Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H07: Interferometry, Tunneling, and Edge Physics 
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Sponsoring Units: DCMP Chair: Roy Ashuri, Massachusetts Institute of Technology Room: LACC 153B 
Tuesday, March 6, 2018 2:30PM  2:42PM 
H07.00001: Interference properties of charges at filling factor 5/2 Robert Willett, Michael Manfra, Loren Pfeiffer Excitations of charge e/4 at 5/2 filling factor are proposed to obey nonAbelian statistics, and we perform experiments with interferometers operated at fractional quantum Hall states to test this. The interferometers allow variation in the number of flux and quasiparticles encircled by one of the two edge paths that interfere, with those numbers dictating the interference properties. Our recent focus has been on expanding control of those enclosed flux and quasiparticle numbers, and examining the difference in interference presumably due to edge charge e/4 and edge charge e/2 encircling the enclosed area. We observe the expected interference periods corresponding to these quasiparticle charges, displayed in simple magnetic field sweep measurements, but also observe an important difference in the relative magnitudes of the e/4 versus e/2 edge generated interference. For interference to occur the encircling charge must backscatter at the narrowings that define the interference device. As the size of these narrowings is changed the magnitude of the e/2 interference is observed to be sensitive to this size, while the e/4 interference is relatively insensitive, as expected in theoretical models. We review this data taken in multiple heterostructures and device designs. 
Tuesday, March 6, 2018 2:42PM  2:54PM 
H07.00002: Robust Integer and Fractional Helical Modes in the Quantum Hall Effect Yonatan Cohen, Yuval Ronen, Daniel Banitt, Wenmin Yang, Mordehai Heiblum, Vladimir Umansky Electronic systems harboring onedimensional helical modes, where spin and momentum are locked, have lately become an important objective. When coupled to a conventional superconductor, such systems are expected to manifest topological superconductivity; a unique phase hosting Majorana zero modes. Even more interesting are fractional helical modes, yet to be observed, which open the route for realizing generalized parafermions. Possessing nonabelian exchange statistics, these quasiparticles may serve as building blocks in topological quantum computing. Here, we present a new approach to form protected helical and fractional helical modes in the quantum Hall regime. The novel platform is based on a carefully designed doublequantumwell structure in a GaAs based system hosting two electronic subbands; each tuned to the quantum Hall regime. By gating different areas of the system, counterpropagating integer as well as fractional edge modes with opposite spins are formed. We demonstrate that due to spin protection, these helical modes remain ballistic for large distances. In addition to formation of helical modes, this platform can serve as a rich playground for artificial induction of compounded fractional edge modes, and for construction of edge modes based interferometers. 
(Author Not Attending)

H07.00003: Measurement of electronic FabryPerot interferometers optimized for high edge state velocity James Nakamura, Qi Qian, Saeed Fallahi, Robert Willett, Geoffrey Gardner, Michael Manfra Electronic FabryPerot interferometers may be used to probe the properties of electrons and quasiparticles in the quantum Hall regime. The visibility of interference is limited by finite coherence time and edge state velocity. We present two methods for enhancing the edge state velocity in GaAs/AlGaAs heterostructures by increasing the sharpness of the confining potential at the edge. The first method involves a gating scheme utilizing a combination of negatively biased gates to define the interference path and positively biased helper gates; the abrupt interface between positive and negative gate bias yields a sharp edge potential in the 2DEG. The second method involves novel heterostructures with parallel conducting quantum wells positioned with a short setback from the primary quantum well; when negative bias is applied to surface gates, the proximity of the additional quantum wells results in sharp confining potential in the primary quantum well. The devices are measured in a dilution refrigerator at T~10mK in high magnetic field. Efforts are underway to utilize these interferometers in the fractional quantum Hall regime, where interference may be used to probe exotic quasiparticle statistics. 
