The dark curve is also presented. For a temperature of 0.4 K, we observe an intense spike at w ≈ 2w c. Finally, we obtain the usual radiation-induced R x x oscillations and ZRS as in standard samples. Conclusions In this letter, we have presented a theoretical approach to the striking result of the magnetoresistance spike in the second harmonic of the cyclotron frequency. According to our model, the strong change
in the density of Landau states in ultraclean samples affects dramatically the electron impurity scattering and eventually the conductivity. LEE011 The final result is that the scattered electrons perceive radiation as of half frequency. The calculated results are in good agreement with experiments. Authors’ information JI is an associate professor at the University Carlos III of Madrid. He is currently studying the effect of radiation on two-dimensional electron systems. Acknowledgements This work is supported by the MCYT (Spain) under grant MAT2011-24331 and ITN grant 234970 (EU). References 1. Iñarrea J, Platero G: Photoinduced current bistabilities in a semiconductor double barrier. Europhys Lett 1996, 34:43–47.CrossRef 2. Iñarrea J, Platero G: Photoassisted sequential tunnelling through superlattices. Europhys Lett 1996, 33:477–482.CrossRef 3. Iñarrea J, Aguado R, Platero G: Electron-photon interaction in resonant tunneling diodes. Europhys Lett 1997, 40:417–422.CrossRef 4. Mani RG, Smet JH, von Klitzing
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