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EN
We discuss the calculations of the ac Hall conductivity for superconductors with the time reversal symmetry breaking states. In the weak coupling theories these states show vanishing Hall response in one band models, even though one expects otherwise on symmetry grounds. On the other hand, the strong coupling approach based on the anti-de Sitter-conformal field theory correspondence leads to the non-vanishing Hall conductivity. We discuss the possible reasons of the discrepancy. The weak coupling many orbital theory leading to the Hall conductivity with correct temperature dependence is also briefly presented.
EN
The superconducting state can be destroyed by the increase of temperature, magnetic field or current flow beyond their critical values. The critical current I_{c} 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 j_{c}, the critical magnetic field H_{c} and the penetration depth λ. For type II superconductors the role of the thermodynamic critical field H_{c} is played by the lower critical field H_{c1} 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 I_{c} ∝ (T_{c}-T)^{3/2} and agrees with that observed in thin films (d < λ). Similar calculations for 3d systems (d > λ) reveal linear T-dependence I_{c} ∝ (T_{c}-T).
EN
The holographic approach to study strongly coupled superconductors in the presence of dark matter is reviewed. We discuss the influence of dark matter on the superconducting transition temperature of both s-wave and p-wave holographic superconductors. The upper critical field, coherence length, penetration depth of holographic superconductors as well as the metal-insulator transitions have also been analysed. Issues related to the validity of anti-de Sitter/conformal field theory correspondence for the description of superconductors studied in the laboratory and possible experiments directed towards the detection of dark matter are discussed. In doing so we shall compare our assumptions and assertions with those generally accepted in the elementary particle experiments aimed at the detection of dark matter particles.
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