Universality, frustration, and conformal invariance in two-dimensional random Ising magnets

Article

关键词: SPIN-GLASS;    CRITICAL-BEHAVIOR;    ANTIFERROMAGNET RB2CU0.12CO0.88F4;    MULTICRITICAL POINT;    NEUTRON-SCATTERING;    PHASE-TRANSITION;    POTTS MODELS;    HEAT;    FERROMAGNET;    PERCOLATION;   

DOI  :  10.1103/PhysRevB.60.6740

来源: SCIE

【 摘 要 】

We consider long, finite-width strips of Ising spins with randomly distributed couplings. Frustration is introduced by allowing both ferromagnetic and antiferromagnetic interactions. Free energy and spin-spin correlation functions are calculated by transfer-matrix methods. Numerical derivatives and finite-size scaling concepts allow estimates of the usual critical exponents gamma/nu, alpha/nu, and /nu to be obtained, whenever a second-order transition is present. Low-temperature ordering persists for suitably small concentrations of frustrated bonds, with a transition governed by pure-Ising exponents. Contrary to the unfrustrated case, subdominant terms do not fit a simple, logarithmic-enhancement form. Our analysis also suggests a vertical critical line at and below the Nishimori point. Approaching this point along either the temperature axis or the Nishimori line, one finds nondiverging specific heats. A percolationlike ratio gamma/nu is found upon analysis of the uniform susceptibility at the Nishimori point. Our data are also consistent with frustration inducing a breakdown of the relationship between correlation-length amplitude and critical exponents, predicted by conformal invariance for pure systems. [S0163-1829(99)07533-5].

【 授权许可】

Free