Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session X51: Fractional QHE: Measurement Methodologies |
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Sponsoring Units: FIAP Chair: John Cumings, University of Maryland Room: Hilton Baltimore Holiday Ballroom 2 |
Friday, March 18, 2016 8:00AM - 8:12AM |
X51.00001: Surface Acoustic Wave Study of Exciton Condensation in Bilayer Quantum Hall Systems J. Pollanen, J.P. Eisenstein, L.N. Pfeiffer, K.W. West In bilayer two-dimensional electron systems (2DES) in GaAs a strongly correlated many-electron state forms at low temperature and high magnetic field when the total electron density $n_{T}$ becomes equal to the degeneracy of a single spin split Landau level. This state corresponds to a total filling factor $\nu_{T}=1$ and can be described in terms of pseudospin ferromagnetism, or equivalently, Bose condensation of bilayer excitons. We have simultaneously measured magneto-transport and the propagation of pulsed surface acoustic waves (SAWs) at a frequency of 747 MHz to explore the phase transition between two independent layers at $\nu_{T}=1/2+1/2$ and the correlated state at $\nu_{T}=1$ in a high quality double quantum well device. We tune through this transition by varying the total electron density in our device with front and backside electrostatic gates. [Preview Abstract] |
Friday, March 18, 2016 8:12AM - 8:24AM |
X51.00002: Vibrational modes in the quantum Hall system Rachel Wooten, Bin Yan, Kevin Daily, Chris H. Greene The hyperspherical adiabatic technique is more familiar to atomic and nuclear few-body systems, but can also be applied with high accuracy to the many-body quantum Hall problem\footnote{K. M. Daily, R. E. Wooten, and C. H. Greene, Phys. Rev. B, \textbf{92} 125427 (2015).}. This technique reformulates the Schr\"odinger equation for $N$ electrons into hyperspherical coordinates, which, after extracting the trivial center of mass, describes the system in terms of a single global size coordinate known as the hyperradius $R$, and $2N-3$ remaining internal angular coordinates. The solutions are approximately separable in the hyperradial coordinate, and solutions in the system are found by treating the hyperradius as an adiabatic coordinate. The approximate separability of the wave functions in this coordinate suggests the presence of hyperradial vibrational modes which are not described in conventional theories. The vibrationally excited states share the internal geometry of their quantum Hall ground states, and their excitation frequencies may vary with the number of participating particles or the strength of the confinement. We plan to discuss the features of these vibrational modes and their possible detection in quantum Hall systems. [Preview Abstract] |
Friday, March 18, 2016 8:24AM - 8:36AM |
X51.00003: Surface acoustic waves as a probe of the Wigner crystal in n-GaAs/AlGaAs in vicinity of $\bf{^{\circ}\nu=1/5}$, 1, and 2 A.V.~ Suslov, I.L. Drichko, I.Yu. Smirnov, L.N. Pfeiffer, K.W. West, Y.M. Galperin Both attenuation of a surface acoustic wave (SAW) and variation of its speed due to interaction with 2D electrons in n-GaAlAs/GaAs/GaAlAs structures are measured versus perpendicular magnetic field of up to 18 T in the frequency range of (28.5 -- 306) MHz and at temperatures (40 -- 380) mK. The study is performed on $\delta$-doped from both sides 65~nm wide GaAs quantum well with the carrier density of n = $5\cdot10^{10}$~cm$^{-2}$ and their mobility of $\mu$ = $8\cdot10^6$~cm$^2$/V·s. The complex AC conductance, $\sigma$ is calculated. Analysis of $\sigma$ shows that at low temperatures and at the filling factor of 2, 1, and 1/5 the electron system resides in the integer and fractional quantum Hall states, respectively. However, in vicinities to these values, namely at $\nu$ = 1.9, (1.1 and 0.9), (0.21 and 0.19), the electron states can be interpreted as so-called pinning modes of Wigner crystal (WC). Temperature dependences of $\sigma$ indicates a crossover between the localized modes (at $\nu$ = 1 and 2) and a pinned WC. When the temperature (or the SAW intensity) increases the behavior of the complex conductance can be understood as manifestation of WC melting. [Preview Abstract] |
Friday, March 18, 2016 8:36AM - 8:48AM |
