Electron Correlations in Strongly Interacting Systems

V. Janiš, R. Teplý

Massimo Capone, Claudio Castellani, M. Grilli

The Hubbard-Holstein model is a simple model including both electron-phonon interaction and electron-electron correlations. We review a body of theoretical work investigating, the effects of strong correlations on the electron-phonon interaction. We focus on the regime, relevant to high- T c superconductors, in which the electron correlations are dominant. We find that electron-phonon interaction can still have important signatures, even if many anomalies appear, and the overall effect is far from conventional. In particular in the paramagnetic phase the effects of phonons are much reduced in the low-energy properties, while the high-energy physics can still be affected by phonons. Moreover, the electron-phonon interaction can give rise to important effects, like phase separation and charge-ordering, and it assumes a predominance of forward scattering even if the bare interaction is assumed to be local (momentum independent). Antiferromagnetic correlations reduce the screening effects due to electron-electron interactions and revive the electron-phonon effects.

Rishab Dutta

Strong electron correlation is ubiquitous in chemistry and physics. The importance of strong correlation in diverse chemical systems and the failure of traditional electronic structure methods to capture it motivate the current work. We highlight the role of electron pairing in strong correlation and introduce conceptually appealing wavefunction ansätze that can accurately describe strong pairing interactions. Our work builds the foundations of a new generation of quantum chemistry methods which would expand the space of many-electron systems that are accurately understood.

Pavel V. Shevchenko

Ryota Mizuno, Masayuki Ochi, Kazuhiko Kuroki

Recent experiments revealed a striking asymmetry in the phase diagram of the high temperature cuprate superconductors. The correlation effect seems strong in the hole-doped systems and weak in the electron-doped systems. On the other hand, a recent theoretical study shows that the interaction strengths (the Hubbard U) are comparable in these systems. Therefore, it is difficult to explain this asymmetry by their interaction strengths. Given this background, we analyze the one-particle spectrum of a single band model of a cuprate superconductor near the Fermi level using the dynamical mean field theory. We find the difference in the "visibility" of the strong correlation effect between the hole- and electron-doped systems. This can explain the electron-hole asymmetry of the correlation strength without introducing the difference in the interaction strength.

Stig Lundqvist