AHARONOV-CASHER EFFECT IN THE HEISENBERG SPIN CHAIN WITH MANY IMPURITIES

The Aharonov-Casher effect is a quantum interference arising in mesosc opic rings involving particles with magnetic moments. The wave functio n acquires a phase due to an electric-field flux F enclosed by the rin g and gives rise to flux-dependent oscillations in persistent spin cur rents. In the ground state of the spin-1/2 Heisenberg chain the period and amplitude of the oscillations are associated with the properties of the Fermi surface of the elementary excitations of the spin chain ( spinons). We consider an anti-ferromagnetic spin-1/2 Heisenberg ring w ith a concentration x of impurity spins S. The calculations are perfor med within the framework of Bethe's ansatz. Due to the finite concentr ation of impurities the ground state consists of two (rather than one) Dirac seas, corresponding to spinons and 2S strings of rapidities. Th e persistent spin current reveals two periods of oscillation associate d with the properties of the two Fermi seas. The interference pattern as a function of F is discussed for several external magnetic fields.