arXiv subjects

Shaolong Wan

Publications and source records attributed to Shaolong Wan.

At least 37 records · Page 2Linked to original sources

arXiv2014

Topological phases, topological flat bands, and topological excitations in a one-dimensional dimerized lattice with spin-orbit coupling

The Su-Schrieffer-Heeger (SSH) model describes a one-dimensional $Z_{2}$ topological insulator, which has two topological distinct phases corresponding to two different dimerizations. When spin-orbit coupling is introduced into the SSH model, we find the structure of the Bloch bands can be greatly changed, and most interestingly, a new topological phase with single zero-energy bound state which exhibits non-Abelian statistics at each end emerges, which suggests that a new topological invariant is needed to fully classify all phases. In a comparatively large range of parameters, we find that spin-orbit coupling induces completely flat band with nontrivial topology. For the case with non-uniform dimerizaton, we find that spin-orbit coupling changes the symmetrical structure of topological excitations known as solitons and antisolitons and when spin-orbit coupling is strong enough to induce a topological phase transition, the whole system is topologically nontrivial but with the disappearance of solitons and antisolitons, consequently, the system is a real topological insulator with well-protected end states.

cond-mat.str-el↗

arXiv2014

Long-range Order in One-dimensional Spinless Fermi Gas with Attractive Dipole-Dipole Interaction

One-dimensional spinless Fermi gas with attractive dipole-dipole interaction is investigated. Results obtained show when the interaction is weak, the excitation spectrum is linear and the superconducting correlation function decays as power law, indicating the validity of the Tomonaga-Luttinger (TL) liquid picture. However, when the interaction reaches a critical value, the excitation spectrum is nonlinear and the superconducting correlation function keeps finite for infinity separation, indicating real long-range order established and the breakdown of the TL liquid picture. We prove that the existence of long-range order is not in contradiction with the Hohenberg theorem and show that this system is related to the Kitaev toy model, therefore, it has potential applications for the future topological quantum computation.

cond-mat.quant-gas↗

arXiv2014

Study on the tunneling spectroscopy of $N-pS$ junction and $N-hS$ junction

We study the complete tunneling spectroscopy of a normal metal/$p$-wave superconductor junction ($N-pS$) and normal metal/heterostructure superconductor junction ($N-hS$) by Blonder-Tinkham-Klapwijk (BTK) method. We find that, for $p$-wave superconductor with non-trivial topology, there exists a quantized zero-bias conductance peak stably, for heterostructure superconductor with non-trivial topology, the emerging zero-bias conductance peak is non-quantized and usually has a considerable gap to the quantized value. Furthermore, it is sensitive to parameters, especially to spin-orbit coupling and the $s$-wave pairing potential. Results obtained suggest that the observation of a small zero-bias conductance peak, instead of a quantized zero-bias conductance peak, in current tunneling experiments can be a natural result if the spin-orbit coupling turns out to be several times smaller than the reported one. Results obtained also suggest that both a stronger spin-orbit coupling and proximity $s$-wave superconductor with relative weaker pairing potential can produce a much more striking zero-bias conductance peak (compared to the experiments), even an almost quantized one. As $s$-wave superconductors are common in nature, the prediction can be verified within current experiment ability.

cond-mat.str-el↗

arXiv2013

Insights into the gamma* N -> Delta transition

The γ* N -> Δ(1232) transition is a window on hadron shape deformation, the applicability of perturbative QCD at moderate momentum transfers, and the influence of nonperturbative phenomena on hadronic observables. We explain that the Ash-convention magnetic transition form factor must fall faster than the neutron's magnetic form factor and nonzero values for the associated quadrupole ratios reveal the impact of quark orbital angular momentum within the nucleon and Δ(1232); and show that these quadrupole ratios do approach their predicted asymptotic limits, albeit slowly.

nucl-th↗

arXiv2013

Elastic and transition form factors of the Δ(1232)

Predictions obtained with a confining, symmetry-preserving treatment of a vector-vector contact interaction at leading-order in a widely used truncation of QCD's Dyson-Schwinger equations are presented for Δand Ωbaryon elastic form factors and the γN -> Δtransition form factors. This simple framework produces results that are practically indistinguishable from the best otherwise available, an outcome which highlights that the key to describing many features of baryons and unifying them with the properties of mesons is a veracious expression of dynamical chiral symmetry breaking in the hadron bound-state problem. The following specific results are of particular interest. The Δelastic form factors are very sensitive to m_Δ. Hence, given that the parameters which define extant simulations of lattice-regularised QCD produce Δ-resonance masses that are very large, the form factors obtained therewith are a poor guide to properties of the Δ(1232). Considering the Δ-baryon's quadrupole moment, whilst all computations produce a negative value, the conflict between theoretical predictions entails that it is currently impossible to reach a sound conclusion on the nature of the Δ-baryon's deformation in the infinite momentum frame. Results for analogous properties of the Ωbaryon are less contentious. In connection with the N->Δtransition, the Ash-convention magnetic transition form factor falls faster than the neutron's magnetic form factor and nonzero values for the associated quadrupole ratios reveal the impact of quark orbital angular momentum within the nucleon and Δ; and, furthermore, these quadrupole ratios do slowly approach their anticipated asymptotic limits.

