CPHT Condensed Matter seminar


Tuesday, April 4 at 14:00

Conference room Louis Michel (CPHT)

Erik Linnér (CPHT, École Polytechnique)

A theoretical description of the interplay of collective fluctuations in strongly correlates systems

Abstract: Correlated fermion systems often display complex phase diagrams with different competing orderings. A theoretical description of competing instabilities remains one of the major challenges of modern condensed matter physics. We introduce a multi-channel extension of the recently developed fluctuating field approach to tackle this problem, based on a variational optimization of a trial action that explicitly contains the leading fluctuation channels [1]. Application of the approach to extended Hubbard models captures the interplay of competing charge density wave, antiferromagnetic, s-wave superconductivity, and phase separation fluctuations [1,2]. For the case of the attractive model, our approach has allowed us to identify a novel phase that is characterised by the coexistence of s-wave superconductivity and phase separation [2]. Our findings resonate with previous observations of interplaying phase separation and superconducting phases in electronic systems, most importantly in high-temperature superconductors.

[1] E. Linnér, A. I. Lichtenstein, S. Biermann, E. A. Stepanov, Multi-channel fluctuating field approach to competing instabilities in interacting electronic systems, arXiv:2210.05540 (2022).

[2] E. Linnér, C. Dutreix, S. Biermann, E. A. Stepanov, Coexistence of s-wave superconductivity and phase separation in the half-filled extended Hubbard model with attractive interactions, arXiv:2301.10755 (2023).