arXiv subjects

Xiao-Mei Kuang

Publications and source records attributed to Xiao-Mei Kuang.

102 records · Page 6Linked to original sources

arXiv2013

Building a Holographic Superconductor with Higher-derivative Couplings

We discuss the gravitational dual of a holographic superconductor consisting of a U(1) gauge field, a complex scalar field coupled to a charged AdS black hole and a higher-derivative coupling between the U(1) gauge field and the scalar with coupling constant η. In the presence of a magnetic field, the system possesses localized spatially dependent droplet solutions which, in the low temperature limit, have smaller critical temperature for η>0 than the droplet solutions without the interaction term (η=0). In the weak magnetic field limit, the opposite behavior is observed: the critical temperature increases as we increase η. We also calculate the energy gap in the probe limit and find that it is larger for η<0 than the energy gap in the conventional case (η=0).

hep-th↗

arXiv2013

Observing the inhomogeneity in the holographic models of superconductors

We study the gravity duals of striped holographic superconductors in the AdS black hole and AdS soliton backgrounds. We show the dependences of the condensation and the critical temperature/critical chemical potential on the inhomogeneity in these two different spacetimes. By exploring the dynamics of the normal phase through the scalar field perturbation, we argue that the pair susceptibility and the conductivity can be possible phenomenological indications to disclose the property of inhomogeneity.

hep-th↗

arXiv2013

Dynamical gap from holography in the charged dilaton black hole

We study the holographic non-relativistic fermions in the presence of bulk dipole coupling in charged dilatonic black hole background. We explore the nontrivial effects of the bulk dipole coupling, the fermion charge as well as the dilaton field on the flat band, the Fermi surface and the emergence of the gap by investigating the spectral function of the non-relativistic fermion system. In particular, we find that the presence of the flat band in the non-relativistic case will suppress the Fermi momentum. Besides, we observe that the effect of the dipole coupling in the dilaton gravity is more explicit. Finally, we consider the non-relativistic fermions at nonzero temperature. A phase transition from insulator to a conducting state is observed as the fermion system becomes hotter.

hep-th↗

arXiv2012

Holographic fermions in charged Lifshitz theory

We investigate the properties of holographic fermions in charged Lifshitz black holes at finite temperature through the AdS/CFT correspondence. In the charged Lifshitz background with the dynamical exponent $z=2$, we find that the dispersion relation is linear. The scaling behavior of the imaginal part of the Green function relative to $k_{\perp}=k-k_F$ is also discussed. We find, although the system has linear dispersion relation and quadratic quasi-particle width, it does not satisfy Luttinger's theorem. We also find that the variation of the scaling parameters $α$ and $β$ is small as the charge $q$ varies. Furthermore, we also discuss the effect of the dynamical exponent $z$ by considering the cases $z=4$ and $z=6$ and show that $ImG_{ii}$ become smooth when the dynamical exponent $z$ increases.

hep-th↗

arXiv2012

Observing various phase transitions in the holographic model of superfluidity

We study the gravity duals of supercurrent solutions in the AdS black hole background with general phase structure to describe both the first and the second order phase transitions at finite temperature in strongly interacting systems. We argue that the conductivity and the pair susceptibility can be possible phenomenological indications to distinguish the order of phase transitions. We extend our discussion to the AdS soliton configuration. Different from the black hole spacetime, in the probe limit the first order phase transition cannot be brought by introducing the spatial component of the vector potential of the gauge field in the AdS soliton background.

hep-th↗

arXiv2012

Dipole Coupling Effect of Holographic Fermion in the Background of Charged Gauss-Bonnet AdS Black Hole

We investigate the holographic fermions in the charged Gauss-Bonnet $AdS_{d}$ black hole background with the dipole coupling between fermion and gauge field in the bulk. We show that in addition to the strength of the dipole coupling, the spacetime dimension and the higher curvature correction in the gravity background also influence the onset of the Fermi gap and the gap distance. We find that the higher curvature effect modifies the fermion spectral density and influences the value of the Fermi momentum for the appearance of the Fermi surface. There are richer physics in the boundary fermion system due to the modification in the bulk gravity.

