Abstract:
Inhomogeneous superconductors with nested Fermi surface (FS) sections were studied. We calculated conductances G(V) = dJ/dV(V), where J(V) is a quasiparticle current, V is voltage, for nonsymmetric (SIN) and symmetric (SIS) tunnel junctions. S, N and I stand for superconductor, normal metal and insulator. Below a structural transition temperature Td > Tc a charge-density wave (CDW) emerges. Tc is a superconducting transition temperature. G(V) were averaged over distributions of Cooper, D, and CDW, S, order parameters. The inhomogeneity of S is responsible for smooth but conspicuous dip-hump structures (DHSs) of G(V) at T << Tc. The positions of DHSs are determined by both D and S. DHSs may be observed for one or both V polarities, in agreement with experiment for high- Tc oxides. For higher T, G(V) transforms into broad so-called pseudogap (PG) depletion of the density of states, which is often observed for different cuprates both below and above Tc. G(V) for break junctions made of high- Tc BSCCO and YBCO were measured. Good agreement was observed between theoretically calculated and experimental G(V) dependences. Thus, both DHSs and PGs are due to CDW formation.