BCS-BEC transition in a Dilute Bose Gas with Spin-Orbit Coupling

We study a two-component Bose gas with a symmetric spin-orbit coupling, and find that two atoms can form a bound state with any intra- or inter-species scattering length. Consequently, in the dilute limit, the BCS-pairing state of bosons can be formed with weakly attractive interspecies and repulsive intraspecies interactions. The quasiparticle excitation energies are anisotropic due to spin-orbit coupling. This BCS-pairing state is energetically favored over Bose-Einstein condensation (BEC) of atoms at low densities. As the density increases, there is a first-order transition from the BCS to BEC states.We study a two-component Bose gas with a symmetric spin-orbit coupling, and find that two atoms can form a bound state with any intra- or inter-species scattering length. Consequently, in the dilute limit, the BCS-pairing state of bosons can be formed with weakly attractive interspecies and repulsive intraspecies interactions. The quasiparticle excitation energies are anisotropic due to spin-orbit coupling. This BCS-pairing state is energetically favored over Bose-Einstein condensation (BEC) of atoms at low densities. As the density increases, there is a first-order transition from the BCS to BEC states.

arXiv:1609.09691Physical Review AJul 7, 20177 citations

Critical temperature of pair condensation in a dilute Bose gas with spin–orbit coupling

Dekun Luo, Lan Yin

We study the Bardeen–Cooper–Shrieffer (BCS) pairing state of a two-component Bose gas with a symmetric spin–orbit coupling (SOC). In the dilute limit at low temperature, this system is essentially a dilute gas of diatomic molecules. We compute the effective mass of the molecule and find that it is anisotropic in momentum space. The critical temperature of the pairing state is about eight times smaller than the Bose–Einstein condensation (BEC) transition temperature of an ideal Bose gas with the same density.We study the Bardeen–Cooper–Shrieffer (BCS) pairing state of a two-component Bose gas with a symmetric spin–orbit coupling (SOC). In the dilute limit at low temperature, this system is essentially a dilute gas of diatomic molecules. We compute the effective mass of the molecule and find that it is anisotropic in momentum space. The critical temperature of the pairing state is about eight times smaller than the Bose–Einstein condensation (BEC) transition temperature of an ideal Bose gas with the same density.

arXiv:1709.10239International Journal of Modern Physics BAug 29, 20171 citation

Pairing transitions in a Binary Bose Gas

Shen, Zesheng, Lan Yin

The stable Bardeen-Schrieffer-Cooper (BCS) pairing state of a bosonic system has long been sought theoretically and experimentally. Here we study the BCS state of a binary Bose gas with $s$ -wave intra-species repulsions and an inter-species attraction in the mean-field-stable region. We find that above the Bose-Einstein-Condensation (BEC) transtion temperature, there is a phase transtion from the normal state to the BCS state due to inter-species pairing. When the temperature decreases, another phase transtion from the BCS state to the mixture state with both atomic BEC and inter-species pairs occurs. As the temperature is further lowered, the mixuture state is taken over by the BEC state. The phase diagram of this system is presented and experimental implications are discussed.The stable Bardeen-Schrieffer-Cooper (BCS) pairing state of a bosonic system has long been sought theoretically and experimentally. Here we study the BCS state of a binary Bose gas with $s$-wave intra-species repulsions and an inter-species attraction in the mean-field-stable region. We find that above the Bose-Einstein-Condensation (BEC) transtion temperature, there is a phase transtion from the normal state to the BCS state due to inter-species pairing. When the temperature decreases, another phase transtion from the BCS state to the mixture state with both atomic BEC and inter-species pairs occurs. As the temperature is further lowered, the mixuture state is taken over by the BEC state. The phase diagram of this system is presented and experimental implications are discussed.

arXiv:2409.01565Sep 3, 20240 citations

Pair condensation in a dilute Bose gas with Rashba spin–orbit coupling

Rong Li, Lan Yin

We show that in a two-component Bose gas with Rashba spin–orbit coupling (SOC), two atoms can form bound states (Rashbons) with any intra-species scattering length. At zero center-of-mass momentum, there are two degenerate Rashbons due to time-reversal symmetry, but the degeneracy is lifted at finite in-plane momentum with two different effective masses. A stable Rashbon condensation can be created in a dilute Bose gas with attractive intra-species and repulsive inter-species interactions. The critical temperature of Rashbon condensation is about six times smaller than the Bose–Einstein condensation transition temperature of an ideal Bose gas. Due to the Rashba SOC, excitations in the Rashbon condensation phase are anisotropic in momentum space.We show that in a two-component Bose gas with Rashba spin–orbit coupling (SOC), two atoms can form bound states (Rashbons) with any intra-species scattering length. At zero center-of-mass momentum, there are two degenerate Rashbons due to time-reversal symmetry, but the degeneracy is lifted at finite in-plane momentum with two different effective masses. A stable Rashbon condensation can be created in a dilute Bose gas with attractive intra-species and repulsive inter-species interactions. The critical temperature of Rashbon condensation is about six times smaller than the Bose–Einstein condensation transition temperature of an ideal Bose gas. Due to the Rashba SOC, excitations in the Rashbon condensation phase are anisotropic in momentum space.

