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| Open AccessUncovering the spin ordering in magic-angle graphene via edge state equilibration
The hierarchy of symmetry breaking in magic-angle twisted bilayer graphene remains a topic of intense fundamental study. Here, the authors determine the spin polarization of symmetry-broken quantum Hall states and Chern insulators in MATBG using a twist-decoupled graphene probe.
- Jesse C. Hoke
- , Yifan Li
- & Benjamin E. Feldman
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Article
| Open AccessCurrent-sensitive Hall effect in a chiral-orbital-current state
In most materials, the hall conductivity has a scaling to the longitudinal resistance that varies between linear and quadratic. Here, Zhang et al demonstrate a hall conductivity proportional to the fifth power of the longitudinal conductivity in Mn3Si2Te6, which they attribute to enhanced force on charge carriers due to chiral orbital currents.
- Yu Zhang
- , Yifei Ni
- & Gang Cao
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Article
| Open AccessMeasuring statistics-induced entanglement entropy with a Hong–Ou–Mandel interferometer
Measuring quantum entanglement remains a demanding task. The authors introduce two functions to quantify entanglement induced by fermionic or bosonic statistics, in transport experiments. Both functions, in theory and experiment, are remarkably resilient against the nonuniversal effects of interactions.
- Gu Zhang
- , Changki Hong
- & Yuval Gefen
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Article
| Open AccessProbing the tunable multi-cone band structure in Bernal bilayer graphene
Bernal-stacked bilayer graphene (BLG) has been extensively studied due to its tunable band gap and emerging electronic properties, but its low-energy band structure remains debated. Here, the authors report magnetotransport measurements of Bernal BLG, showing evidence of four Dirac cones and electrically induced topological transitions.
- Anna M. Seiler
- , Nils Jacobsen
- & R. Thomas Weitz
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Article
| Open AccessEvidence for Topological Protection Derived from Six-Flux Composite Fermions
Huang et al. study fractional quantum Hall (fQH) states in high-quality GaAs/AlGaAs samples. They report evidence for a fQH state at filling factor ν = 9/11, which they associate with the formation of six-flux composite fermions.
- Haoyun Huang
- , Waseem Hussain
- & G. A. Csáthy
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| Open AccessAxion insulator state in hundred-nanometer-thick magnetic topological insulator sandwich heterostructures
A zero Hall conductance plateau has been taken as evidence of the axion insulator state in magnetically doped topological insulator heterostructures, but it can also originate from surface state hybridization. Here the authors establish such a state in a ~106 nm thick sample, where hybridization is negligible.
- Deyi Zhuo
- , Zi-Jie Yan
- & Cui-Zu Chang
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Article
| Open AccessTime, momentum, and energy resolved pump-probe tunneling spectroscopy of two-dimensional electron systems
Pump-probe techniques—where a system is driven into a nonequilibrium state and then studied as a function of time—provide rich information about the behaviour of charge carriers and their interactions. Here, Yoo et al extend this class of techniques by injecting electrons at a selected energy and observing their decay in energy and momentum space.
- H. M. Yoo
- , M. Korkusinski
- & R. C. Ashoori
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Article
| Open AccessLarge composite fermion effective mass at filling factor 5/2
The fractional quantum Hall state at the filling factor 5/2 has been intensively studied due to its predicted non-Abelian statistics. Petrescu et al. measure the composite fermion effective mass of this state and find that it is several times larger than that in the half-filled lowest Landau level.
- M. Petrescu
- , Z. Berkson-Korenberg
- & G. Gervais
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Article
| Open AccessSpin skyrmion gaps as signatures of strong-coupling insulators in magic-angle twisted bilayer graphene
Magic-angle twisted bilayer graphene (MATBG) hosts flat electronic bands allowing for a rich variety of correlated electronic states. Here, using a scanning single electron transistor, Yu et al find thermodynamically gapped ground states in MATBG at several filling factors, with spin-skyrmion charge excitations.
- Jiachen Yu
- , Benjamin A. Foutty
- & Benjamin E. Feldman
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Article
| Open AccessSimulating Chern insulators on a superconducting quantum processor
Quantum simulations of topological matter with superconducting qubits have been attracting attention recently. Xiang et al. realize 2D and bilayer Chern insulators with synthetic dimensions on a programmable 30-qubit-ladder superconducting processor, showing bulk-boundary correspondence.
