New Type of $B$-Periodic Magneto-Oscillations in a Two-Dimensional Electron System Induced by Microwave Irradiation

We observe a new type of magneto-oscillations in the photovoltage and the longitudinal resistance of a two-dimensional electron system. The oscillations are induced by microwave radiation and are periodic in magnetic field. The period is determined by the microwave frequency, the electron density, and the distance between potential probes. The phenomenon is accounted for by interference of coherently excited edge magnetoplasmons in the contact regions and offers perspectives for developing new tunable microwave and terahertz detection schemes and spectroscopic techniques.

Figure 1

(a) $R_{xx}$ as a function of $B$ without microwaves (the lower curve) and in the presence of microwaves for two different frequencies at the electron density $n_s=2.5\times {10}^{11}{\mathrm{cm}}^{-1}$ (the arrow marks the Landau-level filling factor $\nu =4$). (b) Evolution of $R_{xx}$ vs $B$ with microwave power $P_{\mathrm{\mu w}}$ (from bottom to top: 10, 30, and $100\mu \mathrm{W}$) at $n_s=2.75\times {10}^{11}{\mathrm{cm}}^{-2}$. The temperature $T=4.2\mathrm{K}$ and the distance between the contacts $L=0.5\mathrm{mm}$ are the same for both plots.

Figure 2

Oscillation maxima are assigned an integer index $N$. Their $B$-field position is plotted versus this index for various microwave frequencies ($n_s=2.61\times {10}^{11}{\mathrm{cm}}^{-2}$; $L=0.5\mathrm{mm}$).

Figure 3

(a) The period $\Delta B$ of the oscillations versus inverse microwave frequency for various electron densities and $L=0.5\mathrm{mm}$ (Hall bar geometry of type $A$). (b) $\Delta B$ versus $1/f$ for different distances between potential contacts (types $B$, $C$, and $D$) and $n_s=3.1\times {10}^{11}{\mathrm{cm}}^{-2}$.

Figure 4

Magnetoresistance $R_{xx}$ and photovoltage $V_{xx}$ versus applied $B$ field for 40 GHz incident microwave radiation, $n_s=2.75\times {10}^{11}{\mathrm{cm}}^{-2}$, $L=0.5\mathrm{mm}$, and a $1\mathrm{\mu A}$ sample current.

Figure 5

The oscillation index $N$ calculated from the dispersion equation $D(2\pi N/L,\omega )=0$ as a function of $B$ for the parameters of our samples: $n_s=2.61\times {10}^{11}{\mathrm{cm}}^{-2}$, $L=d_2=0.5\mathrm{mm}$, and $d_1=0.21\mu \mathrm{m}$ (solid symbols). The curve with open symbols is plotted for $f=53\mathrm{GHz}$ and $d_1=0\mu \mathrm{m}$ (no cover layers). The inset schematically illustrates the distribution of microwave-induced charges near contacts.