Magnetic gap and magnetization curve for a mixed valent semiconductor: A variational approach

Abstract

The ground state properties of the nondegenerate periodic Anderson model, which includes an external magnetic field, are studied variationally. We takef 1−f 2 valence mixing with two electrons per site, when the ground state is expected to be nonmetallic. A modified Stevens-Brandow-type trial wavefunction is used, which describes the condensate of a linear combination of singlet and tripletfd pair states. There are two variational parameters: the hybridization temperature, and a parameter to control the total magnetization. Up to a threshold fieldH t, the singlet ground state prevails, while forH>H t, the magnetization increases steeply withH. The magnetic gap derived fromH t is of the order of magnitude found by Jullien and Martin. The magnetization is dominated by the contribution off-electrons which become gradually extracted from the singlet bound state (dehybridization). The valence depends on the magnetic field.