Impact of nonlocal spatial correlations for different lattice geometries

TL;DR

This paper investigates how different lattice geometries influence magnetic phase transitions in strongly interacting electron systems, highlighting the importance of nonlocal correlations and geometric frustration in accurately predicting transition temperatures.

Contribution

It compares local and nonlocal correlation effects on magnetic transitions across various lattice geometries using DMFT and DΓA methods, revealing significant differences especially in frustrated lattices.

Findings

Nonlocal correlations lower transition temperatures in bipartite lattices.

Transition temperature differences decrease with higher coordination numbers.

Frustrated fcc lattice shows no magnetic order within DΓA, unlike DMFT predictions.

Abstract

We analyze the impact of the lattice geometry on the thermodynamic transition to magnetically ordered phases in strongly interacting electron systems for various Bravais lattices in three and four dimensions, including both local and nonlocal correlation effects. In a first step we use the dynamical mean field theory (DMFT), which takes into account purely local correlations, to calculate the magnetic susceptibilities of the Hubbard model on three (3d-sc) and four dimensional (4d-sc) simple cubic/hypercubic, as well as on three dimensional body- (bcc) and face-centered (fcc) cubic lattices, and determine the transition temperature to the corresponding magnetically-ordered state. In a second step, we exploit the dynamical vertex approximation (D$\Gamma$A), a diagrammatic extension of DMFT, to include the effect of nonlocal correlations which are particularly important in the vicinity of the corresponding phase transition. For the bipartite 3d-sc, 4d-sc and bcc lattices nonlocal fluctuations lead to a substantial reduction of the DMFT transition temperature consistent to the overall tendency of mean-field approaches to overestimate the stability of ordered phases. As expected, the magnitude of the difference between the DMFT, being exact in the limit of large connectivity/dimensions, and D$\Gamma$A transition temperatures decreases with increasing coordination number. On a more practical perspective, these results also provide a reasonable guidance to evaluate the expected overestimation of the DMFT ordering temperature for different material geometries. For the fcc lattice, on the other hand, the ordered phase observed in DMFT vanishes completely within D$\Gamma$A which is consistent with the existence of strong geometric frustration in this lattice.