Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B54: Fractional Excitations in the Quantum Hall Effect 
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Sponsoring Units: DCMP Room: Mile High Ballroom 2A 
Monday, March 2, 2020 11:15AM  11:27AM 
B54.00001: Fermionic parity stability and interference measurements of nonAbelian e/4 and Abelian e/2 quasiparticle braiding at 7/2 and 5/2 filling factors Robert Willett, Kirill Shtengel, Chetan Nayak, Loren Pfeiffer, Edwin Chung, K. W. Baldwin, Kenneth West The 5/2 state is expected to have Abelian charge e/2 quasiparticles and nonAbelian charge e/4 quasiparticles; past interference measurements are consistent with this [1]. Recent [2] interferometer experiments present 3 new findings: 1) at 5/2 four dominant resistance oscillation periods are observed at the expected values for the full complement of braids of nonAbelian e/4 and Abelian e/2: e/2 braiding e/2, e/4 braiding e/2, and modulated oscillations specifically attributable to nonAbelian e/4 braiding e/4, the evenodd effect. Parameters controlling expression of these oscillations are delineated. 2) at 7/2 this full complement of e/4 and e/2 braiding oscillations is also observed, but at different periods as expected for that filling factor. 3) most importantly, the oscillations attributable to nonAbelian e/4 evenodd effect are stable against fermionic parity fluctuations over long times (hours) near 5/2 and 7/2; this observed stability strengthens the case for using nonAbelian e/4 quasiparticles for topological quantum computation. 
Monday, March 2, 2020 11:27AM  11:39AM 
B54.00002: NonAbelian braiding statistics via Aharonov–Bohm interferometry Kirill Shtengel, Robert Willett, Chetan Nayak, Loren Pfeiffer, Edwin Chung, Milton Peabody, K. W. Baldwin, Kenneth West One of the most striking consequences of the nonAbelian braiding statistics in the ν=5/2 quantum Hall state has been the socalled even–odd effect theoretically predicted over a decade ago. While signatures consistent with the theoretical prediction have been seen in quantum Hall Fabry–Pérot interferometers, the key ingredient – controlling the number of quaiparticles inside the interferometer – remains a challenging experimental problem. Fortunately, signatures of the nonAbelian statistics can emerge in a simpler setting, namely in Aharonov–Bohmtype experiments where interference patterns are produced solely by changing the magnetic field. This nucleates new quasiparticles inside the interferometer, and if those include nonAbelian particles, the Aharonov–Bohm oscillations are expected to have distinct spectral features that would be absent otherwise. This talk will focus on the theoretical predictions and their comparison with the recent observations [1], arguing that the preponderance of experimental evidence unmistakably points towards the nonAbelian nature of ν=5/2 and 7/2 quantum Hall states and provides strong evidence of nonAbleian braiding. 
Monday, March 2, 2020 11:39AM  11:51AM 
B54.00003: Contacts and Equilibration in the ν=5/2 Quantum Hall Effect Hamed Asasi, Michael C Mulligan The thermal Hall conductance K_{T} of the fractional quantum Hall state at ν=5/2 has recently been measured to be K_{T}≈2.5(π^{2}k_{B}^{2}T/3h)[1]. The halfinteger value of this result provides strong evidence for the presence of a Majorana edge mode and a corresponding quantum Hall state hosting quasiparticles with nonAbelian statistics. Whether this measurement points to the realization of the PHPfaffian state or the antiPfaffian state has been the subject of debate [2][3]. Here we consider various edgestate scenarios which may explain the measured thermal conductance, paying close attention to the role of contacts and edgestate equilibration. Through a study of the kinetic equations describing the lowtemperature transport in the antiPfaffian and PH Pfaffian edge states, we determine regimes of parameter space, controlling the interactions between the different edge modes, that agree with experiment. We also discuss how pointcontact tunneling can distinguish various edgestate scenarios. 
Monday, March 2, 2020 11:51AM  12:03PM 
B54.00004: Patterns in paired electron additions to fractional quantum Hall edge states in large GaAs quantum dots Raymond Ashoori, Ahmet Demir, Neal Edward Staley, Samuel Aronson, Spencer Tomarken, K. W. Baldwin, Kenneth West, Loren Pfeiffer

Monday, March 2, 2020 12:03PM  12:15PM 
B54.00005: Flux superperiods and periodicity transitions in quantum Hall interferometers Bernd Rosenow, Ady Stern For strongly screened Coulomb interactions, quantum Hall interferometers can operate in a novel regime: the intrinsic energy gap can be larger than the charging energy, and addition of flux quanta can occur without adding quasiparticles. We show that flux superperiods are possible, and reconcile their appearance with the ByersYang theorem. We explain that the observation of anyonic statistical phases is possible by tuning to the transition from a regime with constant chemical potential to a regime with constant particle density, where a flux superperiod changes to a periodicity with one flux quantum at a critical magnetic field strength. 
