Orientation peculiarities of dc Josephson tunneling betweend-wave superconductors with charge density waves

Abstract

The theory of the stationary Josephson tunnel current Ic was devised for junctions involving superconductors partially gapped by biaxial or unidirectional charge density waves (CDWs) and possessing a superconducting order parameter of d-wave symmetry. Specific calculations were carried out for symmetric junctions between two identical CDW superconducting electrodes and nonsymmetric ones composed of a CDW superconductor and a conventional isotropic s-wave superconductor. Two kinds of superconducting pairing symmetries were studied, namely, that appropriate to cuprates (dx2−y2) and the dxy one. The corresponding calculations were also carried out for the extended s-wave symmetry of the superconducting order parameter. Allowances were made for the directionality of tunneling. In all the cases studied, the dependences of Ic on the angle γ between the chosen crystal direction and the normal to the junction plane were found to be significantly influenced by CDWs. It was shown in particular that the d-wave driven periodicity of Ic(γ) in the CDW-free case is transformed into double-period beatings depending on the parameters of the system. The results of calculations testify that the orientation-dependent patterns Ic(γ) measured for CDW superconductors allow the CDW configuration (unidirectional or checkerboard) and the symmetry of superconducting order parameter to be determined. The predicted effects can be used to indirectly reveal CDWs in underdoped cuprates where pseudogaps are observed. The break-junction technique is an appropriate tool for this purpose.