We study the nonequilibrium steady states of an Ising chain in a transverse field $h$ by investigating the effect of a field $\lambda$, which drives the current of energy. The zero-temperature, $h$- $\lambda$ phase diagram is determined exactly, and it is found that the energy current appears continuously above a threshold $\lambda >{\lambda }_c\left(h\right)$. The long-range magnetic order (present for $h<\mathrm{}{h}_c,\lambda <{\lambda }_c$) is destroyed in the current-carrying state where the correlations are characterized by power-law, oscillatory decay. The mechanism which generates the power-law correlations in the current-carrying state is discussed.

• Received 21 June 1996

DOI:https://doi.org/10.1103/PhysRevLett.78.167