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Register a new userTracing the Mott-Hubbard transition in one-dimensional Hubbard models without Umklapp scattering
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We apply the density-matrix renormalization group (DMRG) method to a one-dimensional Hubbard model that lacks Umklapp scattering and thus provides an ideal case to study the Mott-Hubbard transition analytically and numerically. The model has a linear dispersion and displays a metal-to-insulator transition when the Hubbard interaction~$U$ equals the band width, $U_{rm c}=W$, where the single-particle gap opens linearly, $Delta(Ugeq W)=U-W$. The simple nature of the elementary excitations permits to determine numerically with high accuracy the critical interaction strength and the gap function in the thermodynamic limit. The jump discontinuity of the momentum distribution $n_k$ at the Fermi wave number $k_{rm F}=0$ cannot be used to locate accurately $U_{rm c}$ from finite-size systems. However, the slope of $n_k$ at the band edges, $k_{rm B}=pm pi$, reveals the formation of a single-particle bound state which can be used to determine $U_{rm c}$ reliably from $n_k$ using accurate finite-size data.
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We study the superfluid-insulator transition in Bose-Hubbard models in one-, two-, and three-dimensional cubic lattices by means of a recently proposed variational wave function. In one dimension, the variational results agree with the expected Berezinskii-Kosterlitz-Thouless scenario of the interaction-driven Mott transition. In two and three dimensions, we find evidences that, across the transition,most of the spectral weight is concentrated at high energies, suggestive of pre-formed Mott-Hubbard side-bands. This result is compatible with the experimental data by Stoferle et al. [Phys. Rev. Lett. 92, 130403 (2004)].
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