7,350 research outputs found
Metallic and Insulating Adsorbates on Graphene
We directly compare the effect of metallic titanium (Ti) and insulating
titanium dioxide (TiO2) on the transport properties of single layer graphene.
The deposition of Ti results in substantial n-type doping and a reduction of
graphene mobility by charged impurity scattering. Subsequent exposure to oxygen
largely reduces the doping and scattering by converting Ti into TiO2. In
addition, we observe evidence for short-range scattering by TiO2 impurities.
These results illustrate the contrasting scattering mechanisms for identical
spatial distributions of metallic and insulating adsorbates
Mott transitions in two-orbital Hubbard systems
We investigate the Mott transitions in two-orbital Hubbard systems. Applying
the dynamical mean field theory and the self-energy functional approach, we
discuss the stability of itinerant quasi-particle states in each band. It is
shown that separate Mott transitions occur at different Coulomb interaction
strengths in general. On the other hand, if some special conditions are
satisfied for the interactions, spin and orbital fluctuations are equally
enhanced at low temperatures, resulting in a single Mott transition. The phase
diagrams are obtained at zero and finite temperatures. We also address the
effect of the hybridization between two orbitals, which induces the Kondo-like
heavy fermion states in the intermediate orbital-selective Mott phase.Comment: 21 Pages, 17 Figures, to appear in Progress of Theoretical Physics
(YKIS2004 Proceedings
Graphene Spintronics
The isolation of graphene has triggered an avalanche of studies into the
spin-dependent physical properties of this material, as well as graphene-based
spintronic devices. Here we review the experimental and theoretical
state-of-art concerning spin injection and transport, defect-induced magnetic
moments, spin-orbit coupling and spin relaxation in graphene. Future research
in graphene spintronics will need to address the development of applications
such as spin transistors and spin logic devices, as well as exotic physical
properties including topological states and proximity-induced phenomena in
graphene and other 2D materials.Comment: 47 Pages, 6 figure
Unveiling hidden topological phases of a one-dimensional Hadamard quantum walk
Quantum walks, whose dynamics is prescribed by alternating unitary coin and
shift operators, possess topological phases akin to those of Floquet
topological insulators, driven by a time-periodic field. While there is ample
theoretical work on topological phases of quantum walks where the coin
operators are spin rotations, in experiments a different coin, the Hadamard
operator is often used instead. This was the case in a recent photonic quantum
walk experiment, where protected edge states were observed between two bulks
whose topological invariants, as calculated by the standard theory, were the
same. This hints at a hidden topological invariant in the Hadamard quantum
walk. We establish a relation between the Hadamard and the spin rotation
operator, which allows us to apply the recently developed theory of topological
phases of quantum walks to the one-dimensional Hadamard quantum walk. The
topological invariants we derive account for the edge state observed in the
experiment, we thus reveal the hidden topological invariant of the
one-dimensional Hadamard quantum walk.Comment: 11 pages, 4 figure
Zero-temperature Phase Diagram of Two Dimensional Hubbard Model
We investigate the two-dimensional Hubbard model on the triangular lattice
with anisotropic hopping integrals at half filling. By means of a self-energy
functional approach, we discuss how stable the non-magnetic state is against
magnetically ordered states in the system. We present the zero-temperature
phase diagram, where the normal metallic state competes with magnetically
ordered states with and structures. It is shown
that a non-magnetic Mott insulating state is not realized as the ground state,
in the present framework, but as a meta-stable state near the magnetically
ordered phase with structure.Comment: 4 pages, 4 figure
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