Monday, March 2, 2020 12:15PM  12:27PM 
B54.00006: Probing the photonassisted processes of anyons of charge e/3 and e/5 in the FQHE regime Christian Glattli, Imen Taktak, Preden Roulleau Recently, the microwave excitation of fractional edge channels at GHz frequency f have demonstrated time domain manipulation of e*=e/3 and e*=e/5 charged anyons in the FQHE regime [1]. The signature of anyons absorbing a single photon was observed a shot noise ingularity when the applied voltage obeying the fractional Josephson relation e*V=hf. Going beyond these observations we analyze the amplitude of the microwave field propagating from the excited contact to a Quantum Point Contact. Using photonassisted current, the microwave amplitude is shown to display interference when sweeping the frequency from 2 to 18GHz. We attribute these interference features to different propagation velocities of neutral and charged electron (or anyon) modes when several integer or fractional edge propagates in parallel. This study provide the necessary information to realize single anyon sources similar to Leviton [2] sources. 
Monday, March 2, 2020 12:27PM  12:39PM 
B54.00007: Sublattice resolved spin wave transport through graphene fractional quantum Hall states as a probe of isospin order Haoxin Zhou, Hryhoriy Polshyn, Takashi Taniguchi, Kenji Watanabe, Andrea Young High quality graphene heterostructures host an array of fractional quantum Hall isospin ferromagnets with diverse spin and valley orders. While a variety of phase transitions have been observed, disentangling the isospin phase diagram of these states is hampered by the absence of direct probes of spin and valley order. I will describe nonlocal transport measurements based on launching spin waves from a gate defined lateral heterojunction, performed in ultraclean Corbino geometry graphene devices. At high magnetic fields, we find that the spinwave transport signal is detected in all FQH states between ν = 0 and 1; however, between ν = 1 and 2 only odd numerator FQH states show finite nonlocal transport, despite the identical ground state spin polarizations in odd and even numerator states. The results reveal that the neutral spinwaves are both spin and sublattice polarized making them a sensitive probe of ground state sublattice structure. Armed with this understanding, we use nonlocal transport signal to a magnetic field tuned isospin phase transition, showing that the emergent even denominator state at ν = 1/2 in monolayer graphene is indeed a multicomponent state featuring equal populations on each sublattice. 
Monday, March 2, 2020 12:39PM  12:51PM 
B54.00008: Microscopic theory of fractional excitations in gapless bilayer quantum Hall states: semiquantized quantum Hall states Oguz Turker, Tobias Meng Recent experiments in quantum Hall bilayer systems have revealed a new strongly correlated state: the semiquantized quantum Hall state. This state arises in a bilayer quantum Hall system with strong interlayerinteractions, has a quantized Hall resistance and vanishing longitudinal resistance, while at the same time featuring a gapless sector that allows this state to exist for a continuum of filling factors. In this talk, I will explain what a semiquantized quantum Hall state is, and use a coupledwire construction to predict possible future experiments in the already existing experimental platforms. 
Monday, March 2, 2020 12:51PM  1:03PM 
B54.00009: Nonlinear transport and noise measurements in reentrant integer quantum Hall states Jian Sun, Jiasen Niu, Pengjie Wang, Yang Liu, Loren Pfeiffer, Kenneth West, Xi Lin Twodimensional electron gas (2DEG) system in strong magnetic field is an ideal platform to explore interesting physics such as reentrant integer quantum Hall (RIQH) effect in second and higher Landau levels. We have carried out nonlinear transport and noise measurements in ultrahigh mobility GaAs/AlGaAs 2DEG to study RIQH states in Corbinogeometry samples. By increasing the DC bias gradually, we found the insulating phase of RIQH states disappeared, and the depinning trace can be divided into three regions according to different DC bias values. The narrowband noise only appears in the middle region. 
Monday, March 2, 2020 1:03PM  1:15PM 
B54.00010: Edge Mode Engineering and Interferometry in the Quantum Hall Regime Rajarshi Bhattacharyya, Mordehai Heiblum, Diana Mahalu, Vladimir Umansky The interference of fractional charges is a much sought after goal in a variety of electronic interferometers. It has been shown before in an electronic MachZehnder interferometer that neutral modes, topological or nontopological (via edgereconstruction), cause dephasing in the fractional quantum Hall effect regime [1]. Recently interference of fractional charges has been observed in an electronic FabryPerot interferometer [2], though anionic statistics was not revealed. Here, we have adapted a novel route of engineering edge channels away from the physical boundary in order to minimize edge reconstruction. First, we show that these engineered edge channels, especially fractional ones, can have different edge structures (with a different thermal conductance) compared to ubiquitous edge channels that have the same electrical conductance. We then used a modified MachZehnder interferometer to interfere such synthetic edge modes, with initial promising results. 
