Joonbum Park

Anisotropic Dirac fermions in a Bi square net of SrMnBi2.

We report the observation of highly anisotropic Dirac fermions in a Bi square net of SrMnBi(2), based on a first-principles calculation, angle-resolved photoemission spectroscopy, and quantum oscillations for high-quality single crystals. We found that the Dirac dispersion is generally induced in the (SrBi)(+) layer containing a double-sized Bi square net. In contrast to the commonly observed isotropic Dirac cone, the Dirac cone in SrMnBi(2) is highly anisotropic with a large momentum-dependent disparity of Fermi velocities of ~8. These findings demonstrate that a Bi square net, a common building block of various layered pnictides, provides a new platform that hosts highly anisotropic Dirac fermions.

Gate-tuned differentiation of surface-conducting states in Bi1.5Sb0.5Te1.7Se1.3topological-insulator thin crystals

Using field-angle, temperature, and back-gate-voltage dependence of the weak anti-localization (WAL) and universal conductance fluctuations of thin Bi1.5Sb0.5Te1.7Se1.3 topological-insulator single crystals, in combination with gate-tuned Hall resistivity measurements, we reliably separated the surface conduction of the topological nature from both the bulk conduction and topologically trivial surface conduction. We minimized the bulk conduction in the crystals and back-gate tuned the Fermi level to the topological bottom-surface band while keeping the top surface insensitive to back-gating with the optimal crystal thickness of ~?100 nm. We argue that the WAL effect occurring by the coherent diffusive motion of carriers in relatively low magnetic ?fields is more essential than other transport tools such as the Shubnikov-de Hass oscillations for confirming the conduction by the topologically protected surface state. Our approach provides a highly coherent picture of the surface transport properties of TIs and a reliable means of investigating the fundamental topological nature of surface conduction and possible quantum-device applications related to momentum-locked spin polarization in surface states.

Edge and interfacial states in a two-dimensional topological insulator: Bi(111) bilayer onBi2Te2Se

The electronic states of a single Bi(111) bilayer and its edges, suggested as a two dimensional topological insulator, are investigated by scanning tunneling spectroscopy (STS) and first-principles calculations. Well-ordered bilayer films and islands with zigzag edges are grown epitaxially on a cleaved Bi

Effects of oxygen annealing on the physical properties and surface microstructures of La0.8Ba0.2MnO3 films

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Strain effects on in-plane conductance of the topological insulator Bi2Te3

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Transforming a surface state of a topological insulator by a Bi capping layer

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Local and Nonlocal Fraunhofer-like Pattern from an Edge-Stepped Topological Surface Josephson Current Distribution

Se crystal. The calculation shows that the band gap of the Bi bilayer closes with a formation of a new but small hybridization gap due to the strong interaction between Bi and Bi

Microscopic mechanism for asymmetric charge distribution in Rashba-type surface states and the origin of the energy splitting scale

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Topological phase transition and quantum spin Hall edge states of antimony few layers

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Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI

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