Rounding the First-Order Quantum Phase Transitions by Disorder in the Quantum Ashkin-Teller Model

We study the influence of quenched disorder on the quantum phase transitions in the two-dimensional three-color quantum Ashkin-Teller model by Monte Carlo simulations. We show that in the weak-coupling regime the quenched disorder rounds the first-order quantum phase transition to a second-order one. This agrees with the predictions of a strong-disorder renormalization group analysis. However, in the strong-coupling regime there are two distinct transitions separating the paramagnetic, product and Baxter (ferromagnetic) phases.