Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session E07: Fractional Quantum Hall 1Focus

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Sponsoring Units: DCMP Chair: Michael Zudov, University of Minnesota Room: LACC 153B 
Tuesday, March 6, 2018 8:00AM  8:36AM 
E07.00001: Quantitative comparisons between theory and experiment in fractional quantum Hall effect Invited Speaker: Jainendra Jain Comparisons with exact computer experiments have demonstrated the composite fermion theory to be quantitatively accurate at the level of a few percent, but the discrepancy with actual experiments is much larger because of corrections due to finite quantum well width, Landau level mixing and disorder. We carry out detailed calculations for spin phase transitions [1] including the effect Landau level mixing through a nonperturbative fixed phase diffusion Monte Carlo method [2], and find excellent agreement with experimental results. In particular, we explain a substantial difference between spin phase transitions for states at $\nu=n/(2n+1)$ and $\nu=2n/(2n+1)$ which are related by an exact particle hole symmetry in the absence of Landau level mixing. We also study [3] the competition between the fractional quantum Hall liquid and the crystal phases in the presence of Landau level mixing and explain the reentrant transitions between FQHE and insulator in the vicinity of $nu=1/3$ in low density hole type samples. 
Tuesday, March 6, 2018 8:36AM  8:48AM 
E07.00002: Loop Models, Modular Symmetry and Duality Eduardo Fradkin, Hart Goldman We will discuss the connection between loop mopdels of particlehole invariant theories of anyons to field theoreric dualities. We will discuss both systems in two space dimensions and boundaries of 3D systems, and the role of quantum anomalies. We will discuss the signifcance of our results to theories of quantum phase transitions in fractional quantum Hall fluids and other two and threedimensional topological fluids. 
Tuesday, March 6, 2018 8:48AM  9:00AM 
E07.00003: Studies of Localization in a Fraction of the Lowest Landau Level Akshay Krishna, Matteo Ippoliti, Ravindra Bhatt The problem of localization in the lowest Landau level has been studied extensively and is known to exhibit a diverging localization length due to the presence of topological extended states. In the presence of interactions, these states were shown to delocalize the entire spectrum [1]. We consider the case of a disordered twodimensional electron system in a high magnetic field with a periodic deltafunction potential, which splits the lowest Landau level into Hofstadter subbands. Our particular choice of potential allows us to isolate a set of subbands with vanishing total Chern number and with tunable bandwidthtobandgap ratio. By projecting the system into one such set of bands, we are able to investigate the nature of localization in a topologically trivial fraction of the lowest Landau level. We study the projected problem by numerical exact diagonalization and compare the results to those obtained without the projection procedure, thus shedding light on the role of topological extended states in hindering localization. The stability of the localized phase to interactions and the possibility of a manybody localized regime is also studied. 
Tuesday, March 6, 2018 9:00AM  9:12AM 
E07.00004: Bimetric Theory of Fractional Quantum Hall States Andrey Gromov, Dam Son I will describe the recently developed bimetric theory of fractional quantum Hall states. This effective theory includes the ChernSimons theory that describes the topological properties of the fractional quantum Hall states and a la quantum bimetric gravity theory that describes the massive GirvinMacDonaldPlatzman mode at long wavelengths. The theory reproduces universal features of the chiral lowest Landau level (LLL) FQH states that lie beyond the reach of pure ChernSimons theory, such as the projected static structure factor and the GMP algebra. The LLL projection and particlehole ``symmetry'' of the theory are particularly transparent. Familiar quantum Hall observables acquire a curious geometric interpretation in the bimetric language. 
Tuesday, March 6, 2018 9:12AM  9:24AM 
E07.00005: The 16fold Way and the Quantum Hall Effect at ν=5/2 Ken K. W. Ma, Phillip Zucker, Dmitri Feldman Numerous topological orders were proposed in the QHE at the filling factor ν=5/2. We show that the popular Pfaffian, SU(2)_{2}, 113, K=8, 331, PHPfaffian orders, and their particlehole conjugates can be classified in terms of Kitaev's 16fold way. The experimental evidence for composite fermions at ν=5/2 suggests that only the topological orders of the 16fold way are viable 5/2 states. We use a coupled QHE strip construction to generate Hamiltonians for all 16 orders from the parent Hamiltonians for the Pfaffian and K=8 states. We address the signatures of the 16 orders in MachZehnder and FabryPérot interferometry, and electrical and thermal transport. Only the PHPfaffian order is compatible with the existing data in GaAs at charge densities n∼3×10^{11}cm^{−2}. 
