Contactless measurement of the conductivity of two-dimensional electrons in the regime of microwave-induced giant magnetoresistance oscillations

Magnetic-field dependences of the conductivity of a two-dimensional electron system obtained by contact and contactless measurements in the regime of microwave-induced giant magnetoresistance oscillations have been comparatively analyzed. The contactless technique for studying the conductivity of two-dimensional electrons is based on measuring the attenuation of the RF signal propagating along a coplanar waveguide manufactured using lithography on the sample surface. It has been found that Shubnikov-de Haas oscillations of conductivity are observed in both techniques, whereas the microwave-induced giant magnetoresistance oscillations appear only in the contact measurements. This contradiction indicates that the contact and/or boundary regions of the two-dimensional system with a strong potential gradient play an important role for the observation of the induced magnetoresistance oscillations.