1,007 research outputs found
Renormalization of f-levels away from the Fermi energy in electron excitation spectroscopies: Density functional results of NdCeCuO
Relaxation energies for photoemission, when an occupied electronic state is
excited, and for inverse photoemission, when an empty state is filled, are
calculated within the density functional theory with application to
NdCeCuO. The associated relaxation energies are obtained by
computing differences in total energies between the ground state and an excited
state in which one hole or electron is added into the system. The relaxation
energies of f-electrons are found to be of the order of several eV's,
indicating that f-bands will appear substantially away from the Fermi energy
() in their spectroscopic images, even if these bands lie near . Our
analysis explains why it would be difficult to observe f electrons at the
even in the absence of strong electronic correlations.Comment: 6 pages, 1 figure, 1 tabl
Proposal to determine the Fermi-surface topology of a doped iron-based superconductor using bulk-sensitive Fourier-transform Compton scattering
We have carried out first-principles calculations of the Compton scattering
spectra to demonstrate that the filling of the hole Fermi surface in
LaOFFeAs produces a distinct signature in the Fourier transformed
Compton spectrum when the momentum transfer vector lies along the [100]
direction. We thus show how the critical concentration , where hole Fermi
surface pieces are filled up and the superconductivity mediated by
antiferromagnetic spin fluctuations is expected to be suppressed, can be
obtained in a bulk-sensitive manner.Comment: 4 pages, 6 figures, accepted in Physical Review
Electronic structure and magnetism of FeVX (X = Si, Ga and Al) alloys by the KKR-CPA method
We present first principles charge- and spin-selfconsistent electronic
structure computations on the Heusler-type disordered alloys FeVX
for three different metalloids X=(Si, Ga and Al). In these calculations we use
the methodology based on the Korringa-Kohn- Rostoker formalism and the
coherent-potential approximation (KKR-CPA), generalized to treat disorder in
multi-component complex alloys.Comment: RevTeX, 17 pages, 15 figures, to appear in Phys. Rev. B on Nov. 15
199
Entropic Origin of Pseudogap Physics and a Mott-Slater Transition in Cuprates
We propose a new approach to understand the origin of the pseudogap in the
cuprates, in terms of bosonic entropy. The near-simultaneous softening of a
large number of different -bosons yields an extended range of short-range
order, wherein the growth of magnetic correlations with decreasing temperature
is anomalously slow. These entropic effects cause the spectral weight
associated with the Van Hove singularity (VHS) to shift rapidly and nearly
linearly toward half filling at higher , consistent with a picture of the
VHS driving the pseudogap transition at a temperature . As a
byproduct, we develop an order-parameter classification scheme that predicts
supertransitions between families of order parameters. As one example, we find
that by tuning the hopping parameters, it is possible to drive the cuprates
across a {\it transition between Mott and Slater physics}, where a
spin-frustrated state emerges at the crossover.Comment: 24 pgs, 15 figs + Supp. Material [6pgs, 3 figs]. Major revision of
arXiv:1505.0477
Raising Bi-O bands above the Fermi energy level of hole-doped BiSrCaCuO and other cuprate superconductors
The Fermi surface (FS) of BiSrCaCuO
(Bi2212) predicted by band theory displays Bi-related pockets around the
point, which have never been observed experimentally. We show that
when the effects of hole doping either by substituting Pb for Bi or by adding
excess O in Bi2212 are included, the Bi-O bands are lifted above the Fermi
energy () and the resulting first-principles FS is in remarkable accord
with measurements. With decreasing hole-doping the Bi-O bands drop below
and the system self-dopes below a critical hole concentration. Computations on
other Bi- as well as Tl- and Hg-based compounds indicate that lifting of the
cation-derived band with hole doping is a general property of the electronic
structures of the cuprates.Comment: 4 pages, 4 figures; PRL (2006, in press
The Resonating-Valence-Bond Ground State of Li Nanoclusters
We have performed Diffusion Quantum Monte Carlo simulations of Li clusters
showing that Resonating-Valence-Bond (RVB) pairing correlations between
electrons provide a substantial contribution to the cohesive energy. The RVB
effects are identified in terms of electron transfers from s- to p-like
character, constituting a possible explanation for the breakdown of the Fermi
liquid picture observed in recent high resolution Compton scattering
experiments for bulk Li.Comment: 4 pages, 2 figures, 3 table
Direct observation of localization in the minority-spin-band electrons of magnetite below the Verwey temperature
Two-dimensional spin-uncompensated momentum density distributions, s, were reconstructed in magnetite at 12K and 300K from
several measured directional magnetic Compton profiles. Mechanical de-twinning
was used to overcome severe twinning in the single crystal sample below the
Verwey transition. The reconstructed in the first
Brillouin zone changes from being negative at 300 K to positive at 12 K. This
result provides the first clear evidence that electrons with low momenta in the
minority spin bands in magnetite are localized below the Verwey transition
temperature.Comment: 13 pages, 4 figures, accepted in Physical Review
Single-Dirac-Cone topological surface states in TlBiSe2 class of Topological Insulators
We have investigated several strong spin-orbit coupling ternary chalcogenides
related to the (Pb,Sn)Te series of compounds. Our first-principles calculations
predict the low temperature rhombohedral ordered phase in TlBiTe2, TlBiSe2, and
TlSbX2 (X=Te, Se, S) to be topologically Kane-Mele Z2 = -1 nontrivial. We
identify the specific surface termination that realizes the single Dirac cone
through first-principles surface state computations. This termination minimizes
effects of dangling bonds making it favorable for photoemission (ARPES)
experiments. Our analysis predicts that thin films of these materials would
harbor novel 2D quantum spin Hall states, and support odd-parity topological
superconductivity. For a related work also see arXiv:1003.2615v1. Experimental
ARPES results will be published elsewhere.Comment: Accepted for publication in Phys. Rev. Lett. (2010). Submitted March
201
A Novel 2D Folding Technique for Enhancing Fermi Surface Signatures in the Momentum Density: Application to Compton Scattering Data from an Al-3at%Li Disordered Alloy
We present a novel technique for enhancing Fermi surface (FS) signatures in
the 2D distribution obtained after the 3D momentum density in a crystal is
projected along a specific direction in momentum space. These results are
useful for investigating fermiology via high resolution Compton scattering and
positron annihilation spectroscopies. We focus on the particular case of the
(110) projection in an fcc crystal where the standard approach based on the use
of the Lock-Crisp-West (LCW) folding theorem fails to give a clear FS image due
to the strong overlap with FS images obtained through projection from higher
Brillouin zones. We show how these superposed FS images can be disentangled by
using a selected set of reciprocal lattice vectors in the folding process. The
applicability of our partial folding scheme is illustrated by considering
Compton spectra from an Al-3at%Li disordered alloy single crystal. For this
purpose, high resolution Compton profiles along nine directions in the (110)
plane were measured. Corresponding highly accurate theoretical profiles in
Al-3at%Li were computed within the local density approximation (LDA)-based
Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA)
first-principles framework. A good level of overall accord between theory and
experiment is obtained, some expected discrepancies reflecting electron
correlation effects notwithstanding, and the partial folding scheme is shown to
yield a clear FS image in the (110) plane in Al-3%Li.Comment: 24 pages, 8 figures, to appear in Phys. Rev.
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