Relation between the structural phase transition and superconductivity in Cu_xIrTe_(2-y)Se_y

摘要

We have investigated the relation between structural transition with Ir-dimer formation and superconductivity in IrTe_2 by combining the Se substitution and the Cu intercalation. Regardless of the structural transition temperature (T_s), which increases with increasing the Se content (y) in IrTe_(2-y)Se_y, superconductivity emerges robustly by the Cu intercalation. As the Cu content x in Cu_xIrTe_(2-y)Se_y increases, T_s tends to decrease, followed by the emergence of superconductivity with showing the highest critical temperature (T_c) at the optimum Cu concentration (x_(opt)) close to the structural phase boundary. Based on the transport and thermodynamic properties, the electron-phonon coupling constant is found to be enhanced near the structural phase boundary, which suggests an essential role of the structural instability for the superconductivity in doped IrTe_2. With increasing y from 0 to 0.5 in Cu_xIrTe_(2-y)Se_y, T_s at x= 0 increases by about 80%, whereas T_c at c= x_(opt) decreases by about 20%. This can be understood by the weakening of the interlayer hybridization upon the Se substitution, resulting in the weak but negative correlation between T_s and T_c through y.