Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Q4: Invited Session: Fractional Quantum Hall Effect: New Directions |
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Sponsoring Units: DCMP Chair: Jainedra Jain, Pennsylvania State University Room: Mayor Cockrell Room 004 |
Wednesday, March 4, 2015 2:30PM - 3:06PM |
Q4.00001: Interacting Flatland Electrons Never Stop Surprising Invited Speaker: Mansour Shayegan I will present the highlights of several new magneto-transport experiments that probe the physics of interacting two-dimensional (2D) electrons (or holes) at high magnetic fields and low temperatures. These include: (1) observation of rare fractional quantum Hall states at even-denominator (1/2) filling factor in 2D hole systems at an unusual crossing of the two lowest Landau levels [1,2]; (2) tuning and measuring the shape and anisotropy of the composite fermion (CF) Fermi contours [3-5], and (3) data suggesting that CFs themselves can be interacting and form their own fractional quantum Hall and Wigner solid states [6]. I will also discuss a bilayer experiment where the CFs in one layer are used to probe an electron Wigner solid in the other layer [7]. \\[4pt](Work done in collaboration with Yang Liu, D. Kamburov, M.A. Mueed, S. Hasdemir, I. Jo, H. Deng, L.N. Pfeiffer, K.W. West, and K.W. Baldwin. Supported by the NSF, DOE, Keck, and Moore Foundations.) \\[4pt] [1] Yang Liu et al., Phys. Rev. Lett. \textbf{112}, 046804 (2014). \\[0pt] [2] Yang Liu et al., Phys. Rev. B \textbf{89}, 165313 (2014). \\[0pt] [3] Kamburov et al., Phys. Rev. Lett. \textbf{110}, 206801 (2013). \\[0pt] [4] Kamburov et al., Phys. Rev. B \textbf{89}, 085304 (2014). \\[0pt] [5] Kamburov et al., Phys. Rev. Lett. \textbf{113}, 196801 (2014). \\[0pt] [6] Yang Liu et al., Phys. Rev. Lett. \textbf{113}, in press (2014); arXiv:1407.7846. \\[0pt] [7] Yang Liu et al., arXiv:1410.3435. [Preview Abstract] |
Wednesday, March 4, 2015 3:06PM - 3:42PM |
Q4.00002: Composite Fermions and Broken Symmetries in Graphene Invited Speaker: David Goldhaber-Gordon |
Wednesday, March 4, 2015 3:42PM - 4:18PM |
Q4.00003: Even-denominator fractional quantum Hall physics in ZnO Invited Speaker: Jurgen Smet The study of even denominator fractional quantum Hall physics has for a long time been the exclusive privilege of the III-V semiconductor community. Its discovery at filling 5/2 and 7/2 in GaAs unleashed a flood of theoretical as well as experimental work, because these states are in essence thought to be $p$-wave superconducting ground states possessing non-abelian excitations. Recently however even-denominator fractional quantum Hall physics has been observed outside of the realm of III-V heterostructures in the emergent ZnO 2D electron system. ZnO not only exhibits a robust quantum Hall state at filling 7/2, but also at unconventional fillings. There is an incipient 9/2 state in perpendicular field and a fully resolved 3/2-state emerges when tilting. The latter is believed to be, just like the 7/2 state, a genuine single component state analogous to the 5/2 and 7/2 states in GaAs. Alternatively, it could be a two component spin state, a variant two-component state that has not previously been reported. The use of ZnO for investigating this even denominator FQH-physics offers a powerful additional degree of freedom. Because the Zeeman splitting and the cyclotron energy are comparable, it is possible to alter the orbital character of the partially filled level at fixed filling by tilting the sample. Our studies show unequivocally that the orbital nature of the partially filled level is crucial for the appearance of even-denominator fractional quantum Hall physics. While a basic understanding has been developed, key features remain to be understood with the spin degree of freedom likely playing a prominent role. This work has been performed together with J. Falson (University of Tokyo), D. Maryenko (RIKEN), B. Friess (MPI-FKF), D. Zhang (MPI-FKF), Y. Kozuka (University of Tokyo), A. Tsukazaki (Tohuku University and JST), M. Kawasaki (University of Tokyo and RIKEN). [Preview Abstract] |
Wednesday, March 4, 2015 4:18PM - 4:54PM |
Q4.00004: Proliferation of Neutral Modes in Fractional Quantum Hall Regimes Invited Speaker: Hiroyuki Inoue The fractional quantum Hall effect (FQHE) is a canonical example of 2D topological phases. Being incompressible in the bulk, available low-energy charged excitations are only at the edge: gapless chiral 1D edge channels. Various collective phenomena can emerge when interactions take place between coexisting multiple edge channels. Recently, there is a surge of energy transport in FQHEs besides the charge transport. A notable example is upstream neutral edge modes in so-called hole-like fractional FQHEs, arising from the interacting channels, which remained elusive despite of an early theoretical prediction. In this talk, I will describe the observation of such neutral modes revealed via our sensitive shot noise measurents. Surprisingly, they were found not only in the hole-like FQHEs, as theoretically expected, but also in particle-like FQHEs and, furthermore, in the bulk. Our result presents a new picture of energy transport in FQHEs. The presence of various neutral modes may imply their unfavorable roles as potential decoherers for fractional quasiparticles. Hence, understanding the properties of the neutral modes may allow us to control decoherence and thus to conclusively observe quantum oscillations of the fractional quasiparticles.\\[4pt] In collaboration with Anna Grivnin, Yuval Ronen, Moty Heiblum, Vladimir Umansky, Diana Mahalu, Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science. [Preview Abstract] |
Wednesday, March 4, 2015 4:54PM - 5:30PM |
Q4.00005: NMR probing of quantum electron solids in high magnetic fields Invited Speaker: Trevor David Rhone In the presence of a high magnetic field, a two dimensional electron system (2DES) is expected to manifest Wigner crystal phases. Over thirty years ago, the search for the Wigner solid led to the discovery of the fractional quantum Hall effect (FQHE). Since then, with the advent of GaAs quantum wells with increasingly high mobility, 2DESs in the quantum Hall regime have proved to be a hunting ground for exceedingly rich many-body physics. Incompressible liquid FQHE states were found to occur in the first Landau level at several fractional filling factors $v$ with odd-denominator. The sequence of FQHE states is truncated by the formation of a Wigner crystal of electrons at very low filling factors, the transition being affected by disorder. In the second Landau level, composite fermions, the quasiparticles of the FQHE, can pair to yield a remarkable even-denominator FQHE state, whose properties are at the forefront of investigation. More recently, electron solid phases have been shown to emerge around integer quantum Hall states. In this talk, I will discuss a new tool, resistively detected NMR, which serves as a direct local probe of in-plane charge density modulations in the 2DES. In our recent work [1] we probe the local charge density landscape of Wigner solids in the vicinity of $v=$2 and $v$\textless 1/3 revealing quantum correlations. This unprecedented access to the microscopic behavior of these exotic solid phases opens up new venues in FQH studies. Furthermore, our NMR technique can probe in-plane charge density fluctuations due to disorder, allowing increased access to understanding roles of disorder in quantum Hall systems. In addition, our latest NMR measurements reveal evidence for charge inhomogeneity in the third Landau level which leads to the possibility of studying bubble and stripe phases in this regime. Future directions may find our NMR technique applied to other exotic phases such as quasiparticle solid phases, which have been proposed to emerge near the $v=$1/3 and 5/2 FQHE states. [Preview Abstract] |
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