- Zhong-Cheng Xiang
- , Kaixuan Huang
- & Heng Fan
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Article
| Open AccessAnomalous Landau quantization in intrinsic magnetic topological insulators
Tunability of the electronic properties of magnetic topological insulators is highly desired for future device applications. Here, the authors study the effect of substitutional impurities on the topological properties of Sb-doped MnBi2Te4 devices and uncover tunable layer-dependent electronic states.
- Su Kong Chong
- , Chao Lei
- & Kang L. Wang
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Article
| Open AccessSpin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2
Twisted bilayer graphene hosts a zoo of rich correlated electronic phases. Here, the authors explore the phase diagram of a twisted bilayer graphene/tungsten diselenide heterostructure and uncover a series of delicate Fermi surface reconstructions and signatures of orbital magnetism.
- Saisab Bhowmik
- , Bhaskar Ghawri
- & U. Chandni
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Article
| Open AccessGeometric fluctuation of conformal Hilbert spaces and multiple graviton modes in fractional quantum Hall effect
Graviton modes are long-wavelength neutral collective excitations of fractional quantum Hall fluids that are analogous to gravitons. Here the authors develop a microscopic theory of multiple graviton modes and show that they are associated with geometric fluctuations of hierarchical conformal Hilbert subspaces.
- Wang Yuzhu
- & Yang Bo
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Article
| Open AccessDisorder-enabled Andreev reflection of a quantum Hall edge
The properties of edge states at the boundary between a quantum Hall insulator and a superconductor have recently been under scrutiny. Here, the authors find theoretically that Andreev reflection of an edge state is possible only if the superconductor is in the disordered limit, leading to stochastic edge state conductance and providing an explanation of a recent experiment.
- Vladislav D. Kurilovich
- , Zachary M. Raines
- & Leonid I. Glazman
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Article
| Open AccessAnomalous quantized plateaus in two-dimensional electron gas with gate confinement
A quantized plateau is typically considered to be the feature of a fractional quantum Hall state. Yan et al. report a series of plateaus quantized at unusual fractions in a confined two-dimensional electron gas, which is attributed to enhanced density in the confined region.
- Jiaojie Yan
- , Yijia Wu
- & Xi Lin
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| Open AccessCreation of chiral interface channels for quantized transport in magnetic topological insulator multilayer heterostructures
Quantum anomalous Hall junctions show great promise for advancing next-generation electronic circuits. Here, the authors demonstrate a scalable method for synthesizing heterostructures of magnetic topological insulators with regions of distinct Chern numbers and characterize the chiral interface modes that emerge at the interface.
- Yi-Fan Zhao
- , Ruoxi Zhang
- & Cui-Zu Chang
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Article
| Open AccessChiral excitonic order from twofold van Hove singularities in kagome metals
Recent experiments have found a two-fold van Hove singularity (TvHS) in the kagome metal CsV3Sb5. Here, the authors use perturbative renormalization group calculations to find that the leading instability in a model of TvHS is a chiral condensate of electron-hole pairs, breaking time-reversal symmetry.
- Harley D. Scammell
- , Julian Ingham
- & Oleg P. Sushkov
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Article
| Open AccessQuasiparticle Andreev scattering in the ν = 1/3 fractional quantum Hall regime
Quantum transport of fractional quasiparticles can drastically differ from conventional charge transport. Here the authors demonstrate Andreev-like reflection of a fractional quasiparticle incident on a barrier in the fractional quantum Hall regime.
- P. Glidic
- , O. Maillet
- & F. Pierre
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Article
| Open AccessPhonon-mediated room-temperature quantum Hall transport in graphene
Monolayer graphene can support the quantum Hall effect up to room temperature. Here, the authors provide evidence that graphene encapsulated in hexagonal boron nitride realizes a novel transport regime where dissipation in the quantum Hall phase is mediated predominantly by electron-phonon scattering rather than disorder scattering.
- Daniel Vaquero
- , Vito Clericò
- & Sergio Pezzini
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| Open AccessPerpendicular electric field drives Chern transitions and layer polarization changes in Hofstadter bands
Moiré superlattices offer a rich platform fort the study of correlated and topological phases. Here, by using low-temperature magneto-transport measurements, the authors demonstrate electric-field induced switching between Chern states in twisted double-layer graphene in the Hofstadter regime.
