Photon-Induced Vanishing of Magnetoconductance in 2D Electrons on Liquid Helium

We report on a novel transport phenomenon realized by optical pumping in surface state electrons on helium subjected to perpendicular magnetic fields. The electron dynamics is governed by the photon-induced excitation and scattering-mediated transitions between electric subbands. In a range of magnetic fields, we observe vanishing longitudinal conductivity ${\sigma }_{xx}\to 0$. Our result suggests the existence of radiation-induced zero-resistance states in the nondegenerate 2D electron system.

Figure 1

Electron dynamics in perpendicular magnetic fields. Microwave photons of energy $hf$ drive the transition $n=1\to 2$ (wavy arrow) without changing the quantum state $l$. Excited electrons can be scattered elastically (dashed arrow) and fill the state $l^{\prime }>l$ of the first subband.

Figure 2

Longitudinal conductivity ${\sigma }_{xx}$ versus $B$ for irradiated electrons with $n_s=0.9\times {10}^6{\mathrm{cm}}^{-2}$ at four different temperatures: $T=0.4$ (blue line), 0.35 (green line), 0.3 (brown line), and 0.2 K (red line). Black triangles indicate the values of $B$ where $hf=l\hslash {\omega }_c$, for $l=4$, 5, and 6.

Figure 3

${\sigma }_{xx}$ versus $B$ for $n_s=0.9\times {10}^6{\mathrm{cm}}^{-2}$, $T=0.2\mathrm{K}$, and $P=-25$ (blue line) and $-10\mathrm{dB}$ (red line).

Figure 4

${\sigma }_{xx}$ versus $2\pi f/{\omega }_c$ obtained without radiation (dashed line, black) and with radiation of frequency $f\approx f_{21}$ at $P=-10\mathrm{dB}$ (solid line, blue). Inset: ${\sigma }_{xx}$ in the vicinity of $2\pi f/{\omega }_c=4$ for three different power levels.

Figure 5

${\sigma }_{xx}$ obtained in upward (solid circles, red) and downward (open circles, blue) sweeps of $B$ at $T=0.2\mathrm{K}$, $n_s=1.1\times {10}^6{\mathrm{cm}}^{-2}$, and $P=-10\mathrm{dB}$. In the zero-resistance regime, ${\sigma }_{xx}$ is complex with a negative imaginary part (squares) and a real part (circles) attaining slightly negative values (see explanation in the text).