arXiv subjects

Qiyuan Pan

Publications and source records attributed to Qiyuan Pan.

At least 73 records · Page 4Linked to original sources

arXiv2018

Refractive index in generalized superconductors with Born-Infeld electrodynamics

We investigate, in the probe limit, the negative refraction in the generalized superconductors with the Born-Infeld electrodynamics. We observe that the system has a negative Depine-Lakhtakia index in the superconducting phase at small frequencies and the greater the Born-Infeld corrections the larger the range of frequencies or the range of temperatures for which the negative refraction occurs. Furthermore, we find that the tunable Born-Infeld parameter can be used to improve the propagation of light in the holographic setup. Our analysis indicates that the Born-Infeld electrodynamics plays an important role in determining the optical properties of the boundary theory.

hep-th↗

arXiv2017

Detect black holes using photons for coupling model of electromagnetic and gravitational fields

For a model of the electromagnetic field coupled to Weyl tensor, Maxwell equations are modified and photons at low frequencies no longer propagate along light cone. If we detect a black hole using these photons, some difficulties appear because we can not determine the position of event horizon which is defined by null surface. To overcome these difficulties, the simplest way may be an effective description by introducing an effective spacetime in which the photons propagate along the light cone. Then, we find, comparing the results with those of the original spacetime, that the event horizon and temperature do not change, but the area of the event horizon and Bekenstein-Hawking entropy become different. We show that the total entropy for this system, which is still the same as that of original spacetime, consists of two parts, one is the Bekenstein-Hawking entropy and the other is the entropy arising from the coupling of electromagnetic field and Weyl tensor. We also present the effective descriptions for the Smarr relation and first law of thermodynamics.

gr-qc↗

arXiv2017

Split degenerate states and stable p+ip phases from holography

In this paper, we investigate the p+$i$p superfluid phases in the complex vector field holographic p-wave model. We find that in the probe limit, the p+$i$p phase and the p-wave phase are equally stable, hence the p and $i$p orders can be mixed with an arbitrary ratio to form more general p+$λi$p phases, which are also equally stable with the p-wave and p+$i$p phases. As a result, the system possesses a degenerate thermal state in the superfluid region. We further study the case with considering the back reaction on the metric, and find that the degenerate ground states will be separated into p-wave and p+$i$p phases, and the p-wave phase is more stable. Finally, due to the different critical temperature of the zeroth order phase transitions from p-wave and p+$i$p phases to the normal phase, there is a temperature region where the p+$i$p phase exists but the p-wave phase doesn't. In this region we find the stable p+$i$p phase for the first time.

hep-th↗

arXiv2016

Holographic p-wave superfluid in Gauss-Bonnet gravity

We construct the holographic p-wave superfluid in Gauss-Bonnet gravity via a Maxwell complex vector field model and investigate the effect of the curvature correction on the superfluid phase transition in the probe limit. We obtain the rich phase structure and find that the higher curvature correction hinders the condensate of the vector field but makes it easier for the appearance of translating point from the second-order transition to the first-order one or for the emergence of the Cave of Winds. Moreover, for the supercurrents versus the superfluid velocity, we observe that our results near the critical temperature are independent of the Gauss-Bonnet parameter and agree well with the Ginzburg-Landau prediction.

hep-th↗

arXiv2016

A general holographic insulator/superconductor model away from the probe limit

We investigate holographic phase transitions affected by dark matter sector in the AdS soliton background away from the probe limit. When neglecting backreaction, the scalar charge q can be scaled unity without loss of generality. While considering backreaction in this work, we obtain much more richer physics by choosing various scalar charge q. Firstly, we observe unstable retrograde condensation appears due to the dark matter sector and also derive stable conditions. For stable solutions, we find that the larger coupling parameter $α$ makes the gap of condensation shallower and the critical chemical potential keeps as a constant with a large scalar charge q, which is similar to cases in the probe limit. In contrast, the dark matter sector could affect the critical chemical potential and the order of phase transitions for very small charge q. We also arrive at the same conclusion from the holographic topological entanglement entropy approach. Moreover, we state that the entanglement entropy approach is especially powerful in studying the effects of the dark matter sector in this general insulator/superconductor system.

hep-th↗

arXiv2016

Analytical study on holographic superfluid in AdS soliton background

We analytically study the holographic superfluid phase transition in the AdS soliton background by using the variational method for the Sturm-Liouville eigenvalue problem. By investigating the holographic s-wave and p-wave superfluid models in the probe limit, we observe that the spatial component of the gauge field will hinder the phase transition. Moreover, we note that, different from the AdS black hole spacetime, in the AdS soliton background the holographic superfluid phase transition always belongs to the second order and the critical exponent of the system takes the mean-field value in both s-wave and p-wave models. Our analytical results are found to be in good agreement with the numerical findings.

