Coexistence of superconductivity and antiferromagnetism inthe heavy-fermion superconductor CeCu2(Si1-xGex)2probed by means of Cu nuclear quadrupole resonance - a test case forthe SO(5) theory

Abstract

We report, on the basis of Cu nuclear quadrupole resonancemeasurements, that superconductivity (SC) and antiferromagnetism (AF)coexist on a microscopic level in CeCu2(Si1-xGex)2,once a tiny amount of 1% Ge (x = 0.01) is substituted for Si. Thiscoexistence arises because Ge substitution expands the unit-cellvolume in nearly homogeneous CeCu2Si2 where the SC coexistswith slowly fluctuating magnetic waves. We propose that theunderlying exotic phases of SC and AF in nearly homogeneousand in slightly Ge-substituted CeCu2Si2 can be accounted for onthe basis of the SO(5) theory that unifies the SC and AF. Wesuggest that the SC and AF in CeCu2Si2 have a commonmechanism.