Webinar :: Nonperturbative Fingerprints of the Many-Electron Physics ... and their Surprising Implications. (Alessandro Toschi)

Thursday 18 February 2021, 15:00

Alessandro Toschi

In this talk I start by illustrating how to read fundamental physical features
of electronic correlations from the two-particle description of the Anderson impurity
model. In particular, I will discuss the precise way in which the formation of a local
magnetic moment and its Kondo screening are encoded in the generalized charge
susceptibility. The sharpness of this identification even pinpoints a novel criterion to
determine the Kondo temperature of strongly correlated systems in the charge sector [1].
The identified structures on the two-particle level directly reflect the appearance of
divergences of the irreducible vertex functions. These singularities were long believed to be a mere mathematical formality, associated to the breakdown of many-body perturbation theory and to the multivaluedness of the Luttinger-Ward functional. Instead, novel DMFT calculations of the Hubbard model, demonstrate that they also have a precise physical meaning [2]: They are responsible for flipping the sign (from repulsive to attractive!) of the effective electronic interaction in specific scattering channels. As a result, entering the non-perturbative regime triggers an enhancement of the uniform charge response. This mechanism is ultimately responsible for the phase-separation instabilities emerging close to the Mott metal-insulator transitions as soon as the condition of perfect particle-hole symmetry is released [3].

[1]: P. Chalupa, T. Schäfer, M. Reitner, S. Andergassen, and A. Toschi, arXiv: 2003.07829,
PRL in press (2021).
[2]: M. Reitner, P. Chalupa, L. Del Re, D. Springer, S. Ciuchi, G. Sangiovanni, and A.
Toschi, PRL 125 196403 (2020).
[3]: D. Springer, P. Chalupa, S. Ciuchi, G. Sangiovanni, and A. Toschi, PRB 101, 155148
(2020).