Condensation Transition of Ultracold Bose Gases with Rashba Spin-Orbit Coupling

We report the anomalous D'yakonov-Perel' spin relaxation in ultracold spin-orbit-coupled 40 K gas when the coupling between |9/2,9/2 and |9/2,7/2 states, acting as an effective Zeeman magnetic field, is much stronger than the spin-orbit coupled field. Both the transverse and longitudinal spin relaxations are investigated with small and large spin polarizations. It is found that with small spin polarization, the transverse (longitudinal) spin relaxation is divided into four (two) regimes: the normal weak scattering regime, the anomalous D'yakonov-Perel'-like regime, the anomalous Elliott-Yafet-like regime, and the normal strong scattering regime (the anomalous Elliott-Yafet-like regime and the normal strong scattering regime). With large spin polarization, we find that the Hartree-Fock self-energy, which acts as an effective magnetic field, can markedly suppress the transverse spin relaxation in both weak and strong scattering limits. Moreover, by noting that as both the momentum relaxation time and the Hartree-Fock effective magnetic field vary with the scattering length in cold atoms, the anomalous D'yakonov-Perel'-like regime is suppressed and the transverse spin relaxation is hence divided into three regimes in the scattering length dependence: the normal weak scattering regime, the anomalous Elliott-Yafet-like regime, and the strong scattering regime. On the other hand, the longitudinal spin relaxation is again divided into the anomalous Elliott-Yafet-like and normal strong scattering regimes. Furthermore, it is found that the longitudinal spin relaxation can be either enhanced or suppressed by the Hartree-Fock effective magnetic field if the spin polarization is parallel or antiparallel to the effective Zeeman magnetic field.

Section: Introductionmentioning

confidence: 99%

Spin relaxation in an ultracold spin-orbit-coupled40K gas

2013

“…At the mean-field level, spin-orbit coupling (SOC) introduces degenerate ground states expected to enhance fluctuation effects and giving rise to new, exotic quantum phases. The occurrence and nature of finite temperature transitions in these systems have not yet been fully established [7][8][9][10][11][12].In the following we consider a two-dimensional homogeneous gas of Rashba-Dresselhaus spin-orbit coupled bosons. Mean-field calculations [10-14] indicate a Bose condensed ground state of a single plane wave with nonvanishing momentum or a linear superposition of two plane waves with opposite momenta, called plane wave state (PW) and stripe phase (SP), respectively.…”

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confidence: 99%

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confidence: 99%

Finite-temperature phases of two-dimensional spin-orbit-coupled bosons

Kawasaki

Holzmann

2017

We determine the finite temperature phase diagram of two dimensional bosons with two hyperfine (pseudo-spin) states coupled via Rashba-Dresselhaus spin-orbit interaction using classical field Monte Carlo calculations. For anisotropic spin-orbit coupling, we find a transition to a BerenzinskiiKosterlitz-Thouless superfluid phase with quasi-long range order. We show that the spin-order of the quasi-condensate is driven by the anisotropy of interparticle interaction, favoring either a homogeneous plane wave state or stripe phase with broken translational symmetry. Both phases show characteristic behavior in the algebraically decaying spin density correlation function. For fully isotropic interparticle interaction, our calculations indicate a fractionalized quasi-condensate where the mean-field degeneracy of plane wave and stripe phase remains robust against critical fluctuations. In the case of fully isotropic spin-orbit coupling, the circular degeneracy of the single particle ground state destroys the algebraic ordered phase in the thermodynamic limit, but a cross-over remains for finite size systems.Introduction. The coupling of artificial gauge fields to ultracold atomic gases [1] has opened the possibility of studying spin-orbit coupled Bose gases [2][3][4][5] where translational symmetry may be broken spontaneously in the superfluid ground state [6]. At the mean-field level, spin-orbit coupling (SOC) introduces degenerate ground states expected to enhance fluctuation effects and giving rise to new, exotic quantum phases. The occurrence and nature of finite temperature transitions in these systems have not yet been fully established [7][8][9][10][11][12].In the following we consider a two-dimensional homogeneous gas of Rashba-Dresselhaus spin-orbit coupled bosons. Mean-field calculations [10-14] indicate a Bose condensed ground state of a single plane wave with nonvanishing momentum or a linear superposition of two plane waves with opposite momenta, called plane wave state (PW) and stripe phase (SP), respectively. For spinindependent particle interaction, PW and SP remain degenerate at the mean-field level. In addition, in the case of isotropic SOC, ground states with momenta lying on a circle are connected by symmetry. These degeneracies may be broken by classical or quantum fluctuations.In this work we explore the phase diagram using classical field Monte Carlo calculations. We show that for anisotropic SOC, the systems undergoes a KosterlitzThouless phase transition from a normal to superfluid state. In the superfluid state, the single particle density matrix decays algebraically and directly reflects the PW/SP character of the mean-field ground state. In the limit of isotropic interparticle interaction, the PW/SP degeneracy is unaffected by the transition. Thus, at large but finite system sizes, fragmentation [15] of the condensate occurs. In the case of isotropic SOC, we show that the transition temperature decreases with increasing system size due to the increasing number of degenerate mean-field ground s...

