arXiv subjects

S. -K. Yip

Publications and source records attributed to S. -K. Yip.

At least 19 recordsLinked to original sources

arXiv2025

Vortex nucleations in spinor Bose condensates under localized synthetic magnetic fields

Gauge fields are ubiquitous in modern quantum physics. In superfluids, quantized vortices can be induced by gauge fields. Here we demonstrate the first experimental observation of vortex nucleations in light-dressed spinor Bose-Einstein condensates under radially-localized synthetic magnetic fields. The light-induced spin-orbital-angular-momentum coupling creates azimuthal gauge potentials $\vec{A}$ for the lowest-energy spinor branch dressed eigenstate. The observation of the atomic wave function in the lowest-energy dressed eigenstate reveals that vortices nucleate from the cloud center of a vortex-free state with canonical momentum $\vec{p} = 0$. This is because a large circulating azimuthal velocity field $\propto \vec{p}-\vec{A}$ at the condensate center results in a dynamically unstable localized excitation that initiates vortex nucleations. Furthermore, the long-time dynamics to reach the ground state stops in a metastable state when $|\vec{A}|$ is not sufficiently large. Our observation has reasonable agreement with the time-dependent Gross-Pitaevskii simulations.

cond-mat.quant-gas↗

arXiv2023

Coupling of acoustic phonon to a spin-orbit entangled pseudospin

We consider coupling of acoustic phonon to pseudospins consisting of electronic spins locked to orbital angular momentum states. We show that a Berry phase term arises from projection onto the time-dependent lowest energy manifold. We examine consequences on the phonon modes, in particular mode splitting, induced chirality and Berry curvatures under an external magnetic field which Zeeman couples to the pseudospin.

cond-mat.str-el↗

arXiv2020

Visible stripe phases in spin-orbital-angular-momentum coupled Bose-Einstein condensates

Recently, stripe phases in spin-orbit coupled Bose-Einstein condensates (BECs) have attracted much attention since they are identified as supersolid phases. In this paper, we exploit experimentally reachable parameters and show theoretically that annular stripe phases with large stripe spacing and high stripe contrast can be achieved in spin-orbital-angular-momentum coupled (SOAMC) BECs. In addition to using Gross-Pitaevskii numerical simulations, we develop a variational ansatz that captures the essential interaction effects to first order, which are not present in the ansatz employed in previous literature. Our work should open the possibility toward directly observing stripe phases in SOAMC BECs in experiments.

cond-mat.quant-gas↗

arXiv2018

Rotating atomic quantum gases with light-induced azimuthal gauge potentials and the observation of Hess-Fairbank effect

We demonstrate synthetic azimuthal gauge potentials for Bose-Einstein condensates from engineering atom-light couplings. The gauge potential is created by adiabatically loading the condensate into the lowest energy Raman-dressed state, achieving a coreless vortex state. The azimuthal gauge potentials act as effective rotations and are tunable by the Raman coupling and detuning. We characterize the spin textures of the dressed states, in agreements with the theory. The lowest energy dressed state is stable with a 4.5-s half-atom-number-fraction lifetime. In addition, we exploit the azimuthal gauge potential to demonstrate the Hess-Fairbank effect, the analogue of Meissner effect in superconductors. The atoms in the absolute ground state has a zero quasi-angular momentum and transits into a polar-core vortex when the synthetic magnetic flux is tuned to exceed a critical value. Our demonstration serves as a paradigm to create topological excitations by tailoring atom-light interactions where both types of SO(3) vortices in the $|\langle \vec{F}\rangle|=1$ manifold, coreless vortices and polar-core vortices, are created in our experiment. The gauge field in the stationary Hamiltonian opens a path to investigating rotation properties of atomic superfluids under thermal equilibrium.

cond-mat.quant-gas↗

arXiv2018

Spin-orbital-angular-momentum coupled Bose-Einstein condensates

We demonstrate coupling between the atomic spin and orbital-angular-momentum (OAM) of the atom's center-of-mass motion in a Bose-Einstein condensate (BEC). The coupling is induced by Raman-dressing lasers with a Laguerre-Gaussian beam, and creates coreless vortices in a $F=1$ $^{87}$Rb spinor BEC. We observe correlations between spin and OAM in the dressed state and characterize the spin texture; the result is in good agreement with the theory. In the presence of the Raman field our dressed state is stable for 0.1~s or longer, and it decays due to collision-induced relaxation. As we turn off the Raman beams, the vortex cores in the bare spin $|m_F=1\rangle$ and $|-1\rangle$ split. These spin-OAM coupled systems with the Raman-dressing approach have great potential for exploring new topological textures and quantum states.

