Electromagnetic drag in partly gated 2d electron system via highly confined screened plasmons

TL;DR

The paper addresses PDE in a partly gated 2DES, showing that edge-induced field nonuniformity can generate a sizable photovoltage even when photon momentum is small. It introduces an exact Wiener–Hopf diffraction approach to relate the local field to gated plasmon excitations, identifying $\eta = 2\pi \sigma / c$ and $k_0 d$ as the key dimensionless controls. The main finding is that plasmonic launching at the gate edge yields a large PDE, with maximum momentum transfer when the in-plane conductivity is inductive ($\mathrm{Im}\,\eta \sim 1$, $\mathrm{Re}\,\eta \ll 1$), while capacitive ($\mathrm{Im}\eta < 0$) conductivity suppresses the effect; importantly, the drag directs under the gate, opposite to metal-2DES contacts. These results provide design principles for fast, subwavelength PDE detectors and connect to Dyakonov–Shur rectification, offering clear experimental paths including graphene-based platforms where $\mathrm{Im}\eta$ can be tuned.

Abstract

Generation of photocurrent via photon drag effect enables very fast light detection with response time limited by momentum relaxation. At the same time, photon drag in bulk uniform samples is small by the virtue of small photon momentum. We show that the edge of metal gate placed above a two-dimensional electron system (2DES) provides highly non-uniform electromagnetic field that enhances the drag effect. We study the drag photovoltage using an exact solution of diffraction problem for 2DES with semi-infinite metal gate. We show that the only non-trivial dimensionless parameters governing the drag responsivity are the 2DES conductivity scaled by the free-space impedance η and gate-2DES separation scaled by the incident wavelength d/λ0. For radiation with electric field polarized orthogonal to the gate edge, the responsivity is maximized for inductive 2d conductivity with Imη ~ 1 and Reη << 1, and becomes very small for the capacitive 2d conductivity. The electromagnetic ponderomotive force pushes the charge carriers under the gate at arbitrary 2d conductivity, and the force direction is opposite to that at metal-2DES lateral contact. These patterns are explained by the dominant role of gated 2d plasmons in the formation of PDE photovoltage.

Figures (5)

• Figure 1: Schematic of the studied structure: a partly gated 2DES illuminated by a normally incident plane wave with electric field orthogonal to the edge. Diffraction of the incident wave results in efficient launching of both gated and ungated plasmons (least for inductive 2DES conductivity), which produce drag force $f_{pd}$ on the charge carriers.
• Figure 2: Drag in partly gated 2DES for purely real conductivity. (A) Dependence of momentum transfer coefficient on dimensionless conductivity $\eta$ for various gate-2DES separations indicated in legend. Red curve shows the result for drag at the contact between metal and 2DES (B) Dependence of momentum transfer coefficient on gate-2DES separation $k_0d$ for selected values of $\eta$.
• Figure 3: Drag in partly gated 2DES for weakly dissipative 2DES conductivity. Dependence of momentum transfer coefficient on imaginary part of dimensionless conductivity $\eta"$ for various gate-2DES separations (indicated in legend). Real part of 2DES conductivity is taken constant and equal to $\eta\ = 10^{-2}$.
• Figure 4: Structure of the diffracted field and plasmonic origin of drag force. The dependence of Fourier spectrum of electric field in 2DES weighted with wave vector $q|E(q)|$ as a function of wave vector $q/k_0$ for several situations: metal-2DES contact (violet), partly gated 2DES with proximity gate ($k_0d=10^{-2}$) and inductive conductivity (blue), real conductivity (yellow), capacitive conductivity (red). In inductive case, the diffracted field develops resonances at plasma wave vectors $q=+q_g$ and $q=-q_u$. Some enhancement of field at $q\sim q_g$ persists for purely dissipative conductivity, while for capacitive conductivity the field is suppressed.
• Figure 5: Color maps of the momentum transfer coefficient $\alpha$ vs complex 2d conductivity $\eta'+i\eta"$ for small gate-2DES separation [panel (A), $k_0d=2\times10^{-3}$] and moderately large gate-2DES separation [panel (A), $k_0d=2\times10^{-2}$]. Hot colors correspond to large values of $\alpha$, cold colors -- to the values of $\alpha$ close to zero