  We explore a variant of the Katz-Lebowitz-Spohn (KLS) driven lattice gas in
two dimensions, where the lattice is split into two regions that are coupled to
heat baths with distinct temperatures. The temperature boundaries are oriented
parallel to the external particle drive. If the hopping rates at the interfaces
satisfy particle-hole symmetry, the current difference across them generates a
vector flow diagram akin to a vortex sheet. We have studied the finite-size
scaling of the particle density fluctuations in both temperature regions, and
observed that it is controlled by the respective temperature values. If the
colder subsystem is maintained at the KLS critical temperature, while the
hotter subsystem's temperature is set much higher, the interface current
greatly suppresses particle exchange between the two regions. As a result of
the ensuing effective subsystem decoupling, strong fluctuations persist in the
critical region, whence the particle density fluctuations scale with the KLS
critical exponents. However, if both temperatures are set well above the
critical temperature, the particle density fluctuations scale according to the
totally asymmetric exclusion process (TASEP). We have also measured the entropy
production rate in both subsystems; it displays intriguing algebraic decay in
the critical region, while it saturates quickly at a small but non-zero level
in the hotter region. We have also considered another possible choice of the
hopping rates across the temperature interfaces that explicitly breaks
particle-hole symmetry. In that case the boundary rates induce a net particle
flux across the interfaces that displays power-law behavior, until ultimately
the particle exclusion constraints generate a clogging transition to an inert
state.
