arXiv subjects

Tae-Hwan Kim

Publications and source records attributed to Tae-Hwan Kim.

22 records · Page 2Linked to original sources

arXiv2014

Influence of Molecular Solvation on the Conformation of Star Polymers

We have used neutron scattering to investigate the influence of concentration on the conformation of a star polymer. By varying the contrast between the solvent and isotopically labeled stars, we obtain the distributions of polymer and solvent within a star polymer from analysis of scattering data. A correlation between the local desolvation and the inward folding of star branches is discovered. From the perspective of thermodynamics, we find an analogy between the mechanism of polymer localization driven by solvent depletion and that of the hydrophobic collapse of polymers in solutions.

physics.chem-ph↗

arXiv2014

Edge and Interfacial States in a 2D Topological Insulator:Bi(111) Bilayer on Bi$_{2}$Te$_{2}$Se

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$_{2}$Te$_{2}$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$_{2}$Te$_{2}$Se. Nevertheless, the topological nature of the Bi bilayer and the topological edge state are preserved only with an energy shift. The edge-enhanced local density of states are identified and visualized clearly by STS in good agreement with the calculation. This can be the sign of the topological edge state, which corresponds to the quantum spin Hall state. The interfacial state between Bi and Bi$_{2}$Te$_{2}$Se is also identified inside the band gap region. This state also exhibits the edge modulation, which was previously interpreted as the evidence of the topological edge state [F. Yang et al., Phys. Rev. Lett. 109, 016801 (2012)].

cond-mat.mes-hall↗

arXiv2013

Visualizing Atomic-Scale Negative Differential Resistance in Bilayer Graphene

We investigate the atomic-scale tunneling characteristics of bilayer graphene on silicon carbide using the scanning tunneling microscopy. The high-resolution tunneling spectroscopy reveals an unexpected negative differential resistance (NDR) at the Dirac energy, which spatially varies within the single unit cell of bilayer graphene. The origin of NDR is explained by two near-gap van Hove singularities emerging in the electronic spectrum of bilayer graphene under a transverse electric field, which are strongly localized on two sublattices in different layers. Furthermore, defects near the tunneling contact are found to strongly impact on NDR through the electron interference. Our result provides an atomic-level understanding of quantum tunneling in bilayer graphene, and constitutes a useful step towards graphene-based tunneling devices.

cond-mat.mtrl-sci↗

arXiv2012

Topological Solitons versus Non-Solitonic Phase Defects in Quasi-One-Dimensional Charge Density Wave

We investigated phase defects in a quasi-one-dimensional commensurate charge density wave (CDW) system, an In atomic wire array on Si(111), using low temperature scanning tunneling microscopy. The unique four-fold degeneracy of the CDW state leads to various phase defects, among which intrinsic solitons are clearly distinguished. The solitons exhibit a characteristic variation of the CDW amplitude with a coherence length of about 4 nm, as expected from the electronic structure, and a localized electronic state within the CDW gap. While most of the observed solitons are trapped by extrinsic defects, moving solitons are also identified and their novel interaction with extrinsic defects is disclosed.

cond-mat.mes-hall↗