X51.00004: Examining the Influence of Alloy Disorder on the $\nu \quad =$ 7/3 Fractional Quantum Hall State Ethan Kleinbaum, Nianpei Deng, Geoffrey Gardner, Michael Manfra, Gabor Csathy The fractional quantum Hall states of the second Landau level elicit interest from their potential to realize novel many-body ground states. In addition to the notable even denominator FQHSs, the odd denominator states in this region are worthy of considerable attention. Specifically, the nature of the most prominent odd denominator state, $\nu =$7/3, remains unknown -- admitting both the conventional Laughlin-Jain state and more exotic candidate states. We examine the $\nu =$7/3 state in a series of samples with alloy disorder intentionally added during MBE growth. In these samples, we measure the energy gap at $\nu =$7/3 to explore the influence of disorder on the $\nu =$7/3 FQHS. A comparison of these data to the energy gap measurements of the even denominator $\nu =$5/2. This work was supported by DOE DE-SC000671. [Preview Abstract] |
Friday, March 18, 2016 8:48AM - 9:00AM |
X51.00005: Diagnosis of phase transitions in disordered fractional quantum Hall liquids using quantum entanglement Zhao Liu, R. N. Bhatt The conventional method to study phase transitions from fractional quantum Hall (FQH) liquids to a localized phase induced by disorder has relied on the collapse of the mobility gap and Hall conductance [1,2]. Here, we scrutinize this issue from the perspective of quantum entanglement. We consider electrons in the disordered lowest Landau level at Laughlin filling fractions $\nu=1/m$ with either Haldane's pseudopotentials or Coulomb interaction. We find that the derivative of the orbital-cut von-Neumann entropy with respect to the disorder strength has a sharp peak, which diverges with system size, providing a clear fingerprint of the transition from FQH liquids to a localized phase. Further, the fluctuation of the entropy with different cut boundaries is utilized to examine whether the ground states are localized in some region. We also investigate the level statistics of the entanglement spectrum, as well as the low-lying spectrum of the Hamiltonian to extract more information about the phase transition. Our method can be applied to study many-body localization in other topological systems. [1] D. N. Sheng \emph{et al.}, Physical Review Letters {\bf 90}, 256802 (2003). [2] Xin Wan \emph{et al.}, Physical Review B {\bf 72}, 075325 (2005). [Preview Abstract] |
Friday, March 18, 2016 9:00AM - 9:12AM |
X51.00006: Excitation spectra of unconventional FQHE states in the SLL from Light Scattering Experiments Ursula Wurstbauer, Antonio Levy, Aron Pinczuk, John Watson, Geoff Gardner, Michael Manfra, Ken West, Loren Pfeiffer The fascinating interaction physics in the second Landau level (SLL) supports the emergence of exotic quantum phases and unconventional possibly FQHE states such as e.g. at $\nu =$ 5/2 and 2$+$1/3 and the weaker state at $\nu =$ 2$+$3/8 and 2$+$2/5. We observe clear signatures for gapped collective excitations in inelastic light scattering experiments just for these `magic' filling factors and only for low temperatures substantiating access to the physics of the incompressible quantum fluids [1]. The lowest excitation feature in the spectrum at 2$+$1/3 occurs at around 70 $\mu $eV. The analysis of spectral lineshapes suggests magnetoroton features that are characteristic of 2D neutral excitations in a perpendicular magnetic field. The striking polarization dependence observable in light scattering experiments in the SLL are consistent with nematic FQHE states. [1] U. Wurstbauer \textit{et al.}, arXiv:1507.04939v2 (2015). [Preview Abstract] |
Friday, March 18, 2016 9:12AM - 9:24AM |
X51.00007: High Pressure Studies of the Second Landau Level Region of a Two-Dimensional Electron System Katherine Schreiber, Nodar Samkharadze, Geoffrey Gardner, Eduardo Fradkin, Michael Manfra, Gabor Csathy Hydrostatic pressure has become a prevalent tool in condensed matter systems because the application of pressure to crystalline structures results in the shrinking of the lattice constant. This allows one to tune the Bloch wavefunction of the electrons and therefore all band parameters such as effective carrier mass, carrier density, and effective g-factor. In this manner, pressure acts as a probe into various strongly interacting electronic states. Motivated in particular by the capability to discern the spin polarization of quantum Hall states, we apply hydrostatic pressure up to 10 kbar to a two dimensional electron system (2DES) in a high-mobility GaAs/AlGaAs quantum well. This 2DES is subjected to milliKelvin temperatures and strong magnetic fields to observe the effect of pressure on fractional quantum Hall states, especially those in higher Landau levels, a regime not previously studied under pressure. We report our findings, focusing on the observation of a pressure-driven transition from a fractional quantum Hall state to the quantum Hall nematic phase in the second Landau level. [Preview Abstract] |
