Impurity-induced Shiba bound state in the BCS–BEC crossover regime of two-dimensional Fermi superfluid*

Abstract

For a two-dimensional ultra-cold Fermi superfluid with an effective static magnetic impurity, we theoretically investigated the variation of the Yu–Shiba–Rusinov (YSR) bound state in the Bardeen–Cooper–Schrieffer (BCS) to Bose–Einstein condensation (BEC) crossover regime. Within the framework of mean-field theory, analytical results of the YSR bound state energy were obtained as a function of the interaction parameters. First, when the background Fermi superfluid system stays in the weakly interacting BCS regime, we found that the YSR bound state energy is linearly dependent on the gap parameter with its coefficient slightly different from previous results. Second, we discovered re-entrance phenomena for the YSR state and an upper bound of the strength of the interaction between the paired atoms. By carefully analyzing the bound state energy as a function of the interaction parameters, we obtained a phase diagram showing the existence of the YSR state. Finally, we concluded that the re-entrance phenomena and the critical point can be easily experimentally detected through measurement of radio-frequency spectroscopy and density of states using current experimental techniques.

Temperature and doping dependent flat-band superconductivity on the Lieb-lattice*

“…The superconducting critical temperature is determined by the Berezinskii-Kosterlitz-Thouless temperature rather than the vanishing of the superfluid weight. [28][29][30]36] Therefore, it is crucial to examine the BKT transition on the Lieb model with a strong correlation to understand superfluid in the ultracold atoms or the superconductivity in the high-T c superconductors. In this paper, we investigate the superconducting properties of Lieb lattice in the strong electron-electron correlation limit based on the t-J model using the Gutzwiller renormalization mean-field method.…”

Simple and robust method for rapid cooling of 87Rb to quantum degeneracy*

“…Preparation of degenerate atomic quantum gases is an important tool for studying their fundamental properties [1][2][3][4] or their applications in atomic inertial sensors [5] and gravimeters, [6] as well as in microgravity. [7] A simple and robust method for the generation of Bose-Einstein condensates (BECs) with decent particle number and repetition rate could pave the way for a new generation of atom-based quantum sensors.…”

Exact solution of a topological spin ring with an impurity*

“…[27] The effects of impurity scattering on the surface of topological insulators have been investigated extensively. [28][29][30] A key issue is to determine the conditions for the stability of the current-carrying states at the edge of the sample, [31,32] as this is the feature that most directly impacts prospect for future applications in electronics and spintronics. [33] Therefore, it is worthwhile to investigate the effects of impurity when the impurity locates at the twisted boundary.…”