Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C46: Fractional Quantum Hall Effect III: Quasiparticle ExcitationsLive
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Sponsoring Units: DCMP Chair: Matteo Ippoliti |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C46.00001: Fractional statistics in anyon collisions hugo BARTOLOMEI, manohar Kumar, Remi Bisognin, Arthur Marguerite, Jean-Marc Berroir, Erwann Bocquillon, bernard Placais, Antonella Cavanna, Ulf Gennser, yong jin, Gwendal Fève Two-dimensional systems can host exotic particles called anyons [1,2] whose quantum statistics are neither bosonic nor fermionic. For example, the elementary excitations of the fractional quantum Hall effect at filling factor ν = 1/m (where m is an odd integer) have been predicted to obey Abelian fractional statistics, with a phase phi associated with the exchange of two particles equal to π/m. However, despite numerous experimental attempts, clear signatures of fractional statistics have remained elusive. We experimentally demonstrate Abelian fractional statistics at filling factor ν = 1/3 by measuring the current correlations resulting from the collision between anyons at a beamsplitter [3]. By analyzing their dependence on the anyon current impinging on the splitter and comparing with recent theoretical models, we extract phi = π/3, in agreement with predictions [4]. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C46.00002: Microwave photons emitted by fractionally charged quasiparticles Remi Bisognin, Hugo Bartoloemi, Manohar Kumar, Inès Safi, Jean-Marc Berroir, Erwan Bocquillon, bernard Placais, Antonella Cavanna, Ulf Gennser, yong jin, Gwendal Fève Two-dimensional systems at low temperatures and high magnetic fields can host exotic particles called “anyons” that are very different from bosons and fermions. They carry a fractional charge and have fractional statistics1,2. Their fractional charge has been studied successfully using low-frequency shot noise measurement3. However, the experimental outcomes intertwined with the scattering properties of the conductor4. Here, by measuring the high-frequency noise generated by the partitioning of a continuous stream of anyons, we probe the fractional charge, independent of details of the quantum conductor. The high-frequency noise is suppressed above the cutoff frequency f related to the applied dc bias V by a Josephson type relation: f=e*V/h, where e* is the fractional charge. This provides direct evidence of fractional charge of anyons5,6. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C46.00003: Valley-controlled even-denominator fractional quantum Hall effect in bilayer graphene Ke Huang, Hailong Fu, Kenji Watanabe, Takashi Taniguchi, Xi Lin, Jun Zhu In a magnetic field, strong electron-electron interaction leads to the celebrated fractional quantum Hall(FQH) effect. FQH states with even-denominators are particularly interesting as they are predicted to host non-Abelian excitations that are foundations of topological quantum computing. Bernal-stacked bilayer graphene has been shown to support even-denominator FQH states at large perpendicular displacement field D at filling factors ν = -5/2, -1/2, 3/2, and 7/2. Here we report the observation of a new even-denominator state at filling factor ν = 5/2 in bilayer graphene. Thanks to higher device quality, we are able to access the regime of very small D-field and probe the gap of the 5/2 state Δ5/2 in the limit of vanishing valley splitting EV. We find that Δ5/2 increases with increasing D and extrapolates to a finite value in the limit of EV = 0. This result indicates the spontaneous valley polarization of the 5/2 state and provides support for the Moore-Read Pfaffian/anti-Pfaffian wave functions. The exquisite control we have in manipulating the valley pseudospin opens the door to exciting valley-coherent many-body phenomena. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C46.00004: Topological Interface between Pfaffian and anti-Pfaffian Order in $\nu=5/2$ Quantum Hall Effect Wei Zhu, Donna Sheng, Kun Yang Recent thermal Hall experiment triggered renewed interest in the problem of $\nu=5/2$ quantum Hall effect, which motivated novel interpretations based on formation of mesoscopic puddles made of Pfaffian and anti-Pfaffian topological orders. Here, we study an interface between the Pfaffian and anti-Pfaffian states, which may play crucial roles in thermal transport, by means of state-of-the-art density-matrix renormalization group simulations. We demonstrate an intrinsic electric dipole moment emerges at the interface, similar to the ``p-n" junction sandwiched between N-type and P-type semiconductor. Importantly, we elucidate the topological origin of this dipole moment, whose formation is to counterbalance the mismatch of guiding-center Hall viscosity of bulk Pfaffian and anti-Pfaffian state. In addition, these results imply that the formation of dipole moment could be helpful to stabilize the puddles made of Pfaffian and anti-Pfaffian state in experimental conditions. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C46.00005: Paired Electron Additions to Fractional Quantum Hall Edge States in Large GaAs Quantum Dots Samuel Aronson, Ahmet Demir, Neal Edward Staley, Spencer Tomarken, Ken W. West, Kirk Baldwin, Loren Pfeiffer, Raymond Ashoori Using single electron capacitance spectroscopy, we determine the energies required to add single electrons to a large (0.8 μm) 2D GaAs quantum dot. We observe capacitance peaks from electron additions to edge states over a wide range of Landau level filling factors. As a function of magnetic flux through the dot, between filling factors ν = 1 and ν = 2, these peaks are regularly spaced with periodicity h/e. Surprisingly, over the range ν = 2 to ν = 5, the peaks double in height and form exact pairs. In this regime, the mean periodicity of capacitance peaks is halved to h/2e, indicating the addition of four electrons to the edge for each flux quantum threading the dot. Remarkably, these pairs themselves bunch together at all filling factors except those close to ν = 5/2. The observed pairing violates the Coulomb blockade picture in which a charging energy would separate the two electron peaks that comprise a pair. Instead the sequence of successive paired tunneling events behaves in the same way as tunneling of electrons into superconducting quantum dots. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C46.00006: Precise experimental test of the Luttinger theorem and particle-hole symmetry in composite fermions Md. Shafayat Hossain, M A Mueed, Meng Ma, Kevin Villegas Rosales, Edwin Yoonjang Chung, Loren Pfeiffer, Ken W. West, Kirk Baldwin, Mansour Shayegan We study a strongly interacting, flat-band system of composite fermions (CFs) in the half-filled lowest Landau level (v = ½), employing a geometric resonance technique. Our technique provides a direct measurement of the Fermi wave vector of the CF Fermi sea. The data reveal the following properties of CFs that have important implications in the physics of strong correlation [1]: (i) Luttinger theorem states that the Fermi sea and its area should be unchanged in the presence of interaction. As a function of interaction strength, our measurements reveal that indeed the area of the CF Fermi sea remains fixed to a great precision, consistent with the Luttinger theorem. (ii) We experimentally show that particle-hole symmetry is also precisely obeyed in the CF Fermi sea. (iii) We find that the density of the CFs is equal to the minority-carrier density in the lowest Landau level, i.e., electrons for ν < ½ and holes for v > ½. Surprisingly, this is very similar to p- or n-doped semiconductors. (iv) Finally, we show that our experimental results deviate from the predictions of the existing Dirac and Halperin-Lee-Read theories, the leading theories that are believed to describe the properties of CFs. |
Monday, March 15, 2021 4:12PM - 4:24PM Live |
C46.00007: Time, momentum, and energy resolved pump probe tunneling spectroscopy of the nonequilibrium electrons in a Landau level (part 1). Raymond Ashoori, Heun Mo Yoo, Kirk Baldwin, Ken W. West, Loren Pfeiffer Spectroscopy of nonequilibrium systems can uncover intricate relaxation mechanisms and short-lived metastable states that are hidden in strongly correlated materials. Here, we developed a novel time, momentum, and energy resolved pump-probe tunneling spectroscopy (Tr-MERTS) that allows visualization of nonequilibrium states in a two-dimensional electronic system. Tr-MERTS operates on samples and regimes inaccessible to standard optical pump-probe spectroscopy. First, Tr-MERTS can easily function in the millikelvin temperature range where many correlated electronic phases emerge. In addition, Tr-MERTS permits a precision control of the pumping electron density. Finally, the electrons can be pumped into a specific energy state even for a system with equidistant energy levels, whereas optical methods excite electrons into any available states when a transition energy equals pump photon energy. In this talk, I will discuss the operational principle of Tr-MERTS and describe basic transient features observed in a quantum Hall system. |
Monday, March 15, 2021 4:24PM - 4:36PM Live |
C46.00008: Intertwined order in fractional Chern insulators from finite-momentum pairing of composite fermions Ramanjit Sohal, Eduardo Fradkin We investigate the problem of intertwined orders in fractional Chern insulators by considering lattice fractional quantum Hall (FQH) states arising from pairing of composite fermions in the square-lattice Hofstadter model. At certain filling fractions, magnetic translation symmetry ensures the composite fermions form Fermi surfaces with multiple pockets, leading to the formation of finite-momentum Cooper pairs in the presence of attractive interactions. We obtain mean-field phase diagrams exhibiting a rich array of striped and topological phases, establishing paired lattice FQH states as an ideal platform to investigate the intertwining of topological and conventional broken symmetry order. |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C46.00009: Composite-fermion Fermi surface at the half-filled Landau level with 2n-fold rotational symmetry Prashant Kumar, Ravindra Nautam Bhatt The nature of the composite-fermi liquid state that occurs at the half-filled Landau level remains an exciting problem in the theory of quantum Hall effect. In this work, we look at its response to anisotropic electron-electron interactions of various types with 2n-fold rotational symmetry. Using the infinite-cylinder density matrix renormalization group (iDMRG) method, we determine the shape of the composite-fermion (CF) Fermi surface and study the amount of anisotropy transferred from the interactions. We find that for n>1, CFs respond very weakly to the anisotropy for the case of Coulomb (~ 1/r) interactions. Our results shed light on the relation between the CF effective mass tensor and electron-electron interactions. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C46.00010: Bardeen-Cooper-Schrieffer pairing of composite fermions Anirban Sharma, Songyang Pu, Jainendra Jain The pairing of composite fermions is thought to lead to remarkable physics, such as the topological superconductivity and non-Abelian Majorana modes [1,2]. We investigate the problem by constructing a p-wave paired BCS wave function of composite fermions [3] on torus geometry and minimizing the energy as a function of the gap parameter. Our results show clear evidence of pairing at ν=5/2, but no evidence of pairing at ν=1/2. We find that the lowest energy BCS function has the highest overlap with the Pfaffian wavefunction. We search for but do not find the spin-singlet pairing of composite fermions at ν=1/2. We also consider other pairing symmetries and investigate the Hall viscosity for the BCS wavefunction in different phases. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C46.00011: Hall viscosity of the composite-fermion Fermi seas for fermions and bosons Songyang Pu The Hall viscosity has been proposed as a topological property of incompressible fractional quantum Hall states and can be evaluated as Berry curvature. This paper reports on the Hall viscosities of composite-fermion Fermi seas at $\nu=1/m$, where $m$ is even for fermions and odd for bosons. A well-defined value for the Hall viscosity is not obtained by viewing the $1/m$ composite-fermion Fermi seas as the $n\rightarrow \infty$ limit of the Jain $\nu=n/(nm\pm 1)$ states, whose Hall viscosities $(\pm n+m)\hbar \rho/4$ ($\rho$ is the two-dimensional density) approach $\pm \infty$ in the limit $n\rightarrow \infty$. A direct calculation shows that the Hall viscosities of the composite-fermion Fermi sea states are finite and relatively stable with system size variation. However, they are not topologically quantized in the entire $\tau$ space. I find that the $\nu=1/2$ composite-fermion Fermi sea wave function for a square torus yields a Hall viscosity that is expected from particle-hole symmetry and is also consistent with the orbital spin of $1/2$ for Dirac composite fermions. I compare my numerical results with some theoretical conjectures. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C46.00012: Observation of anyonic statistics through quantum Hall interferometry James Nakamura, Shuang Liang, Geoff C Gardner, Michael Manfra Fractional quantum Hall states have been predicted to have quasiparticle excitations which obey anyonic braiding statistics. Interferometry has been proposed as an experimental method to probe these exotic statistics. We present measurements of interference at the ν = 1/3 fractional quantum Hall state. We observe discrete jumps in phase which are consistent with the anyonic phase contribution when the number of localized quasiparticles changes. We also observe a transition in interference behavior when the magnetic field is varied away from the center of the state, which is consistent with a recent theoretical analysis predicting a shift from simple Aharonov-Bohm interference to regimes in which quasiparticles are created with period Φ0. |
Monday, March 15, 2021 5:24PM - 5:36PM Live |
C46.00013: Entanglement Negativity and Topological Degeneracy Pak Kau Lim, Hamed Asasi, Jeffrey C. Y. Teo, Michael Mulligan We study the spatial distribution of entanglement in (2+1)d topological phases. Specifically, we use the coupled-wire construction to study the logarithmic negativity[1] for various spatial partitions of the ground state. We show how monogamy-type relations [2,3] for the logarithmic negativity can reveal the degeneracy of the ground state wave functions on a torus. |
Monday, March 15, 2021 5:36PM - 5:48PM Live |
C46.00014: Time, momentum, energy resolved pump probe tunneling spectroscopy of the nonequilibrium electrons in a Landau level (part2) Heun Mo Yoo, Ken W. West, Kirk Baldwin, Loren Pfeiffer, Raymond Ashoori We use time, momentum, and energy resolved pump probe tunneling spectroscopy (Tr-MERTS) to study the nonequilibrium electronic states in a quantum Hall system. Our Tr-MERTS spectra show the slow relaxation of the spin polarized electrons in a ferromagnetic quantum Hall state at \nu = 1. In addition, the spectra reveal a transient splitting with a lifetime of a few microseconds that appears when a small number of electrons is pumped into the \nu = 1 state. Our results demonstrate a potential broad applicability of Tr-MERTS for studying the nonequilibrium physics in unconventional quantum Hall states or other flat-band systems realized in two-dimensional materials. |
Monday, March 15, 2021 5:48PM - 6:00PM Live |
C46.00015: Non-Abelian properties at 5/2 and 7/2 filling factors exposed using controlled e/4 population of Fabry-Perot interferometers. Robert Willett, Kirill Shtengel, Chetan Nayak, Loren Pfeiffer, Kirk Baldwin, Ken W. West
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