Tuesday, March 6, 2018 3:06PM  3:18PM 
H07.00004: Full Momentum and Energy Resolved Spectral Function of a 2D Electronic System: Part I Raymond Ashoori, Joonho Jang, Heun Mo Yoo, Loren Pfeiffer, K West, K Baldwin The singleparticle spectral function measures the density of electronic states (DOS) in a material as a function of both momentum and energy, providing central insights into phenomena such as superconductivity and Mott insulators. While scanning tunneling microscopy (STM) and other tunneling methods have provided partial spectral information [1] , until now only angleresolved photoemission spectroscopy (ARPES) has permitted a comprehensive determination of the spectral function of materials in both momentum and energy. However, ARPES operates only on electronic systems at the material surface and cannot work in the presence of applied magnetic fields. Here, we demonstrate a new method (MERTS) for determining the full momentum and energy resolved electronic spectral function of a twodimensional (2D) electronic system embedded in a semiconductor [2]. The technique remains operational in the presence of large externally applied magnetic fields and functions even for electronic systems with zero electrical conductivity or with zero electron density. *[1] O. E. Dial et al. Nature 448, 176, (2007) [2] J. Jang, H. M. Yoo, L. N. Pfeiffer, K. West, K. W. Baldwin, and R. C. Ashoori, Science (Accepted, 2017) 
Tuesday, March 6, 2018 3:18PM  3:30PM 
H07.00005: Full Momentum and Energy Resolved Spectral Function of a 2D Electronic System: Part II Joonho Jang, Heun Mo Yoo, Loren Pfeiffer, K West, K Baldwin, Raymond Ashoori We use a new momentum and energy resolved tunneling spectroscopic method (MERTS) for studying a 2D electron system for highquality semiconducting structures [1]. It provides a direct highresolution and highfidelity probe of the dispersion and dynamics of the interacting 2D electron system. Using this technique, we uncover signatures of manybody effects involving electronphonon interactions, plasmons, polarons with unprecedented resolution. When a perpendicular magnetic field is applied, the spectra evolve into discrete Landau levels. The massively degenerate electronic states strongly interact with nearly dispersionless LOphonons and give rise to a novel phonon analog of the vacuum Rabi splitting in atomic systems. I will discuss how this technique will be instrumental to probe emergent quantum phases in the quantum Hall limit, such as stripe, bubble phases, and fractional quantum Hall states. *[1] J. Jang, H. M. Yoo, L. N. Pfeiffer, K. West, K. W. Baldwin, and R. C. Ashoori, Science (Accepted, 2017) 
Tuesday, March 6, 2018 3:30PM  3:42PM 
H07.00006: Constructing Composite Fermion Fermi Liquid States with "Squeezed" Jain States Anthony Cressman, Edward Rezayi We consider the composite fermion Fermi liquid (CFFL) state on the spherical geometry. We construct the CFFL wave functions from those of Jain states by requiring the flux in the two cases to be equal (aliasing). We use the squeezing rules of Regnault, Bernevig and Haldane (RBH) to obtain the appropriate truncated basis of squeezed states. We obtain the Jain states by diagonalizing the angular momentum operator in the truncated basis, as prescribed by RBH. We study the ReadRezayi (RR) CFFL state for N=9 in two ways: directly from the (N=9, ν=3/7) Jain state, and from particlehole (PH) conjugations of the (N=8, ν=2/5) Jain state. Similar considerations apply to the (N=15, ν=3/7) Jain state and its PH conjugate for the N=16 CFFL filled shell Fermi sea. We also consider N=12 as a case of a PH symmetric CFFL (which is aliased with the (N=12, ν=3/7) Jain state) and measure the degree of its PH symmetry. We note that none of the states past N=9 can feasibly be obtained from the method used by RR, which involves O(N!) complexity. Whenever appropriate we compare our construction to the KamillaJain determinant form of the states. 
Tuesday, March 6, 2018 3:42PM  3:54PM 
H07.00007: Dynamics, interferometry and fractional statistics of bulk Quantum Hall coherent states Varsha Subramanyan, Smitha Vishveshwara We present a description of lowest Landau level coherent states and their dynamics in the presence of various potential landscapes. In particular, we study the time evolution of such states in harmonic and saddle potentials, as building blocks for exploring tunneling, interferometry and anyonic exchange statistics. Using these components, we model features of the MachZehnder interferometer for both single and multiple Quantum Hall excitations. We identify possible settings for tunneling processes that are sensitive to fractional statistics, and exchange of anyonic states, both Abelian as well as those exhibiting braiding. Our analyses are applicable to well established solid state based Quantum Hall geometries as well as to novel realizations in photonic and cold atomic settings. 
Tuesday, March 6, 2018 3:54PM  4:06PM 
H07.00008: Induced Edge States and Domain Walls in the Fractional Quantum Hall Effect Spin Transition Jingcheng Liang, George Simion, Yuli LyandaGeller Search for parafermions and Fibonacci anyons, which are excitations obeying nonAbelian statistics, is driven both by the quest for deeper understanding of nature and prospects for universal topological quantum computation. However, physical systems that can host these exotic excitations are rare and hard to realize in experiments. Here we study the domain walls and the edge states formed in spin transitions in the fractional quantum Hall regime. Exact diagonalization of the Hamiltonian in a disk and torus geometries proves the existence of the counterpropagating edge modes with different spin polarizations on the boundaries between areas of the electron liquid in different phase states. We argue that these systems may host parafermions when coupled to an swave superconductor and are experimentally feasible. 
Tuesday, March 6, 2018 4:06PM  4:18PM 
H07.00009: Controlled equilibration between an integer and a fractional counterpropagating edge modes Yuval Ronen, Yonatan Cohen, Daniel Banitt, Wenmin Yang, Vladimir Umansky, Mordehai Heiblum Edge reconstruction occurs at the edges of a twodimensional electron gas placed at the holeconjugate filling factor in the fractional quantum Hall effect regime. Such is the case of filling factor 2/3, predicted to realize as two counter propagating edges; downstream filling factor 1 edgemode and an upstream 1/3 edgemode. However, experiments have shown equilibration between the edges takes place leading to reconstruction of the edge density profile manifesting counter propagating edges of a downstream 2/3 current edge accompanied by an upstream neutral edge. 
