Numerical study of the random dimerized XX spin-1/2 chain

The effects of randomness and dimerization on the spin-1/2 XX chain are studied by a mapping to free fermions. Results are presented for the transverse and longitudinal components of the average and typical spin- and string-correlation functions. Contrary to previous numerical evidence, the decay exponents of all the above correlation functions are found to be in good agreement with the theoretical renormalization-group predictions for the random singlet phase. We also present crossover functions for the above correlation functions in the random dimer phase. Disorder averages have been taken for system sizes up to N = 1024, about ten times larger than in previous studies.