136 research outputs found
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
Zoology of domain walls in quasi-2D correlated charge density wave of 1T-TaS2
Domain walls in correlated charge density wave compounds such as 1T-TaS2 can
have distinct localized states which govern physical properties and
functionalities of emerging quantum phases. However, detailed atomic and
electronic structures of domain walls have largely been elusive. We identify
using scanning tunneling microscope and density functional theory calculations
the atomic and electronic structures for a plethora of discommensuration domain
walls in 1T-TaS2 quenched metastably with nanoscale domain wall networks. The
domain walls exhibit various in-gap states within the Mott gap but metallic
states appear in only particular types of domain walls. A systematic
understanding of the domain-wall electronic property requests not only the
electron counting but also including various intertwined interactions such as
structural relaxation, electron correlation, and charge transfer. This work
guides the domain wall engineering of the functionality in correlated van der
Waals materials.Comment: 7 pages, 4 figure
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