Inverted many-body mobility edge in a central qudit problem

Many interesting experimental systems, such as cavity QED or central spin models, involve global coupling to a single harmonic mode. Out-of-equilibrium, it remains unclear under what conditions localized phases survive such global coupling. We study energy-dependent localization in the disordered Ising model with transverse and longitudinal fields coupled globally to a $d$-level system (qudit). Strikingly, we discover an inverted mobility edge, where high energy states are localized while low energy states are delocalized. Our results are supported by shift-and-invert eigenstate targeting and Krylov time evolution up to $L=13$ and $18$ respectively. We argue for a critical energy of the localization phase transition which scales as $E_c \propto L^{1/2}$, consistent with finite size numerics. We also show evidence for a reentrant MBL phase at even lower energies despite the presence of strong effects of the central mode in this regime. Similar results should occur in the central spin-$S$ problem at large $S$ and in certain models of cavity QED

Topological Floquet-Thouless energy pump

We explore adiabatic pumping in the presence of periodic drive, finding a new phase in which the topologically quantized pumped quantity is energy rather than charge. The topological invariant is given by the winding number of the micromotion with respect to time within each cycle, momentum, and adiabatic tuning parameter. We show numerically that this pump is highly robust against both disorder and interactions, breaking down at large values of either in a manner identical to the Thouless charge pump. Finally, we suggest experimental protocols for measuring this phenomenon.Comment: 4 pages, 4 figures. Minor replacements and references adde

Nonequilibrium phononic first-order phase transition in a driven fermion chain

We study the direct laser drive of infrared-active phonons that are quadratically coupled to a spinless fermion chain. Feedback is incorporated by phonon dressing of the electronic dispersion, which enables effective non-linearities in the phonon dynamics. We uncover a first-order phase transition in the phononic steady state in which hysteretic effects allow either large or small phonon occupation depending on the drive protocol. We discuss the implications of these findings for probing phase transitions in real driven materials.Comment: 7+7 pages, 4+6 figure

Laser-enhanced magnetism in SmFeO3_3

The cross-talk between two magnetic ions, Sm$^{3+}$ and Fe$^{2+}$, in samarium ferrite (SmFeO$_3$) leads to a strong interaction of spins and phonons at low temperatures, while the magnetic interactions are weak. In this work, we simulate the dissipative spin dynamics in SmFeO$_3$ that are coupled to laser-driven infrared-active phonons via linear and quadratic modulation of the exchange energy to coherently enhance spin interactions, referred to as magnetophononics. When linear coupling dominates, we discover a dynamical first-order phase transition in the nonequilibrium steady state which can inhibit strong enhancement of magnetic interactions. By contrast, when quadratic spin-phonon coupling dominates, no phase transition exists at experimentally relevant parameters. By utilizing a chirp protocol, we see that the phase transition can be engineered, enabling stronger magnetic interactions in the steady state, a key goal of magnetophononics. We also discuss the route for experimental observation of our results, as well as the potential application of our theory for functional materials and spintronics

Ultrafast dynamics of a fermion chain in a terahertz field-driven optical cavity

We study the effect of a terahertz field-driven single cavity mode for ultrafast control of a fermion chain with dissipation-induced nonlinearity and quadratic coupling to an infrared-active phonon mode. Without photon loss from the cavity, we uncover a first-order phase transition in the nonequilibrium steady state only for the lower phonon-polariton, accompanied by polaritons whose frequency response is asymmetric with respect to the photon frequency due to the direct laser-induced dressing effect on the photon. A weak laser field fails to induce the phase transition but renders the polaritons symmetrical. Finally, we show that sufficiently strong photon loss from the cavity eliminates the polaritons and the associated phase transition. The experimental feasibility of these phenomena is also proposed

Landau levels, Bardeen polynomials and Fermi arcs in Weyl semimetals: the who's who of the chiral anomaly

Condensed matter systems realizing Weyl fermions exhibit striking phenomenology derived from their topologically protected surface states as well as chiral anomalies induced by electromagnetic fields. More recently, inhomogeneous strain or magnetization were predicted to result in chiral electric $\mathbf{E}_5$ and magnetic $\mathbf{B}_5$ fields, which modify and enrich the chiral anomaly with additional terms. In this work, we develop a lattice-based approach to describe the chiral anomaly, which involves Landau and pseudo-Landau levels and treats all anomalous terms on equal footing, while naturally incorporating Fermi arcs. We exemplify its potential by physically interpreting the largely overlooked role of Fermi arcs in the covariant (Fermi level) contribution to the anomaly and revisiting the factor of $1/3$ difference between the covariant and consistent (complete band) contributions to the $\mathbf{E}_5\cdot\mathbf{B}_5$ term in the anomaly. Our framework provides a versatile tool for the analysis of anomalies in realistic lattice models as well as a source of simple physical intuition for understanding strained and magnetized inhomogeneous Weyl semimetals.Comment: 10 pages, 7 figure