W. Berdanier, T. Scaffidi and J. E. Moore. “Energy drag in particle-hole symmetric systems as a quantum quench.” Phys. Rev. Lett. 123, 246603 (2019).
The Coulomb drag effect, where a current in an "drive" layer pulls along a reciprocal current in a "response" layer through quantum interactions alone, has proven a sensitive probe of quantum transport. However, in particle-hole symmetric systems, traditional Coulomb drag vanishes to lowest order. Here we studied a thermal analogue of the Coulomb drag cast in terms of heat currents, finding that it dominates in these systems and displays radically different scaling behavior.
Abstract:
Two conducting quantum systems coupled only via interactions can exhibit the phenomenon of Coulomb drag, in which a current passed through one layer can pull a current along in the other. However, in systems with particle-hole symmetry -- for instance, the half-filled Hubbard model or graphene near the Dirac point -- the Coulomb drag effect vanishes to leading order in the interaction. Its thermal analogue, whereby a thermal current in one layer pulls a thermal current in the other, does not vanish and is indeed the dominant form of drag in particle-hole symmetric systems. By studying a quantum quench, we show that thermal drag, unlike charge drag, displays a non-Fermi's Golden Rule growth at short times due to a logarithmic scattering singularity generic to one dimension. Exploiting the integrability of the Hubbard model, we obtain the long-time limit of the quench for weak interactions. Finally, we comment on thermal drag effects in higher dimensional systems.
W. Berdanier, J. Marino and E. Altman. "Universal Dynamics of Stochastically Driven Quantum Impurities ." Phys. Rev. Lett. 123, 230604 (2019).
Generically, noise washes out delicate quantum coherences and tends to lead to classical critical exponents (generally coming from a Langevin equation). In this work, we showed that a stochastic quantum dot coupled to a conformal field theory (1-D quantum wire) can show truly quantum critical exponents, inherited from the CFT, shedding light on the possible universality classes of quantum noise.
Abstract:
We show that the dynamics of a quantum impurity subject to a stochastic drive on one side and coupled to a quantum critical system on the other display a universal behavior inherited from the quantum critical scaling. Using boundary conformal field theory, we formulate a generic ansatz for the dynamical scaling form of the typical Loschmidt echo and corroborate it with exact numerical calculations in the case of a spin impurity driven by shot noise in a quantum Ising chain. We find that due to rare events the dynamics of the mean echo can follow very different dynamical scaling than the typical echo for certain classes of drives. Our results are insensitive to irrelevant perturbations of the bulk critical model and apply to all the microscopic models in the same universality class.
W. Berdanier, M. Kolodrubetz, S. Parameswaran and R. Vasseur. "Strong-Disorder Renormalization Group for Periodically Driven Systems." Phys. Rev. B. 98, 174203 (2018).
We developed a microscopic real-space renormalization group method for Floquet systems generally, and used it to microscopically derive the criticality of the driven Ising chain -- in agreement with our earlier arguments.
Abstract:
Quenched randomness can lead to robust non-equilibrium phases of matter in periodically driven (Floquet) systems. Analyzing transitions between such dynamical phases requires a method capable of treating the twin complexities of disorder and discrete time-translation symmetry. We introduce a real-space renormalization group approach, asymptotically exact in the strong-disorder limit, and exemplify its use on the periodically driven interacting quantum Ising model. We analyze the universal physics near the critical lines and multicritical point of this model, and demonstrate the robustness of our results to the inclusion of weak interactions.
W. Berdanier, M. Kolodrubetz, S. Parameswaran and R. Vasseur. "Floquet Quantum Criticality." Proc. Natl. Acad. Sci. USA 115 (38) 9491-9496 (2018).
We gave an argument based on topological domain walls (in the same vein as an earlier argument of Damle and Huse) that allowed us to identify the criticality in the periodically driven Ising model. We were also the first to identify the criticality of the clean case.
Abstract:
We study transitions between distinct phases of one-dimensional periodically driven (Floquet) systems. We argue that these are generically controlled by infinite-randomness fixed points of a strong-disorder renormalization group procedure. Working in the fermionic representation of the prototypical Floquet Ising chain, we leverage infinite randomness physics to provide a simple description of Floquet (multi)criticality in terms of a new type of domain wall associated with time-translational symmetry-breaking and the formation of `Floquet time crystals'. We validate our analysis via numerical simulations of free-fermion models sufficient to capture the critical physics.
W. Berdanier, M. Kolodrubetz, R. Vasseur and J. E. Moore. “Floquet Dynamics of Boundary-Driven Systems at Criticality.” Phys. Rev. Lett. 118, 260602 (2017).
We considered the effects of a periodic boundary drive on a generic gapless quantum wire (CFT). This should be relevant to, for instance, experimental probes of periodically driven quantum dots. Interestingly, this was the first observation of a boundary Kibble-Zurek mechanism, to our knowledge.
Abstract:
A quantum critical system described at low energy by a conformal field theory (CFT) and subjected to a time-periodic boundary drive displays multiple dynamical regimes, depending on the drive frequency. We compute the behavior of quantities including the entanglement entropy and Loschmidt echo, confirming analytic predictions from field theory by exact numerics on the transverse field Ising model and demonstrate universality by adding nonintegrable perturbations. The dynamics naturally separate into three regimes: a slow-driving limit, which has an interpretation as multiple quantum quenches with amplitude corrections from CFT; a fast-driving limit, in which the system behaves as though subject to a single quantum quench; and a crossover regime displaying heating. The universal Floquet dynamics in all regimes can be understood using a combination of boundary CFT and Kibble-Zurek scaling arguments.