165 research outputs found
Topological Solitons versus Nonsolitonic Phase Defects in a 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 fourfold 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. DOI: 10.1103/PhysRevLett.109.246802X1115sciescopu
Restructure science in South Korea
A switch to projects led by independent principal investigators would build on the success of the nation's centralized research agenda, urges Han Woong Yeom. © 2018 Nature.11Ysciescopu
Radial Band Structure of Electrons in Liquid Metals
The electronic band structure of a liquid metal was investigated by measuring
precisely the evolution of angle-resolved photoelectron spectra during the
melting of a Pb monolayer on a Si(111) surface. We found that the liquid
monolayer exhibits a free-electron-like band and it undergoes a coherent radial
scattering, imposed by the radial correlation of constituent atoms, to form a
characteristic secondary hole band. This unique double radial bands and their
gradual evolution during melting can be quantitatively reproduced, including
detailed spectral intensity profiles, with our radial scattering model based on
a theoretical prediction of 1962. Our result establishes the radial band
structure as a key concept for describing the nature of electrons in strongly
disordered states of matter.Comment: 4 pages, 4 figures, accepted to Physical Review Letter
Atomistic origin of metal versus charge-density-wave phase separation in indium atomic wires on Si(111)
We investigate in atomic scale the electronic phase separation occurring in
the well known quasi 1D charge-density wave (CDW) phase of the In atomic wire
array on a Si(111) surface. The characteristic atomic scale defects, originated
from excess In atoms, are found to be actively involved in the formation of the
phase boundary between the metallic and the CDW phases by extensive analysis of
scanning tunneling microscopy images at various temperatures. These particular
defects flip the phase of the quasi 1D CDW to impose strong local constraints
in the CDW correlation. We show that such local constraints and the substantial
interwire CDW interaction induce local condensates of CDW and the phase
separation between the metallic and the CDW phases. This work unveils the
atomistic origin of the electronic phase separation, highlighting the
importance of atomic scale structures of defects and their collective
interaction in electronically inhomogeneous materials
Topological Landscape of Competing Charge Density Waves in 2H-NbSe2
Despite decades of studies of the charge density wave (CDW) of 2H-NbSe2, the origin of its incommensurate CDW ground state has not been understood. We discover that the CDW of 2H-NbSe2 is composed of two different, energetically competing, structures. The lateral heterostructures of two CDWs are entangled as topological excitations, which give rise to a CDW phase shift and the incommensuration without a conventional domain wall. A partially melted network of topological excitations and their vertices explain an unusual landscape of domains. The unconventional topological role of competing phases disclosed here can be widely applied to various incommensuration or phase coexistence phenomena in materials. © 2019 American Physical Societ
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