EXACT-DIAGONALIZATION STUDY OF THE ONE-DIMENSIONAL DISORDERED XXZ MODEL

We investigate the one-dimensional quantum XXZ model in the presence o f diagonal disorder. Recently the model has been analyzed with the hel p of field-theoretical renormalization-group methods, and a phase diag ram has been predicted. We study the model with exact diagonalization techniques up to chain lengths of 16 sites. Using finite-size scaling methods we estimate critical exponents and the phase diagram and find reasonably good agreement with the field-theoretical results, namely, that any amount of disorder destroys the superfluidity for XXZ anisotr opy DELTA between -1/2 and 1, while the superfluidity persists to fini te disorder strength for -1 < DELTA < -1/2 and then undergoes a Koster litz-Thouless-type transition.