Metal-insulator transition in the Edwards model

To understand how charge transport is affected by a background medium and vice versa we study a two-channel transport model which captures this interplay via a novel, effective fermion-boson coupling. By means of (dynamical) DMRG we prove that this model exhibits a metal-insulator transition at half-filling, where the metal typifies a repulsive Luttinger liquid and the insulator constitutes a charge density wave. The quantum phase transition point is determined consistently from the calculated photoemission spectra, the scaling of the Luttinger liquid exponent, the charge excitation gap, and the entanglement entropy.Comment: 4 pages, 3 figures, contributions to SCES 201

DMRG analysis of the SDW-CDW crossover region in the 1D half-filled Hubbard-Holstein model

In order to clarify the physics of the crossover from a spin-density-wave (SDW) Mott insulator to a charge-density-wave (CDW) Peierls insulator in one-dimensional (1D) systems, we investigate the Hubbard-Holstein Hamiltonian at half filling within a density matrix renormalisation group (DMRG) approach. Determining the spin and charge correlation exponents, the momentum distribution function, and various excitation gaps, we confirm that an intervening metallic phase expands the SDW-CDW transition in the weak-coupling regime.Comment: revised versio

Random dispersion approximation for the Hubbard model

We use the Random Dispersion Approximation (RDA) to study the Mott-Hubbard transition in the Hubbard model at half band filling. The RDA becomes exact for the Hubbard model in infinite dimensions. We implement the RDA on finite chains and employ the Lanczos exact diagonalization method in real space to calculate the ground-state energy, the average double occupancy, the charge gap, the momentum distribution, and the quasi-particle weight. We find a satisfactory agreement with perturbative results in the weak- and strong-coupling limits. A straightforward extrapolation of the RDA data for $L\leq 14$ lattice results in a continuous Mott-Hubbard transition at $U_{\rm c}\approx W$. We discuss the significance of a possible signature of a coexistence region between insulating and metallic ground states in the RDA that would correspond to the scenario of a discontinuous Mott-Hubbard transition as found in numerical investigations of the Dynamical Mean-Field Theory for the Hubbard model.Comment: 10 pages, 11 figure

Tomonaga-Luttinger parameters for doped Mott insulators

The Tomonaga--Luttinger parameter $K_{\rho}$ determines the critical behavior in quasi one-dimensional correlated electron systems, e.g., the exponent $\alpha$ for the density of states near the Fermi energy. We use the numerical density-matrix renormalization group method to calculate $K_{\rho}$ from the slope of the density-density correlation function in momentum space at zero wave vector. We check the accuracy of our new approach against exact results for the Hubbard and XXZ Heisenberg models. We determine $K_{\rho}$ in the phase diagram of the extended Hubbard model at quarter filling, $n_{\rm c}=1/2$, and confirm the bosonization results $K_{\rho}=n_{\rm c}^2=1/4$ on the critical line and $K_{\rho}^{\rm CDW}=n_{\rm c}^2/2=1/8$ at infinitesimal doping of the charge-density-wave (CDW) insulator for all interaction strengths. The doped CDW insulator exhibits exponents $\alpha>1$ only for small doping and strong correlations.Comment: 7 pages, 4 figure

One-Dimensional Quantum Transport Affected by a Background Medium: Fluctuations versus Correlations

We analyze the spectral properties of a very general two-channel fermion-boson transport model in the insulating and metallic regimes, and the signatures of the metal-insulator quantum phase transition in between. To this end we determine the single particle spectral function related to angle-resolved photoemission spectroscopy, the momentum distribution function, the Drude weight and the optical response by means of a dynamical (pseudo-site) density-matrix renormalization group technique for the one-dimensional half-filled band case. We show how the interplay of correlations and fluctuations in the background medium controls the charge dynamics of the system, which is a fundamental problem in a great variety of advanced materials.Comment: 6 pages, 5 figures, final versio

Thermodynamics of the one-dimensional half-filled Hubbard model in the spin-disordered regime

We analyze the Thermodynamic Bethe Ansatz equations of the one-dimensional half-filled Hubbard model in the "spin-disordered regime", which is characterized by the temperature being much larger than the magnetic energy scale but small compared to the Mott-Hubbard gap. In this regime the thermodynamics of the Hubbard model can be thought of in terms of gapped charged excitations with an effective dispersion and spin degrees of freedom that only contribute entropically. In particular, the internal energy and the effective dispersion become essentially independent of temperature. An interpretation of this regime in terms of a putative interacting-electron system at zero temperature leads to a metal-insulator transition at a finite interaction strength above which the gap opens linearly. We relate these observations to studies of the Mott-Hubbard transition in the limit of infinite dimensions.Comment: 15 pages, 3 figure