930 research outputs found
Holographic Superconductors from Einstein-Maxwell-Dilaton Gravity
We construct holographic superconductors from Einstein-Maxwell-dilaton
gravity in 3+1 dimensions with two adjustable couplings and the charge
carried by the scalar field. For the values of and we
consider, there is always a critical temperature at which a second order phase
transition occurs between a hairy black hole and the AdS RN black hole in the
canonical ensemble, which can be identified with the superconducting phase
transition of the dual field theory. We calculate the electric conductivity of
the dual superconductor and find that for the values of and where
is small the dual superconductor has similar properties to the
minimal model, while for the values of and where is
large enough, the electric conductivity of the dual superconductor exhibits
novel properties at low frequencies where it shows a "Drude Peak" in the real
part of the conductivity.Comment: 25 pages, 13 figures; v2, typos corrected; v3, refs added, to appear
in JHE
Analytic study of properties of holographic p-wave superconductors
In this paper, we analytically investigate the properties of p-wave
holographic superconductors in -Schwarzschild background by two
approaches, one based on the Sturm-Liouville eigenvalue problem and the other
based on the matching of the solutions to the field equations near the horizon
and near the asymptotic region. The relation between the critical
temperature and the charge density has been obtained and the dependence of the
expectation value of the condensation operator on the temperature has been
found. Our results are in very good agreement with the existing numerical
results. The critical exponent of the condensation also comes out to be 1/2
which is the universal value in the mean field theory.Comment: Latex, To appear in JHE
Low temperature properties of holographic condensates
In the current work we study various models of holographic superconductors at
low temperature. Generically the zero temperature limit of those models are
solitonic solution with a zero sized horizon. Here we generalized simple
version of those zero temperature solutions to small but non-zero temperature
T. We confine ourselves to cases where near horizon geometry is AdS^4. At a
non-zero temperature a small horizon would form deep inside this AdS^4 which
does not disturb the UV physics. The resulting geometry may be matched with the
zero temperature solution at an intermediate length scale. We understand this
matching from separation of scales by setting up a perturbative expansion in
gauge potential. We have a better analytic control in abelian case and
quantities may be expressed in terms of hypergeometric function. From this we
calculate low temperature behavior of various quatities like entropy, charge
density and specific heat etc. We also calculate various energy gaps associated
with p-wave holographic superconductor to understand the underlying pairing
mechanism. The result deviates significantly from the corresponding weak
coupling BCS counterpart.Comment: 17 Page
Supersymmetric AdS_4 black holes and attractors
Using the general recipe given in arXiv:0804.0009, where all timelike
supersymmetric solutions of N=2, D=4 gauged supergravity coupled to abelian
vector multiplets were classified, we construct the first examples of genuine
supersymmetric black holes in AdS_4 with nonconstant scalar fields. This is
done for various choices of the prepotential, amongst others for the STU model.
These solutions permit to study the BPS attractor flow in AdS. We also
determine the most general supersymmetric static near-horizon geometry and
obtain the attractor equations in gauged supergravity. As a general feature we
find the presence of flat directions in the black hole potential, i.e.,
generically the values of the moduli on the horizon are not completely
specified by the charges. For one of the considered prepotentials, the
resulting moduli space is determined explicitely. Still, in all cases, we find
that the black hole entropy depends only on the charges, in agreement with the
attractor mechanism.Comment: 25 pages, uses JHEP3.cl
Emergent Gauge Fields in Holographic Superconductors
Holographic superconductors have been studied so far in the absence of
dynamical electromagnetic fields, namely in the limit in which they coincide
with holographic superfluids. It is possible, however, to introduce dynamical
gauge fields if a Neumann-type boundary condition is imposed on the
AdS-boundary. In 3+1 dimensions, the dual theory is a 2+1 dimensional CFT whose
spectrum contains a massless gauge field, signaling the emergence of a gauge
symmetry. We study the impact of a dynamical gauge field in vortex
configurations where it is known to significantly affect the energetics and
phase transitions. We calculate the critical magnetic fields H_c1 and H_c2,
obtaining that holographic superconductors are of Type II (H_c1 < H_c2). We
extend the study to 4+1 dimensions where the gauge field does not appear as an
emergent phenomena, but can be introduced, by a proper renormalization, as an
external dynamical field. We also compare our predictions with those arising
from a Ginzburg-Landau theory and identify the generic properties of Abrikosov
vortices in holographic models.Comment: 19 pages, 14 figures, few comments added, version published in JHE
One-Dimensional Approximation of Viscous Flows
Attention has been paid to the similarity and duality between the
Gregory-Laflamme instability of black strings and the Rayleigh-Plateau
instability of extended fluids. In this paper, we derive a set of simple