hep-th↗

arXiv2012

Phase transition in the holographic model of superfluidity with backreactions

In the fully back reacted geometry we develop a supercurrent solution which corresponds to a deformation of superconducting black holes by the spatial component of gauge fields with a non- trivial radial dependence. We investigate the influence of the backreaction on the condensation and the phase structure in the AdS black hole spacetime. Different from that observed in the probe limit, we find that two operators cannot give consistent information on the phase diagram. We argue that only one of these two operators can reflect the real property of the condensation and phase structure in the holographic superconductor. We also generalize our study to the associated phase diagram in the AdS soliton background.

hep-th↗

arXiv2012

Holographic p-wave Superconductors in Quasi-topological Gravity

We construct a holographic p-wave superconductor model in the framework of quasi-topological gravity in the probe limit. The relation between the critical temperature and the coupling parameters of higher curvature terms is investigated. The numerical results for conductivity are presented as well. It turns out that our data fits the Drude model very well in the low frequency limit, and the values of DC conductivity as well as the relaxation time are obtained numerically.

hep-th↗

arXiv2011

The 3+1 holographic superconductor with Weyl corrections

In this paper we study $3+1$ holographic superconductors with Weyl corrections. We find that the critical temperature of a superconductor with Weyl corrections increases as we amplify the Weyl coupling parameter $γ$, indicating the condensation will be harder when the parameter $γ$ decreases. We also calculate the conductivity and the ratio of gap frequency over critical temperature $ω_{g}/T_{c}$ numerically for various coupling parameters. We find that the ratio $ω_g/T_c$ becomes larger when the Weyl coupling parameter $γ$ decreases. We also notice that when $γ< 0$ there is an extra spike that appears inside the gap.

hep-th↗

arXiv2010

Holographic Superconductors in Quasi-topological Gravity

In this paper we study (3+1) dimensional holographic superconductors in quasi-topological gravity which is recently proposed by R. Myers {\it et.al.}. Through both analytical and numerical analysis, we find in general the condensation becomes harder with the increase of coupling parameters of higher curvature terms. In particular, comparing with those in ordinary Gauss-Bonnet gravity, we find that positive cubic corrections in quasi-topological gravity suppress the condensation while negative cubic terms make it easier. We also calculate the conductivity numerically for various coupling parameters. It turns out that the universal relation of $ω_g/T_c\simeq 8$ is unstable and this ratio becomes larger with the increase of the coupling parameters. A brief discussion on the condensation from the CFT side is also presented.

hep-th↗

arXiv2010

Thermal fluctuations in viscous cosmology

In this paper we investigate the power spectrum of thermal fluctuations in very early stage of viscous cosmology. When the state parameter as well as the viscous coefficient of a barotropic fluid is properly chosen, a scale invariant spectrum with large non-Gaussianity can be obtained. In contrast to the results previously obtained in string gas cosmology and holographic cosmology, we find the non-Gaussianity in this context can be k-independent such that it is not suppressed at large scale, which is expected to be testified in future observation.

gr-qc↗

arXiv2009

Viscous gravitational aether and the cosmological constant problem

Recently a notion of gravitational aether is advocated to solve the cosmological constant problem.Through the modification of the source of gravity one finds that the effective Newton's constant is source dependent so as to provide a simple but consistent way to decouple gravity from the vacuum energy.However,in the original paper the ratio of the effective Newton's constants for pressureless dust and radiation has an upper bound which is 0.75.In this paper we propose a scheme to loose this bound by introducing a bulk viscosity for the gravitational aether,and expect this improvement will provide more space for matching predictions from this theoretical programm with observational constraints.

gr-qc↗