Sustained temporal resistance oscillations in constrained geometries at the nu 2/3 spin phase transition

S. Hennel¹, B. A. Bräm¹, S. Baer¹, L. Tiemann¹, C. R¨ossler¹, C. Reichl¹, W. Wegscheider¹, T. Ihn¹, K. Ensslin¹, M. S. Rudner² and B. Rosenow<sup>3

1</sup> Solid State Physics Laboratory, ETH Zürich, Switzerland
²Niels Bohr International Academy and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Denmark
³Institut für Theoretische Physik, Universität Leipzig, Germany

We observe highly visible temporal oscillations of the resistance measured across a tunable quantum point contact (QPC) in the  nu 2/3 fractional quantum Hall state, with a precise periodicity of the order of several minutes. Our observations are reminiscent of previously reported effects of electron-nuclear spin coupling in mesoscopic devices [1]. We perform a careful study of bias dependence and find that the oscillations are driven by a constant DC current and strongly depend on the polarity of the current. The effect is only qualitatively symmetric under reversal of both bias and magnetic field direction, and does not depend on the filling factor in the bulk of the sample but rather on the filling factor in the constriction. Using standard NMR techniques, we show that the oscillations are fully suppressed when the sample is irradiated with radio frequency in resonance with Ga or As nuclei. Short NMR sequences affect the oscillations only if coinciding in time with a sharp resistance maximum. Furthermore, the frequency of oscillations increases with increasing temperature. We develop a phenomenological model combining spin filtering and dynamic nuclear polarization at the  nu 2/3 spin phase transition [2] with nuclear spin diffusion.

References
[1] G. Yusa et al., Phys. Rev. B 69, 16302(R) (2004)
[2] S. Kronm¨uller et al., Phys. Rev. Lett. 82, 4070 (1999)