nucl-th↗

arXiv2013

Dirac Point Structure in a Bose-Einstein Condensate in a Honeycomb Optical Lattice

We study the Bose-Einstein condensate in a honeycomb optical lattice within Bogoliubov theory and find that for a ${\bf k} = 0$ condensate, the Dirac points appear in the Bogoliubov excitation spectrum when $0 < β< 2$, which illustrates that the bose-bose interaction does not change the Dirac point structure but only give a modification of the velocity of the Dirac cone. When the bosons are driven to condense at ${\bf k} = {\bf K}$, however, we find that the topology of the Dirac points will be altered by arbitrary weak interaction. Furthermore, we find that the next-nearest-neighbor hopping in an isotropic and an anisotropic lattice has different effects to the dynamics of the condensate and it should be taken into account when the lattice is not sufficiently deep.

cond-mat.quant-gas↗

arXiv2012

Excitation Spectrum and Momentum Distribution of Bose-Hubbard Model with On-site Two- and Three-body Interaction

An effective action for Bose-Hubbard model with two- and three-body on-site interaction in a square optical lattice is derived in the frame of a strong-coupling approach developed by Sengupta and Dupuis. From this effective action, superfluid-Mott insulator (MI) phase transition, excitation spectrum and momentum distribution for two phases are calculated by taking into account Gaussian fluctuation about the saddle-point approximation. In addition the effects of three-body interaction are also discussed.

cond-mat.quant-gas↗

arXiv2012

Features and flaws of a contact interaction treatment of the kaon

Elastic and semileptonic transition form factors for the kaon and pion are calculated using the leading-order in a global-symmetry-preserving truncation of the Dyson-Schwinger equations and a momentum-independent form for the associated kernels in the gap and Bethe-Salpeter equations. The computed form factors are compared both with those obtained using the same truncation but an interaction that preserves the one-loop renormalisation-group behaviour of QCD and with data. The comparisons show that: in connection with observables revealed by probes with |Q^2|<~ M^2, where M~0.4GeV is an infrared value of the dressed-quark mass, results obtained using a symmetry-preserving regularisation of the contact-interaction are not realistically distinguishable from those produced by more sophisticated kernels; and available data on kaon form factors do not extend into the domain whereupon one could distinguish between the interactions. The situation is different if one includes the domain Q^2>M^2. Thereupon, a fully consistent treatment of the contact interaction produces form factors that are typically harder than those obtained with QCD renormalisation-group-improved kernels. Amongst other things also described are a Ward identity for the inhomogeneous scalar vertex, similarity between the charge distribution of a dressed-u-quark in the K^+ and that of the dressed-u-quark in the pi^+, and reflections upon the point whereat one might begin to see perturbative behaviour in the pion form factor. Interpolations of the form factors are provided, which should assist in working to chart the interaction between light-quarks by explicating the impact on hadron properties of differing assumptions about the behaviour of the Bethe-Salpeter kernel.

nucl-th↗

arXiv2012

Supersolid in Bose-Bose-Fermi Mixtures subjected to a Square Lattice

Two-component Bose condensates with repulsive interaction are stable when $g_{\rm \scriptscriptstyle 1} g_{\rm \scriptscriptstyle 2}<g_{\rm \scriptscriptstyle 12}^{2}$ is satisfied. By tuning the interactions, we show that the instability corresponding to bose-bose phase separation always happens at a higher temperature than corresponding to bose-fermi phase separation happens. Moreover, we find both the transition temperature $T_{\rm \scriptscriptstyle DW}$ of supersolid and the coherence peak at $k_{\rm \scriptscriptstyle DW}$ are enhanced in the mixtures studied. These will make the observation of supersolid in experiments more reachable.

cond-mat.quant-gas↗

arXiv2012

A New Non-Abelian Topological Phase of Cold Fermi Gases in Anisotropic and Spin-Dependent Optical Lattices

To realize non-Abelian s-wave topological superfluid (TS) of cold Fermi gases, generally a Zeeman magnetic field larger than superfluid pairing gap is necessary. In this paper we find that using an anisotropic and spin-dependent optical lattice (ASDOL) to trap gases, a new non-Abelian TS phase appears, in contrast to an isotropic and spin-independent optical lattice. A characteristic of this new non-Abelian TS is that Zeeman magnetic field can be smaller than the superfluid pairing gap. By self-consistently solving pairing gap equation and considering the competition against normal state and phase separation, this new phase is also stable. Thus an ASDOL supplies a convenient route to realize TS. We also investigate edge states and the effects of a harmonic trap potential.

cond-mat.quant-gas↗

arXiv2012

Quantum anomalous Hall effect on star lattice with spin-orbit coupling and exchange field