Friday, March 18, 2016 9:24AM - 9:36AM |
X51.00008: Spatially resolved breakdown in reentrant quantum Hall states Oleksandr Rossokhaty, Joshua Folk, Yuval Baum, Ady Stern, John Watson, Geoffrey Gardner, Michael Manfra Electrons in a two dimensional electron gas in the fractional quantum Hall regime may rearrange into a quasi-crystalline structure that gives rise to a reentrant Integer Quantum Hall (RIQH) effect in transport. As bias current increases, longitudinal and Hall resistivities measured for these states show multiple sharp breakdown transitions, a signature that is unique to RIQH states and has previously been ascribed to pinning-depinning transitions or to the development of bias-induced anisotropy. We present an alternate interpretation of the characteristic features of RIQH breakdown at high bias, based on spatially-resolved measurements that indicate a phase boundary between broken-down and unbroken regions propagating chirally from source and drain contacts as a function of bias current. As the phase boundary passes various contacts, its spreading generates multi-stage breakdown signatures like those reported elsewhere. Confirming numerical simulations, the chiral sense of the spreading is set not by the chirality of the edge state itself, but instead depends on electron- or hole-like character of the RIQH state. [Preview Abstract] |
Friday, March 18, 2016 9:36AM - 9:48AM |
X51.00009: Observation of an Even-odd Anisotropic Transport in High Landau Levels Guangtong Liu, Changli Yang, Qin Wang, Yuying Zhu, Yuan Pang, Jie Fan, Xiunian Jing, Zhongqing Ji, Li Lu, Rui-Rui Du, Loren Pfeiffer, Ken West Magnetotransport experiments (including tilt fields) were performed on ultrahigh mobility L-shaped Hall-bar samples of GaAs/AlGaAs quantum wells. The low-temperature longitudinal resistance Rxx data demonstrate that a striking even-odd anisotropic transport exists only along the [110] direction at half filling in $N\ge $2 high Landau levels. Although the origin for the peculiar even-odd anisotropy remains unclear, we propose that the coupling strength between electrons within the same Landau level and between the neighboring two Landau levels should be considered in future studies. The tilt field data show that the in-plane field can suppress the formation of both bubble and stripe phases. [Preview Abstract] |
Friday, March 18, 2016 9:48AM - 10:00AM |
X51.00010: ABSTRACT MOVED TO L51.012 |
Friday, March 18, 2016 10:00AM - 10:12AM |
X51.00011: New Method for Studying Localization effects in Quantum Hall Systems R. N. Bhatt, Scott Geraedts Disorder is central to the study of the fractional quantum Hall effect. It is responsible for the finite width of the quantum Hall plateaus, and it is of course present in experiment. Numerical studies of the disordered fractional quantum Hall effect are nonetheless very difficult, because the lack of symmetry present in clean systems limits the size of systems that can be studied [1,2]. We introduce a new method for studying the integer and fractional quantum Hall effect in the presence of disorder that allows larger system sizes to be studied. The method relies on truncating the single particle Hilbert space, which leads to an exponential reduction in the Hilbert space of the many-particle system while preserving the essential topological nature of the state. We apply the model to the study of disorder transitions in the quantum Hall effect, both for the ground state and excited states. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, through Grant DE-SC0002140. [1] D. N. Sheng, Xin Wan, E. H. Rezayi, Kun Yang, R. N. Bhatt and F. D. M. Haldane, Physical Review Letters 90, 256802 (2003) [2] Xin Wan, D. N. Sheng, E. H. Rezayi, Kun Yang, R. N. Bhatt and F. D. M. Haldane, Physical Review B 72, 075325 (2005). [Preview Abstract] |
Friday, March 18, 2016 10:12AM - 10:24AM |
