Narrow Results

A new class of doped layered superconductors has been discovered recently: the metallochloronitrides. Intercalating metallic atoms (Na, Li) into the layered parent compounds MNX (M=Zr, Hf and X=Cl, Br) superconductivity was found below a transition temperature that can be as high as T_c~26 K. We show that the dominant contribution to the pairing interaction is electronic and comes from the screened dynamical Coulomb interaction characteristic of layered systems. With use of parameters for Li_0.48(THF)_yHfNCl we show that the calculated T_c is in quantitative agreement with experiment.

We study the transport phenomena in layered conductors with rather general electron energy spectrum placed in a high magnetic field $H$, under conditions when the distance between various sheets of the Fermi surface (FS) may become small under the external effects, such as hydrostatic pressure or impurity atom doping, and electrons can transfer from one sheet of the FS to another due to magnetic breakdown. We calculate the dependence of the in-plane electrical conductivity and magnetoresistance on magnetic field and probability of magnetic breakdown and show that the field-induced quadratic increase of the in-plane resistance in the absence of magnetic breakdown is changed by a linear dependence on $H$. With a further reduction of the energy gap between FS sheets, the in-plane resistance is saturated.