8 research outputs found
Proximity induced topological state in graphene
The appearance of topologically protected states at the surface of an
ordinary insulator is a rare occurrence and to date only a handful of materials
are known for having this property. An intriguing question concerns the
possibility of forming topologically protected interfaces between different
materials. Here we propose that a topological phase can be transferred to
graphene by proximity with the three-dimensional topological insulator
BiSe. By using density functional and transport theory we prove that,
at the verge of the chemical bond formation, a hybrid state forms at the
graphene/BiSe interface. The state has Dirac-cone-like dispersion at
the point and a well-defined helical spin-texture, indicating its
topologically protected nature. This demonstrates that proximity can transfer
the topological phase from BiSe to graphene.Comment: 6 pages, 4 figure
Chain metallicity and antiferro-paramagnetism competition in underdoped YBaCuO: a first principles description
We describe from advanced first principles calculations the energetics of
oxygen doping and its relation to insulator-metal transitions in underdoped
YBaCuO. We find a strong tendency of doping oxygens to order
into non-magnetic CuO chains at any . Ordering produces
one-dimensional metallic bands, while configurations with non-aligned oxygens
are insulating. The CuO planes remain insulating and
antiferromagnetic up to a threshold between =0.25 and 0.5, above which a
paramagnetic normal-metal state prevails. The in-plane antiferro-paramagnetic
competition depends on , but only weakly on the ordering state of the
chains.Comment: 4 pages, 6 figures, 2 table
"Scattered surface charge density: A tool for surface characterization"
We demonstrate the use of nonlocal scanning tunneling spectroscopic measurements to characterize the local structure of adspecies in their states where they are significantly less perturbed by the probe, which is accomplished by mapping the amplitude and phase of the scattered surface charge density. As an example, we study single-H-atom adsorption on the n-type Si(100)-(4 ? 2) surface, and demonstrate the existence of two different configurations that are distinguishable using the nonlocal approach and successfully corroborated by density functional theory
Single-Atom Based Coherent Quantum Interference Device Structure
We
describe the fabrication, operation principles, and simulation
of a coherent single-atom quantum interference device (QID) structure
on Si(100) controlled by the properties of single atoms. The energy
and spatial distribution of the wave functions associated with the
device are visualized by scanning tunneling spectroscopy and the amplitude
and phase of the evanescent wave functions that couple into the quantum
well states are directly measured, including the action of an electrostatic
gate. Density functional theory simulations were employed to simulate
the electronic structure of the device structure, which is in excellent
agreement with the measurements. Simulations of device transmission
demonstrate that our coherent single-atom QID can have ON-OFF ratios
in excess of 10<sup>3</sup> with potentially minimal power dissipation