Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C07: Electron SolidsFocus

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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 EunAh 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 F_{l}≤ 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 F_{l} of the composite Fermi liquid interacting with 1/r coulomb interaction. We consider F_{l} 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 MassAnisotropyDriven Stripe Phase in Two Dimensions Md. Shafayat Hossain , Meng Ma , Edwin Chung , Loren Pfeiffer , K West , K Baldwin , Mansour Shayegan Evendenominator fractional quantum Hall states observed in high quality twodimensional (2D) electron systems in the first excited (N = 1) Landau level, such as the wellknown ν = 5/2 state, are candidates for nonAbelian MooreRead states. One possible application of such states is faulttolerant topological quantum computing. Here we study a 2D electron system, confined to an AlAs quantum well, which exhibits a rich sequence of odddenominator fractional quantum Hall states in the lowest (N = 0) Landau level. In the N = 1 Landau level, instead of a topologically ordered evendenominator fractional quantum Hall state, our experiments reveal an emergent stripe phase, signaling a spontaneous breakdown of the translational symmetry. Such symmetrybreaking 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 massanisotropyinduced stripes are quite robust; they cannot be reoriented by the application of a large inplane 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 twodimensional 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: Joonho Jang , Benjamin Hunt , Loren Pfeiffer , K West , 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 longrange 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 longrange 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: Temperatureinduced transport asymmetry around halffilling 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 ultralow disorder GaAs twodimensional electron system around halffilling of the N = 2 Landau level. In this study, we performed measurements of both the zerobias magnetoresistance R_{xx} and the differential resistance dV_{xx}/dI along the hard transport direction around filling factor ν = 9/2 at different temperatures. At high temperature, T = 100 mK, both R_{xx} and dV_{xx}/dI are symmetric around ν = 9/2. However, as temperature is decreased towards T = 10 mK both R_{xx} and dV_{xx}/dI become asymmetric: the R_{xx} peak shifts to lower magnetic field away from exact halffilling, and dV_{xx}/dI shows strong nonlinearity on the high field side of the R_{xx} peak. Our data suggests that a temperature induced breakdown of particlehole symmetry occurs at low temperatures. At high temperature T = 100 mK where the system behaves as a standard anisotropic nematic, particlehole symmetry is restored. 
Monday, March 5, 2018 3:54PM  4:06PM 
C07.00006: Straininduced resistance anisotropy of GaAs twodimensional electrons Alexander Stern , Johannes Pollanen , James Eisenstein , K West , Loren Pfeiffer , Jing Xia We report straindependent low temperature magnetotransport measurements of twodimensional electrons confined in GaAs single quantum wells. The samples are mounted to a piezoelectricbased 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 twodimensional electron system confined in the quantum well becomes anisotropic relative to the principle inplane axes of the host crystal. Additionally, we find that this straininduced 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 highdensity 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 [110] direction) when the electron density is sufficiently high. It was recently demonstrated for stripe phases with conventional orientation that the number of inplane magnetic fieldinduced reorientations depends sensitively on the carrier density. In particular, it was shown that the inplane magnetic field does not reorient stripes when the density exceeds a certain value. Here, we investigate the effect of the inplane magnetic field on stripe phases in highdensity GaAs quantum wells. We find that the native stripes are still aligned along [110] and usually prefer to align perpendicular to the inplane 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 particlehole 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 particlehole 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 lowdensity holetype 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 reentrant 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 compositefermion 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 highdensity 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 singlelayer Wigner crystal (1/5), and shows a strong dependence on the interlayer distance and layer densities. The data highlight the competition between the intralayer and interlayer interactions. 
Monday, March 5, 2018 5:06PM  5:18PM 
C07.00012: Transport and reflection from the microwave and mmwave photoexcited high mobility GaAs/AlGaAs 2D electron system Annika Kriisa , R.L. Samaraweera , M.S. Heimbeck , Henry Everitt , Werner Wegscheider , Ramesh Mani The microwave and mmwave photoexcited GaAs/AlGaAs 2DES exhibits phenomena such as the radiationinduced zero resistance states and associated magnetoresistance oscillations in the large filling factor, low magnetic field limit, which depends upon ω/ω_{c} where ω=2πf, and ω_{c} 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 microwaveinduced oscillatory differentialresistance 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 photoexcitation of the high mobility GaAs/AlGaAs samples has revealed interesting lightmatter coupling properties, and many studies have been carried out to study the associated microwaveinduced oscillatory magnetoresistance [1,2]. Here, we report on the oscillatory differential resistance that seems to follow the lowfrequency monochromatic response at lower magnetic fields and highfrequency 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. 
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