“…It was suggested that interacting fermions could be studied using the same technique [3,4]. Estimulated by the dense literature of the effects of Rashba spin-orbit coupling (SOC) encountered in condensed matter physics [1,2], several theoretical groups investigated the effects of Rashba SOC for interacting ultra-cold fermions using mean field theories [5][6][7][8] or for interacting bosons [9,10]. Unfortunately, the experimental study of Rashba SOC requires more lasers and further developments are necessary to overcome several difficulties [11].…”

mentioning

confidence: 99%

Formation of Feshbach molecules in the presence of artificial spin-orbit coupling and Zeeman fields

Kürkçüoğlu

Melo

2016

We derive general conditions for the emergence of singlet Feshbach molecules in the presence of artificial Zeeman fields for arbritary mixtures of Rashba and Dresselhaus spin-orbit orbit coupling in two or three dimensions. We focus on the formation of two-particle bound states resulting from interactions between ultra-cold spin-1/2 fermions, under the assumption that interactions are shortranged and occur only in the s-wave channel. In this case, we calculate explicitly binding energies of Feshbach molecules and analyze their dependence on spin-orbit couplings, Zeeman fields, interactions and center of mass momentum, paying particular attention to the experimentally relevant case of spin-orbit couplings with equal Rashba and Dresselhaus (ERD) amplitudes. The effects of spin-orbit interactions is ubiquitous in nature, from the macroscopic scale of the Earth-Moon complex in astronomy and astrophysics, to the microscopic scale of the electron in the hydrogen atom in atomic physics. The interest in spin-orbit coupled systems has been revived in condensed matter physics due the emergence of non-trivial topological properties of insulators and superconductors subject to Rashba spinorbit fields [1,2], and in atomic physics due to the creation of artificial spin-orbit coupling in ultra-cold atoms [3], which made possible the study of special quantum phase transitions in bosonic systems.This new tool in the toolbox of atomic physics was experimentally developed first to study interacting bosonic atoms where an equal Rashba-Dresselhaus (ERD) artificial spin-orbit coupling was created [3]. It was suggested that interacting fermions could be studied using the same technique [3,4]. Estimulated by the dense literature of the effects of Rashba spin-orbit coupling (SOC) encountered in condensed matter physics [1,2], several theoretical groups investigated the effects of Rashba SOC for interacting ultra-cold fermions using mean field theories [5][6][7][8] or for interacting bosons [9,10]. Unfortunately, the experimental study of Rashba SOC requires more lasers and further developments are necessary to overcome several difficulties [11]. Thus, presently, artificial Rashba SOC has not yet been created in the context of ultra-cold atoms. However, simultaneous theoretical studies of superfluidity for the experimentally relevant ERD spin-orbit coupling were performed for ultra-cold bosons by others [12,13] and for ultra-cold fermions by our group [14][15][16].One of the benchmarks of experimental studies of Fermi superfluidity of cold atoms without artificial spinorbit coupling was the emergence of molecular bound states via the use of Feshbach resonances [17], which lead to the formation of molecules [18] To address the important issue of the emergence of Feshbach molecules for interacting fermions in the presence of artificial SOC and Zeeman fields, we start from the Hamiltonian for two non-interacting fermionswritten as the sum of two contributions, which have the generic form (withh = 1)The term containing h R = v R k x e y −k ...