Effects of a magnetic field on superconductivity and quantum criticality in quasi-two-dimensional systems with Dirac electrons

Abstract

We study the effects of an external magnetic field on the superconducting phase diagram of a quasi-two-dimensional system of Dirac electrons at an arbitrary temperature. At zero temperature, there is a quantum phase transition connecting a normal and a superconducting phase, occurring at a critical line that corresponds to a magnetic field dependent critical coupling parameter, which should be observed in planar materials containing Dirac electrons, such as Cu x TiSe 2 . Moreover, the superconducting gap is obtained as a function of temperature, magnetic field and coupling parameter ( λ R ) . From this, we extract the critical magnetic field B c as a function of the temperature. For small values of B c , we obtain a linear decay of the critical field, which is similar to the behavior observed experimentally in the copper doped dichalcogenide Cu x TiSe 2 and also in intercalated graphite.