Tuesday, March 6, 2018 9:24AM  9:36AM 
E07.00006: Imaging electron density variations in a high mobility GaAs modulationdoped quantum well Loren Pfeiffer, K Baldwin, Nicholas Haug, Dobromir Kamburov, Mansour Shayegan, Edwin Chung, K West We use microphotoluminescence (microPL) to measure the local electron density in a GaAs MBE quantum well under a 40 µm diameter laser excitation spot^{[1]}. When the laser excitation spot is rasterscanned across the sample, we observe in the PL signal, local variations in the Fermi filling that correspond to spatial variations in the electron density of the 2D system. 
Tuesday, March 6, 2018 9:36AM  9:48AM 
E07.00007: Effect of lowtemperature illumination on quantum lifetime in GaAs quantum wells Michael Zudov, X Fu, Mikhail Borisov, Geoffrey Gardner, John Watson, Michael Manfra, K Baldwin, Loren Pfeiffer, K West It is well known that low temperature illumination of a highmobility twodimensional electron gas hosted in GaAs quantum wells can greatly improve the quality of magnetotransport data even when the carrier density and mobility remain essentially unchanged. In high magnetic fields, this improvement is evident from the appearance or better development of fractional quantum Hall states as well as stripe and bubble phases. However, what exactly drives this improvement remain unclear. Here, we investigate the effect of illumination on microwave photoresistance in low magnetic fields. We find that the amplitude of microwaveinduced resistance oscillations increases dramatically after lowtemperature illumination. Dingle analysis reveals that illumination leads to a substantial increase in the single particle lifetime. 
Tuesday, March 6, 2018 9:48AM  10:00AM 
E07.00008: The Fractional Quantum Hall to Nematic Phase transition at ν = 7/2 Katherine Schreiber, Nodar Samkharadze, Geoffrey Gardner, Michael Manfra, Gabor Csathy Recently, we observed the hydrostatic pressuredriven transition from the fractional quantum Hall state to the quantum Hall nematic phase at ν = 5/2 in the GaAs two dimensional electron system. This discovery breaks expectations about the half filled Landau level, despite thirty years of research on these filling factors. The data we obtain is consistent with a quantum phase transition from the topologically ordered fractional quantum Hall state to the broken rotational symmetry quantum Hall nematic phase. Many aspects of this transition are still unknown, however. 
Tuesday, March 6, 2018 10:00AM  10:12AM 
E07.00009: Phase transitions at filling ν = 5/2 in ZnO heterostructures Joseph Falson, Daniela Tabrea, ding zhang, Inti Sodemann, Yusuke Kozuka, Atsushi Tsukazaki, Masashi Kawasaki, Jurgen Smet Halffilled Landau levels (LL) elicit competing phases which intimately depend on the nature of interparticle interaction effects. The competition between emergent Fermisurfaces, the fractional quantum Hall (FQH) effect and broken symmetry nematic ground states is now well documented. Here we report a complex cascade of phases which exist at filling ν = 5/2 in high mobility ZnO heterostructures and the ability to tune between them by selectively enhancing the Zeeman energy through sample rotation. We are able to induce a series of phase transitions between an incompressible FQH state, a compressible ground state, an anisotropic nematic state and an isotropic insulating state. These occur in the vicinity of the coincidence of the N = 1 and 0 LL as electrons are transferred between opposing spin branches. The even denominator FQH incompressibility only occurs when significant population of N = 1 exists, reinforcing the role of the orbital character of carriers for the development of this ground state. The anisotropic transport shows Bfield sweep direction dependent hysteresis, suggesting the underlying nematic texture may be from magnetic domains of electrons of differing spin and orbital character close to the level crossing. 
