Magnetic-field-controlled negative differential conductance in scanning tunneling spectroscopy of graphene 
<i>npn</i>
 junction resonators

Li, Siyu; Liu, Haiwen; Qiao, Jia-Bin; Jiang, Hua; He, Lin

doi:10.1103/physrevb.97.115442

Cited by 20 publications

(16 citation statements)

References 44 publications

(59 reference statements)

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“…1f. Previous studies demonstrated that the existence of an energy gap is necessary to observe the NDC in the tunneling spectra of graphene systems 30,31 . Therefore, the observed NDC is a clear signature that there is a gap between the low-energy VHSs and the remote bands in the topmost TBG, which agrees well with that observed in slightly TBG [9][10][11][12][13][14][20][21][22][23]32,33 .…”

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confidence: 99%

Experimental evidence for orbital magnetic moments generated by moiré-scale current loops in twisted bilayer graphene

Zhang

Ren

et al. 2020

Phys. Rev. B

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A remarkable property of twisted bilayer graphene (TBG) with small twist angle is the presence of a well-defined and conserved low-energy valley degrees of freedom 1 , which can potentially bring about new types of valley-associated spontaneous-symmetry breaking phases. Electron-electron (e-e) interactions in the TBG near the magic angle ~ 1.1º can lift the valley degeneracy, allowing for the realization of orbital magnetism and topological phases 2-11 . However, direct measurement of the orbital-based magnetism in the TBG is still lacking up to now. Here we report evidence for orbital magnetic moment generated by the moiréscale current loops in a TBG with a twist angle θ ~ 1.68º . The valley degeneracy of the 1.68º TBG is removed by e-e interactions when its low-energy van Hove singularity (VHS) is nearly half filled. A large and linear response of the valley splitting to magnetic fields is observed, attributing to coupling to the large orbital magnetic moment induced by chiral current loops circulating in the moiré pattern.According to our experiment, the orbital magnetic moment is about 10.7 B per moiré supercell. Our result paves the way to explore magnetism that is purely orbital in slightly twisted graphene system.

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confidence: 99%

Experimental evidence for orbital magnetic moments generated by moiré-scale current loops in twisted bilayer graphene

Zhang

Ren

et al. 2020

Phys. Rev. B

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“…9(a) and (b). The external magnetic fields quantize the continuous band stucture of graphene into discrete LLs [58,71,[131][132][133][134]. The probing STM tip, acting as a moveable top gate, bends the LLs of the region beneath the tip into the gaps between the LLs of the surrounding regions, which leads to an edge-free GQD beneath the tip with confined orbital states [16,17,22,23,126].…”

Section: Stm Tip-induced Edge-free Gqdsmentioning

confidence: 99%

Recent progresses of quantum confinement in graphene quantum dots

2021

Front. Phys.

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Graphene quantum dots (GQDs) not only have potential applications on spin qubit, but also serve as essential platforms to study the fundamental properties of Dirac fermions, such as Klein tunneling and Berry phase. By now, the study of quantum confinement in GQDs still attract much attention in condensed matter physics. In this article, we review the experimental progresses on quantum confinement in GQDs mainly by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Here, the GQDs are divided into Klein GQDs, bound-state GQDs and edge-terminated GQDs according to their different confinement strength. Based on the realization of quasi-bound states in Klein GQDs, external perpendicular magnetic field is utilized as a manipulation approach to trigger and control the novel properties by tuning Berry phase and electron-electron (e-e) interaction. The tip-induced edge-free GQDs can serve as an intuitive mean to explore the broken symmetry states at nanoscale and single-electron accuracy, which are expected to be used in studying physical properties of different two-dimensional materials. Moreover, high-spin magnetic ground states are successfully introduced in edge-terminated GQDs by designing and synthesizing triangulene zigzag nanographenes.

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“…The ballistic electron propagation in 2D materials allows the observation of analogies from optics [42,[48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66]. For example, it has been shown that an electron beam, which hits the interface of a pn junction, is refracted similar to a light beam at the interface of two different media.…”

Section: Introductionmentioning

confidence: 99%

Phosphorene pnp junctions as perfect electron waveguides

Betancur-Ocampo,

Paredes-Rocha,

Stegmann

2020

Preprint

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The current flow in phosphorene pnp junctions is studied. At the interfaces of the junction, omnidirectional total reflection takes place, named anti-super-Klein tunneling, as this effect is not due to an energetically forbidden region but due to pseudo-spin blocking. The anti-super-Klein tunneling confines electrons within the junction, which thus represents a perfect lossless electron waveguide. Calculating the current flow by applying the Green's function method onto a tight-binding model of phosphorene, it is observed that narrow electron beams propagate in these waveguides like light beams in optical fibers. The perfect guiding is found for all steering angles of the electron beam as the total reflection does not rely on the existence of a critical angle. For low electron energies and narrow junctions, the guided modes of the waveguide are observed. The waveguide operates without any loss only for a specific orientation of the junction. For arbitrary orientations, minor leakage currents are found, which however decay for low electron energies and grazing incidence angles. It is shown that a crossroad shaped pnp junction can be used to split and direct the current flow in phosphorene. The proposed device, a phosphorene pnp junction as a lossless electron waveguide, may not only find applications in nanoelectronics but also in quantum information technology.

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Magnetic-field-controlled negative differential conductance in scanning tunneling spectroscopy of graphene npn junction resonators

Cited by 20 publications

References 44 publications

Experimental evidence for orbital magnetic moments generated by moiré-scale current loops in twisted bilayer graphene

Experimental evidence for orbital magnetic moments generated by moiré-scale current loops in twisted bilayer graphene

Recent progresses of quantum confinement in graphene quantum dots

Phosphorene pnp junctions as perfect electron waveguides

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