Commensurability Oscillations in the Radio-Frequency Conductivity of Unidirectional Lateral Superlattices: Measurement of Anisotropic Conductivity by Coplanar Waveguide

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We have measured the rf magnetoconductivity of unidirectional lateral superlattices (ULSLs) by detecting the attenuation of microwave through a coplanar waveguide placed on the surface. ULSL samples with the principal axis of the modulation perpendicular (S_{\bot}) and parallel (S_{\|}) to the microwave electric field are examined. For low microwave power, we observe expected anisotropic behavior of the commensurability oscillations (CO), with CO in samples S_{\bot} and S_{\|} dominated by the diffusion and the collisional contributions, respectively. Amplitude modulation of the Shubnikov--de Haas oscillations is observed to be more prominent in sample S_{\|}. The difference between the two samples is washed out with the increase of the microwave power, letting the diffusion contribution govern the CO in both samples. The dominance of the diffusion contribution even in sample S_{\|} in the CO measured with high microwave power is interpreted in terms of large-angle electron--phonon scattering.
2013-05-15