Abstract
The collective plasmonic modes of a metal comprise a pattern of charge density and tightly-bound electric fields that oscillate in lock-step to yield enhanced light-matter interaction. Here we show that metals with non-zero Hall conductivity host plasmons with a fine internal structure: they are characterized by a current density configuration that sharply departs from that of ordinary zero Hall conductivity metals. This non-trivial internal structure dramatically enriches the dynamics of plasmon propagation, enabling plasmon wavepackets to acquire geometric phases as they scatter. Strikingly, at boundaries these phases accumulate allowing plasmon waves that reflect off to experience a non-reciprocal parallel shift along the boundary displacing the incident and reflected plasmon trajectories. This plasmon Hall shift, tunable by Hall conductivity as well as plasmon wavelength, displays the chirality of the plasmon's current distribution and can be probed by near-field photonics techniques. Anomalous plasmon dynamics provide a real-space window into the inner structure of plasmon bands, as well as new means for directing plasmonic beams.
Highlights
The internal structure of quasiparticles [1,2,3,4,5,6], e.g., spin, valley degrees of freedom, while typically hidden from view can dramatically alter the behavior of particles when they are coupled with kinematic variables
While we focused on conventional 2D metals at finite magnetic field above, a nontrivial plasmon band geometry can be achieved at zero field
A focused plasmon wave packet can be launched at a reflecting boundary
Summary
The internal structure of quasiparticles [1,2,3,4,5,6], e.g., spin, valley degrees of freedom, while typically hidden from view can dramatically alter the behavior of particles when they are coupled with kinematic variables. The unusual plasmon dynamics and trajectories we discuss here manifest directly because of the current density texture that is hidden in the motion of electrons in the 2D metal plane yielding striking experimental signatures This is akin to how (in electron transport) the inner (pseudo)spin degrees of freedom of an electron can alter its motion [9,10,11], or (in photonics) the spin-orbit interaction of light enables light polarizations to couple to its spatial degrees of freedom [22]. The exposed 2D surface of these materials (e.g., those found in graphene heterostructures [14,15,20,21]) are a ripe venue to observe the associated plasmon Hall shift and can be directly probed by scanning near-field scattering microscopy techniques [14,15] recently developed to map out plasmon trajectories These can provide a sensitive window into the internal structure of plasmon quasiparticles. This unusual effect of the internal structure of plasmon quasiparticles opens new means for manipulating plasmons in the extreme subwavelength regime
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