Low-temperature properties of two interacting magnetic impurities

Abstract

We discuss a simple model consisting of four spins ; S1 and S2 representing the impurity spins and s1 and s2 the conduction electron spin-densities at the impurity sites, coupled by three antiferromagnetic coupling: TK describing the local Kondo singlet-triplet splitting, J is the RKKY and K is a cross coupling between S1(S2) and s2(s1). This model has a critical point at J = 2K = 2TK with similar properties as the unstable fixed recently discovered by Jones, Varma and Wilkins: (i) a specific heat anomaly, (ii) a well-behaved uniform magnetic field susceptibility, (iii) a divergent staggered susceptibility, and (iv) a strongly varying expectation value S1[middle dot]S2> with an average value of .