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"... We add a periodic potential to the simplest gravitational model of a superconductor and compute the optical conductivity. In addition to a superfluid component, we find a normal component that has Drude behavior at low frequency followed by a power law falloff. Both the exponent and coefficient of ..."
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We add a periodic potential to the simplest gravitational model of a superconductor and compute the optical conductivity. In addition to a superfluid component, we find a normal component that has Drude behavior at low frequency followed by a power law falloff. Both the exponent and coefficient of the power law are temperature independent and agree with earlier results computed above Tc. These results are in striking agreement with measurements on some cuprates. We also find a gap ∆ = 4.0 Tc, a rapidly decreasing scattering rate, and “missing spectral weight ” at low frequency, all of which also agree with experiments. 1 ar X iv
Quantum critical systemd from AdS/CFT
, 2013
"... The AdS/CFT (antide Sitter/conformal field theory) correspondence enables us to construct some strongly coupled quantum field theories by means of general relativity, and this approach provides new universality classes of condensed matter systems. In this dissertation, we will consider three system ..."
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The AdS/CFT (antide Sitter/conformal field theory) correspondence enables us to construct some strongly coupled quantum field theories by means of general relativity, and this approach provides new universality classes of condensed matter systems. In this dissertation, we will consider three systems. The first system (chapter 2) is the ReissnerNordstrom (RN)AdS4 black hole at finite temperature. By solving the Dirac equation for a massive, charged spinor in this background, we find that the fermions have a Rashbalike dispersion relation, and the Fermi surface has a spinorbit helical locking structure. We use an improved WKB method that takes into account the spinorbit coupling. The effective potential has a potential well with a barrier. The quasibound states in the potential well can tunnel through the barrier into the horizon, giving an imaginary part to the mode. The second system (chapter 3) is the twocharge black hole in AdS5 at zero temperature, which gives an analytically solvable model for the holographic Fermi surface. Descending from type IIB supergravity, the twocharge black hole describes N coincident D3branes with equal, nonzero angular momenta in two of the three independent planes of rotation orthogonal to the D3brane world volume. The IR geometry of the extremal twocharge black hole is conformal to AdS2 × R3, and the electric field vanishes in the near horizon limit. The third system (chapter 4) is the extremal RNAdS5 black hole, in which quantum criticality is studied by solving the KleinGordon equation. The Green’s function near quantum critical points is analytically obtained. There are two types of instability: the first one is triggered by a zero mode, and gives a hybridized critical point; the second one is triggered by the instability of the IR geometry, and gives a bifurcating critical point.
Preprint typeset in JHEP style HYPER VERSION Response of Holographic QCD to Electric and
, 802
"... Abstract: We study the response of the SakaiSugimoto holographic model of large Nc QCD at nonzero temperature to external electric and magnetic fields. In the electric case we find a firstorder insulatorconductor transition in both the confining and deconfining phases of the model. In the deconfi ..."
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Abstract: We study the response of the SakaiSugimoto holographic model of large Nc QCD at nonzero temperature to external electric and magnetic fields. In the electric case we find a firstorder insulatorconductor transition in both the confining and deconfining phases of the model. In the deconfining phase the conductor is described by the parallel 8braneanti8brane embedding with a current of quarks and antiquarks. We compute the conductivity and show that it agrees precisely with a computation using the Kubo formula. In the confining phase we propose a new kind of 8brane embedding, corresponding to a baryonic conductor. In the magnetic field case we show that the critical temperature for chiralsymmetry restoration in the deconfined phase increases with the field and approaches a finite value in the limit of an infinite magnetic field. We also illustrate the nonlinear behavior of the electric and magnetic susceptibilities in the different phases.
Imperial/TP/2014/JG/04 The thermoelectric properties of inhomogeneous holographic lattices
"... We consider inhomogeneous, periodic, holographic lattices of D = 4 EinsteinMaxwell theory. We show that the DC thermoelectric conductivity matrix can be expressed analytically in terms of the horizon data of the corresponding black hole solution. We numerically construct such black hole solutions ..."
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We consider inhomogeneous, periodic, holographic lattices of D = 4 EinsteinMaxwell theory. We show that the DC thermoelectric conductivity matrix can be expressed analytically in terms of the horizon data of the corresponding black hole solution. We numerically construct such black hole solutions for lattices consisting of one, two and ten wavenumbers. We numerically determine the AC electric conductivity which reveals Drude physics as well as resonances associated with sound modes. No evidence for an intermediate frequency scaling regime is found. All of the monochromatic lattice black holes that we have constructed exhibit scaling behaviour at low temperatures which is consistent with the appearance of AdS2 × R2 in the far IR at T = 0. ar X iv