hep-th↗

arXiv2016

Holographic superconductor in hyperscaling violation geometry with Maxwell-dilaton coupling

We re-investigate the holographic superconductor in hyperscaling violation geometry by considering the coupling between the probed Maxwell field and the background dilaton. We find that the phenomenon of superconductivity still exists, but with properties affected by such a coupling. The critical temperature decreases as the hyperscaling violation exponent is increased. The influence of the dynamical exponent on the critical temperature becomes complicated which depends on the mass of the probed scalar field and the hyperscaling violation exponent. The results of the frequency gap show a large deviation from the expected universal relation.

hep-th↗

arXiv2015

Regular Phantom Black Hole and Holography: very high temperature superconductors

Holographic superconductors containing a non-minimal derivative coupling for scalar field in a regular phantom plane symmetric black hole have been considered. We show that the parameter of the regular black hole $b$ as well as the non-minimal derivative coupling parameter $η$ affect the formation of the condensate as well as the conductivity in the superconductor. Moreover, $b$ has a critical value in which the critical temperature $T_c$ increases without a bound. We argue that an unlimited critical temperature is an evidence that high $T_c$ superconductor must be related to the absence of a singularity in the bulk in the AdS/CFT context.

gr-qc↗

arXiv2015

Revisiting holographic superconductors with hyperscaling violation

We investigate the effect of the hyperscaling violation on the holographic superconductors. In the s-wave model, we find that the critical temperature decreases first and then increases as the hyperscaling violation increases, and the mass of the scalar field will not modify the value of the hyperscaling violation which gives the minimum critical temperature. We analytically confirm the numerical results by using the Sturm-Liouville method with the higher order trial function and improve the previous findings in J. High Energy Phys. {\bf 09}, 048 (2013). However, different from the s-wave case, we note that the critical temperature decreases with the increase of the hyperscaling violation in the p-wave model. In addition, we observe that the hyperscaling violation affects the conductivity of the holographic superconductors and changes the expected relation in the gap frequency in both s-wave and p-wave models.

hep-th↗

arXiv2015

Geometric optics for a coupling model of the electromagnetic and gravitational fields

The coupling between the electromagnetic and gravitational fields results in "faster than light" photons and invalids the Lorentz invariance and some laws of physics. A typical example is that the first and third laws of geometric optics are invalid in the usual spacetime. By introducing an effective spacetime, we find that the wave vector can be casted into null and then it obeys the geodesic equation, the polarization vector is perpendicular to the rays, and the number of photons is conserved. That is to say, the laws of geometric optics are still valid for the modified theory in the effective spacetime. We also show that the focusing theorem of light rays for the modified theory in the effective spacetime takes the same form as usual.

gr-qc↗

arXiv2015

On analytical study of holographic superconductors with Born-Infeld electrodynamics

Based on the Sturm-Liouville eigenvalue problem, Banerjee \emph{et al.} proposed a perturbative approach to analytically investigate the properties of the ($2+1$)-dimensional superconductor with Born-Infeld electrodynamics [Phys. Rev. D {\bf 87}, 104001 (2013)]. By introducing an iterative procedure, we will further improve the analytical results and the consistency with the numerical findings, and can easily extend the analytical study to the higher-dimensional superconductor with Born-Infeld electrodynamics. We observe that the higher Born-Infeld corrections make it harder for the condensation to form but do not affect the critical phenomena of the system. Our analytical results can be used to back up the numerical computations for the holographic superconductors with various condensates in Born-Infeld electrodynamics.

hep-th↗

arXiv2015

Condensation for non-relativistic matter in Hořava-Lifshitz gravity

We study condensation for non-relativistic matter in a Hořava-Lifshitz black hole without the condition of the detailed balance. We show that, for the fixed non-relativistic parameter $α_2$ (or the detailed balance parameter $ε$), it is easier for the scalar hair to form as the parameter $ε$ (or $α_2$) becomes larger, but the condensation is not affected by the non-relativistic parameter $β_2$. We also find that the ratio of the gap frequency in conductivity to the critical temperature decreases with the increase of $ε$ and $α_2$, but increases with the increase of $β_2$. The ratio can reduce to the Horowitz-Roberts relation $ω_g/T_c\approx 8$ obtained in the Einstein gravity and Cai's result $ω_g/T_c\approx 13$ found in a Hořava-Lifshitz gravity with the condition of the detailed balance for the relativistic matter. Especially, we note that the ratio can arrive at the value of the BCS theory $ω_g/T_c\approx 3.5$ by taking proper values of $ε$, $α_2$, $β_2$ and $m$.

