Effect of crystal damage on superconductivity in the transition-metal layer compounds

Abstract

The superconducting properties of the transition-metal dichalcogenides Ta${\mathrm{S}}_2$, Ta${\mathrm{Se}}_2$, Nb${\mathrm{S}}_2$, and Nb${\mathrm{Se}}_2$ have been studied as a function of structural disorder induced by heavy-ion bombardment and by deintercalation at temperatures between 300 and 800 K. Changes in $T_c$ similar to those seen on intercalation by metal ions and organic molecules were observed but there was no increase in the anisotropy of the critical magnetic fields. The changes in $T_c$ are attributed to changes in the electronic structure at the respective Fermi surfaces beyond previously considered changes in the density of states at the Fermi surface on intercalation.