The stability of the replica-symmetric state in finite-dimensional spin glasses

According to the droplet picture of spin glasses, the low-temperature phase of spin glasses should be replica symmetric. However, analysis of the stability of this state suggested that it was unstable and this instability lends support to the Parisi replica symmetry breaking picture of spin glasses. The finite-size scaling functions in the critical region of spin glasses below T c in dimensions greater than 6 can be determined and for them the replica-symmetric solution is unstable order by order in perturbation theory. Nevertheless the exact solution can be shown to be replica symmetric. It is suggested that a similar mechanism might apply in the low-temperature phase of spin glasses in less than six dimensions, but that a replica symmetry broken state might exist in more than six dimensions.