arXiv subjects

Jian-Pin Wu

Publications and source records attributed to Jian-Pin Wu.

At least 109 records · Page 6Linked to original sources

arXiv2016

A Novel Insulator by Holographic Q-lattices

We construct a bulk geometry with Q-lattice structure, which is implemented by two gauge fields and a coupling between the lattice and the Maxwell field. This gravity dual model can describe a novel insulator which exhibits some key features analogous to Mott insulator. In particular, a hard gap in insulating phase as well as vanishing DC conductivity can be simultaneously achieved. In addition, we discuss the non-Drude behavior of the optical conductivity in low frequency region in insulating phase, which exhibits some novel characteristics different from ordinary Mott insulator.

hep-th↗

arXiv2016

The pseudo-gap phase and the duality in holographic fermionic system with dipole coupling on Q-lattice

We classify the different phases by the "pole-zero mechanism" for a holographic fermionic system which contains a dipole coupling with strength $p$ on a Q-lattice background. A complete phase structure in $p$ space can be depicted in terms of Fermi liquid, non-Fermi liquid, Mott phase and pseudo-gap phase. In particular, we find that in general the region of the pseudo-gap phase in $p$ space is suppressed when the Q-lattice background is dual to a deep insulating phase, while for an anisotropic background, we have an anisotropic region for the pseudo-gap phase in $p$ space as well. In addition, we find that the duality between zeros and poles always exists regardless of whether or not the model is isotropic.

hep-th↗

arXiv2015

Scalar Boundary Conditions in Hyperscaling Violating Geometry

We study the possible boundary conditions of scalar field modes in a hyperscaling violation(HV) geometry with Lifshitz dynamical exponent $z (z\geqslant1)$ and hyperscaling violation exponent $θ(θ\neq0)$. For the case with $θ>0$, we show that in the parameter range with $1\leq z\leq 2,~-z+d-1<θ\leq (d-1)(z-1)$ or $z>2,~-z+d-1<θ\leq d-1$, the boundary conditions have different types, including the Neumann, Dirichlet and Robin conditions, while in the range with $θ\leq-z+d-1$, only Dirichlet type condition can be set. In particular, we further confirm that the mass of the scalar field does not play any role in determining the possible boundary conditions for $θ>0$, which has been addressed in Ref. \cite{1201.1905}. Meanwhile, we also do the parallel investigation in the case with $θ<0$. We find that for $m^2<0$, three types of boundary conditions are available, but for $m^2>0$, only one type is available.

hep-th↗

arXiv2015

Fermionic phase transition induced by the effective impurity in holography

We investigate the holographic fermionic phase transition induced by the effective impurity in holography, which is introduced by massless scalar fields in Einstein-Maxwell-massless scalar gravity. We obtain a phase diagram in $(α, T)$ plane separating the Fermi liquid phase and the non-Fermi liquid phase.

hep-th↗

arXiv2015

Transport coefficients from hyperscaling violating black brane: shear viscosity and conductivity

We investigate two transport coefficients, shear viscosity and conductivity, in a non-relativistic boundary filed theory without hyperscaling symmetry, which is dual to a bulk charged hyperscaling violating black brane. Employing matching method, we obtain that the ratio of shear viscosity and the entropy density is alway $1/4π$ at any temperature, which satisfies the Kovtun-Starinets-Son (KSS) bound. Besides, we also present the universal formulas of AC conductivity, which is closely dependent on the relation between geometrical parameters $z$ and $θ$. The optical conductivity at high frequency limit behaves with a (non)-power law scaling or approaches to be constant, depending on the choice of $z$ and $θ$. This feature is different from the observes in Lifshitz black brane that the optical conductivity always complies with a (non)-power law scaling in high frequency limit when the Lifshitz exponent $z>1$. We also argue that the temperate has no print on the exponent of (non)-power law scaling in large frequency while it will affect the strength of conductivity at low frequency.

