Nonreciprocal electron hydrodynamics under magnetic fields: Applications to nonreciprocal surface magnetoplasmons

Abstract

Recent experiments have elucidated that novel nonequilibrium states inherent in the so-called hydrodynamic regime are realized in ultrapure metals with sufficiently strong momentum-conserving scattering. In this letter, we formulate a theory of electron hydrodynamics with broken inversion symmetry under magnetic fields and find that novel terms emerge in hydrodynamic equations which play a crucial role for the realization of the nonreciprocal responses. Specifically, we clarify that there exist a novel type of nonreciprocal collective modes dubbed nonreciprocal surface magnetoplasmons arising from an interplay between magnetic fields and the orbital magnetic moment. We reveal that these nonreciprocal collective modes indeed give rise to the nonreciprocity in magneto-optical responses such as the reflectivity. The physics discussed here will bridge the two important notions of magnetoplasmonics and nonreciprocity in electron hydrodynamic materials with inversion symmetry breaking and magnetic fields.

Valley filtering and valley-polarized collective modes in bulk graphene monolayers

“…[125][126][127] For 2D electron systems with broken inversion symmetry and under a vertical magnetic field, a theory of electron hydrodynamics was formulated in Ref. [129]. In the hydrodynamic equations, novel terms emerge due to coupling of the magnetic field, Berry curvature and OMM, which lead to nonreciprocal surface magnetoplasmons and the nonreciprocity in magneto-optical responses.…”

“…( 25), the valley-dependent drift velocity 𝑢 τ may vary with the position 𝑟 and time t, k B is the Boltzmann constant, T is the temperature, and µ is the chemical potential. By multiplying the Boltzmann equation with the quasiparticle velocity and then summing over all single-particle states [129,131] with the distribution function (33), one yields the continuity equation and Euler equation for electron density n τ and drift velocity 𝑢 τ . The extremes of OMM and Berry curvature in the momentum space are valley-resolved due to the strain-related vector potential.…”

Quantum Plasmonic Nonreciprocity in Parity-Violating Magnets

“…The bulk, intrinsic (i.e., passive without driving), and magnetic-field-free nature of QMP nonreciprocity distinguishes it from other types of chiral plasmons that include edges of Hall metals, 26−30 out-ofequilibrium protocols, 31−35 or magneto-hydrodynamic modes. 36 Semiclassical Picture of Quantum Metric Plasmons. To illustrate the origins of QMPs, we first analyze the semiclassical collective dynamics of an electron liquid in a slowly varying electric field E(r, t).…”

“…In such systems, the Hall effect vanishes, while BDC and intrinsic plasmonic nonreciprocity persists. The bulk, intrinsic (i.e., passive without driving), and magnetic-field-free nature of QMP nonreciprocity distinguishes it from other types of chiral plasmons that include edges of Hall metals, − out-of-equilibrium protocols, − or magneto-hydrodynamic modes …”

Quantum geometry and chiral responses in van der Waals heterostructures

“…The passive generation of non-reciprocal plasmons, proposed in chapter 4, goes beyond current schemes to drive non-reciprocal collective oscillations. Current schemes rely on active driving of the system [146] or magnetohydrodynamics [147]. As discussed in chapter 1 and chapter 3, second order responses in electric field vanish in inversion symmetric systems.…”