cond-mat.quant-gas↗

arXiv2018

Spin-incoherent Luttinger liquid of one-dimensional SU($κ$) fermions

We theoretically investigate one-dimensional (1D) SU($κ$) fermions in the regime of spin-incoherent Luttinger liquid. We specifically focus on the Tonks-Girardeau gas limit where its density is sufficiently low that effective repulsions between atoms become infinite. In such case, spin exchange energy of 1D SU($κ$) fermions vanishes and all spin configurations are degenerate, which automatically puts them into spin-incoherent regime. In this limit, we are able to express the single-particle density matrices in terms of those of anyons. This allows us to numerically simulate the number of particles up to $N=32$. We numerically calculate single-particle density matrices in two cases: (1) equal populations for each spin components (balanced) and (2) all $S_z$ manifolds included. In contrast to noninteracting multi-component fermions, the momentum distributions are broadened due to strong interactions. As $κ$ increases, the momentum distributions are less broadened for fixed $N$, while they are more broadened for fixed number of particle per spin component. We then compare numerically calculated high momentum tails with analytical predictions which are proportional to $1/p^4$, in good agreement. Thus, our theoretical study provides a comparison with the experiments of repulsive multicomponent alkaline-earth fermions with a tunable SU($κ$) spin-symmetry in the spin-incoherent regime.

cond-mat.quant-gas↗

arXiv2018

Non-Analytic Crossover Behavior of SU($\mathcal{N}_c$) Fermi Liquid

We consider the thermodynamic potential of a dilute Fermi gas with a contact interaction, at both finite temperature $T$ and non-zero effective magnetic fields $\mathbf{H}$, and derive the equation of state analytically using second order perturbation theory. Special attention is paid to the non-analytic dependence of $Ω$ on temperature $T$ and (effective) magnetic field $\mathbf{H}$, which exhibits a crossover behavior as the ratio of the two is continuously varied. This non-analyticity is due to the particle-hole pair excitation being always gapless and long-ranged. The non-analytic crossover found in this paper can therefore be understood as an analog of the Ginzberg-Landau critical scaling, albeit only at the sub-leading order. We extend our results to an $\mathcal{N}_c$- component Fermi gas with an $\mathrm{SU}(\mathcal{N}_c)$-symmetric interaction, and point out possible enhancement of the crossover behavior by a large $\mathcal{N}_c$.

cond-mat.quant-gas↗

arXiv2017

Spin-incoherent Luttinger liquid of one-dimensional spin-1 Tonks-Girardeau Bose gas: Spin-dependent properties

Spin-incoherent Luttinger liquid (SILL) is a different universal class from the Luttinger liquid.\ This difference results from the spin incoherence of the system when the thermal energy of the system is higher than the spin excitation energy.\ We consider one-dimensional spin-$1$ Bose gas in the SILL regime and investigate its spin-dependent many-body properties.\ In Tonks-Girardeau limit, we are able to write down the general wave functions in a harmonic trap.\ We numerically calculate the spin-dependent (spin-plus, minus, and $0$) momentum distributions in the sector of zero magnetization which allows to demonstrate the most significant spin-incoherent feature compared to the spinless or spin-polarized case.\ In contrast to the spinless Bose gas, the momentum distributions are broadened and in the large momentum limit follow the same asymptotic $1/p^4$ dependence but with reduced coefficients.\ While the density matrices and momentum distributions differ between different spin components for small $N$, at large $N$ they approach each other.\ We show these by analytic arguments and numerical calculations up to $N$ $=$ $16$.

cond-mat.quant-gas↗

arXiv2017

SU(N) Fermi liquid at finite temperature

We consider the thermodynamic potential $Ω$ of an N component Fermi gas with a short range interaction obeying SU(N) symmetry. We analyze especially the part of $Ω$ that depends on the temperature T non-analytically for small T . We examine the temperature range where one can observe this $T^4 ln T$ contribution and discuss how it can be extracted experimentally.

cond-mat.quant-gas↗

arXiv2016

Spin-incoherent one-dimensional spin-1 Bose Luttinger liquid

We investigate spin-incoherent Luttinger liquid of a one-dimensional spin-1 Bose gas in a harmonic trap. In this regime highly degenerate spin configurations emerge since the spin exchange energy is much less than the thermal energy of the system, while the temperature is low enough that the lowest energetic orbitals are occupied. As an example we numerically study the momentum distribution of a one-dimensional spin-1 Bose gas in Tonks- Girardeau gas limit and in the sector of zero magnetization.We find that the momentum distributions broaden as the number of atoms increase due to the averaging of spin function overlaps. Large momentum ($p$) asymptotic is analytically derived, showing the universal $1/p^4$ dependence. We demonstrate that the spin-incoherent Luttinger liquid has a momentum distribution also distinct from spinless bosons at finite temperature.

cond-mat.quant-gas↗

arXiv2015

Current response of a topological insulator to a static Zeeman field

We study the magnetoelectric coupling at the surface of a topological insulator. We are in particular interested in the surface current induced by a static Zeeman/exchange field. This surface current can be related to the orbital magnetization of the system. For an insulator with zero Chern number, the orbital magnetization is independent of the details at the boundary. With the appearance of surface states in the topological insulator, it is not immediately obvious if the response is not affected by the conditions at the surface. We investigate this question using exact diagonalization to a lattice model. By applying a time-reversal symmetry-breaking term near the boundary, no matter if the surface states are gapped out, we still find no change in the surface current. This arises from cancelations between Pauli and Van-Vleck contributions between surface and bulk scattering states. We also show that the surface current response is independent of the chemical potential when it is within the bulk gap. Our results are consistent with the claim that orbital magnetization is a bulk property.

