Percolation transition in quantum Ising and rotor models with sub-Ohmic dissipation

Abstract

We investigate the influence of sub-Ohmic dissipation on randomly diluted quantum Ising and rotor models. The dissipation causes the quantum dynamics of sufficiently large percolation clusters to freeze completely. As a result, the zero-temperature quantum phase transition across the lattice percolation threshold separates an unusual super-paramagnetic cluster phase from an inhomogeneous ferromagnetic phase. We determine the lowtemperature thermodynamic behavior in both phases, which is dominated by large frozen and slowly fluctuating percolation clusters. We relate our results to the smeared transition scenario for disordered quantum phase transitions, and we compare the cases of sub-Ohmic, Ohmic, and super-Ohmic dissipation.

Percolation via Combined Electrostatic and Chemical Doping in Complex Oxide Films

“…While at low enough temperatures thermal fluctuations are indeed weak, quantum fluctuations remain present. However, previous studies of diluted quantum magnetic systems found that the percolation threshold and certain percolation critical exponents (such as β and ν) are unaffected by quantum fluctuations [35,36], even in the presence of dissipation [37,38], which is expected to occur on the metallic side of the transition. Finally, we have focused on electrostatic gating, our conclusions also apply to electrochemical doping describing, for example, the transfer of oxygen vacancies into the surface of a sample.…”

Smeared nematic quantum phase transitions due to rare-region effects in inhomogeneous systems

“…As we show here, the rare regions completely change the nature of the simultaneous first-order nematic-DW quantum transition in a two-dimensional itinerant system. This is because of the crucial role of the droplet's dissipative quantum dynamics [35][36][37], which allows longrange Ising-nematic order in finite-size droplets at T = 0 (see also Ref. [18]), but not long-range DW order (for spin or incommensurate charge density-waves).…”