283 research outputs found
Magnetic Ground State of PrLaCeCuO with Varied Oxygen Depletion Probed by Muon Spin Relaxation
The magnetic ground state of an electron-doped cuprate superconductor
PrLaCeCuO () has been
studied by means of muon spin rotation/relaxation (\msr) over a wide variety of
oxygen depletion, . Appearance of weak random magnetism
over entire crystal volume has been revealed by a slow exponential relaxation.
The absence of -dependence for the random magnetism and the multiplet
pattern of muon Knight shift at higher fields strongly suggest that the random
moments are associated with excited Pr ions under crystal electric
field.Comment: 6 pages, 4 figures, submitted to J. Phys. Soc. Jp
DETERMINATION OF THE THIXOCASTING TEMPERATURES OF AZ91D AND OTHER Mg ALLOYS USING A QUENCHING METHOD
Magnons in real materials from density-functional theory
We present an implementation of the adiabatic spin-wave dynamics of Niu and
Kleinman. This technique allows to decouple the spin and charge excitations of
a many-electron system using a generalization of the adiabatic approximation.
The only input for the spin-wave equations of motion are the energies and Berry
curvatures of many-electron states describing frozen spin spirals. The latter
are computed using a newly developed technique based on constrained
density-functional theory, within the local spin density approximation and the
pseudo-potential plane-wave method. Calculations for iron show an excellent
agreement with experiments.Comment: 1 LaTeX file and 1 postscript figur
Electron-phonon coupling induced pseudogap and the superconducting transition in Ba0.67K0.33BiO3
We study the single particle density of states (DOS) across the
superconducting transition (Tc = 31 K) in single-crystal Ba0.67K0.33BiO3 using
ultrahigh resolution angle-integrated photoemission spectroscopy. The
superconducting gap opens with a pile-up in the DOS, Delta(5.3 K) = 5.2 meV and
2Delta(0)/kBTc = 3.9. In addition, we observe a pseudogap below and above Tc,
occurring as a suppression in intensity over an energy scale up to the
breathing mode phonon(~ 70 meV). The results indicate electron-phonon coupling
induces a pseudogap in Ba0.67K0.33BiO3.Comment: 5 pages with 4 figures, submitted to Phys. Rev. Let
Linear Response Calculations of Spin Fluctuations
A variational formulation of the time--dependent linear response based on the
Sternheimer method is developed in order to make practical ab initio
calculations of dynamical spin susceptibilities of solids. Using gradient
density functional and a muffin-tin-orbital representation, the efficiency of
the approach is demonstrated by applications to selected magnetic and strongly
paramagnetic metals. The results are found to be consistent with experiment and
are compared with previous theoretical calculations.Comment: 11 pages, RevTex; 3 Figures, postscript, high-resolution printing
(~1200dpi) is desire
The Hydration Structure at Yttria-Stabilized Cubic Zirconia (110)-Water Interface with Sub-Angstrom Resolution
The interfacial hydration structure of yttria-stabilized cubic zirconia (110) surface in contact with water was determined with ~0.5 Å resolution by high-resolution X-ray reflectivity measurement. The terminal layer shows a reduced electron density compared to the following substrate lattice layers, which indicates there are additional defects generated by metal depletion as well as intrinsic oxygen vacancies, both of which are apparently filled by water species. Above this top surface layer, two additional adsorbed layers are observed forming a characteristic interfacial hydration structure. The first adsorbed layer shows abnormally high density as pure water and likely includes metal species, whereas the second layer consists of pure water. The observed interfacial hydration structure seems responsible for local equilibration of the defective surface in water and eventually regulating the long-term degradation processes. The multitude of water interactions with the zirconia surface results in the complex but highly ordered interfacial structure constituting the reaction front.ope
Phase diagram of the one-dimensional extended attractive Hubbard model for large nearest-neighbor repulsion
We consider the extended Hubbard model with attractive on-site interaction U
and nearest-neighbor repulsions V. We construct an effective Hamiltonian
H_{eff} for hopping t<<V and arbitrary U<0. Retaining the most important terms,
H_{eff} can be mapped onto two XXZ models, solved by the Bethe ansatz. The
quantum phase diagram shows two Luttinger liquid phases and a region of phase
separation between them. For density n<0.422 and U<-4, singlet superconducting
correlations dominate at large distances. For some parameters, the results are
in qualitative agreement with experiments in BaKBiO.Comment: 6 pages, 3 figures, submitted to Phys. Rev.
Heavy Fermion scaling: Uranium versus Cerium and Ytterbium compounds
In an effort to explore the differences between rare-earth-based and
uranium-based heavy Fermion (HF) compounds that reflect the underlying
difference between local 4 moments and itinerant 5 moments we analyze
scaling laws that relate the low temperature neutron spectra of the primary
("Kondo-esque") spin fluctuation to the specific heat and susceptibility. While
the scaling appears to work very well for the rare earth intermediate valence
compounds, for a number of key uranium compounds the scaling laws fail badly.
There are two main reasons for this failure. First, the presence of
antiferromagnetic (AF) fluctuations, which contribute significantly to the
specific heat, alters the scaling ratios. Second, the scaling laws require
knowledge of the high temperature moment degeneracy, which is often
undetermined for itinerant 5 electrons. By making plausible corrections for
both effects, better scaling ratios are obtained for some uranium compounds. We
point out that while both the uranium HF compounds and the rare earth
intermediate valence (IV) compounds have spin fluctuation characteristic
energies of order 5 - 25 meV, they differ in that the AF fluctuations that are
usually seen in the U compounds are never seen in the rare earth IV compounds.
This suggests that the 5f itineracy increases the f-f exchange relative to the
rare earth case
4f-spin dynamics in La(2-x-y)Sr(x)Nd(y)CuO(4)
We have performed inelastic magnetic neutron scattering experiments on
La(2-x-y)Sr(x)Nd(y)CuO(4) in order to study the Nd 4f-spin dynamics at low
energies. In all samples we find at high temperatures a quasielastic line
(Lorentzian) with a line width which decreases on lowering the temperature. The
temperature dependence of the quasielastic line width Gamma/2(T) can be
explained with an Orbach-process, i.e. a relaxation via the coupling between
crystal field excitations and phonons. At low temperatures the Nd-4f magnetic
response S(Q,omega) correlates with the electronic properties of the
CuO(2)-layers. In the insulator La(2-y)Nd(y)CuO(4) the quasielastic line
vanishes below 80 K and an inelastic excitation occurs. This directly indicates
the splitting of the Nd3+ ground state Kramers doublet due to the static
antiferromagnetic order of the Cu moments. In La(1.7-x)Sr(x)Nd(0.3)CuO(4) with
x = 0.12, 0.15 and La(1.4-x)Sr(x)Nd(0.6)CuO(4) with x = 0.1, 0.12, 0.15, 0.18
superconductivity is strongly suppressed. In these compounds we observe a
temperature independent broad quasielastic line of Gaussian shape below T about
30 K. This suggests a distribution of various internal fields on different Nd
sites and is interpreted in the frame of the stripe model. In
La(1.8-y)Sr(0.2)Nd(y)CuO(4) (y = 0.3, 0.6) such a quasielastic broadening is
not observed even at lowest temperature.Comment: 8 pages, 10 figures included, to appear in Phys. Rev.
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