Condensate flow in holographic models in the presence of dark matter

Wysokiński

2018

Phys. Rev. D

Self Cite

The electrons in graphene for energies close to the Dirac point have been found to form strongly interacting fluid. Taking this fact into account we have extended previous work on the transport properties of graphene by taking into account possible interactions between the currents and adding the external magnetic field directed perpendicularly to the graphene sheet. The perpendicular magnetic field B severely modifies the transport parameters. In the present approach the quantization of the spectrum and formation of Landau levels is ignored. Gauge/gravity duality has been used in the probe limit. The dependence on the charge density of the Seebeck coefficient and thermo-electric parameters α ij nicely agree with recent experimental data for graphene. The holographic model allows for the interpretation of one of the fields representing the currents as resulting from the dark matter sector. For the studied geometry with electric field perpendicular to the thermal gradient the effect of dark sector has been found to modify the transport parameters but mostly in a quantitative way only. This makes difficult the detection of this elusive component of the Universe by studying transport properties of graphene. PACS numbers: 11.25.Tq, 04.50.-h, 98.80.Cq I. INTRODUCTIONThe crossroads between gravity theory and condensed matter physics have recently become an intense field of research with at least two-fold goal. On one side, the expectation of the condensed matter community is that the approach providing strong coupling analysis of problems will shed some light on those aspects being difficult to access by other means [1,2]. On the other hand, such studies can shed the light on the question whether the holographic approach is able to describe real phenomena observed in experiments.The exploit of the gauge/gravity correspondence [3][4][5] in studying strongly correlated systems resulted, among others, in establishing the lower bound /4π on the ratio of the shear viscosity η s to entropy density s in holographic fluid [6]. This interesting result has contributed to the deeper understanding of the state of strongly interacting quark-gluon plasma obtained at RHIC [7]- [9]. Related studies based on the gauge/gravity duality [10,11] have also triggered the shear viscosity measurements in the ultra-cold Fermi gases [12], and more recently in the condensed matter systems such as graphene [13,14] and strongly correlated oxide [15]. The comprehensive discussion of this novel set of experiments is given in [16].Recently, a great resurgence of the interests in holographic lattice studies of the thermoelectric DC transport has been observed. Breaking of the translation invariance provides the mechanism of momentum dissipation in the underlying field theory and disposes to the finite values of holographic DC kinetic coefficients including thermoelectric matrix elements.The number of results have already been obtained by this technique for a similar model of dissipation and valid in principle for arbitrary value of temperature and the ...

Section: A Dark Matter Interpretationmentioning

confidence: 99%

Two interacting current model of holographic Dirac fluid in graphene

Wysokiński

2018

Phys. Rev. D

Self Cite

“…Various other settings of the model in question were described in [52][53][54][55][56][57][58][59][60][61], where was mimicked that the dark matter sector influences the properties of superconductors and superfluids.…”

Section: Background Holographic Modelmentioning

confidence: 99%

DC conductivities and Stokes flows in Dirac semimetals influenced by hidden sector

2020

Eur. Phys. J. C

Self Cite

In the holographic model of Dirac semimetals, the Einstein–Maxwell scalar gravity with the auxiliary U(1)-gauge field, coupled to the ordinary Maxwell one by a kinetic mixing term, the black brane response to the electric fields and temperature gradient has been elaborated. Using the foliation by hypersurfaces of constant radial coordinate we derive the exact form of the Hamiltonian and equations of motion in the phase space considered. Examination of the Hamiltonian constraints enables us, to the leading order expansion of the linearised perturbations at the black brane event horizon, to derive the Stokes equations for an incompressible doubly charged fluid. Solving the aforementioned equations, one arrives at the DC conductivities for the holographic Dirac semimetals.

“…In the next Section we review the issue of the critical current in superconductors and various arguments of its rationalisation. Section 3 presents basic facts of holographic approach [5] to study the strongly interacting superconductors and present the results. We end with summary and conclusions.…”

Section: πRmentioning

confidence: 99%

On the Current Flow in Superconductors: Universal Trends and Holographic Analysis

Wysokiński

2018

Acta Phys. Pol. A

The superconducting state can be destroyed by the increase of temperature, magnetic field or current flow beyond their critical values. The critical current Ic is of special interest as most of the practical applications of superconductors crucially depend on its limiting value. Recent analysis of experimental data in many families of type I and type II superconductors have discovered an interesting universal relation between critical current density jc, the critical magnetic field Hc and the penetration depth λ. For type II superconductors the role of the thermodynamic critical field Hc is played by the lower critical field Hc1 and ratio between the relevant dimension of the system d with respect to the penetration depth matters. Thus the effective dimensionality of the system is important and rules the system behaviour. It turns out that the holographic analogy provides an interesting justification of the above findings. We have calculated the temperature dependence of the critical current in the strongly coupled holographic superconductors with the current flow. It has been found that, independently of the symmetry of the order parameter, the critical current depends on temperature in 2d systems as IcWpTc ¡ T q 3{2 and agrees with that observed in thin films (d λ). Similar calculations for 3d systems (d ¡ λ) reveal linear T-dependence IcWpTc ¡ T q.