A novel solution of the 2D Hubbard model within a 4-pole approximation: electronic dispersion and Fermi surface evolution

We present and characterize a novel solution of the 2D Hubbard model within the Composite Operator Method [1,2] in a 4-pole approximation [3]. We have chosen a basis of four fields: the two Hubbard operators plus two fields describing the Hubbard transitions dressed by nearest-neighbor spin fluctuations, which play a crucial role for strong correlations. This 4-pole solution performs very well once compared with advanced (semi-)numerical methods for all relevant values of interaction, doping and temperature, being considerably less computational-resource demanding. By carefully treating spin fluctuations and featuring momentum selectivity, this solution can address the underdoped-cuprate puzzle (Fermi arcs, pseudogap, non-Fermi liquid behavior, …). We adopt this approximation to study the single-particle properties of the model in the strong coupling regime, where spin fluctuations are responsible for anomalous features in the analyzed properties. We focus on the investigation of the electronic dispersion and of the Fermi surface, studying their evolution with doping and temperature.
1. F. Mancini and A. Avella, Adv. Phys. 53, 537 (2004).
2. A. Di Ciolo and A. Avella, Condens. Matter Phys. 21, 33701 (2018).
3. A. Di Ciolo and A. Avella, AIP Adv. 8, 101327 (2018).