Tuesday, March 6, 2018 10:12AM  10:24AM 
E07.00010: Tunability of Landau Level Crossings and Fractional Quantum Hall Phases in Few Layer Ballistic Graphene Biswajit Datta, Hitesh Agarwal, Abhisek Samanta, Amulya Ratnakar, Kenji Watanabe, Takashi Taniguchi, Rajdeep Sensarma, Mandar Deshmukh Bernal stacked trilayer graphene (TLG) has four low energy mirror symmetric bands. These bands are very electric field sensitive because electric field breaks the original mirror symmetry with respect to the middle layer of TLG. Electric field hybridizes the bands and consequently the Landau level (LL) spectrum in presence of magnetic field gets modified. We study the dependence of the LLs in TLG on electric field. TLG has many naturally occurring LL crossings due to its differently dispersing bands. This provides a great platform for studying electric field effect in terms of its LL crossing locations in phase space. Electric field couples only a specific set of LLs which led to the observation of mostly crossings rather than avoided crossing at the degeneracy points. However, interestingly, we see signatures of valley coupling due to short range electronic interaction at the crossing point of two opposite valleys of zeroth LL (N_{M}=0). These opposite valleys are brought into degeneracy by an electric field. We also observe some signatures of fractional quantum Hall effect in TLG. 
Tuesday, March 6, 2018 10:24AM  10:36AM 
E07.00011: Observation of new collective mode in the partially populated second Landau level Ursula Wurstbauer, Lingjie Du, Aron Pinczuk, Michael Manfra, Loren Pfeiffer, K West We present the observation of a new collective mode in the partially populated second Landau level. The mode is measured in experiments of resonant inelastic light scattering (RILS) at temperature of 40mK. Its energy is proportional to the square root of the filling factor of quasiholes for electron filling factors v equal or greater than v= 5/2 or quasiparticles for v equal or less than v= 5/2. This collective mode exists in the range 2.1 < v < 2.8. While the mode coexists with the fractional quantum Hall state at v= 7/3, it is absent at v= 5/2. Possible interpretations of this intriguing observation will be considered. 
Tuesday, March 6, 2018 10:36AM  10:48AM 
E07.00012: Berry Phase and Anomalous Transport of the Composite Fermions at the HalfFilled Landau Level Wei Pan, Woowon Kang, K Baldwin, K West, Loren Pfeiffer, Daniel Tsui Recent developments in the theory of composite fermions (CFs) have led to a prediction of a π Berry phase for the CFs circling around the Fermi surface at halffilling ν=1/2 (where ν is the Landau level filling factor). In this talk, we provide the first experimental evidence for the detection of the Berry phase of CFs in the fractional quantum Hall effect by studying their densitydependent magnetotransport in heterojunction insulatedgate fieldeffect transistors (HIGFETs), in which the electron density can be tuned over a large range. Our measurements of the Shubnikovde Haas oscillations of CFs as a function carrier density at a fixed magnetic field provide a strong support for an existence of a π Berry phase at ν = 1/2. We also discover that the conductivity of composite fermions at ν = 1/2 displays an anomalous linear density dependence, whose origin remains mysterious yet tantalizing. 
Tuesday, March 6, 2018 10:48AM  11:00AM 
E07.00013: 3/2 fractional quantum Hall plateau in a single layer twodimensional electron gas Xi Lin, Hailong Fu, Yijia Wu, Pujia Shan, Pengjie Wang, Zheyi Zhu, Loren Pfeiffer, K West, Haiwen Liu, Xincheng Xie In a single layer twodimensional electron gas, we observed a new evendenominator fractional quantum Hall plateau quantized at (h/e^2 )/(3/2) under confinement, at a bulk filling factor of 5/3. This unexpected plateau develops below 300 mK with a quantization of 0.02%. The conductance transmitting through the confined region is also quantized at 3/2 e^2/h, and the conductance of 1/6 e^2/h is backscattered. A new elemental excitation with e/6 effective charge, the further fractionalization of the e/3 quasiparticles, through topological soliton and topological phase transition is proposed as a tentative explanation. 
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