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Correlation Effects in Quantum Spin-Hall Insulators: A Quantum Monte Carlo Study

We consider the Kane-Mele model with spin-orbit coupling supplemented by a Hubbard U term. On the basis of projective auxiliary field quantum Monte Carlo simulations on lattice sizes up to 15 x 15, we map out the phase diagram. The quantum spin-liquid state found in the Hubbard model is shown to be robust against weak spin-orbit interaction, and is not adiabatically connected to the spin-Hall insulating state. Beyond a critical value of U > U_c both states are unstable toward magnetic ordering. Within the quantum spin-Hall state we study the spin, charge and single-particle dynamics of the helical Luttinger liquid by retaining the Hubbard interaction only on the edge of a ribbon. The Hubbard interaction greatly suppresses charge currents along the edge, promotes edge magnetism, but leaves the single-particle signatures of the helical liquid intact.