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TT: Tiefe Temperaturen

TT 12: Correlated Electrons: Low-dimensional Systems - Models

TT 12.3: Vortrag

Dienstag, 28. März 2006, 10:00–10:15, HSZ 304

Effective model for the band insulator - Mott insulator transition — •Leonildo Tincani¹, Reinhard Noack¹, and Dionys Baeriswyl² — ¹Fachbereich Physik, Philipps Universität Marburg, D-35032 Marburg, Germany — ²Département de Physique, Université de Friburg, CH-1700 Fribourg, Switzerland

Starting from the ionic Hubbard model, we derive an effective spin-one model which contains the relevant physics for the band insulator-Mott insulator transition found at half filling and study it numerically using the density-matrix renormalization group. We find that the effective model yields the same sequence of two transitions and critical behavior as the ionic Hubbard model. We then perform scaling studies of the charge, spin and mass gaps in order to clarify the nature of the two quantum phase transitions. We present numerical evidence that there is an Ising-like transition between the band insulator and a spontaneously dimerized insulating phase and a Berezinskii-Kosterlitz-Thouless-like transition between the dimerized and the Mott phase. We then discuss the application of similar methods to more general models such as one with three ions of two types in the unit cell.