Isotropic transverse XY chain with energy and magnetization currents

The ground-state correlations are investigated for an isotropic transverse XY chain that is constrained to carry either a current of magnetization (J(M)) or a current of energy (J(E)). We find that the effect of J(M) not equal 0 on the large-distance decay of correlations is twofold: (i) Oscillations are introduced and (ii) the amplitude of the power-law decay increases with increasing current. The effect of energy current is more complex. Generically, correlations in current carrying states are found to decay faster than in the J(E)=0 states, contrary to expectations that correlations are increased by the presence of currents. However, increasing the current, one reaches a special line where the correlations become comparable to those of the J(E)=0 states. On this line, the symmetry of the ground state is enhanced and the transverse magnetization vanishes. A further increase of the current destroys the extra symmetry, but the transverse magnetization remains at the high-symmetry zero value.