Xian-Hui Ge

Analytical study on holographic superconductors in external magnetic field

We investigate the holographic superconductors immersed in an external magnetic field by using the analytical approach. We obtain the spatially dependent condensate solutions in the presence of the magnetism and find analytically that the upper critical magnetic field satisfies the relation given in the Ginzburg-Landau theory. The external magnetic field expels the condensate and makes the condensation harder to form. Extending to the D-dimensional Gauss-Bonnet AdS black holes, we examine the influence given by the Gauss-Bonnet coupling on the condensation. Different from the positive coupling, we find that the negative Gauss-Bonnet coupling enhances the condensation when the external magnetism is not strong enough.

Shear viscosity, instability and the upper bound of the Gauss-Bonnet coupling constant

We compute the dimensionality dependence of �/s for charged black branes with Gauss-Bonnet correction. We find that both causality and stability constrain the value of Gauss-Bonnet coupling constant to be bounded by 1/4 in the infinite dimensionality limit. We further show that higher dimensionality stabilize the gravitational perturbation. The stabilization of the perturbation in higher dimensional space-time is a straightforward consequence of the Gauss-Bonnet coupling constant bound.

Shear viscosity and instability from third order Lovelock gravity

We calculate the ratio of shear viscosity to entropy density for charged black branes in third order Lovelock theory. For chargeless black branes, the result turns out to be consistent with the prediction made by Brustein and Medved [Phys. Rev. D 79, 021901 (2009)]. We find that the third order Lovelock gravity term does not contribute to causality violation unlike the Gauss-Bonnet term. The stability of the black brane again requires the value of the Lovelock coupling constant to be bounded by 1/4 in the infinite dimensionality limit.

Anisotropic plasma at finite

A bstractWe present a type IIB supergravity solution dual to a spatially anisotropic N

chemical potential

\mathcal{N}

Thermoelectric DC conductivities with momentum dissipation from higher derivative gravity

=4 super Yang-Mills plasma at finite U(1) chemical potential and finite temperature. The effective five-dimensional gravitational theory is a consistent Einstein-Maxwell-dilaton-Axion truncation of the gauged supergravity. We obtain the solutions both numerically and analytically. We study the phase structure and thermodynamic instabilities of the solution, and find new instabilities independent of the renormalization scheme.

Holographic fermions in charged Lifshitz theory

Abstract Generically, the black brane solution with planar horizons is thermodynamically stable. We find a counter-example to this statement by demonstrating that an anisotropic black brane is unstable. We present a charged black brane solution dual to a spatially anisotropic finite temperature N = 4 super Yang–Mills plasma at finite U ( 1 ) chemical potential. This static and regular solution is obtained both numerically and analytically. We uncover rich thermodynamic phase structures for this system by considering the cases when the anisotropy constant “a” takes real and imaginary values, respectively. In the case a 2 > 0 , the phase structure of this anisotropic black brane is similar to that of Schwarzschild–AdS black hole with S 3 horizon topology, yielding a thermodynamical instability at smaller horizon radii. For the condition a 2 ≤ 0 , the thermodynamics is dominated by the black brane phase for all temperatures.

d-wave holographic superconductors with backreaction in external magnetic fields

A bstractWe present a mechanism of momentum relaxation in higher derivative gravity by adding linear scalar fields to the Gauss-Bonnet theory. We analytically computed all of the DC thermoelectric conductivities in this theory by adopting the method given by Donos and Gauntlett in [arXiv:1406.4742]. The results show that the DC electric conductivity is not a monotonic function of the effective impurity parameter β: in the small β limit, the DC conductivity is dominated by the coherent phase, while for larger β, pair creation contribution to the conductivity becomes dominant, signaling an incoherent phase. In addition, the DC heat conductivity is found independent of the Gauss-Bonnet coupling constant.