1,422 research outputs found
Novel theoretical approach in photoemission spectroscopy: application to isotope effect and boron-doped diamond
A new path-integral theory is developed to calculate the photoemission
spectra (PES) of correlated many-electron systems. The application to the study
on Bi2Sr2CaCu2O8 (Bi2212) and boron-doped diamond (BDD) is discussed in
details. It is found that the isotopic shift in the angle-resolved
photoemission spectra of Bi2212 is due to the off-diagonal quadratic
electron-phonon (e-ph) coupling, whereas the presence of electron-electron
repulsion partially suppresses this effect. For the BDD, a semiconductor-metal
phase transition, which is induced by increasing the e-ph coupling and dopant
concentration, is reproduced by our theory. Additionally, the presence of Fermi
edge and phonon step-like structure in PES is found to be due to a co-existence
of itinerant and localized electronic states in BDD.Comment: 6 pages, 4 figures, Procs. of LEHTSC 2007, submitted to J. Phys.:
Conf. Se
Coherent dynamics of photoinduced nucleation processes
We study the dynamics of initial nucleation processes of photoinduced
structural change of molecular crystals. In order to describe the nonadiabatic
transition in each molecule, we employ a model of localized electrons coupled
with a fully quantized phonon mode, and the time-dependent Schr\"odinger
equation for the model is numerically solved. We found a minimal model to
describe the nucleation induced by injection of an excited state of a single
molecule in which multiple types of intermolecular interactions are required.
In this model coherently driven molecular distortion plays an important role in
the successive conversion of electronic states which leads to photoinduced
cooperative phenomena.Comment: 14 pages, 5 figure
Orbital Compass Model as an Itinerant Electron System
Two-dimensional orbital compass model is studied as an interacting itinerant
electron model. A Hubbard-type tight-binding model, from which the orbital
compass model is derived in the strong coupling limit, is identified. This
model is analyzed by the random-phase approximation (RPA) and the
self-consistent RPA methods from the weak coupling. Anisotropy for the orbital
fluctuation in the momentum space is qualitatively changed by the on-site
Coulomb interaction. This result is explained by the fact that the dominant
fluctuation is changed from the intra-band nesting to the inter-band one by
increasing the interaction.Comment: 7 pages, 8 figure
Fermionic response from fractionalization in an insulating two-dimensional magnet
Conventionally ordered magnets possess bosonic elementary excitations, called
magnons. By contrast, no magnetic insulators in more than one dimension are
known whose excitations are not bosons but fermions. Theoretically, some
quantum spin liquids (QSLs) -- new topological phases which can occur when
quantum fluctuations preclude an ordered state -- are known to exhibit Majorana
fermions as quasiparticles arising from fractionalization of spins. Alas,
despite much searching, their experimental observation remains elusive. Here,
we show that fermionic excitations are remarkably directly evident in
experimental Raman scattering data across a broad energy and temperature range
in the two-dimensional material -RuCl. This shows the importance of
magnetic materials as hosts of Majorana fermions. In turn, this first
systematic evaluation of the dynamics of a QSL at finite temperature emphasizes
the role of excited states for detecting such exotic properties associated with
otherwise hard-to-identify topological QSLs.Comment: 5 pages, 3 figure
Doubly degenerate orbital system in honeycomb lattice: Implication of orbital state in layered iron oxide
Electronic structure and electric-field gradients analysis in
Electric field gradients (EFG's) were calculated for the compound at
both and sites. The calculations were performed within
the density functional theory (DFT) using the augmented plane waves plus local
orbital (APW+lo) method employing the so-called LDA+U scheme. The
compound were treated as nonmagnetic, ferromagnetic, and antiferromagnetic
cases. Our result shows that the calculated EFG's are dominated at the
site by the Ce-4f states. An approximately linear relation is
intuited between the main component of the EFG's and total density of states
(DOS) at Fermi level. The EFG's from our LDA+U calculations are in better
agreement with experiment than previous EFG results, where appropriate
correlations had not been taken into account among 4f-electrons. Our result
indicates that correlations among 4f-electrons play an important role in this
compound and must be taken into account
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