NMR STUDY OF THE COEXISTENCE OF SUPERCONDUCTIVITY AND ANTIFEROMAGNETISM IN HEAVY FERMION SYSTEM Ce(Ir, Rh)In_5

点击翻译按钮获取中文摘要

CeMIn_5 (M=Ir, Co, Rh) is a new class of heavy fermion compounds. CelrIn_5 and CeCoIn_5 are superconductors with T_c=400mK and 2.3K, respectively. CeRhIn5 is an antiferromagnet with T_N=3.7K but becomes superconducting under high pressures. Also, upon alloying, Ce(Rh_<1-x>Ir_x)In_5 was suggested to exhibit a coexistence of antiferromagnetism (AF) and superconductivity (SC) over a wide range of Ir concentration, x.The purpose of this study is to investigate, through nuclear quadrupole resonance (NQR), how the coexistence of antiferrormagnetism and superconductivity takes place in Ce(Rh_<1-x>Ir_x)In_5 and to explore a possible coexistence of AF and SC in CeRhIn_5 under pressure.We have found that in AF and SC coexist microscopically in CeRhln5, in the pressure range of 1.6 Gpa<P<1.9 Gpa. In this pressure range, the magnetic moment was reduced substantially.In Ce(Rh_<1-x>Ir_x)In_5, we have found strong evidence for the microscopic coexistence of AF and SC in the range of 0.35<x<0.55. Specifically, for x=0.5,T_N is observed at 3K with a subsequent onset of SC at T_c=0.9K. Detailed analysis of the measured spectra indicate that the same electrons participate in both SC and AF. The nuclear spin-lattice relaxation rate.1/T_1 shows a broad peak at T_N and follows a T^3 variation below T_c, the latter property indicating unconventional SC as in CeIrIn_5. We further find that, in the coexistence region, the T^3 dependence of 1/T_1 is replaced by a T-linear variation below 0.4K, likely due to low-lying magnetic excitations associated with the coexisting magnetism.