hep-th↗

arXiv2015

Building a doped Mott system by holography

We construct a holographic model in the framework of Q-lattices whose dual exhibits metal-insulator transitions. By introducing an interacting term between the Q-lattice and the electromagnetic field in bulk geometry, we find such kind of transition can be Mott-like. The evidences are presented as follows. i) The transition from a metallic phase to an insulating phase occurs when the lattice constant becomes larger. ii) A hard gap in the insulating phase can be manifestly observed in the optical conductivity. Nevertheless, in the zero temperature limit this model exhibits novel metallic behavior, featured by a gap as well as a zero-frequency mode with tiny spectral weight. It implies that our model is dual to a doped Mott system in one dimension where umklapp scattering is frozen at zero temperature. The similarity between this model and some organic linear chain conductors is briefly discussed.

hep-th↗

arXiv2015

DC and Hall conductivity in holographic massive Einstein-Maxwell-Dilaton gravity

We investigate the holographic DC and Hall conductivity in massive Einstein-Maxwell-Dilaton (EMD) gravity. Two special EMD backgrounds are considered explicitly. One is dyonic Reissner-Nordstr$\ddot{o}$m-AdS (RN-AdS) geometry and the other one is hyperscaling violation AdS (HV-AdS) geometry. We find that the linear-T resistivity and quadratic-T inverse Hall angle can be simultaneously achieved in HV-AdS models, providing a hint to construct holographic models confronting with the experimental data of strange metal in future.

hep-th↗

arXiv2015

Anisotropic Fermi surface from holography

We investigate the probe holographic fermions by using an anisotropic charged black brane solution. We derive the equation of motion of probe bulk fermions with one Fermi momentum along the anisotropic and one along the isotropic directions. We then numerically solve the equation and analyze the properties of Green function with these two momentums. We find in this case the shape of Fermi surface is anisotropic. However, for both Fermi momentums perpendicular to the anisotropic direction, the Fermi surface is isotropic. We verify that our system obeys the recently conjectured bound for thermoelectric diffusion constants for the stable branch of the black brane solutions.

hep-th↗

arXiv2015

Dynamically generated gap from holography in the charged black brane with hyperscaling violation

We holographically investigate the effects of a dipole coupling between a fermion field and a $U(1)$ gauge field on the dual fermionic sector in the charged gravity bulk with hyperscaling violation. We analytically study the features of the ultraviolet and infrared Green's functions of the dual fermionic system and we show that as the dipole coupling and the hyperscaling violation exponent are varied, the fluid possess Fermi, marginal Fermi, non-Fermi liquid phases and also an additional Mott insulating phase. We find that the increase of the hyperscaling violation exponent which effectively reduces the dimensionality of the system makes it harder for the Mott gap to be formed. We also show that the observed duality between zeros and poles in the presence of a dipole moment coupling still persists in theories with hyperscaling violation.

hep-th↗

arXiv2015

Holographic Superconductor on Q-lattice

We construct the simplest gravitational dual model of a superconductor on Q-lattices. We analyze the condition for the existence of a critical temperature at which the charged scalar field will condense. In contrast to the holographic superconductor on ionic lattices, the presence of Q-lattices will suppress the condensate of the scalar field and lower the critical temperature. In particular, when the Q-lattice background is dual to a deep insulating phase, the condensation would never occur for some small charges. Furthermore, we numerically compute the optical conductivity in the superconducting regime. It turns out that the presence of Q-lattice does not remove the pole in the imaginary part of the conductivity, ensuring the appearance of a delta function in the real part. We also evaluate the gap which in general depends on the charge of the scalar field as well as the Q-lattice parameters. Nevertheless, when the charge of the scalar field is relatively large and approaches the probe limit, the gap becomes universal with $ω_g \simeq 9T_c$ which is consistent with the result for conventional holographic superconductors.

hep-th↗

arXiv2014

Holographic fermionic system with dipole coupling on Q-lattice

We construct a holographic model for a fermionic system on Q-lattice and compute the spectral function in the presence of a dipole coupling. Both key features of doped Mott insulators, the dynamical generation of a gap and spectral weight transfer, are observed when adjusting the value of the coupling parameter $p$. Of particular interest is that when the background is in a deep insulating phase, the Mott gap opens much easier with a smaller coupling parameter in comparison with a metallic background. The effects of lattice parameters on the width of the gap $Δ/μ$ are studied and a turning point is observed near the critical regime of metal-insulator transitions of the background. Furthermore, the temperature dependence of the spectral function is studied. Finally, we also observe that the anisotropic Q-lattice generates anisotropic peaks with different magnitudes, indicating that insulating and metallic phases arise in different directions.

