Hallmark of strong electronic correlations in LaNiO$_3$: photoemission
  kink and broadening of fully occupied bands

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Abstract

Recent angular-resolved photoemission experiments on LaNiO$_3$ reported a renormalization of the Fermi velocity of $e_g$ quasiparticles, a kink in their dispersion at $ -0.2$ eV and a large broadening and weakened dispersion of the occupied $t_{2g}$ states. We show here that all these features result from electronic correlations and are quantitatively reproduced by calculations combining density-functional theory and dynamical mean-field theory. The importance and general relevance of correlation effects in filled bands coupled by inter-orbital interactions to a partially-filled band are pointed out.

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Continuous-time Monte Carlo methods for quantum impurity models

Matthias Troyer, Alexey N. Rubtsov, Alexander I. Lichtenstein … (2010)

Quantum impurity models describe an atom or molecule embedded in a host material with which it can exchange electrons. They are basic to nanoscience as representations of quantum dots and molecular conductors and play an increasingly important role in the theory of "correlated electron" materials as auxiliary problems whose solution gives the "dynamical mean field" approximation to the self energy and local correlation functions. These applications require a method of solution which provides access to both high and low energy scales and is effective for wide classes of physically realistic models. The continuous-time quantum Monte Carlo algorithms reviewed in this article meet this challenge. We present derivations and descriptions of the algorithms in enough detail to allow other workers to write their own implementations, discuss the strengths and weaknesses of the methods, summarize the problems to which the new methods have been successfully applied and outline prospects for future applications.

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A continuous-time solver for quantum impurity models

Armin Comanac, Philipp Werner, Luca de’ Medici … (2005)

We present a new continuous time solver for quantum impurity models such as those relevant to dynamical mean field theory. It is based on a stochastic sampling of a perturbation expansion in the impurity-bath hybridization parameter. Comparisons to quantum Monte Carlo and exact diagonalization calculations confirm the accuracy of the new approach, which allows very efficient simulations even at low temperatures and for strong interactions. As examples of the power of the method we present results for the temperature dependence of the kinetic energy and the free energy, enabling an accurate location of the temperature-driven metal-insulator transition.