Near-Field Optical Mapping of Quantum Hall Edge States

Ito, H.; Furuya, Kenji; Shibata, Yusuke; Kashiwaya, Satoshi; Yamaguchi, M.; Akazaki, Tatsushi; Tamura, Hiroyuki; Ootuka, Youiti; Nomura, Shintaro

doi:10.1103/physrevlett.107.256803

Cited by 21 publications

(31 citation statements)

References 28 publications

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“…Recent scanning probe microscopy experiments [20][21][22][23] have demonstrated the existence of these strips several magnetic lengths away from the edge. In the opposite limit, l s o ol B , the case of the experiments reported here, the strips are absent, and the Nth LL shifts monotonically away from the DP for distances within ffiffiffiffi N p l B of the edge [5][6][7] .…”

Section: Resultsmentioning

confidence: 99%

“…However, in the semiconductor-based 2DES studied thus far, this 'topologically protected' correspondence is notoriously difficult to realize 11,12 . The most likely cause of the discrepancy between theory and experiment is the generic occurrence of edge reconstruction [13][14][15][16][17][18][19][20][21][22][23] in the semiconductor 2DES, which induces additional edge modes that are not tied to the bulk topology and disrupt the predicted universality 24 . In these systems, the lithographically defined edges have soft confinement potentials, caused by the gates and dopant layer being far away from the 2DES, which favour the reconstruction of the edge states into alternating compressible and incompressible strips (Fig.…”

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confidence: 99%

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Evolution of Landau levels into edge states in graphene

Luican‐Mayer

Abanin

et al. 2013

Nat Commun

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Two-dimensional electron systems in the presence of a magnetic field support topologically ordered states, in which the coexistence of an insulating bulk with conducting one-dimensional chiral edge states gives rise to the quantum Hall effect. For systems confined by sharp boundaries, theory predicts a unique edge-bulk correspondence, which is central to proposals of quantum Hall-based topological qubits. However, in conventional semiconductor-based two-dimensional electron systems, these elegant concepts are difficult to realize, because edge-state reconstruction due to soft boundaries destroys the edge-bulk correspondence. Here we use scanning tunnelling microscopy and spectroscopy to follow the spatial evolution of electronic (Landau) levels towards an edge of graphene supported above a graphite substrate. We observe no edge-state reconstruction, in agreement with calculations based on an atomically sharp boundary. Our results single out graphene as a system where the edge structure can be controlled and the edge-bulk correspondence is preserved.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Evolution of Landau levels into edge states in graphene

Luican‐Mayer

Abanin

et al. 2013

Nat Commun

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“…Because the electrons reside at the graphene surface, in contrast to the case of semiconductor-based 2DEGs, it should be possible to directly probe the level bending at the edges and perform systematic studies of the edge states for testing theoretical ideas of quantum Hall edge physics [118]. Numerous works have addressed this subject, mainly using optical and transport measurements [119][120][121]. Direct experimental observation of the LL bending can be achieved by STM and STS at different edge terminations of graphene on the graphite surface [72].…”

Section: Ll Bendingmentioning

confidence: 99%

Landau quantization of Dirac fermions in graphene and its multilayers

et al. 2017

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When electrons are confined in a two-dimensional (2D) system, typical quantum-mechanical phenomena such as Landau quantization can be detected. Graphene systems, including the single atomic layer and few-layer stacked crystals, are ideal 2D materials for studying a variety of quantum-mechanical problems. In this article, we review the experimental progress in the unusual Landau quantized behaviors of Dirac fermions in monolayer and multilayer graphene by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Through STS measurement of the strong magnetic fields, distinct Landau-level spectra and rich level-splitting phenomena are observed in different graphene layers. These unique properties provide an effective method for identifying the number of layers, as well as the stacking orders, and investigating the fundamentally physical phenomena of graphene. Moreover, in the presence of a strain and charged defects, the Landau quantization of graphene can be significantly modified, leading to unusual spectroscopic and electronic properties.

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“…The optical excitation power was kept to be small to avoid any heating of carriers, and was 25 pW and 1.1 nW for the excitation photon energy of 1.5194 and 1.5140 eV, respectively. The former and the latter correspond to 11.1 and 5.7 meV above the onset of absorption of GaAs single heterojunction of 1.5083 eV, 10 respectively. The change of the electron density due to local optical excitation was negligibly small because of the small excitation power.…”

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confidence: 99%

Circularly Polarized Near-Field Optical Mapping of Spin-Resolved Quantum Hall Chiral Edge States

et al. 2015

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We have successfully developed a circularly polarized near-field scanning optical microscope (NSOM) that enables us to irradiate circularly polarized light with spatial resolution below the diffraction limit. As a demonstration, we perform real-space mapping of the quantum Hall chiral edge states near the edge of a Hall-bar structure by injecting spin polarized electrons optically at low temperature. The obtained real-space mappings show that spin-polarized electrons are injected optically to the two-dimensional electron layer. Our general method to locally inject spins using a circularly polarized NSOM should be broadly applicable to characterize a variety of nanomaterials and nanostructures.

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Near-Field Optical Mapping of Quantum Hall Edge States

Cited by 21 publications

References 28 publications

Evolution of Landau levels into edge states in graphene

Evolution of Landau levels into edge states in graphene

Landau quantization of Dirac fermions in graphene and its multilayers

Circularly Polarized Near-Field Optical Mapping of Spin-Resolved Quantum Hall Chiral Edge States

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