Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J2: Non-equilibrium Phenomena in Very High Landau Levels |
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Sponsoring Units: DCMP Chair: Myriam Sarachik, City College of New York, CUNY Room: Oregon Ballroom 202 |
Tuesday, March 16, 2010 11:15AM - 11:51AM |
J2.00001: Magneto-resistance oscillations in very high Landau levels of two-dimensional electron systems Invited Speaker: Michael Zudov When a two-dimensional electron system (2DES), most famous for quantum Hall effects, is subject to a weak perpendicular magnetic field and low temperature, the resistivity exhibits well-known Shubnikov-de Haas oscillations. If a high-mobility 2DES is further exposed to microwave radiation, dc electric field or elevated temperatures, other classes of magneto-oscillations emerge. These oscillations are known as microwave-, Hall field- and phonon-induced resistance oscillations, respectively. Under certain conditions oscillation minima can extend all the way to zero producing zero-resistance and zero-differential resistance states. This talk will discuss recent experimental developments focusing on the effects of strong dc electric fields and electron-electron interactions responsible for the temperature dependence of magneto-oscillations in a high-mobility 2DES. [Preview Abstract] |
Tuesday, March 16, 2010 11:51AM - 12:27PM |
J2.00002: Non-linear transport in a two-dimensional electron gas in magnetic fields Invited Speaker: Maxim Vavilov Transport through high-mobility two-dimensional electron systems placed in moderate perpendicular magnetic fields shows a rich variety of phenomena, associated with a non-linear differential resistivity at strong currents, microwave-induced and phonon-induced resistance oscillations. These phenomena can be described within a quantum kinetic theory of electron transport in disorder potential within the self-consistent Born approximation. This talk will focus on magneto-oscillations of the differential resistivity in the presence of microwave radiation. A qualitative explanation of the origin of resistivity oscillations will be combined with a quantitative analysis of recent experiments. Special attention will be devoted to evaluation of a relative strength of short-scale and long-scale disorder potential and the rate of electron-electron scattering. Non-linear dependence of the differential resistivity on the power of microwave radiation will also be analyzed. [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 1:03PM |
J2.00003: Nonlinear Transport of 2D Electrons in Crossed Electric and Quantizing Magnetic Fields Invited Speaker: Sergey Vitkalov Nonlinear transport of highly mobile two-dimensional electrons placed in crossed electric and quantizing magnetic fields will be discussed. The nonlinearity is remarkably strong and is unusual for degenerate electron systems. At small electric fields the nonlinear response originates from an energy dependent heating, which occurs in conducting systems with quantized or discrete spectrum. The quantal heating results in nontrivial spectral distribution of 2D carriers, radical change of the electron transport, transition of the electrons into a state with zero differential resistance (ZDR)[1,2,3]. Finally the heating leads to an apparent dc-driven metal-insulator transition, which coincides with the transition into the ZDR state. The phenomena are very unexpected and are not understood. \\[4pt] [1] J.Q.Zhang, S.Vitkalov, A.A. Bykov, Phys.Rev. \textbf{B} \textbf{80},045310 (2009); \\[0pt] [2] A.A. Bykov, J.Q. Zhang, S. Vitkalov, A.K. Kalagin, and A.K. Bakarov, Phys. Rev. Lett. \textbf{99}, 116801 (2007); \\[0pt] [3] S. A. Vitkalov, Int. Journal of Modern Physics \textbf{B}, \textbf{23}, 4727 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:39PM |
J2.00004: Microwave-Induced Nonlinear Transport in Spatially Modulated 2D Electron Systems Invited Speaker: Rui-Rui Du We have studied experimentally the MW-induced photoresistance in a periodically modulated 2DES where a shallow triangular antidot lattice is patterned by electron-beam lithography. This work is primarily motivated by the theoretical work considering the effect of long-wavelength ($>>$ magnetic length $l_B =\sqrt {\hbar e/B} )$ disorder potentials on ZRS/ZCS, in particular, on the domain formation in this regime. Introducing an antidot lattice in a high-mobility 2DES allows for studies of scattering process in ZRS/ZCS in a more controlled fashion. Since the system is readily tunable by parameters like $a $(lattice constant), $d$ (antidot diameter), and the ``softness'' of the antidot potential, the modulated 2DES is a rich system for studies of MIRO and ZRS. Our experiments have shown unexpected resistance features in this system. For example, we have observed resistance oscillations (periodic in B) in addition to MIRO (periodic in 1/B), which we tentatively attribute to ``microwave-induced Aharonov-Bohm effect in an antidot lattice.'' The presence of A-B oscillations in 2DES consisting of a large number ($>$ 200) of dots, together with the fact that such features are absent without MW irradiation, is rather remarkable. These experiments suggest the roles of edge transport and quantum interference in the MIRO. We will present a systematic study of the resistance features as a function of dot diameter, lattice constant, and the amplitude of the potential modulation. Another interesting question pertains to the effect of modulation on the ZRS, in particular, the dynamics of the domains in a periodic potential. We will report on our preliminary observations of resistance fluctuations in the ZRS in the modulated 2DES as well as that in ultrahigh mobility, unpatterned GaAs/AlGaAs quantum wells. Z. Q. Yuan et al, Phys. Rev. B 74, 075313 (2006); A. Auerbach et al, Phys. Rev. Lett. 94, 196801 (2005); I. G. Finkler and B. I. Halperin, Phys. Rev. B 79, 085315 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 1:39PM - 2:15PM |
J2.00005: Photogalvanic effects originating from the violation of the Einstein relation in a 2D electron gas in high Landau levels Invited Speaker: Ivan Dmitriev This talk will present a quantum kinetic theory [1] of the microwave-induced photocurrent and photovoltage magnetooscillations emerging in a spatially nonuniform 2D electron system in the absence of external dc driving [2]. It will show that in an irradiated sample the Landau quantization leads to violation of the Einstein relation between the dc conductivity and diffusion coefficient. Then, in the presence of a built-in electric field in a sample, the microwave illumination causes photo-galvanic signals which oscillate as a function of magnetic field as observed in the experiment. The discussed effects should also play an essential role for the transport in the zero resistance states where the system breaks into current domains and peculiarities of the transport properties of the inhomogeneous system become of central importance.\\ {[1]} I. A. Dmitriev, S. I. Dorozhkin, and A. D. Mirlin, ``Theory of microwave-induced photocurrent and photovoltage magneto-oscillations in a spatially nonuniform two-dimensional electron gas '', Phys. Rev. B {\bf 80}, 125418 (2009).\\ {[2]} S. I. Dorozhkin, I. V. Pechenezhskiy, L. N. Pfeiffer, K. W. West, V. Umansky, K. von Klitzing, and J. H. Smet, ``Photocurrent and Photovoltage Oscillations in the Two-Dimensional Electron System: Enhancement and Suppression of Built-In Electric Fields'', Phys. Rev.Lett. {\bf 102}, 036602 (2009). [Preview Abstract] |
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