hep-th↗

arXiv2015

Holographic p-wave superconductor models with Weyl corrections

We study the effect of the Weyl corrections on the holographic p-wave dual models in the backgrounds of AdS soliton and AdS black hole via a Maxwell complex vector field model by using the numerical and analytical methods. We find that, in the soliton background, the Weyl corrections do not influence the properties of the holographic p-wave insulator/superconductor phase transition, which is different from that of the Yang-Mills theory. However, in the black hole background, we observe that similar to the Weyl correction effects in the Yang-Mills theory, the higher Weyl corrections make it easier for the p-wave metal/superconductor phase transition to be triggered, which shows that these two p-wave models with Weyl corrections share some similar features for the condensation of the vector operator.

hep-th↗

arXiv2014

Notes on analytical study of holographic superconductors with Lifshitz scaling in external magnetic field

We employ the matching method to analytically investigate the holographic superconductors with Lifshitz scaling in an external magnetic field. We discuss systematically the restricted conditions for the matching method and find that this analytic method is not always powerful to explore the effect of external magnetic field on the holographic superconductors unless the matching point is chosen in an appropriate range and the dynamical exponent $z$ satisfies the relation $z=d-1$ or $z=d-2$. From the analytic treatment, we observe that Lifshitz scaling can hinder the condensation to be formed, which can be used to back up the numerical results. Moreover, we study the effect of Lifshitz scaling on the upper critical magnetic field and reproduce the well-known relation obtained from Ginzburg-Landau theory.

hep-th↗

arXiv2014

Holographic entanglement entropy in general holographic superconductor models

We study the entanglement entropy of general holographic dual models both in AdS soliton and AdS black hole backgrounds with full backreaction. We find that the entanglement entropy is a good probe to explore the properties of the holographic superconductors and provides richer physics in the phase transition. We obtain the effects of the scalar mass, model parameter and backreaction on the entropy, and argue that the jump of the entanglement entropy may be a quite general feature for the first order phase transition. In strong contrast to the insulator/superconductor system, we note that the backreaction coupled with the scalar mass can not be used to trigger the first order phase transition if the model parameter is below its bottom bound in the metal/superconductor system.

hep-th↗

arXiv2013

Horizon instability of massless scalar perturbations of an extreme Reissner-Nordström-AdS black hole

We study the stability of extreme Reissner-Nordström-AdS black hole under massless scalar perturbations. We show that the perturbation on the horizon of the extreme Reissner-Nordström-AdS black hole experiences a power-law decay, instead of an exponential decay as observed in the nonextreme AdS black hole. On the horizon of the extreme Reissner-Nordström-AdS black hole, the blow up happens at lower order derivative of the scalar field compared with that of the extreme Reissner-Nordström black hole, which shows that extreme AdS black holes tend to instability in comparison to black holes in asymptotic flat space-times.

hep-th↗

arXiv2013

Holographic superconductors in quintessence AdS black hole

We present a solution of Einstein equations describing a $d$-dimensional planar quintessence AdS black hole which depends on the state parameter $w_q$ of quintessence. We investigate holographic superconductors in this background and probe effects of the state parameter $w_q$ on the critical temperature $T_c$, the condensation formation and conductivity. The larger absolute value of $w_q$ leads to the lower critical temperature $T_c$ and the higher ratio between the gap frequency in conductivity to the critical temperature for the condensates. Moreover, we also find that the scalar condensate there exists an additional constraint condition originating from the quintessence $(d-1)w_q+λ_{\pm}>0$ for the operators $\mathcal{O}_{\pm}$, respectively. Our results show that the scalar condensation is harder to form and the occurrence of holographic dual superconductor needs the stronger coupling in the quintessence AdS black hole spacetime.

gr-qc↗

arXiv2013

Notes on holographic superconductor models with the nonlinear electrodynamics

We investigate systematically the effect of the nonlinear correction to the usual Maxwell electrodynamics on the holographic dual models in the backgrounds of AdS black hole and AdS soliton. Considering three types of typical nonlinear electrodynamics, we observe that in the black hole background the higher nonlinear electrodynamics correction makes the condensation harder to form and changes the expected relation in the gap frequency, which is similar to that caused by the curvature correction. However, in strong contrast to the influence of the curvature correction, we find that in the AdS soliton background the nonlinear electrodynamics correction will not affect the properties of the holographic superconductor and insulator phase transitions, which may be a quite general feature for the s-wave holographic superconductor/insulator system.

hep-th↗