cond-mat.mes-hall↗

arXiv2015

Kinetic equation and magneto-conductance for Weyl metal in the clean limit

We discuss the semi-classical kinetic equation in the clean limit, with the presence of Berry curvatures and magnetic field B, with the aim of applying to Weyl semi-metals. Special attention is given to the conservation laws for the collision integrals. It is found that the magneto-resistance second order in B is in general negative, with or without Weyl points, though in the later case it is in general much smaller.

cond-mat.str-el↗

arXiv2015

Fragmented Many-body States of Spin-2 Bose Gas

We investigate the fragmented many-body ground states of a spin-2 Bose gas in zero magnetic field.\ We point out that the exact ground state is not simply an average over rotationally-invariant mean-field states, in contrast to the spin-1 case with even number of particles N.\ We construct the exact ground states and compare them with the angular-averaged polar and cyclic states.\ The angular-averaged polar states fail to retrieve the exact eigenstate at $N$ $\ge$ $6$ while angular-averaged cyclic states sustain only for N with a multiple of $3$.\ We calculate the density matrices and two-particle density matrices to show how deviant the angular-averaged state is from the exact one.

cond-mat.quant-gas↗

arXiv2015

Quantum Critical Spin-2 Chain with Emergent SU(3) Symmetry

We study the quantum critical phase of a SU(2) symmetric spin-2 chain obtained from spin-2 bosons in a one-dimensional lattice. We obtain the scaling of the entanglement entropy and finite-size energies by exact diagonalization and density-matrix renormalization group methods. From the numerical results of the energy spectrum, central charge, and scaling dimension we identify the conformal field theory describing the whole critical phase to be the SU(3)$_1$ Wess-Zumino-Witten model. We find that while in the whole critical phase the Hamiltonian is only SU(2) invariant, there is an emergent SU(3) symmetry in the thermodynamic limit.

cond-mat.str-el↗

arXiv2013

Theory of SU(N) Fermi liquid

We generalized the Fermi liquid theory to N component systems with SU(N) symmetry. We emphasize the important role of fluctuations when N is large. These fluctuations dramatically modifies the properties for repulsive Fermi gases, in particular the spin susceptibility.

cond-mat.quant-gas↗

arXiv2013

Entanglement entropy scaling of the XXZ chain

We study the entanglement entropy scaling of the XXZ chain. While in the critical XY phase of the XXZ chain the entanglement entropy scales logarithmically with a coefficient that is determined by the associated conformal field theory, at the ferromagnetic point, however, the system is not conformally invariant yet the entanglement entropy still scales logarithmically albeit with a different coefficient. We investigate how such an nontrivial scaling at the ferromagnetic point influences the estimation of the central charge $c$ in the critical XY phase. In particular we use the entanglement scaling of the finite or infinite system, as well as the finite-size scaling of the ground state energy to estimate the value of $c$. In addition, the spin-wave velocity and the scaling dimension are also estimated. We show that in all methods the evaluations are influenced by the nearby ferromagnetic point and result in crossover behavior. Finally we discuss how to determine whether the central charge estimation is strongly influenced by the crossover behavior and how to properly evaluate the central charge.

cond-mat.str-el↗

arXiv2013

Mesoscopic p-wave superconductor near the phase transition temperature

We study the finite-size and boundary effects on a p-wave superconductor in a mesoscopic rectangular sample using Ginzburg-Landau (GL) and quasi-classical (QC) Green's function theory. Except for a square sample with parameters far away from the isotropic weak-coupling limit, the ground state near the critical temperature always prefers a time-reversal symmetric state, where the order parameter can be represented by a real vector. For large aspect ratio, this vector is parallel to the long side of the rectangle. Within a critical aspect ratio, it has instead a vortex-like structure, vanishing at the sample center.

cond-mat.supr-con↗

arXiv2013

Models of Superconducting Cu:Bi2Se3: single versus two-band description

Starting from a model Hamiltonian for the normal state of the topological insulator Bi2Se3, we construct a pseudospin basis for the single-particle wavefunctions. Considering weak superconducting pairing near the Fermi surface, we express the recently proposed superconducting order parameters for Cu doped Bi2Se3 in this basis. For the odd parity states, the d-vectors specifying the order parameter can have unusual momentum dependence for certain parameter regimes. Some peculiar results in the literature for surface states are discussed in light of the forms of these d(k)'s. Properties of the even parity states are also illuminated using this pseudospin basis. Results from this single-band description are compared with those from the full two-band model.

cond-mat.supr-con↗