X51.00012: Reorientation of the anisotropic phase of a 2D electron system using a very small density modulation Md Shafayat Hossain, M A MUEED, Hao Deng, Mansour Shayegan, Loren Pfeiffer, K.W. West, Kirk Baldwin A high-quality two-dimensional electron system (2DES) confined to a GaAs quantum well typically exhibits isotropic transport coefficients when the Fermi level resides in the first excited ($N=1$) Landau level. Adding an in-plane magnetic field ($B_{||}$) leads to an anisotropic (stripe) phase with the stripes oriented perpendicular to the $B_{||}$ direction. We study how a periodic density modulation of the 2DES, induced by a surface strain grating from lines of negative electron-beam resist, affects the orientation of the $\nu=7/2$ stripe phase. Our results reveal that the external potential modulation competes against the $B_{||}$-induced orientational order of the stripe phase. Even a minute ($\sim0.5\%$) density modulation is sufficient to reorient the stripes at $\nu=7/2$ along the direction of the surface grating. [Preview Abstract] |
Friday, March 18, 2016 10:24AM - 10:36AM |
X51.00013: Edge mode velocities in the quantum Hall effect from a dc measurement Philip Zucker, D. E. Feldman Because of the bulk gap, low energy physics in the quantum Hall effect is confined to the edges of the 2D electron liquid. The velocities of edge modes are key parameters of edge physics. They were determined in several quantum Hall systems from time-resolved measurements and high-frequency ac transport. We propose a way to extract edge velocities from dc transport in a point contact geometry defined by narrow gates. The width of the gates assumes two different sizes at small and large distances from the point contact. The Coulomb interaction across the gates depends on the gate width and affects the conductance of the contact. The conductance exhibits two different temperature dependencies at high and low temperatures. The transition between the two regimes is determined by the edge velocity. An interesting feature of the low-temperature $I-V$ curve is current oscillations as a function of the voltage. The oscillations emerge due to charge reflection from the interface of the regions defined by the narrow and wide sections of the gates. This work is available at arXiv:1510.01725 [Preview Abstract] |
Friday, March 18, 2016 10:36AM - 10:48AM |
X51.00014: Composite Fermion States near 3/2 Hosted by a High-Mobility 2D Hole System Po Zhang, Ruiyuan Liu, Jianli Wang, Chi Zhang, Changli Yang, Li Lu, Loren Pfeiffer, Ken West, Rui-Rui Du Magnetotransport experiments of Carbon-doped GaAs/AlGaAs 2D hole gas (2DHG) have revealed a variety of interesting phenomena previous not seen in the 2DEG counterpart. For example, it was found that the effective g -factor of 2DHG is large enough to cause Landau level crossing even at $\sim$1 T, and the product of $gm^*$ (where $m^*$ is the hole effective mass) increases with total magnetic field (Yuan et al, Appl. Phys. Lett. 94, 052103 (2009)). Such level crossings could have profound influences on the fractional quantum Hall states in the relevant magnetic fields. We systematically investigate the composite fermion states near 3/2 in C-doped high-mobility 2DHG by tilted-magnetic field experiments, and map out the Landau levels and composite fermion spectra as a function of hole density and tilt angles. Preliminary results and brief discussions will be presented. [Preview Abstract] |
Friday, March 18, 2016 10:48AM - 11:00AM |
X51.00015: Quantum Hall plateau-plateau transition probed by magnon quantum Hall insulator Baolong Xu, Tomi Ohtsuki, Ruiychi Shindou Based on a generalization of quantum Hall physics to quasi-particle boson system, we introduce a magnetic superlattice structure in the dipolar regime whose lowest gapped magnon bands mimic magnon quantum Hall insulator in strong out-of-plane magnetic fields. By calculating two-terminal conductance and localization length, we characterize the critical nature of the localization-delocalization transition in the magnon quantum Hall insulator. Especially, we show that the calculated conductance distribution at the `plateau-plateau' transition in our system exhibits essentially the same distribution as that in the critical point of the Chalker-Corrington network model, demonstrating the `universality' of the conductance distribution at the quantum Hall critical point beyond Fermion system. [Preview Abstract] |
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