ABSENCE OF TEMPERATURE-DRIVEN 1ST-ORDER PHASE-TRANSITIONS IN SYSTEMS WITH RANDOM BONDS

Temperature-driven first-order phase transitions that involve symmetry breaking are converted to second order by the introduction of infinitesimal quenched bond randomness in spatial dimensions d less-than-or-equal-to 2 or d less-than-or-equal-to 4, respectively, for systems of n = 1 or n greater-than-or-equal-to 2 component microscopic degrees of freedom. Even strongly first-order transitions undergo this conversion to second order! Above these dimensions, this phenomenon still occurs, but requires a threshold amount of bond randomness. For example, under bond randomness, the phase transitions of q-state Potts models are second order for all q in d less-than-or-equal-to 2. If no symmetry breaking is involved, temperature-driven first-order phase transitions are eliminated under the above conditions. Another consequence is that bond randomness drastically alters multicritical phase diagrams. Tricritical points and critical endpoints are entirely eliminated (d less-than-or-equal-to 2) or depressed in temperature (d > 2). Similarly, bicritical phase diagrams are converted (d less-than-or-equal-to 2) to reentrant-disorder-line or decoupled-tetracritical phase diagrams. These quenched-fluctuation-induced second-order transitions (a diametric opposite to the previously known annealed-fluctuation-induced first-order transitions) should lead to a multitude of new universality classes of criticality, including many experimentally accessible cases.