Detection of the Electron Spin Resonance of Two-Dimensional Electrons at Large Wave Vectors

We have investigated the electron spin resonance at nonzero wave vector in GaAs single quantum wells by combining the virtues of high frequency surface acoustic wave generation to produce excitations with large wave numbers with a sensitive optical scheme to detect resonant absorption. The observed large deviations from the single particle Zeeman energy are attributed to the exchange interaction. The enhancement of the electronic $g^{*}$ factor is, however, substantially smaller compared with theoretical predictions for spin waves when adopting a bare Coulomb interaction potential.

Figure 1

Polarization resolved luminescence spectra (top trace, ${\sigma }^{-}$; middle trace, ${\sigma }^{+}$) for $n_s=8.8\times {10}^{10}{\mathrm{cm}}^{-2}$, $B=1.3\mathrm{T}$ ($\nu =2.8$), and a temperature $T=0.4\mathrm{K}$. The bottom curve shows the unpolarized differential luminescence spectrum in the presence of 18 GHz SAWs. For the chosen density and $B$ field, resonant absorption takes place. The input power at one of the transducers is 1 mW.

Figure 2

Magnetic field dependence of the SAW absorption for 18, 12, and 9 GHz at the low density of $3\times {10}^9{\mathrm{cm}}^{-2}$. The input power at the transducer is approximately 1 mW for all frequencies. The extracted resonance positions agree well with those expected from the bare Zeeman energy (dashed line).

Figure 3

Dependence of the SAW-absorption spectrum on electron density measured for a fixed SAW frequency of 18 GHz.

Figure 4

Position of the electron spin resonances in the $B$ field vs $n_s$ plane for a SAW frequency of 18 GHz. The dashed line is the expected resonance position in the absence of exchange. Solid symbols are data points extracted from the absorption curves in Fig. 3.

Figure 5

Effective “$g^{*}$ factor” of the spin wave, $g^{*}=h\Omega /{\mu }_{B}B$ determined experimentally for 18 GHz and 12 GHz surface acoustic waves (square and circles) and theoretically using the bare Coulomb interaction (solid lines) and the 2D screened interaction (dotted lines). The blue color refers to the 12 GHz results, and red to the 18 GHz data.