Parity-time symmetry breaking physics of dissipative Mott insulators

An applied electric field causes  dielectric breakdown to an insulator, leading to finite current as the field crosses a certain threshold value. This fact has been understood through the Landau-Zener tunneling mechanism which is analogous to the Schwinger mechanism for vacuum polarization in QED. However, the problem becomes challenging when dissipation is incorporated and the insulating phase occurs due to presence of strong electron-electron repulsion (Mott insulator).      

We propose a parity-time (PT) symmetric non-Hermitian Hubbard model which captures the effect of dissipation plus drive in such systems and solve it using Bethe ansatz for 1-dimension and dynamical mean-field theory (DMFT) for higher dimensions. We find universal critical insulator-to-metal phase transition, signaled by closing of spectral gap of the insulating phase near the PT-symmetry breaking point. We determine the critical exponents for the phase transition. In 1-dimension, the critical exponent agrees with the experiment.