Monday, March 2, 2020 1:15PM  1:27PM 
B54.00011: Paired Electron Additions to Fractional Quantum Hall Edge States in Large GaAs Quantum Dots Samuel Aronson, Ahmet Demir, Neal Edward Staley, Spencer Tomarken, Kenneth West, K. W. Baldwin, Loren Pfeiffer, Raymond Ashoori We measure capacitance signals from additions of single electrons to a large (0.8 μm) 2D GaAs quantum dot and thereby determine the energies required to add electrons to the dot. The dot is sandwiched inside of a “tunnel capacitor” in which electrons can tunnel from the dot to a nearby capacitor electrode. We observe single electron capacitance peaks to edge states over a wide range of filling factors. As a function of magnetic flux through the dot, between filling factors v = 1 and v = 2, these edge state peaks are regularly spaced, with periodicity h/e. Surprisingly, over the range v = 2 to v = 5, the peaks have doubleheight, and the periodicity is halved to h/2e. The pairing cannot be explained in the Coulomb blockade picture, in which the two electrons in a pair would instead be separated by a charging energy, and models involving electron rearrangements fail because they predict a suppression of tunneling rates that we do not observe. Instead the sequence of successive paired tunneling events behaves in the same way as tunneling of electrons into superconducting quantum dots. 
Monday, March 2, 2020 1:27PM  1:39PM 
B54.00012: FabryPerot interferometry of fractional quantum Hall edge states James Nakamura, Saeed Fallahi, Harshad Sahasrabudhe, Shuang Liang, Geoff C Gardner, Michael Manfra Electronic interferometry has been proposed as an experimental probe of the braiding statistics and quasiparticle charge in quantum Hall states. Two significant challenges in FabryPerot interferometers are Coulomb charging effects and poor phase coherence. We have overcome these challenges using a novel GaAs/AlGaAs heterostructure which utilizes auxiliary GaAs screening wells in addition to the primary quantum well in order to screen and suppress Coulomb charging effects. This heterostructure design has enabled measurements of robust AharonovBohm interfere at the ν = 1/3 fractional quantum Hall state. A recent theoretical work has predicted a shift in the interference pattern at ν = 1/3 when the magnetic field is varied from the center of the plateau. We present experimental measurements of AharonovBohm interference across the 1/3 plateau. These results represent progress towards direct observation of anyonic braiding statistics. 
Monday, March 2, 2020 1:39PM  1:51PM 
B54.00013: Phase Diagram of Majorana Island Jie Shen, Georg Wolfgang Winkler, Francesco Borsoi, Sebastian Heedt, Vukan Levajac, Sasa Gazibegovic, Roy Op het Veld, Joon Sue Lee, Mihir Pendharkar, connor dempsey, Chris Palmstrom, Erik P.A.M. Bakkers, Bernard Van Heck, Leo P. Kouwenhoven Scalable topological qubit proposals based on semiconductorsuperconductor systems are built on Majorana islands hosting pairs of Majorana zero modes. Here, by systematically measuring the periodicity of Coulomb blockade oscillations of InSb/Al island, we reconstruct the ground state parity of the island over large ranges of magnetic field and plunger gate voltage (Vpg). The resulting phase diagram can be divided into three regimes compared with numerical simulations. For negative Vpg, subgap states are absent due to strong proximity effect, so the 2e to 1eperiodic transition happens at high Bfields, indicating the poisoning of the superconducting state. For positive Vpg, the 2e1e transition happens instead at a constant but small Bfield. The reason is unproximitized states quickly disperse below the charging energy due to the orbital effect of the magnetic field. The two regimes are separated by an intermediate regime where the 2e1e transition field varies smoothly with Vpg, which is the most promising for locating a robust topological phase according to simulations. In this regime, we observe correlated oscillating peak spacing and heights. This complete phase diagram of Majorana island can lead to a guideline to set up a topological qubit in more complicated devices. 
Monday, March 2, 2020 1:51PM  2:03PM 
B54.00014: Wigner Crystal Melting Phase Diagram of GaAs Twodimensional Holes Meng Ma, Kevin Villegas Rosales, Hao Deng, Loren Pfeiffer, Kenneth West, K. W. Baldwin, Mansour Shayegan In a strongly interacting twodimensional (2D) electron system, when the Coulomb energy dominates over the kinetic energy, the electrons tend to arrange periodically and form a socalled Wigner crystal (WC) ground state. In a GaAs 2D electron system, a magneticfieldinduced quantum WC forms at very low temperature and high magnetic field near filling factor v = 1/5 when the kinetic (Fermi) energy is quenched and the Coulomb energy dominates. In an GaAs 2D hole system, on the other hand, the WC phase forms near v = 1/3 because of the significant Landau level mixing caused by the large hole effective mass. Despite the fact that the 2D hole system has been a subject of intense interest for many years, a WC melting temperature vs filling factor phase diagram has been missing. In this work, we map out such phase diagram using a newly developed technique which probes the melting of the WC via its screening efficiency. The phase diagram shows rich features of the WC phases at low fillings and a clear reentrant behavior around v = 1/3. 
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