Spectroscopic probes of isolated nonequilibrium quantum matter: Quantum quenches, Floquet states, and distribution functions

Abstract

We investigate radio-frequency (rf) spectroscopy, metal-to-superconductor tunneling, and ARPES as probes of isolated out-of-equilibrium quantum systems, and examine the crucial role played by the nonequilibrium distribution function. As an example, we focus on the induced topological time-periodic (Floquet) phase in a 2D $p+ip$ superfluid, following an instantaneous quench of the coupling strength. The post-quench Cooper pairs occupy a linear combination of "ground" and "excited" Floquet states, with coefficients determined by the distribution function. While the Floquet bandstructure exhibits a single avoided crossing relative to the equilibrium case, the distribution function shows a population inversion of the Floquet bands at low energies. For a realization in ultracold atoms, these two features compensate, producing a bulk average rf signal that is well-captured by a quasi-equilibrium approximation. In particular, the rf spectrum shows a robust gap. The single crossing occurs because the quench-induced Floquet phase belongs to a particular class of soliton dynamics for the BCS equation. The population inversion is a consequence of this, and ensures the conservation of the pseudospin winding number. As a comparison, we compute the rf signal when only the lower Floquet band is occupied; in this case, the gap disappears for strong quenches. The tunneling signal in a solid state realization is ignorant of the distribution function, and can show wildly different behaviors. We also examine rf, tunneling, and ARPES for weak quenches, such that the resulting topological steady-state is characterized by a constant nonequilibrium order parameter. In a system with a boundary, tunneling reveals the Majorana edge states. However, the local rf signal due to the edge states is suppressed by a factor of the inverse system size, and is spatially deconfined throughout the bulk of the sample.

22 pages, 15 figures. v2: Added calculated ARPES spectra

References in corpus (12)

• Photovoltaic Hall effect in graphene
• Multiterminal Conductance of a Floquet Topological Insulator
• Out of equilibrium electrons and the Hall conductance of a Floquet topological insulator
• Synchronization in the BCS Pairing Dynamics as a Critical Phenomenon
• Effective Theory of Floquet Topological Transitions
• Dissipative Floquet Topological Systems
• Dynamical vanishing of the order parameter in a fermionic condensate
• Dynamical band flipping in fermionic lattice systems: An ac-field-driven change of the interaction from repulsive to attractive
• Materials design from non-equilibrium steady states: driven graphene as a tunable semiconductor with topological properties
• Dynamical topological phases in quenched spin-orbit coupled degenerate Fermi gas
• Spectroscopic signatures of nonequilibrium pairing in atomic Fermi gases
• Predicted signatures of p-wave superfluid phases and Majorana zero modes of fermionic atoms in RF absorption

Cited by in corpus (13)

• Adiabatic Perturbation Theory and Geometry of Periodically-Driven Systems
• Dynamical phase transitions in the collisionless pre-thermal states of isolated quantum systems: theory and experiments
• Integrable Floquet dynamics
• Twisting Anderson pseudospins with light: Quench dynamics in THz-pumped BCS superconductors
• Topology and entanglement in quench dynamics
• Irradiated three-dimensional Luttinger semimetal: A factory for engineering Weyl semimetals
• Quench Dynamics Across Topological Quantum Phase Transitions
• Time-resolved spectral density of interacting fermions following a quench to a superconducting critical point
• Floquet topological systems in the vicinity of band crossings: Reservoir induced coherence and steady-state entropy production
• Dynamical generation of superconducting order of different symmetries in hexagonal lattices
• Anatomy of a periodically driven p-wave superconductor
• Control over few photon pulses by a time-periodic modulation of the photon-emitter coupling
• Topological quantum control: Edge currents via Floquet depinning of skyrmions in the $\nu =0$ graphene quantum Hall antiferromagnet