- Pratap Chandra Adak
- , Subhajit Sinha
- & Mandar M. Deshmukh
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| Open AccessAccurate graphene quantum Hall arrays for the new International System of Units
The 2019 redefinition of the International System of Units requires a 100 Ω quantum resistance standard for the ideal electrical realization of the kilogram via the Kibble Balance. Here, the authors report the realization of an array of 236 graphene quantum Hall bars, demonstrating a quantized resistance of 109 Ω with an accuracy of 0.2 nΩ/Ω over an extended range of bias currents.
- Hans He
- , Karin Cedergren
- & Gunnar Eklund
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Article
| Open AccessNon-Abelian anyon collider
Colliders are used to probe particles’ quantum statistical properties. Now, a theoretical proposal for a collider for anyons (a type of topological quasiparticles occurring in 2D systems) is reported, which can be used to explore the braiding statistics of various Abelian and non-Abelian anyons.
- June-Young M. Lee
- & H.-S. Sim
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Article
| Open AccessEmergent helical edge states in a hybridized three-dimensional topological insulator
As the thickness of a three-dimensional (3D) topological insulator (TI) becomes comparable to the penetration depth of surface states, hybridization turns their gapless Dirac electronic structure into a gapped spectrum. Here, authors show that 2D topological states can exist in the 3D TI BiSbTeSe2 when the Fermi level is inside the hybridization gap.
- Su Kong Chong
- , Lizhe Liu
- & Vikram V. Deshpande
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Article
| Open AccessBaby skyrmions in Chern ferromagnets and topological mechanism for spin-polaron formation in twisted bilayer graphene
In conventional materials, charge carriers are electron-like quasiparticles, but topological bands allow for more exotic possibilities. Here, the authors predict that in the Chern-ferromagnet phase of twisted bilayer graphene charge is carried by spin polarons, bound states of an electron and a spin flip.
- Eslam Khalaf
- & Ashvin Vishwanath
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Article
| Open AccessTopological current divider in a Chern insulator junction
Topological materials hold great promise for dissipationless information transmission. Here, the authors create Chern insulator junctions between domains with different Chern numbers in MnBi2Te4 to realize the basic operation of a topological circuit.
- Dmitry Ovchinnikov
- , Jiaqi Cai
- & Xiaodong Xu
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Article
| Open AccessTwo-particle time-domain interferometry in the fractional quantum Hall effect regime
Excitations of the fractional quantum Hall states are of great interest because they obey anyonic statistics, but electronic interferometers give contrasting results about their quantum coherence. Here the authors use novel two-particle time-domain interferometry to show that quantum coherence is indeed preserved.
- I. Taktak
- , M. Kapfer
- & D. C. Glattli
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| Open AccessScaling behavior of electron decoherence in a graphene Mach-Zehnder interferometer
Quantum Hall edge channels provide a platform to study electron interference, however understanding decoherence in these systems remains an open problem. Jo et al. realize a regime of suppressed decoherence in an electronic Mach-Zehnder interferometer formed in a graphene quantum Hall pn junction.
- M. Jo
- , June-Young M. Lee
- & P. Roulleau
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| Open AccessDetermination of topological edge quantum numbers of fractional quantum Hall phases by thermal conductance measurements
The knowledge of quantum numbers of the edge modes is essential for understanding fractional Hall states containing counter-propagating downstream and upstream modes. Here the authors identify the edge quantum numbers by probing a crossover from non-equilibrated to equilibrated edge mode regime in thermal conductance.
- Saurabh Kumar Srivastav
- , Ravi Kumar
- & Anindya Das
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Article
| Open AccessInterplay between topological valley and quantum Hall edge transport
In electrostatically-gapped bilayer graphene, topologically-protected states can emerge at naturally occurring stacking domain walls even in the absence of a magnetic field. Here, the authors describe the interplay between such domain wall states and quantum Hall edge transport within the eight-fold degenerate zeroth Landau level of suspended bilayer graphene.