We study the star lattice with Rashba spin-orbit coupling and exchange field and find that there exists the quantum anomalous Hall effect in this system and there are five energy gaps at Dirac points and quadratic band crossing points. We calculate the Berry curvature distribution and obtain the Hall conductivity (Chern number $ν$) quantized as integers, and find that $ν=-1,2,1,1,2$, respectively, when the Fermi level lies in these five gaps. Our model can be view as a general quantum anomalous Hall system and, in limit cases, can give what the honeycomb lattice and kagome lattice gave. We also find there exists a nearly flat band with $ν=1$ which may provide an opportunity to realize the fractional quantum anomalous Hall effect. Finally, the chiral edge states on a zigzag star lattice are given numerically to confirm the topological property of this system.

cond-mat.str-el↗

arXiv2012

Spectrum of hadrons with strangeness

We describe a calculation of the spectrum of strange and nonstrange hadrons that simultaneously correlates the dressed-quark-core masses of meson and baryon ground- and excited-states within a single framework. The foundation for this analysis is a symmetry-preserving Dyson-Schwinger equation treatment of a vector-vector contact interaction. Our results exemplify and highlight the deep impact of dynamical chiral symmetry breaking on the hadron spectrum: an accurate description of the meson spectrum entails a similarly successful prediction of the spectrum of baryons, including those with strangeness. The analysis also provides numerous insights into baryon structure. For example, that baryon structure is largely flavour-blind, the first radial excitation of ground-state baryons is constituted almost entirely from axial-vector diquark correlations, and DCSB is the foundation for the ordering of low-lying baryon levels; viz., (1/2)^+, (1/2)^+, (1/2)^-.

nucl-th↗

arXiv2012

Magnetic Impurities in Two-Dimensional Superfluid Fermi Gas with Spin-Orbit Coupling

We consider magnetic impurities in a two dimensional superfluid Fermi gas in the presence of spin-orbit coupling. By using the methods of t-matrix and Green's function, we find spin-orbit coupling has some dramatic impacts on the effects of magnetic impurities. For the single impurity problem, the number of bound states localized around the magnetic impurity is doubled. For the finite concentration $n$ of impurities, the energy gap is reduced and the density of states in the gapless region is greatly modified.

cond-mat.quant-gas↗

arXiv2012

Surface Spectral Function of Momentum-dependent Pairing Potentials in a Topological Insulator: Application to Cu$_x$Bi$_2$Se$_3$

We propose three possible momentum-dependent pairing potentials for candidate of topological superconductor (for example Cu$_x$Bi$_2$Se$_3$), and calculate the surface spectral function and surface density of state with these pairing potentials. We find that the first two can give the same spectral functions as the fully-gapped and node-contacted pairing potentials given in [Phys. Rev. Lett. 105, 097001], and that the third one can obtain topological non-trivial case which exists flat Andreev bound state and preserves the $C_3$ rotation symmetry. We hope our proposals and results be judged by future experiment.

cond-mat.str-el↗

arXiv2012

Topological Superfluid in one-dimensional Ultracold Atomic System with Spin-Orbit Coupling

We propose a one-dimensional Hamiltonian $H_{1D}$ which supports Majorana fermions when $d_{x^{2}-y^{2}}$-wave superfluid appears in the ultracold atomic system and obtain the phase-separation diagrams both for the time-reversal-invariant case and time-reversal-symmetry-breaking case. From the phase-separation diagrams, we find that the single Majorana fermions exist in the topological superfluid region, and we can reach this region by tuning the chemical potential $μ$ and spin-orbit coupling $α_{R}$. Importantly, the spin-orbit coupling has realized in ultracold atoms by the recent experimental achievement of synthetic gauge field, therefore, our one-dimensional ultra-cold atomic system described by $H_{1D}$ is a promising platform to find the mysterious Majorana fermions.

cond-mat.quant-gas↗

arXiv2011

Fractional charge and statistics in the fractional quantum spin Hall effect

In this paper, we consider there exist two types of fundamental quasihole excitation in the fractional quantum spin Hall state and investigate their topological properties by both Chern-Simons field theory and Berry phase technique. By the two different ways, we obtain the identical charge and statistical angle for each type of quasihole, as well as the identical mutual statistics between two different types of quasihole excitation.

cond-mat.str-el↗

arXiv2011

Phase Diagram of Two-dimensional Polarized Fermi Gas With Spin-Orbit Coupling

We investigate the ground state of the two-dimensional polarized Fermi gas with spin-orbit coupling and construct the phase diagram at zero temperature. We find there exist phase separation when the binding energy is low. As the binding energy increasing, the topological nontrivial superfluid phase coexist with topologically trivial superfluid phase which is topological phase separation. The spin-orbit coupling interaction enhance the triplet pairing and destabilize the phase separation against superfluid phase.

cond-mat.quant-gas↗

arXiv2011

Critical surface band gap of repulsive Casimir interaction between three dimensional topological insulators at finite temperature

We generalize the calculation of Casimir interaction between topological insulators with opposite topological magnetoelectric polarizabilities and finite surface band gaps to finite Temperature cases. We find that finite temperature quantitatively depress the repulsive peak and enlarge the critical surface gap $m_c$ for repulsive Casimir force. However the universal property $m_c a \sim 1/2$ is still valid for various oscillation strength, temperature region and topological magnetoelectric polarizabilities.

cond-mat.other↗