arXiv subjects

Renyuan Liao

Publications and source records attributed to Renyuan Liao.

26 records · Page 2Linked to original sources

arXiv2013

Ground State Properties of Spin-Orbit Coupled Bose Gases for Arbitrary Interactions

We develop a field integral formalism to study spin-orbit-coupled (SOC) Bose gases with arbitrary interspecies interaction. We identify various features arising from the interplay of SOC and interspecies interaction, including a roton minimum in the excitation spectrum and dual effects of SOC on ground-state energies depending on interspecies interactions. Counterintuitively, we find that at low interspecies interaction the SOC stabilizes the system by suppressing the quantum depletion. We show that the static structure factor is immune to the SOC in the phase space where time-reversal symmetry is preserved. Furthermore, we present an alternate way of studying phase fluctuations of the system.

cond-mat.quant-gas↗

arXiv2012

Medium effects close to s- and p-wave Feshbach resonances in atomic Fermi gases

Many-body effects may influence properties, such as scattering parameters, nature of pairing, etc., close to a Feshbach resonance in the fermion BEC-BCS crossover problem. We study effects such as these using a tractable crossing-symmetric approach. This method allow us to include quantum fluctuations, such as, density, current, spin, spin-current and the higher-order fluctuations in a self-consistent fashion. The underlying fermion interaction is reflected in the "driving" term. We perform calculations here on both Bose-Einstein condensate (BEC) and BCS sides, and taking the driving term to be finite range, and of arbitrary strength. These are related to two-body singlet and triplet scattering parameters, and can be connected with experimental s- and p-wave Feshbach resonances. We include the $\ell=0$ density and spin fluctuations, as well as $\ell=1$ current and spin-current fluctuations. We calculate renormalized scattering amplitudes, pairing amplitudes, nature of pairing, etc., on both the BEC and BCS sides. We then compare our results qualitatively with experiments.

cond-mat.quant-gas↗

arXiv2011

Tuning the Tricritical Point with Spin-orbit Coupling in Polarized Fermionic Condensates

We investigate a two-component atomic Fermi gas with population imbalance in the presence of Rashba-type spin-orbit coupling (SOC). As a competition between SOC and population imbalance, the finite-temperature phase diagram reveals a large varieties of new features, including the expanding of the superfluid state regime and the shrinking of both the phase separation and the normal regimes. For sufficiently strong SOC, the phase separation region disappears, giving way to the superfluid state. We find that the tricritical point moves toward regime of low temperature, high magnetic field, and high polarization as the SOC increases.

cond-mat.quant-gas↗

arXiv2011

Thermal-assisted Anisotropy and Thermal-driven Instability in the Superfluidity state of Two-Species Polar Fermi Gas

We study the superfluid state of two-species heteronuclear Fermi gases with isotropic contact and anisotropic long-range dipolar interactions. By explicitly taking account of Fock exchange contribution, we derive self-consistent equations describing the pairing states in the system. Exploiting the symmetry of the system, we developed an efficient way of solving the self-consistent equations by exploiting the symmetries. We find that the temperature tends to increase the anisotropy of the pairing state, which is rather counterintuitive. We study the anisotropic properties of the system by examining the angular dependence of the number density distribution, the excitation spectrum and the pair correlation function. The competing effects of the contact interaction and the dipolar interaction upon the anisotropy are revealed. We derive and compute the superfluid mass density $ρ_{ij}$ for the system. Astonishingly, we find that $ρ_{zz}$ becomes negative above some certain temperature $T^*$($T<T_c$), signaling some instability of the system. This suggests that the elusive FFLO state may be observed in experiments, due to an anisotropic state with a spontaneously generated superflow.

cond-mat.quant-gas↗

arXiv2011

Traveling Dark Solitons in Superfluid Fermi Gases

Families of dark solitons exist in superfluid Fermi gases. The energy-velocity dispersion and number of depleted particles completely determines the dynamics of dark solitons on a slowly-varying background density. For the unitary Fermi gas we determine these relations from general scaling arguments and conservation of local particle number. We find solitons to oscillate sinusoidally at the trap frequency reduced by a factor of $1/\sqrt{3}$. Numerical integration of the time-dependent Bogoliubov-de Gennes equation determines spatial profiles and soliton dispersion relations across the BEC-BCS crossover and proves consistent with the scaling relations at unitarity.

cond-mat.quant-gas↗

arXiv2010

Anisotropic Superfluidity in the Two-Species Polar Fermi Gas

We study the superfluid pairing in a two-species gas of heteronuclear fermionic molecules with equal density. The interplay of the isotropic s-wave interaction and anisotropic long-range dipolar interaction reveals rich physics. We find that the single-particle momentum distribution has a characteristic ellipsoidal shape that can be reasonably represented by a deformation parameter $α$ defined similarly to the normal phase. Interesting momentum-dependent features of the order parameter are identified. We calculate the critical temperatures of both the singlet and triplet superfluid, suggesting a possible pairing symmetry transition by tuning the s-wave or dipolar interaction strength.

cond-mat.quant-gas↗

arXiv2007

P-wave Pairing in Two-Component Fermi Systems with Unequal Population near Feshbach Resonance

We explore p-wave pairing in a single-channel two-component Fermi system with unequal population near Feshbach resonance. Our analytical and numerical study reveal a rich superfluid (SF) ground state structure as a function of imbalance. In addition to the state $Δ_{\pm 1} \propto Y_{1\pm 1}$, a multitude of ``mixed'' SF states formed of linear combinations of $Y_{1m}$'s give global energy minimum under a phase stability condition; these states exhibit variation in energy with the relative phase between the constituent gap amplitudes. States with local energy minimum are also obtained. We provide a geometric representation of the states. A $T$=0 polarization vs. p-wave coupling phase diagram is constructed across the BEC-BCS regimes. With increased polarization, the global minimum SF state may undergo a quantum phase transition to the local minimum SF state.

cond-mat.supr-con↗

arXiv2007

Pairing in Asymmetrical Fermi Systems with Intra- and Inter-Species Correlations

We consider inter- and intra-species pairing interactions in an asymmetrical Fermi system. Using equation of motion method, we obtain coupled mean-field equations for superfluid gap functions and population densities. We construct a phase diagram across BCS-BEC regimes. Due to intra-species correlations, the BCS singlet superfluid state can sustain finite polarizations, $P$. For larger $P$, we find phase separations in BCS and BEC regimes. A superfluid phase exists for all $P$ deep in BEC regime. Our results may apply to pairing in ultracold fermions, nuclear and quark matter physics.

cond-mat.supr-con↗