N. Blümer

ABSENCE OF HVSTERESIS AT THE MOTT-HUBBARD METAL-INSULATOR TRANSITION IN INFINITE DIMENSIONS

The nature of the Mott-Hubbard metal-insulator transition in the infinite-dimensional Hubbard model is investigated by Quantum Monte Carlo simulations down to temperature T=W/140 (W=bandwidth). Calculating with significantly higher precision than in previous work, we show that the hysteresis below T_{IPT}\simeq 0.022W, reported in earlier studies, disappears. Hence the transition is found to be continuous rather than discontinuous down to at least T=0.325T_{IPT}. We also study the changes in the density of states across the transition, which illustrate that the Fermi liquid breaks down before the gap opens.

Fate of the false Mott-Hubbard transition in two dimensions

We have studied the impact of non-local electronic correlations at all length scales on the Mott-Hubbard metal-insulator transition in the unfrustrated two-dimensional Hubbard model. Combining dynamical vertex approximation, lattice quantum Monte-Carlo and variational cluster approximation, we demonstrate that scattering at long-range fluctuations, i.e., Slater-like paramagnons, opens a spectral gap at weak-to-intermediate coupling -- irrespectively of the preformation of localized or short-ranged magnetic moments. This is the reason, why the two-dimensional Hubbard model is insulating at low enough temperatures for any (finite) interaction and no Mott-Hubbard transition is observed.

Superconductivity of SrTiO3-δ

Abstract:Superconducting SrTiO 3 - δ was obtained by annealing single crystalline SrTiO3 samples in ultra high vacuum. An analysis of the V(I) characteristics revealed very small critical currents Ic which can be traced back to an unavoidable doping inhomogeneity. R(T) curves were measured for a range of magnetic fields B at I ≪ Ic, thereby probing only the sample regions with the highest doping level. The resulting curves Bc2(T) show upward curvature, both at small and strong doping. These results are discussed in the context of bipolaronic and conventional superconductivity with Fermi surface anisotropy. We conclude that the special superconducting properties of SrTiO 3 - δ can be related to its Fermi surface and compare this finding with properties of the recently discovered superconductor MgB2.

Efficiency of quantum Monte Carlo impurity solvers for the dynamical mean-field theory

Since the inception of the dynamical mean-field theory, numerous numerical studies have relied on the Hirsch-Fye quantum Monte Carlo (HF-QMC) method for solving the associated impurity problem. Recently developed continuous-time algorithms (CT-QMC) avoid the Trotter discretization error and allow for faster configuration updates, which makes them candidates for replacing HF-QMC. We demonstrate, however, that a state-of-the-art implementation of HF-QMC (with extrapolation of discretization ∆τ → 0) is competitive with CT-QMC. A quantitative analysis of Trotter errors in HF-QMC estimates and of appropriate ∆τ values is included.

Orbital-selective Mott transitions in the 2-band Jz-model: a high-precision quantum Monte Carlo study

Using high-precision quantum Monte Carlo (QMC) simulations within the framework of dynamical mean field theory (DMFT), we show that the anisotropic degenerate two-orbital Hubbard model contains two consecutive orbital-selective Mott transitions (OSMTs) even in the absence of spin-flip terms and pair-hopping processes. In order to reveal the second transition we carefully analyze the low-frequency part of the self-energy and the local spectral functions. This paper extends our previous work to lower temperatures. We discuss the nature - in particular the order - of both Mott transitions and list various possible extensions.

Mott insulator: Tenth-order perturbation theory extended to infinite order using a quantum Monte Carlo scheme

We present a method based on the combination of analytical and numerical techniques within the framework of the dynamical mean-field theory. Building upon numerically exact results obtained in an improved quantum Monte Carlo scheme, tenth-order strong-coupling perturbation theory for the Hubbard model on the Bethe lattice is extrapolated to infinite order. We obtain continuous estimates of energy

Momentum structure of the self-energy and its parametrization for the two-dimensional Hubbard model

E

Orbital-selective Mott transitions in a doped two-band Hubbard model with crystal field splitting

and double occupancy

Green functions for nearest- and next-nearest-neighbor hopping on the Bethe lattice

D

Transport Properties of Correlated Electrons in High Dimensions

with unprecedented precision