1,356 research outputs found
Absence of orbital-selective Mott transition in Ca_2-xSr_xRuO4
Quasi-particle spectra of the layer perovskite SrRuO are calculated
within Dynamical Mean Field Theory for increasing values of the on-site Coulomb
energy . At small the planar geometry splits the bands near
into a wide, two-dimensional band and two narrow, nearly
one-dimensional bands. At larger , however, the spectral
distribution of these states exhibit similar correlation features, suggesting a
common metal-insulator transition for all bands at the same critical
.Comment: 4 pages, 4 figure
Evolution of the electronic structure from electron-doped to hole-doped states in the two-dimensional Mott-Hubbard system La1.17-xPbxVS3.17
The filling-controlled metal-insulator transition (MIT) in a two-dimensional
Mott-Hubbard system La1.17-xPbxVS3.17 has been studied by photoemission
spectroscopy. With Pb substitution x, chemical potential mu abruptly jumps by ~
0.07 eV between x=0.15 and 0.17, indicating that a charge gap is opened at x ~=
0.16 in agreement with the Mott insulating state of the d2 configuration. When
holes or electrons are doped into the Mott insulator of x ~= 0.16, the gap is
filled and the photoemission spectral weight at mu, rho(mu), gradually
increases in a similar way to the electronic specific heat coefficient,
although the spectral weight remains depressed around mu compared to that
expected for a normal metal, showing a pseudogap behavior in the metallic
samples. The observed behavior of varrho(mu)->0 for x->0.16 is contrasted with
the usual picture that the electron effective mass of the Fermi-liquid system
is enhanced towards the metal-insulator boundary. With increasing temperature,
the gap or the pseudogap is rapidly filled up, and the spectra at T=300 K
appears to be almost those of a normal metal. Near the metal-insulator
boundary, the spectra around mu are consistent with the formation of a Coulomb
gap, suggesting the influence of long-range Coulomb interaction under the
structural disorder intrinsic to this system.Comment: 8 pages, 12 figure
Gradual Disappearance of the Fermi Surface near the Metal-Insulator Transition in LaSrMnO
We report the first observation of changes in the electronic structure of
LaSrMnO (LSMO) across the filling-control metal-insulator
(MI) transition by means of in situ angle-resolved photoemission spectroscopy
(ARPES) of epitaxial thin films. The Fermi surface gradually disappears near
the MI transition by transferring the spectral weight from the coherent band
near the Fermi level () to the lower Hubbard band, whereas a pseudogap
behavior also exists in the ARPES spectra in the close vicinity of for
the metallic LSMO. These results indicate that the spectral weight transfer
derived from strong electron-electron interaction dominates the gap formation
in LSMO associated with the filling-control MI transition.Comment: 11 pages, 4 figure
Domain walls with non-Abelian orientational moduli
Domain walls with non-Abelian orientational moduli are constructed in U(N)
gauge theories coupled to Higgs scalar fields with degenerate masses. The
associated global symmetry is broken by the domain walls, resulting in the
Nambu-Goldstone (and quasi-Nambu-Goldstone) bosons, which form the non-Abelian
orientational moduli. As walls separate, the wave functions of the non-Abelian
orientational moduli spread between domain walls. By taking the limit of Higgs
mass differences to vanish, we clarify the convertion of wall position moduli
into the non-Abelian orientational moduli. The moduli space metric and its
Kahler potential of the effective field theory on the domain walls are
constructed. We consider two models: a U(1) gauge theory with several charged
Higgs fields, and a U(N) gauge theory with 2N Higgs fields in the fundamental
representation. More details are found in our paper published in Phys. Rev. D77
(2008) 125008 [arXiv:0802.3135 [hep-th]].Comment: contribution to the Proceedings of he 1st MCCQG conference at Crete,
sept. 2009, to appear in Journal of Physics: Conference Series of IO
Electronic structure of NiS_{1-x}Se_x
We investigate the electronic structure of the metallic NiSSe
system using various electron spectroscopic techniques. The band structure
results do not describe the details of the spectral features in the
experimental spectrum, even for this paramagnetic metallic phase. However, a
parameterized many-body multi-band model is found to be successful in
describing the Ni~2 core level and valence band, within the same model. The
asymmetric line shape as well as the weak intensity feature in the Ni~2 core
level spectrum has been ascribed to extrinsic loss processes in the system. The
presence of satellite features in the valence band spectrum shows the existence
of the lower Hubbard band, deep inside the metallic regime, consistent
with the predictions of the dynamical mean field theory.Comment: To be published in Physical Review B, 18 pages and 5 figure
Disorder Effects in the Bipolaron System TiO Studied by Photoemission Spectroscopy
We have performed a photoemission study of TiO around its two
transition temperatures so as to cover the metallic, high-temperature
insulating (bipolaron-liquid), and low-temperature insulating
(bipolaron-crystal) phases. While the spectra of the low-temperature insulating
phase show a finite gap at the Fermi level, the spectra of the high-temperature
insulating phase are gapless, which is interpreted as a soft Coulomb gap due to
dynamical disorder. We suggest that the spectra of the high-temperature
disordered phase of FeO, which exhibits a charge order-disorder
transition (Verwey transition), can be interpreted in terms of a Coulomb gap.Comment: 4 pages, 3 epsf figures embedde
One particle spectral weight of the three dimensional single band Hubbard model
Dynamic properties of the three-dimensional single-band Hubbard model are
studied using Quantum Monte Carlo combined with the maximum entropy technique.
At half-filling, there is a clear gap in the density of states and well-defined
quasiparticle peaks at the top (bottom) of the lower (upper) Hubbard band. We
find an antiferromagnetically induced weight above the naive Fermi momentum.
Upon hole doping, the chemical potential moves to the top of the lower band
where a robust peak is observed. Results are compared with spin-density-wave
(SDW) mean-field and self consistent Born approximation results, and also with
the infinite dimensional Hubbard model, and experimental photoemission (PES)
for three dimensional transition-metal oxides.Comment: 11 pages, REVTeX, 16 figures included using psfig.sty. Ref.30
correcte
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