The +/- J spin glass in Migdal-Kadanoff approximation

We study the low-temperature phase of the three-dimensional +/-J Ising spin glass in Migdal-Kadnoff approximation. At zero temperature, T = 0, the pro perties of the spin glass result from the ground-state degeneracy and can b e elucidated using scaling arguments based on entropy. The approach to the asymptotic scaling regime is very slow, and the correct exponents are only visible beyond system sizes around 64. At T > 0, a crossover from the zero- temperature behaviour to the behaviour expected from the droplet picture oc curs at length scales proportional to T-2/ds where d(s) is the fractal dime nsion of a domain wall. Canonical droplet behaviour is not visible at any t emperature for systems whose linear dimension is smaller than 16 lattice sp acings, because the data are either affected by the zero-temperature behavi our or the critical point behaviour.