hep-th↗

arXiv2014

Formation of Fermi surfaces and the appearance of liquid phases in holographic theories with hyperscaling violation

We consider a holographic fermionic system in which the fermions are interacting with a U(1) gauge field in the presence of a dilaton field in a gravity bulk of a charged black hole with hyperscaling violation. Using both analytical and numerical methods, we investigate the properties of the infrared and ultaviolet Green's functions of the holographic fermionic system. Studying the spectral functions of the system, we find that as the hyperscaling violation exponent is varied, the fermionic system possesses Fermi, non-Fermi, marginal-Fermi and log-oscillating liquid phases. Various liquid phases of the fermionic system with hyperscaling violation are also generated with the variation of the fermionic mass. We also explore the properties of the flat band and the Fermi surface of the non-relativistic fermionic fixed point dual to the hyperscaling violation gravity.

hep-th↗

arXiv2014

Holographic superconductors from the massive gravity

A holographic superconductor is constructed in the background of a massive gravity theory. In the normal state without condensation, the conductivity exhibits a Drude peak that approaches a delta function in the massless gravity limit as studied by David Vegh. In the superconducting state, besides the infinite DC conductivity, the AC conductivity has Drude behavior at low frequency followed by a power law-fall. These results are in agreement with that found earlier by Horowitz and Santos, who studied a holographic superconductor with an implicit periodic potential beyond the probe limit. The results also agree with measurements on some cuprates.

hep-th↗

arXiv2014

Chaos from the ring string in Gauss-Bonnet black hole in $AdS_5$ space

By the Poincare sections, the dynamical behaviors of the ring string in the AdS-Gauss-Bonnet (AdS-GB) black hole are studied. A threshold value of the Gauss-Bonnet (GB) parameter $λ$ are found by the numerical method, below which the behavior of this dynamical system is no-chaotic and above which the behavior becomes gradually chaotic. The chaotic behavior becomes stronger with the increases of GB parameter. It is different from the case in the AdS-Schwarzschild black hole, which is weakly chaotic. Furthermore, we confirm our findings by the Fast Lyapunov indicators.

hep-th↗

arXiv2013

Holographic Lattice in Einstein-Maxwell-Dilaton Gravity

We construct an ionic lattice background in the framework of Einstein-Maxwell-dilaton theory in four dimensional space time. The optical conductivity of the dual field theory on the boundary is investigated. Due to the lattice effects, we find the imaginary part of the conductivity is manifestly suppressed in the zero frequency limit, while the DC conductivity approaches a finite value such that the previous delta function reflecting the translation symmetry is absent. Such a behavior can be exactly fit by the Drude law at low frequency. Moreover, we find that the modulus of the optical conductivity exhibits a power-law behavior at intermediate frequency regime. Our results provides further support for the universality of such power-law behavior recently disclosed in Einstein-Maxwell theory by Horowitz, Santos and Tong.

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↗

arXiv2013

Holographic fermions in charged dilaton black branes

By imposing the relativistic boundary term and Lorentz violating that in the dilatonic black brane with a Lifshitz like IR geometry and $AdS_4$ boundary, we study the properties of the spectral functions of the fermions. We find that in the two fixed points, there are emergent Fermi-surface structures and many properties seem to be in agreement with that of Fermi liquid. Especially, the low energy behavior exhibits a linear dispersion relation. In addition, we also find that a holographic flat band also emerges in this background of the dilatonic black brane.

hep-th↗

arXiv2013

Anomaly freedom of the vector modes with holonomy corrections in perturbative Euclidean loop quantum gravity

We study the perturbation of the effective Hamiltonian constraint with holonomy correction from Euclidean loop quantum gravity. The Poisson bracket between the corrected Hamiltonian constraint and the diffeomorphism constraint is derived for vector modes. Some specific form of the holonomy correction function $f^{i}_{cd}$ is found, which satisfies that the constraint algebra is anomaly-free. This result confirms the possibility of non-trivial holonomy corrections from full theory while preserving anomaly-free constraint algebra in the perturbation framework. It also gives valuable hints on the possible form of holonomy corrections in effective loop quantum gravity.

gr-qc↗