Dr. Frank Pollmann (Max-Planck-Insitut fur Physik komplexer Systeme, Germany)
"Itinerant electrons on geometrically frustrated lattices"
We study a novel class of systems with electronic degrees of freedom on
frustrated lattices. It has been shown that such systems can have
excitations which carry fractional charges (e/2) in the limit of strong
correlations [1]. In order to understand the mechanism and physical
properties of these fractionalized charges, we firstly consider a model of
spinless fermions on a geometrically frustrated checkerboard lattice. An
effective Hamiltonian is derived which describes the low-lying excitations
in the limit of strong correlations. The ground state of the latter
Hamiltonian is shown to be charged ordered and the fractional charges are
linearly confined [2]. Secondly, we consider a model of spinful fermions
on a kagome lattice and study the interplay between charge- and
spin-degrees of freedom. In particular, we find here a new mechanism
yielding ferromagnetism [3].
[1] P. Fulde and K. Penc and N. Shannon, Ann. Phys. (Leipzig) 11, 892
(2002).
[2] F. Pollmann and P. Fulde, Europhys. Lett. 75, 133 (2006).
[3] F. Pollmann, P. Fulde, and K. Shtengel, arXiv:0705.3941 (2007).