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arXiv:2407.07422 · Physical Review A

Quantum tricriticality of bosonic atomic-molecular mixtures with Feshbach coupling

Yuan-Hong Chen, Dong-Chen Zheng, Renyuan Liao

Published Oct 28, 2024• 1 citation
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Abstract

We identify that coherent interconversion can stabilize bosonic atomic-molecular mixtures by establishing a comprehensive and analytical phase diagram, which can accommodate up to two tricritical points (TPs) with one being intrinsic and the other being conditional. By varying the interaction parameters, the topology of the phase diagram gets modified while changing the number of TPs. We master the quantum tricriticality and concrete signals of the phase transition for this system. Notably, we show that the sound velocity vanishes as the atomic-molecular superfluid phase touches on the border of the phase separation lines.. Correlation functions such as pairing amplitudes and density (spin density) structure factors exhibit characteristic behaviors when the system crosses the phase transitions. Our work paves the way for future advancement toward understanding the salient physics of atom-molecular mixtures.

DOI
10.1103/physreva.110.043321

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We identify that coherent interconversion can stabilize bosonic atomic-molecular mixtures by establishing a comprehensive and analytical phase diagram, which can accommodate up to two tricritical points (TPs) with one being intrinsic and the other being conditional. By varying the interaction parameters, the topology of the phase diagram gets modified while changing the number of TPs. We master the quantum tricriticality and concrete signals of the phase transition for this system. Notably, we show that the sound velocity vanishes as the atomic-molecular superfluid phase touches on the border of the phase separation lines.. Correlation functions such as pairing amplitudes and density (spin density) structure factors exhibit characteristic behaviors when the system crosses the phase transitions. Our work paves the way for future advancement toward understanding the salient physics of atom-molecular mixtures.
We consider a mixture of single-component bosonic and fermionic atoms with an interspecies interaction that is varied using a Feshbach resonance. By performing a mean-field analysis of a two-channel model, which describes both narrow and broad Feshbach resonances, we find an unexpectedly rich phase diagram at zero temperature: Bose-condensed and non-Bose-condensed phases form a variety of phase-separated states that are accompanied by both critical and tricritical points. We discuss the implications of our results for the experimentally observed collapse of Bose-Fermi mixtures on the attractive side of the Feshbach resonance, and we make predictions for future experiments on Bose-Fermi mixtures close to a Feshbach resonance.
We address the possibility of realizing Bose-Einstein condensation as a first-order phase transition by admixture of particles of different species. To this aim we perform a comprehensive analysis of phase diagrams of two-component mixtures of bosons at finite temperatures. As a prototype model, we analyze a binary mixture of Bose particles interacting via an infinite-range (Kac-scaled) two-body potential. We obtain a rich phase diagram, where the transition between the normal and Bose-Einstein-condensed phases may be either continuous or first order. The phase diagram hosts lines of triple points, tricritical points, and quadruple points. We address the structure of the phase diagram depending on the relative magnitudes of the inter- and intraspecies interaction couplings. In addition, even for purely repulsive interactions, we identify a first-order liquid-gas-type transition between noncondensed phases characterized by different particle concentrations. In the obtained phase diagram, a surface of such first-order transitions terminates with a line of critical points.
We study the ground state and the thermal phase diagram of a two-species Bose-Hubbard model, with $\text{U}(1)\ifmmode\times\else\texttimes\fi{}{\mathbb{Z}}_{2}$ symmetry, describing atoms and molecules on a two-dimensional optical lattice interacting via a Feshbach resonance. Using quantum Monte Carlo simulations and mean-field theory, we show that the conversion between the two species, coherently coupling the atomic and molecular states, has a crucial impact on the Mott-superfluid transition and stabilizes an insulating phase with a gap controlled by the conversion term---the Feshbach insulator---instead of a standard Mott-insulating phase. Depending on the detuning between atoms and molecules, this model exhibits three phases: the Feshbach insulator, a molecular condensate coexisting with noncondensed atoms, and a mixed atomic-molecular condensate. Employing finite-size scaling analysis, we observe three-dimensional (3D) XYXYXY (3D Ising) transition when U(1)\text{U}(1)U(1) (Z2{\mathbb{Z}}_{2}Z2​) symmetry is broken, whereas the transition is first order when both U(1)\text{U}(1)U(1) and Z2{\mathbb{Z}}_{2}Z2​ symmetries are spontaneously broken. The finite-temperature phase diagram is also discussed. The thermal disappearance of the molecular superfluid leads to a Berezinskii-Kosterlitz-Thouless transition with unusual universal jump in the superfluid density. The loss of the quasi-long-range coherence of the mixed atomic and molecular superfluid is more subtle since only atoms exhibit conventional Berezinskii-Kosterlitz-Thouless criticality. We also observe a signal compatible with a classical first-order transition between the mixed superfluid and the normal Bose liquid at low temperature.
Abstract We revisit the structure of the phase diagram of the two-component mean-field Bose mixture at finite temperatures, considering both the cases of attractive and repulsive interspecies interactions. In particular, we analyze the evolution of the phase diagram upon driving the system towards collapse and point out its distinctive features in this limit. We provide analytical insights into the global structure of the phase diagram and the properties of the phase transitions between the normal phase and the phases involving Bose–Einstein condensates. Inter alia we analytically demonstrate that for sufficiently weak interspecies interactions a 12 the system generically exhibits a line of quadruple points but has no triple nor tricritical points in the phase diagram spanned by the chemical potentials µ 1, µ 2 and temperature T. In contrast, for sufficiently large, positive values of a 12, the system displays both triple and tricritical points but no quadruple points. As pointed out in recent studies, in addition to the phase transitions involving condensation, the mixture may be driven through a liquid–gas type transition, and we clarify the conditions for its occurrence. We finally discuss the impact of interaction- and mass-imbalance on the phase diagram of the mixture.
We investigate the homogeneous superfluid mixtures of a Bardeen-Cooper-Schrieffer (BCS) superfluid originating from pairing two-species fermionic atoms and superfluidity stemming from condensation of bosonic atoms. By integrating out the freedoms associated with the BCS superfluid, we derive the fermion-mediated interactions between bosons, which is attractive and can be tuned from long range in the BCS region to short range in the region of Bose-Einstein condensation of molecular dimers. By analyzing the Bogoliubov spectrum and the damping rate of bosonic superfluid, we map out the phase diagram spanned by the boson-fermion mass ratio and the boson-fermion coupling strength, which consists of a phase separation region and two phase-mixing regions with and without Landau damping. The three different phases can coexist at a tricritical point, which moves toward a low boson-fermion mass ratio and a high boson-fermion scattering length as the fermion-fermion interaction strength is tuned up on the BCS side.