On the lowest-energy excitations of one-dimensional strongly correlated electrons

Max-Planck-Institute for Physics of Complex Systems Noethnitzer Str. 38, D-01187 Dresden, Germany Theoretical Division, MS-B258, Los Alamos National Laboratory Los Alamos, 87545, New Mexico, USA

Received: 17 June 1998
Accepted: 23 November 1998

Abstract

It is proven that the lowest excitations of one-dimensional half-integer spin generalized Heisenberg models and half-filled extended Hubbard models are π-periodic functions. For Hubbard models at fractional fillings , where , and n is the number of electrons per unit cell. Moreover, if one of the ground states of the system is magnetic in the thermodynamic limit, then for any k, so the spectrum is gapless at any wave vector. The last statement is true for any integer or half-integer value of the spin.