- Fabian R. Geisenhof
- , Felix Winterer
- & R. Thomas Weitz
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Article
| Open AccessCreating boundaries along a synthetic frequency dimension
The exploration of topological boundary effects is one of the important aspects that could foster the development of future topological photonics devices. Here the authors propose a straightforward method to construct sharp boundaries in synthetic dimensions using a modulated ring resonator strongly coupled to an auxiliary ring.
- Avik Dutt
- , Luqi Yuan
- & Shanhui Fan
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Article
| Open AccessIsospin competitions and valley polarized correlated insulators in twisted double bilayer graphene
Previous studies of twisted double bilayer graphene have been limited to AB-AB stacking, featuring spin-polarized correlated insulators. Here, the authors fabricate AB-BA devices and report a competition between spin and valley polarization, along with the emergence of valley-polarized correlated insulators tuned by electric field.
- Le Liu
- , Shihao Zhang
- & Guangyu Zhang
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Article
| Open AccessCounterpropagating topological and quantum Hall edge channels
The quantum spin Hall effect disappears at high magnetic fields when the band inversion is lifted. The authors demonstrate that in contrast, in disordered samples, counter-propagating topological and quantum Hall edge channels prevent the detection of the trivial gap, explaining a previous observation.
- Saquib Shamim
- , Pragya Shekhar
- & Laurens W. Molenkamp
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Article
| Open AccessBound states at partial dislocation defects in multipole higher-order topological insulators
The development of higher-order topological insulators enables robust localization of energy at lower-dimensional boundaries. Here the authors demonstrate that partial dislocation in higher order topological insulators can be intuitively understood as a defect-induced topological phase boundary which supports 0D bound states.
- Sasha S. Yamada
- , Tianhe Li
- & Gaurav Bahl
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Article
| Open AccessElectric control of a canted-antiferromagnetic Chern insulator
Exotic states emerge from the interplay between band topology and ferromagnetism, but it remains less known in canted-antiferromagnetic phase. Here, the authors realize a canted-antiferromagnetic Chern insulator in atomically-thin MnBi2Te4 with electrical control of chiral-edge state transport.
- Jiaqi Cai
- , Dmitry Ovchinnikov
- & Xiaodong Xu
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Article
| Open AccessCooling low-dimensional electron systems into the microkelvin regime
Cooling electrons into the microkelvin temperature range is of interest both for practical purposes and fundamental studies, but current demonstrations are limited to small, specific devices. Here, the authors achieve sub-millikelvin temperatures in a large-area, two-dimensional electron gas.
- Lev V. Levitin
- , Harriet van der Vliet
- & John Saunders
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| Open AccessAbsent thermal equilibration on fractional quantum Hall edges over macroscopic scale
The transport behaviour of counter-propagating edge modes in the hole-conjugate fractional quantum Hall state is not fully understood. Here, by combining local noise thermometry and thermal conductance measurements, the authors show the absence of thermal equilibration on the edge at macroscopic distances.
- Ron Aharon Melcer
- , Bivas Dutta
- & Vladimir Umansky
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Article
| Open AccessImpact of bulk-edge coupling on observation of anyonic braiding statistics in quantum Hall interferometers
Quantum Hall interferometers have proven to be a useful platform for the study of fractional statistics. Here, the authors experimentally study the effect of Coulomb interactions between bulk and edge charges on the interferometer behavior, validating previous theoretical predictions.
- J. Nakamura
- , S. Liang
- & M. J. Manfra
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Article
| Open AccessCornering the universal shape of fluctuations
Fluctuations, both quantum and classical, contain important information about the underlying system. Here, the authors show that for measurements on a subregion with a sharp corner, fluctuations have the same shape dependence for a large variety of systems.
- Benoit Estienne
- , Jean-Marie Stéphan
- & William Witczak-Krempa
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Article
| Open AccessObservation of ballistic upstream modes at fractional quantum Hall edges of graphene
Recently graphene has emerged as a new platform for the study of quantum Hall states. Here, by means of noise measurements, the authors report evidence for the existence of the upstream mode and its ballistic nature in the hole-conjugate fractional quantum Hall state in a bilayer graphene device.
- Ravi Kumar
- , Saurabh Kumar Srivastav
- & Anindya Das
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Article
| Open AccessMagic in twisted transition metal dichalcogenide bilayers
The e moiré superlattice in twisted 2D structures becomes a highly tunable platform of strongly correlated electron systems. Here, the authors predict rich physics at small twist angles in twisted transition metal dichalcogenide bilayers, including a magic angle for flat band, interaction-driven Haldane insulator, fractional quantum anomalous Hall effect and quantum spin Hall insulators.