Tuesday, March 6, 2018 4:18PM  4:30PM 
H07.00010: SubPoissonian shot noise by anyon braiding Byeongmok Lee, Cheolhee Han, HeungSun Sim Fractional charge and fractional statistics of quasiparticles are the distinctive features of anyons in fractional quantum hall (FQH) systems. Fractional charge has been experimentally verified by measuring fano factor, the ratio of shot noise to current, in a tunneling setup of a quantum point contact (QPC) between two FQH edges. In this work, we show that the fractional statistics can be detected in the shot noise measurement where anyons are dilutely injected to the tunneling setup through an additional QPC. In the modified setup, a thermally excited anyon effectively braids around another dilutely injected anyon, resulting in subPoissonian shot noise and anomalous fano factor. Our proposal is within experimental reach. 
Tuesday, March 6, 2018 4:30PM  4:42PM 
H07.00011: Topologically connected processes by nonAbelian braiding in a fractional quantum Hall interferometer. Cheolhee Han, HeungSun Sim We theoretically study a FabryPerot interferometer in the fractional quantum Hall regime at filling factor 5/2, into which anyons are dilutely injected via a quantum point contact. We found that in this setup, there appears an interference process where an anyon thermally excited in the FabryPerot interferometer effectively braids another anyon injected from the quantum point contact. This process is represented by disconnected Feynman diagram, which are topologically connected by the nonAbelian braiding. In a certain experimentally feasible regime, this process dominantly contributes to the interference current of the setup, resulting in a nontrivial phase shift 3π/2 of the interference pattern. The phase shift is experimentally measurable even in the Coulomb dominated regime with strong bulkedge coupling. The measurement of the phase shift will provide an evidence of nonAbelian statistics. 
Tuesday, March 6, 2018 4:42PM  4:54PM 
H07.00012: Quantum Phase Transitions in Fractional Quantum Hall Effect of Graphene: Manybody Chern Number and Chirality Ferromagnetism Koji Kudo, Yasuhiro Hatsugai Fractional quantum Hall (FQH) states of graphene with nearest neighbor (NN) and next nearest neighbor (NNN) interaction are investigated by the pseudopotential projected into the n = 0 Landau band on honeycomb lat tice. Effects of lattice are fully included and the manybody Chern number for the degenerate multiplet defined by twisting the boundary condition is evaluated numerically. 
Tuesday, March 6, 2018 4:54PM  5:06PM 
H07.00013: Study of a weaklocalization like negative magnetoresistance effect in the high mobility GaAs/AlGaAs 2DES Rasanga Samaraweera, Binuka Gunawardana, Annika Kriisa, Tharanga Nanayakkara, C. Rasadi Munasinghe, Christian Reichl, Werner Wegscheider, Ramesh Mani High mobility twodimensional electron systems (2DES) realized with GaAs/AlGaAs heterostructures exhibit interesting electrical and physical phenomena including novel microwave induced zeroresistance states, radiationinduced magnetoresistance oscillations [12], giant magnetoresistance [35], and also a weaklocalization (WL)like magnetoresistance effect. In this contribution, we present a study of the WLlike effect in GaAs/AlGaAs 2DES that appears at low magnetic fields and attempt to fit the effect using 2D WL theory without including the spinorbit correction to the conductivity. This study aims to explore the temperature dependence of the WLlike effect and extract the phase coherence times using the fit. The fit extracted phase coherence times are compared with the single particle scattering time and the transport scattering times to examine whether the observed effect represents the signatures of the wellknown WL effect. 
Tuesday, March 6, 2018 5:06PM  5:18PM 
H07.00014: Stability of Composite Fermions to Disorder Prashant Kumar, Michael Mulligan, Srinivas Raghu A significant problem in Quantum Hall physics concerns the effects of disorder on the global phase diagram. The stability of incompressible states to a small amount of disorder is wellknown. However, the fate of compressible states that occur, for example, near even denominator fillings in the presence of disorder remains poorly understood. We use the theory of composite fermions to analyze this problem. Because composite fermions carry both charge and flux, quenched disorder must involve both random potentials and random magnetic fields. Treating gauge fluctuations within a meanfield approximation, we present numerical and analytical studies of nearly free particles in the presence of both random potential and flux. 
Tuesday, March 6, 2018 5:18PM  5:30PM 
H07.00015: Nonuniform electric response in Chern insulators Albert Brown, Rahul Roy We consider the current response of finite width strips in Chern insulator systems with nonflat Berry curvature. The response to a slowly spatially varying electric potential of the hybrid Wannier centers in the strip gives the charge polarization to lowest subleading order in the external field. We show how this is a result of the quantum geometry of the Chern insulator. Higher order response may provide insight into the projected density algebra of the Chern insulator which controls fractional state stability. 
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