Nonequilibrium Quantum Criticality in Open Electronic Systems

A theory is presented of quantum criticality in open (coupled to reservoirs) itinerant-electron magnets, with nonequilibrium drive provided by current flow across the system. Both departures from equilibrium at conventional (equilibrium) quantum critical points and the physics of phase transitions induced by the nonequilibrium drive are treated. Nonequilibrium-induced phase transitions are found to have the same leading critical behavior as conventional thermal phase transitions.

Figure 1

Upper panel: Schematic view of systems studied; interacting electron system coupled to two leads. Lower panel: Schematic phase diagram in a plane of equilibrium distance from criticality $\delta$ and departure from equilibrium $V$. The quantum critical point ${\delta }_c$ separates the long range ordered ($\delta <{\delta }_c$) and disordered ($\delta >{\delta }_c$) phases. The solid line denotes a nonequilibrium phase transition. The dashed curves indicate the crossover from low $V$ essentially equilibrium physics to the higher-$V$ nonequilibrium-dominated regime.