Disorder-induced insulator-insulator transition in the strong interaction regime

초록

We examined the half-filled disordered Hubbard model with repulsive interaction on a two-dimensional square lattice using the semiclassical approximation (SCA) method. In the absence of disorder, the system becomes a antiferromagnetic (AF) Mott insulator in the strong interaction regime. However, when on-site random potentials are introduced, the AF order is suppressed, and the system can transition into an Anderson insulating phase at sufficiently strong disorder. To distinguish between the AF Mott insulator and the Anderson insulator, we computed the AF order parameter < m >$⟨m⟩$ and its fluctuation $⟨\alpha ⟩$ across varying disorder strengths and temperatures. Our results show that < m >$⟨m⟩$ exhibits a monotonic decrease with increasing disorder strength, although it drops sharply near the transition point. In contrast, the fluctuation $⟨\alpha ⟩$ displays nontrivial, non-monotonic behavior, particularly at intermediate disorder strengths. These features are related to variations in the effective density, as determined by the maximum Matsubara frequency used in the SCA calculations. We interpret this non-monotonic behavior of $⟨\alpha ⟩$ as a potential signature that distinguishes the AF Mott insulating phase from the Anderson insulating phase. Finally, we investigated the behavior of both < m >$⟨m⟩$ and $⟨\alpha ⟩$ as functions of temperature. We found that, at low temperatures, disorder-induced charge fluctuations suppress the AF order more effectively than thermal fluctuations.

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