(1+1)-dimensional equations from the Navier-Stokes equations describing thin
flows of (non-relativistic and incompressible) viscous fluids. This
formulation, a generalization of the theory of drop formation by Eggers and his
collaborators, would make it possible to examine the final fate of
Rayleigh-Plateau instability, its dimensional dependence, and possible
self-similar behaviors before and after the drop formation, in the context of
fluid/gravity correspondence.Comment: 17 pages, 3 figures; v2: refs & comments adde
Holographic Superfluids and Superconductors in Dilaton-Gravity
We investigate holographic models of superfluids and superconductors in which
the gravitational theory includes a dilatonic field. Dilaton extensions are
interesting as they allow us to obtain a better description of low temperature
condensed matter systems. We focus on asymptotically AdS black hole
configurations, which are dual to field theories with conformal ultraviolet
behavior. A nonvanishing value of the dilaton breaks scale invariance in the
infrared and is therefore compatible with the normal phase being insulating (or
a solid in the fluid mechanical interpretation); indeed we find that this is
the case at low temperatures and if one appropriately chooses the parameters of
the model. Not only the superfluid phase transitions, but also the response to
external gauge fields is analyzed. This allows us to study, among other things,
the vortex phase and to show that these holographic superconductors are also of
Type II. However, at low temperatures they can behave in a qualitatively
different way compared to their analogues without the dilaton: the critical
magnetic fields and the penetration depth can remain finite in the small T/T_c
limit.Comment: 20 pages, 8 figures; few comments and references added, a typo fixed
in the equation below eq. (16), article accepted for publication in JHE
p-wave Holographic Superconductors and five-dimensional gauged Supergravity
We explore five-dimensional and
SO(6) gauged supergravities as frameworks for condensed matter applications.
These theories contain charged (dilatonic) black holes and 2-forms which have
non-trivial quantum numbers with respect to U(1) subgroups of SO(6). A question
of interest is whether they also contain black holes with two-form hair with
the required asymptotic to give rise to holographic superconductivity. We first
consider the case, which contains a complex two-form potential
which has U(1) charge . We find that a slight
generalization, where the two-form potential has an arbitrary charge , leads
to a five-dimensional model that exhibits second-order superconducting
transitions of p-wave type where the role of order parameter is played by
, provided . We identify the operator that condenses
in the dual CFT, which is closely related to Super Yang-Mills
theory with chemical potentials. Similar phase transitions between R-charged
black holes and black holes with 2-form hair are found in a generalized version
of the gauged supergravity Lagrangian where the two-forms have
charge .Comment: 35 pages, 14 figure
A General Black String and its Microscopics
Using G2(2) dualities we construct the most general black string solution of
minimal five-dimensional ungauged supergravity. The black string has five
independent parameters, namely, the magnetic one-brane charge, smeared electric
zero-brane charge, boost along the string direction, energy above the BPS
bound, and rotation in the transverse space. In one extremal limit it reduces
to the three parameter supersymmetric string of five-dimensional minimal
supergravity; in another extremal limit it reduces to the three parameter
non-supersymmetric extremal string of five-dimensional minimal supergravity. It
also admits an extremal limit when it has maximal rotation in the
four-dimensional transverse space. The decoupling limit of our general black
string is a BTZ black hole times a two sphere. The macroscopic entropy of the
string is reproduced by the Maldacena-Strominger-Witten CFT in appropriate
ranges of the parameters. When the pressureless condition is imposed, our
string describes the infinite radius limit of the most general class of black
rings of minimal supergravity. We discuss implications our solution has for
extremal and non-extremal black rings of minimal supergravity.Comment: 35 pages; 3 figures; v2 section 4.1.1 rewritten + minor changes + ref
adde
Entangled Dilaton Dyons
Einstein-Maxwell theory coupled to a dilaton is known to give rise to
extremal solutions with hyperscaling violation. We study the behaviour of these
solutions in the presence of a small magnetic field. We find that in a region
of parameter space the magnetic field is relevant in the infra-red and
completely changes the behaviour of the solution which now flows to an
attractor. As a result there is an extensive ground state
entropy and the entanglement entropy of a sufficiently big region on the
boundary grows like the volume. In particular, this happens for values of
parameters at which the purely electric theory has an entanglement entropy
growing with the area, , like which is believed to be a
characteristic feature of a Fermi surface. Some other thermodynamic properties
are also analysed and a more detailed characterisation of the entanglement
entropy is also carried out in the presence of a magnetic field. Other regions
of parameter space not described by the end point are also
discussed.Comment: Some comments regarding comparison with weakly coupled Fermi liquid
changed, typos corrected and caption of a figure modifie
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