Neel-VBS phase boundary of the extended J_1-J_2 model with biquadratic interaction

摘要

The J_1-J_2 model with the biquadratic (plaquette-four-spin) interaction wassimulated with the numerical-diagonalization method. Some limiting cases ofthis model have been investigated thoroughly. Taking the advantage of theextended parameter space, we survey the phase boundary separating the N'eel andvalence-bond-solid phases. According to the deconfined-criticality scenario,the singularity of this phase boundary is continuous, accompanied withunconventional critical indices. Diagonalizing the finite-size cluster with N\le 36 spins, we observe a signature of continuous phase transition. Ourtentative estimate for the correlation-length critical exponent is \nu=1.1(3).In order to elucidate a non-local character of criticality, we evaluated theRoomany-Wyld \beta function around the critical point.