



01597nas a2200145   4500008004100000245003200041210003100073260001400104520121600118100001901334700002901353700001501382700001701397856003701414       2020                        eng d00aSpin-Mediated Mott Excitons0 aSpinMediated Mott Excitons  c4/22/20203 a<p>Motivated by recent experiments on Mott insulators, in both iridates and ultracold atoms, we theoretically study the effects of magnetic order on the Mott-Hubbard excitons. In particular, we focus on spin-mediated doublon-holon pairing in Hubbard materials. We use several complementary theoretical techniques: mean-field theory to describe the spin degrees of freedom, the self-consistent Born approximation to characterize individual charge excitations across the Hubbard gap, and the Bethe-Salpeter equation to identify bound states of doublons and holons. The binding energy of the Hubbard exciton is found to increase with increasing the N{é}el order parameter, while the exciton mass decreases. We observe that these trends rely significantly on the retardation of the effective interaction, and require consideration of multiple effects from changing the magnetic order. Our results are consistent with the key qualitative trends observed in recent experiments on iridates. Moreover, the findings could have direct implications on ultracold atom Mott insulators, where the Hubbard model is the exact description of the system and the microscopic degrees of freedom can be directly accessed.&nbsp;</p>1 aHuang, T., -S.1 aBaldwin, Christopher, L.1 aHafezi, M.1 aGalitski, V.  uhttps://arxiv.org/abs/2004.1082501571nas a2200133   4500008004100000245005700041210005400098260001500152520117000167100002101337700002501358700001701383856003701400       2017                        eng d00aOut-of-time-order correlators in finite open systems0 aOutoftimeorder correlators in finite open systems  c2017/04/273 a<p>We study out-of-time order correlators (OTOCs) of the form hA&circ;(t)B&circ;(0)C&circ;(t)D&circ;(0)i for a quantum system weakly coupled to a dissipative environment. Such an open system may serve as a model of, e.g., a small region in a disordered interacting medium coupled to the rest of this medium considered as an environment. We demonstrate that for a system with discrete energy levels the OTOC saturates exponentially &prop; Paie &minus;t/τi + const to a constant value at t &rarr; &infin;, in contrast with quantum-chaotic systems which exhibit exponential growth of OTOCs. Focussing on the case of a two-level system, we calculate microscopically the decay times τi and the value of the saturation constant. Because some OTOCs are immune to dephasing processes and some are not, such correlators may decay on two sets of parametrically different time scales related to inelastic transitions between the system levels and to pure dephasing processes, respectively. In the case of a classical environment, the evolution of the OTOC can be mapped onto the evolution of the density matrix of two systems coupled to the same dissipative environment.</p>1 aSyzranov, S., V.1 aGorshkov, Alexey, V.1 aGalitski, V.  uhttps://arxiv.org/abs/1704.08442