arXiv:1306.6440New Journal of PhysicsMay 7, 20148 citations

Pairing transitions in a binary Bose gas

Zesheng 泽盛 Shen 沈, Lan Yin

Abstract The stable Bardeen–Schrieffer–Cooper (BCS) pairing state of a bosonic system has long been sought theoretically and experimentally. Here we propose that a stable BCS state of bosons can be realized in a binary Bose gas with s-wave intra-species repulsion and an inter-species attraction in the mean-field-stable region. We find that above the Bose–Einstein condensation (BEC) transition temperature, there is a phase transition from the normal state to a BCS state driven by inter-species pairing. When the temperature decreases, another phase transition from the BCS state to a mixed state featuring both atomic BEC and inter-species pairing occurs. As the temperature is further lowered, the mixed state is eventually taken over by the pure BEC state. We present the phase diagram of this system and discuss its experimental implications.Abstract The stable Bardeen–Schrieffer–Cooper (BCS) pairing state of a bosonic system has long been sought theoretically and experimentally. Here we propose that a stable BCS state of bosons can be realized in a binary Bose gas with s-wave intra-species repulsion and an inter-species attraction in the mean-field-stable region. We find that above the Bose–Einstein condensation (BEC) transition temperature, there is a phase transition from the normal state to a BCS state driven by inter-species pairing. When the temperature decreases, another phase transition from the BCS state to a mixed state featuring both atomic BEC and inter-species pairing occurs. As the temperature is further lowered, the mixed state is eventually taken over by the pure BEC state. We present the phase diagram of this system and discuss its experimental implications.

Chinese Physics BJun 4, 20253 citations

Bardeen-Cooper-Schrieffer–type pairing in a spin- 12 Bose gas with spin-orbit coupling

M. Iskin

We apply the functional path-integral approach to analyze how the presence of a spin-orbit coupling (SOC) affects the basic properties of a BCS-type paired state in a two-component Bose gas. In addition to a mean-field theory that is based on the saddle-point approximation for the intercomponent pairing, we derive a Ginzburg-Landau theory by including the Gaussian fluctuations on top, and use them to reveal the crucial roles played by the momentum-space structure of an arbitrary SOC field in the stability of the paired state at finite temperatures. For this purpose, we calculate the critical transition temperature for the formation of paired bosons, and that of the gapless quasiparticle excitations for a broad range of interaction and SOC strengths. In support of our results for the many-body problem, we also benchmark our numerical calculations against the analytically tractable limits, and provide a full account of the two-body limit including its nonvanishing binding energy for arbitrarily weak interactions and the anisotropic effective mass tensor.We apply the functional path-integral approach to analyze how the presence of a spin-orbit coupling (SOC) affects the basic properties of a BCS-type paired state in a two-component Bose gas. In addition to a mean-field theory that is based on the saddle-point approximation for the intercomponent pairing, we derive a Ginzburg-Landau theory by including the Gaussian fluctuations on top, and use them to reveal the crucial roles played by the momentum-space structure of an arbitrary SOC field in the stability of the paired state at finite temperatures. For this purpose, we calculate the critical transition temperature for the formation of paired bosons, and that of the gapless quasiparticle excitations for a broad range of interaction and SOC strengths. In support of our results for the many-body problem, we also benchmark our numerical calculations against the analytically tractable limits, and provide a full account of the two-body limit including its nonvanishing binding energy for arbitrarily weak interactions and the anisotropic effective mass tensor.

arXiv:2001.02584Physical Review AJan 8, 20200 citations

The stable Bardeen-Schrieffer-Cooper (BCS) pairing state of a bosonic system has long been sought theoretically and experimentally. Here we study the BCS state of a binary Bose gas with

s

-wave intra-species repulsions and an inter-species attraction in the mean-field-stable region. We find that above the Bose-Einstein-Condensation (BEC) transtion temperature, there is a phase transtion from the normal state to the BCS state due to inter-species pairing. When the temperature decreases, another phase transtion from the BCS state to the mixture state with both atomic BEC and inter-species pairs occurs. As the temperature is further lowered, the mixuture state is taken over by the BEC state. The phase diagram of this system is presented and experimental implications are discussed.