superconductors
• Giant amplification of Berezinskii-Kosterlitz-Thouless transition temperature in superconducting systems characterized by cooperative interplay of small-gapped valence and conduction bands
• Landau-Level Quantization and Band Splitting of FeSe Monolayers Revealed by Scanning Tunneling Spectroscopy
• SNS Junctions along the BCS-BEC Crossover
• Spectroscopic evidence of disorder-induced quantum phase transitions in monolayer Fe(Te,Se) superconductor