Seminarium Oddziału Teorii Materii Skondensowanej

11:00 poniedziałek, 20-11-17
budynek II, sala 409a

Strongly Correlated Systems: Composite Operator Method Perspective

prof. Adolfo Avella

University of Salerno, Włochy

The Composite Operator Method (COM) is designed to endorse the systematic emergence in any strongly correlated system of new elementary excitations described by composite operators obeying non-canonical algebras. COM is formulated to deal with the unusual features of such composite operators and compute the unconventional properties of strongly correlated systems in a non-perturbative, fully-analytical and self-consistent way [1]. We here focus on the unconventional and puzzling physics of the cuprates by studying, within COM, the Hubbard model [2-4]. We present a very promising three-pole solution for the two-dimensional Hubbard model [2] where, in addition to the two Hubbard operators, the operatorial basis comprises a third operator describing electronic transitions dressed by nearest-neighbor spin fluctuations. Such a framework has been positively validated through a comprehensive comparison with data for local and single-particle properties obtained by different numerical methods, as well as by other n-pole solutions, on varying all model parameters. Moreover, we report some very preliminary results regarding a quite complex, but extremely insightful, fourpole approximation [3]. Finally, we describe and comment the results of an approximation scheme where the residual interactions, beyond a 2-pole approximation, have been treated within the Non Crossing Approximation [4]. Given this recipe, it is possible to qualitatively describe some of the anomalous features of high-Tc cuprate superconductors such as large vs. small Fermi surface dichotomy, appearance of Fermi arcs, nodal vs. anti-nodal physics, pseudogap, kinks in the electronic dispersion.

[1] Adolfo Avella and Ferdinando Mancini, Springer Series in Solid-State Sciences 171, 103 (2012).
[2] Adolfo Avella, Eur. Phys. J. B 87, 45 (2014).
[3] Andrea Di Ciolo, Adolfo Avella, preprint University of Salerno, Italy (2017).
[4] Adolfo Avella, Adv. Cond. Matt. Phys. 2014, 515698 (2014).

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