Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C07: Electron SolidsFocus
|
Hide Abstracts |
Sponsoring Units: DCMP Chair: Ramesh Mani, Georgia State University Room: LACC 153B |
Monday, March 5, 2018 2:30PM - 2:42PM |
C07.00001: Pomeranchuk instability of composite Fermi liquid Eun-Ah Kim, Kyungmin Lee, Junping Shao, Frederick D Haldane, Edward Rezayi Nematicity in quantum Hall systems has been experimentally well established at excited Landau levels. The mechanism of the symmetry breaking, however, is still unknown. Pomeranchuk instability of Fermi liquid parameter Fl≤ -1 in the angular momentum l=2 channel has been hypothesized to be the relevant mechanism, yet there are no clear theoretical proofs. Here we calculate, using variational Monte Carlo technique, Fermi liquid parameters Fl of the composite Fermi liquid interacting with 1/r coulomb interaction. We consider Fl in different Landau levels n=0,1,2 as functions of layer width η. We find that unlike the lowest Landau level, which shows no sign of Pomeranchuk instability, higher Landau levels show nematic instability below critical values of η. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C07.00002: Observation of a Mass-Anisotropy-Driven Stripe Phase in Two Dimensions Md. Shafayat Hossain, Meng Ma, Edwin Chung, Loren Pfeiffer, K West, K Baldwin, Mansour Shayegan Even-denominator fractional quantum Hall states observed in high quality two-dimensional (2D) electron systems in the first excited (N = 1) Landau level, such as the well-known ν = 5/2 state, are candidates for non-Abelian Moore-Read states. One possible application of such states is fault-tolerant topological quantum computing. Here we study a 2D electron system, confined to an AlAs quantum well, which exhibits a rich sequence of odd-denominator fractional quantum Hall states in the lowest (N = 0) Landau level. In the N = 1 Landau level, instead of a topologically ordered even-denominator fractional quantum Hall state, our experiments reveal an emergent stripe phase, signaling a spontaneous breakdown of the translational symmetry. Such symmetry-breaking can be attributed to the anisotropic effective mass of electrons in AlAs. Intriguingly, the stripes orient themselves along the smaller effective mass direction; this is consistent with the results of recent calculations [1]. We also find that these mass-anisotropy-induced stripes are quite robust; they cannot be reoriented by the application of a large in-plane magnetic field, and persist to high temperatures. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C07.00003: Pinning Mode Frequency Tuned by Asymmetric Bias in a GaAs Two Dimensional Electron System in the Wigner Solid Regime Jeremy Curtis, Matthew Freeman, Anthony Hatke, Lloyd Engel, Mansour Shayegan, Loren Pfeiffer, K West, K Baldwin Electrons in two-dimensional electron systems (2DES) form pinned Wigner crystals at the low Landau filling (ν) termination of the fractional quantum Hall effect (FQHE) series. In clean samples, microwave pinning mode resonances are understood to be indicative of these crystal states. Pinning mode spectroscopy has been used extensively in the study of these solids [1,2]. It has been suggested that disorder arising from interface roughness, due to its small spatial correlation length, contributes the most toward the resonance frequency [3]. |
Monday, March 5, 2018 3:06PM - 3:42PM |
C07.00004: Sharp Tunneling Resonance from Vibrations of a 2D Wigner Crystal Invited Speaker: Raymond Ashoori Microwave conductivity measurements show a rigidity of the 2D electron system around filling factor 1 that may arise from a Wigner crystal of quasiparticles, but these measurements could not determine if a long-range ordered crystal exists. One might expect that the broken symmetry from a Wigner crystal would result in features in the tunneling spectrum that would vary with the interparticle spacing and magnetic field strength. However, measurements of electrons tunneling into 2D system under strong perpendicular magnetic fields face technical challenges; e.g. the lateral conductivity can vanish, prohibiting the tunneled electrons from moving out of the system. We used a method of capacitively detected pulsed tunneling that overcomes this and other issues, allowing accurate measurements of tunneling of 2D holes and electrons in GaAs at 20 mK and in high magnetic field. For 2D holes, we discovered sharp and filling factor dependent resonances that are antisymmetric in energy and density around filling factor 1. Careful study shows similar resonances around filling factors 0 and 2. Analysis of the resonance structure agrees with a picture of holes that are dressed by interactions with vibrational degrees of freedom of the crystal. The dependence of the energy of the resonance on quasiparticle density shows a divergence and upon the approach to the from filling factor 1 to the quantum phase transition tot he 4/5 quantum Hall state and fits closely with a theory by Archer, Park, and Jain (PRL 111, 146804 (2013)). The sharpness of the resonance points to a remarkably long-range ordered Wigner Crystal with lattice correlation length of ~15 lattice spacings. Electron samples also show a similar tunneling resonance appearing near filling factor 1, but it only appears under application of a strong field parallel to the 2D system, along with the perpendicular field. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C07.00005: Temperature-induced transport asymmetry around half-filling in high Landau levels Qi Qian, James Nakamura, Michael Yannell, Saeed Fallahi, Geoffrey Gardner, Michael Manfra We report a temperature dependence study of transport properties in an ultra-low disorder GaAs two-dimensional electron system around half-filling of the N = 2 Landau level. In this study, we performed measurements of both the zero-bias magnetoresistance Rxx and the differential resistance dVxx/dI along the hard transport direction around filling factor ν = 9/2 at different temperatures. At high temperature, T = 100 mK, both Rxx and dVxx/dI are symmetric around ν = 9/2. However, as temperature is decreased towards T = 10 mK both Rxx and dVxx/dI become asymmetric: the Rxx peak shifts to lower magnetic field away from exact half-filling, and dVxx/dI shows strong non-linearity on the high field side of the Rxx peak. Our data suggests that a temperature induced breakdown of particle-hole symmetry occurs at low temperatures. At high temperature T = 100 mK where the system behaves as a standard anisotropic nematic, particle-hole symmetry is restored. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C07.00006: Strain-induced resistance anisotropy of GaAs two-dimensional electrons Alexander Stern, Johannes Pollanen, James Eisenstein, K West, Loren Pfeiffer, Jing Xia We report strain-dependent low temperature magnetotransport measurements of two-dimensional electrons confined in GaAs single quantum wells. The samples are mounted to a piezoelectric-based strain device with which we can apply, and vary, tensile strain in the quantum well in situ. With this apparatus we have achieved strain as large as ~0.3% in GaAs quantum wells at cryogenic temperatures. We find that with increasing strain the magnetoresistance of the two-dimensional electron system confined in the quantum well becomes anisotropic relative to the principle in-plane axes of the host crystal. Additionally, we find that this strain-induced resistance anisotropy exhibits hysteresis in the vicinity of Landau Level filling factor ν=5/2. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C07.00007: Quantum Hall stripes in tilted magnetic fields in high-density GaAs quantum wells X Fu, Qianhui Shi, Michael Zudov, K Baldwin, Loren Pfeiffer, K West Quantum Hall stripe phases in GaAs quantum wells are usually aligned along [110] crystal axis but can exhibit unconventional orientation (along [1-10] direction) when the electron density is sufficiently high. It was recently demonstrated for stripe phases with conventional orientation that the number of in-plane magnetic field-induced reorientations depends sensitively on the carrier density. In particular, it was shown that the in-plane magnetic field does not reorient stripes when the density exceeds a certain value. Here, we investigate the effect of the in-plane magnetic field on stripe phases in high-density GaAs quantum wells. We find that the native stripes are still aligned along [110] and usually prefer to align perpendicular to the in-plane magnetic field. |
Monday, March 5, 2018 4:18PM - 4:30PM |
C07.00008: Stability and competition with bubble phases of the fractional quantum Hall states in the second Landau level Vidhi Shingla, Ashwani Kumar, Loren Pfeiffer, K West, Gabor Csathy The availability of improved quality samples and the achievement of exceedingly lower electron temperatures led to the discovery of an increasing number of fractional quantum Hall states in the second Landau level. While in the lowest Landau level fractional quantum Hall states develop in particle-hole conjugate pairs, in the second Landau level this is often not the case. For example, clear signatures of the $\nu=2+2/5$ fractional quantum Hall state can be seen at low temperatures, while its particle-hole conjugate state at $\nu=2+3/5$ does not develop. In this talk we reexamine these and other fractional quantum Hall states of the second Landau level in light of their competition with the electronic bubble phases. