Opening of a gap in an inhomogeneous external field
Physics Department, University of Wuppertal,
42097 Wuppertal, Germany
Accepted: 21 August 1998
Published online: 15 January 1999
We study the one-dimensional spin-1/2 antiferromagnetic Heisenberg model exposed to an external field, which is a superposition of a homogeneous field h3 and a small periodic field of strength h1. For the case of a transverse staggered field a gap opens, which scales with , where is given by the critical exponent defined through the transverse structure factor of the model at . For the case of a longitudinal periodic field with wave vector and strength hq a plateau is found in the magnetization curve at M=1/4. The difference of the upper- and lower magnetic field scales with , where is given by the critical exponent defined through the longitudinal structure factor of the model at .
PACS: 75.10 -b – General theory and models of magnetic ordering
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999