102 research outputs found
Competing periodicities in fractionally filled one-dimensional bands
We present a variable temperature Scanning Tunneling Microscopy and
Spectroscopy (STM and STS) study of the Si(553)-Au atomic chain reconstruction.
This quasi one-dimensional (1D) system undergoes at least two charge density
wave (CDW) transitions at low temperature, which can be attributed to
electronic instabilities in the fractionally-filled 1D bands of the
high-symmetry phase. Upon cooling, Si(553)-Au first undergoes a single-band
Peierls distortion, resulting in period doubling along the imaged chains. This
Peierls state is ultimately overcome by a competing tripleperiod CDW, which in
turn is accompanied by a x2 periodicity in between the chains. These locked-in
periodicities indicate small charge transfer between the nearly half-filled and
quarter-filled 1D bands. The presence and the mobility of atomic scale
dislocations in the x3 CDW state indicates the possibility of manipulating
phase solitons carrying a (spin,charge) of (1/2,+-e/3) or (0,+-2e/3).Comment: submitted, accepted for publication in Phys. Rev. Let
Theory of the "honeycomb chain-channel" reconstruction of Si(111)3x1
First-principles electronic-structure methods are used to study a structural
model for Ag/Si(111)3x1 recently proposed on the basis of transmission electron
diffraction data. The fully relaxed geometry for this model is far more
energetically favorable than any previously proposed, partly due to the unusual
formation of a Si double bond in the surface layer. The calculated electronic
properties of this model are in complete agreement with data from
angle-resolved photoemission and scanning tunneling microscopy.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Lett (the ugly postscript
error on page 4 has now been repaired
A Field Effect Transitor based on the Mott Transition in a Molecular Layer
Here we propose and analyze the behavior of a FET--like switching device, the
Mott transition field effect transistor, operating on a novel principle, the
Mott metal--insulator transition. The device has FET-like characteristics with
a low ``ON'' impedance and high ``OFF'' impedance. Function of the device is
feasible down to nanoscale dimensions. Implementation with a class of organic
charge transfer complexes is proposed.Comment: Revtex 11pages, Figures available upon reques
Formation of atom wires on vicinal silicon
The formation of atomic wires via pseudomorphic step-edge decoration on
vicinal silicon surfaces has been analyzed for Ga on the Si(112) surface using
Scanning Tunneling Microscopy and Density Functional Theory calculations. Based
on a chemical potential analysis involving more than thirty candidate
structures and considering various fabrication procedures, it is concluded that
pseudomorphic growth on stepped Si(112), both under equilibrium and
non-equilibrium conditions, must favor formation of Ga zig-zag chains rather
than linear atom chains. The surface is non-metallic and presents quasi-one
dimensional character in the lowest conduction band.Comment: submitte
Ga-induced atom wire formation and passivation of stepped Si(112)
We present an in-depth analysis of the atomic and electronic structure of the
quasi one-dimensional (1D) surface reconstruction of Ga on Si(112) based on
Scanning Tunneling Microscopy and Spectroscopy (STM and STS), Rutherford
Backscattering Spectrometry (RBS) and Density Functional Theory (DFT)
calculations. A new structural model of the Si(112)6 x 1-Ga surface is
inferred. It consists of Ga zig-zag chains that are intersected by
quasi-periodic vacancy lines or misfit dislocations. The experimentally
observed meandering of the vacancy lines is caused by the co-existence of
competing 6 x 1 and 5 x 1 unit cells and by the orientational disorder of
symmetry breaking Si-Ga dimers inside the vacancy lines. The Ga atoms are fully
coordinated, and the surface is chemically passivated. STS data reveal a
semiconducting surface and show excellent agreement with calculated Local
Density of States (LDOS) and STS curves. The energy gain obtained by fully
passivating the surface calls the idea of step-edge decoration as a viable
growth method toward 1D metallic structures into question.Comment: Submitted, 13 pages, accepted in Phys. Rev. B, notational change in
Fig.
Strain tuning of topological band order in cubic semiconductors
We theoretically explore the possibility of tuning the topological order of
cubic diamond/zinc-blende semiconductors with external strain. Based on the
tight-binding model, we analyze the evolution of the cubic semiconductor band
structure under hydrostatic or biaxial lattice expansion, by which a generic
guiding principle is established that lattice \emph{expansion} can induce a
topological phase transition of small band-gap cubic semiconductors via a band
inversion, and further breaking of the cubic symmetry leads to a topological
insulating phase. Using density functional theory calculations, we demonstrate
that a prototype topological trivial semiconductor, InSb, is converted to a
nontrivial topological semiconductor with a 2%-3% biaxial lattice expansion.Comment: 4 pages, 3 figure
Spin-triplet superconductivity in repulsive Hubbard models with disconnected Fermi surfaces: a case study on triangular and honeycomb lattices
We propose that spin-fluctuation-mediated spin-triplet superconductivity may
be realized in repulsive Hubbard models with disconnected Fermi surfaces. The
idea is confirmed for Hubbard models on triangular (dilute band filling) and
honeycomb (near half-filling) lattices using fluctuation exchange
approximation, where triplet pairing order parameter with f-wave symmetry is
obtained. Possible relevance to real superconductors is suggested.Comment: 5 pages, 6 figures, RevTeX, uses epsf.sty and multicol.st
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