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C07.00009: Competition between crystal and fractional quantum Hall liquid in the presence of LL mixing Jianyun Zhao, Yuhe Zhang, Jainendra Jain In low-density hole-type GaAs quantum wells, an insulating phase is observed for ν < 1/3 and also between ν = 1/3 and ν = 2/5. In a fixed phase diffusion Monte Carlo calculation, we find re-entrant phase transitions for a range of LL mixing, where the system goes, with increasing magnetic field, from 2/5 FQHE liquid → crystal → 1/3 FQHE liquid → crystal. Our results are in excellent agreement with experiments. It is predicted that for yet higher LL mixing, the crystal phase altogether suppresses the 1/3 and 2/5 FQHE. We also consider the filling factors ν = 1/5 and ν = 2/9 and predict that with increasing LL mixing a transition occurs into a crystal of composite fermions carrying two vortices. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C07.00010: Competing Liquid and Crystal Phases in Bilayer Systems under High Magnetic Field William Faugno, Alexander Duthie, David Wales, Jainendra Jain We investigate the nature of bilayer states in a high magnetic field as a function of the layer separation, filling factor, quantum well width, and electron density. Previous theoretical studies have investigated bilayer liquid states, but experiments have also found an insulating phase for a range of filling factors. We consider several types of liquid and crystal states at total filling factors 1/3, 2/5, 1/2, and 1/5, and determine the phase diagram as a function of the layer separation and density. We find that composite-fermion crystal phases are favored for appropriate parameters at 1/3, 2/5, and 1/5. These have either “binary graphene” or “correlated square” lattice structure. The theoretical phase diagram is compared with experiment. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C07.00011: Formation Filling Factor of 2D Wigner Crystal and the Competition with Interlayer Interaction Hao Deng, Loren Pfeiffer, K West, K Baldwin, Mansour Shayegan In unbalanced bilayer 2D electron systems with different interlayer distances, we find that the filling factor for the formation of the Wigner crystal in the dilute layer is influenced by the presence of the adjacent high-density layer. Our measurements reveal that electrons are transferred between the two layers as a function of increasing magnetic field. Once the field reaches a sufficiently high value, the Wigner crystal forms at a critical filling factor of the dilute layer, and then the layer densities remain constant at higher fields. We find that this critical formation filling factor is significantly smaller than the value for single-layer Wigner crystal (1/5), and shows a strong dependence on the interlayer distance and layer densities. The data highlight the competition between the intra-layer and inter-layer interactions. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C07.00012: Transport and reflection from the microwave and mm-wave photo-excited high mobility GaAs/AlGaAs 2D electron system Annika Kriisa, R.L. Samaraweera, M.S. Heimbeck, Henry Everitt, Werner Wegscheider, Ramesh Mani The microwave and mm-wave photoexcited GaAs/AlGaAs 2DES exhibits phenomena such as the radiation-induced zero resistance states and associated magnetoresistance oscillations in the large filling factor, low magnetic field limit, which depends upon ω/ωc where ω=2πf, and ωc is the cyclotron frequency. In this same regime, magnetoplasmon resonances have been observed and reported which represent hybridization between plasmons and cyclotron resonance. Here, we examine and compare the transport response with the microwave reflection response over the 30GHz to 330 GHz band to separate out the magnetoplasmon and bare cyclotron resonance response in the experiment. The results are compared with observations reported in the literature. |
Monday, March 5, 2018 5:18PM - 5:30PM |
C07.00013: Bichromatic microwave-induced oscillatory differential-resistance in the high mobility GaAs/AlGaAs heterostructure system Binuka Gunawardana, Chathuranga Munasinghe, R.L. Samaraweera, T. R. Nanayakkara, Annika Kriisa, U. Kushan Wijewardena, Christian Reichl, Werner Wegscheider, Ramesh Mani Microwave photo-excitation of the high mobility GaAs/AlGaAs samples has revealed interesting light-matter coupling properties, and many studies have been carried out to study the associated microwave-induced oscillatory magneto-resistance [1,2]. Here, we report on the oscillatory differential resistance that seems to follow the low-frequency monochromatic response at lower magnetic fields and high-frequency monochromatic response at higher magnetic fields [3]. The higher sensitivity in the differential resistivity served to examine the dependency of this oscillatory behavior where the difference of monochromatic and bichromatic results indicates a beats like relation with the magnetic field. This beat like behavior was further studied at different frequency ratios over the 40 < f < 102 GHz band while changing the microwave power systematically. The results of the study are reported here. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700