We propose a theoretical approach, within the framework of the composite operator method, to include the effects of finite cluster correlations into the self-energy of strongly correlated systems. The Hubbard model is analyzed as significant example. The self-energy is rewritten in terms of two-site composite-operator propagators, which are computed by means of a two-site approximation preserving relevant symmetries (e.g., particle-hole symmetry). The involved composite operators describe charge, spin and pair nearest-neighbor correlations and the excitations related to the induced exchange coupling (J = 4t2/U). The procedure results in a very rich band structure going well beyond the results of the two-pole approximation. © 2003 Elsevier Science B.V. All rights reserved.
Effects of two-site correlations in the Hubbard model
AVELLA, Adolfo;MANCINI, Ferdinando;ODASHIMA, SATORU
2003
Abstract
We propose a theoretical approach, within the framework of the composite operator method, to include the effects of finite cluster correlations into the self-energy of strongly correlated systems. The Hubbard model is analyzed as significant example. The self-energy is rewritten in terms of two-site composite-operator propagators, which are computed by means of a two-site approximation preserving relevant symmetries (e.g., particle-hole symmetry). The involved composite operators describe charge, spin and pair nearest-neighbor correlations and the excitations related to the induced exchange coupling (J = 4t2/U). The procedure results in a very rich band structure going well beyond the results of the two-pole approximation. © 2003 Elsevier Science B.V. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