- Trithep Devakul
- , Valentin Crépel
- & Liang Fu
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Article
| Open AccessLaughlin anyon complexes with Bose properties
The microscopic nature of neutral collective excitation of the fractional quantum Hall state is still debated. Here the authors show that a macroscopic ensemble of neutral excitations in the 1/3 state exhibits properties of a Bose system with an exceptionally long coherence time.
- L. V. Kulik
- , A. S. Zhuravlev
- & V. Y. Umansky
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Article
| Open AccessWigner solids of domain wall skyrmions
Skyrmions, a topological spin texture, have been found in a variety of magnetic systems, including quantum hall ferromagnets. Here, Yang et al demonstrate the existence of skyrmions in domain walls in a quantum Hall ferromagnet, and suggest that these skyrmions form a 1D Wigner crystal.
- Kaifeng Yang
- , Katsumi Nagase
- & Hongwu Liu
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Article
| Open AccessQuantum anomalous Hall edge channels survive up to the Curie temperature
The quantum anomalous Hall effect has so far been limited to temperature of the order of 20 mK. Here, Fijalkowski et al. report the existence of chiral edge channels up to the Curie temperature of bulk ferromagnetism of the magnetic topological insulator with a multi-terminal Corbino geometry.
- Kajetan M. Fijalkowski
- , Nan Liu
- & Laurens W. Molenkamp
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Article
| Open AccessTransport in helical Luttinger liquids in the fractional quantum Hall regime
Previous work has shown that helical domain walls can form between states of different spin-polarization during a ferromagnetic spin transition in the fractional quantum Hall regime. Here, the authors study the transport through a single helical domain wall and find strong deviations from a simplified theory of weakly interacting edge channels.
- Ying Wang
- , Vadim Ponomarenko
- & Leonid P. Rokhinson
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Article
| Open AccessSpin-valley locking and bulk quantum Hall effect in a noncentrosymmetric Dirac semimetal BaMnSb2
Valley dependent spin polarization called spin-valley locking appears in absence of magnetism but it is limited to rare examples of transition metal dichalcogenides. Here, the authors report evidence of spin-valley locking and stacked quantum Hall effect in a bulk Dirac semimetal BaMnSb2.
- J. Y. Liu
- , J. Yu
- & Z. Q. Mao
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Article
| Open AccessSpectral signatures of the surface anomalous Hall effect in magnetic axion insulators
Experimentally detectable signature of an axion insulator remains elusive. Here, the authors predict a topological phase diagram of MnBi2Te4/(Bi2Te3)n heterostructure, where the chiral hinge mode induced by the surface anomalous Hall conductivity is identified as a signature of an axion insulator state.
- Mingqiang Gu
- , Jiayu Li
- & Qihang Liu
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Article
| Open AccessQuantized spin Hall conductance in a magnetically doped two dimensional topological insulator
The quantum spin Hall effect is expected not to survive the presence of magnetic impurities. Here, authors report full quantization at very low temperatures in HgTe quantum wells alloyed with a few percent of magnetic Mn atoms, due to Kondo screening.
- Saquib Shamim
- , Wouter Beugeling
- & Laurens W. Molenkamp
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Article
| Open AccessOrigin of the quasi-quantized Hall effect in ZrTe5
A 3D quantum Hall effect has been reported in Dirac semimetal ZrTe5 due to a magnetic-field-driven Fermi surface instability. Here, the authors show evidence of quasi-quantized Hall response without Fermi surface instability, but they argue that it is due to the interplay of the intrinsic properties of ZrTe5 electronic structure and Dirac semi-metallic character.
- S. Galeski
- , T. Ehmcke
- & J. Gooth
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Article
| Open AccessAndreev reflection of fractional quantum Hall quasiparticles
Andreev reflection is normally known to occur at a metal-superconductor interface. Here, Hashisaka et al. observe an Andreev-like process in a narrow junction between fractional and integer quantum Hall states originating from a topological quantum many-body effect instead of superconductivity.
- M. Hashisaka
- , T. Jonckheere
- & K. Muraki