560 research outputs found
Magnetic Anisotropy of Co2+ as Signature of Intrinsic Ferromagnetism in ZnO:Co
We report on the magnetic properties of thoroughly characterized Zn1-xCoxO
epitaxial thin films, with low Co concentration, x=0.003-0.005. Magnetic and
EPR measurements, combined with crystal field theory, reveal that isolated Co2+
ions in ZnO possess a strong single ion anisotropy which leads to an "easy
plane" ferromagnetic state when the ferromagnetic Co-Co interaction is
considered. We suggest that the peculiarities of the magnetization process of
this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co
materials.Comment: 4 pages, 4 figure
CeFePO: f-d hybridization and quenching of superconductivity
Being homologue to the new, Fe-based type of high-temperature
superconductors, CeFePO exhibits magnetism, Kondo and heavy-fermion phenomena.
We experimentally studied the electronic structure of CeFePO by means of
angle-resolved photoemission spectroscopy. In particular, contributions of the
Ce 4f-derived states and their hybridization to the Fe 3d bands were explored
using both symmetry selection rules for excitation and their photoionization
cross-section variations as a function of photon energy. It was experimentally
found - and later on confirmed by LDA as well as DMFT calculations - that the
Ce 4f states hybridize to the Fe 3d states of d_{3z^2-r^2} symmetry near the
Fermi level that discloses their participation in the occurring
electron-correlation phenomena and provides insight into mechanism of
superconductivity in oxopnictides.Comment: 5 pages, 3 figure
How chemical pressure affects the fundamental properties of rare-earth pnictides: an ARPES view
Angle-resolved photoelectron spectroscopy, supplemented by theoretical
calculations has been applied to study the electronic structure of
heavy-fermion material CeFePO, a homologue to the Fe-based high-temperature
superconductors, and CeFeAs_0.7P_0.3O, where the applied chemical pressure
results in a ferromagnetic order of the 4f moments. A comparative analysis
reveals characteristic differences in the Fe-derived band structure for these
materials, implying a rather different hybridization of valence electrons to
the localized 4f orbitals. In particular, our results suggest that the
ferromagnetism of Ce moments in CeFeAs_0.7P_0.3O is mediated mainly by Fe
3d_xz/yz orbitals, while the Kondo screening in CeFePO is instead due to a
strong interaction of Fe 3d_3z^2-r^2 orbitals.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. B (Rapid
Theory of magnetic domains in uniaxial thin films
For uniaxial easy axis films, properties of magnetic domains are usually
described within the Kittel model, which assumes that domain walls are much
thinner than the domains. In this work we present a simple model that includes
a proper description of the magnetostatic energy of domains and domain walls
and also takes into account the interaction between both surfaces of the film.
Our model describes the behavior of domain and wall widths as a function of
film thickness, and is especially well suited for the strong stripe phase. We
prove the existence of a critical value of magneto-crystalline anisotropy above
which stripe domains exist for any film thickness and justify our model by
comparison with exact results. The model is in good agreement with experimental
data for hcp cobalt.Comment: 15 pages, 7 figure
Hole motion in an arbitrary spin background: Beyond the minimal spin-polaron approximation
The motion of a single hole in an arbitrary magnetic background is
investigated for the 2D t-J model. The wavefunction of the hole is described
within a generalized string picture which leads to a modified concept of spin
polarons. We calculate the one-hole spectral function using a large string
basis for the limits of a Neel ordered and a completely disordered background.
In addition we use a simple approximation to interpolate between these cases.
For the antiferromagnetic background we reproduce the well-known quasiparticle
band. In the disordered case the shape of the spectral function is found to be
strongly momentum-dependent, the quasiparticle weight vanishes for all hole
momenta. Finally, we discuss the relevance of results for the lowest energy
eigenvalue and its dispersion obtained from calculations using a polaron of
minimal size as found in the literature.Comment: 13 pages, 8 figures, to appear in Phys. Rev.
Management of Bladder Cancer following Solid Organ Transplantation
Objective. Present our experience managing bladder cancer following liver and renal transplantation. Methods. Single institution retrospective review of patients diagnosed with bladder urothelial carcinoma (BUC) following solid organ transplantation between January 1992 and December 2007. Results. Of the 2,925 renal and 2,761 liver transplant recipients reviewed, we identified eleven patients (0.2%) following transplant diagnosed with BUC. Two patients with low grade T1 TCC were managed by TURBT. Three patients with CIS and one patient with T1 low grade BUC were treated by TURBT and adjuvant BCG. All four are alive and free of recurrence at a mean follow-up of 51 ± 22 months. One patient with T1 high grade BUC underwent radical cystectomy and remains disease free with a follow-up of 98 months. Muscle invasive TCC was diagnosed in four patients at a median of 3.6 years following transplantation. Two patients are recurrence free at 24 and 36 months following radical cystectomy. Urinary diversion and palliative XRT were performed in one patient with un-resectable disease. Conclusions. Bladder cancer is uncommon following renal and liver transplantation, but it can be managed successfully with local and/or extirpative therapy. The use of intravesical BCG is possible in select immunosuppressed patients
Spectral Boundary of Positive Random Potential in a Strong Magnetic Field
We consider the problem of randomly distributed positive delta-function
scatterers in a strong magnetic field and study the behavior of density of
states close to the spectral boundary at in both two and
three dimensions. Starting from dimensionally reduced expression of Brezin et
al. and using the semiclassical approximation we show that the density of
states in the Lifshitz tail at small energies is proportio- nal to in
two dimensions and to in three
dimensions, where is the energy and is the density of scatterers in
natural units.Comment: 12 pages, LaTex, 5 figures available upon request, to appear in Phys.
Rev.
Normal Fermi Liquid Behavior of Quasiholes in the Spin-Polaron Model for Copper Oxides
Based on the t-J model and the self-consistent Born approximation, the
damping of quasiparticle hole states near the Fermi surface is calculated in a
low doping regime. Renormalization of spin-wave excitations due to hole doping
is taken into account. The damping is shown to be described by a familiar form
characteristic of the 2-dimensional
Fermi liquid, in contrast with the earlier statement reported by Li and Gong
[Phys. Rev. B {\bf 51}, 6343 (1995)] on the marginal Fermi liquid behavior of
quasiholes
Tight-binding parameters and exchange integrals of Ba_2Cu_3O_4Cl_2
Band structure calculations for Ba_2Cu_3O_4Cl_2 within the local density
approximation (LDA) are presented. The investigated compound is similar to the
antiferromagnetic parent compounds of cuprate superconductors but contains
additional Cu_B atoms in the planes. Within the LDA, metallic behavior is found
with two bands crossing the Fermi surface (FS). These bands are built mainly
from Cu 3d_{x^2-y^2} and O 2p_{x,y} orbitals, and a corresponding tight-binding
(TB) model has been parameterized. All orbitals can be subdivided in two sets
corresponding to the A- and B-subsystems, respectively, the coupling between
which is found to be small. To describe the experimentally observed
antiferromagnetic insulating state, we propose an extended Hubbard model with
the derived TB parameters and local correlation terms characteristic for
cuprates. Using the derived parameter set we calculate the exchange integrals
for the Cu_3O_4 plane. The results are in quite reasonable agreement with the
experimental values for the isostructural compound Sr_2Cu_3O_4Cl_2.Comment: 5 pages (2 tables included), 4 ps-figure
Angle resolved photoemission spectroscopy of Sr_2CuO_2Cl_2 - a revisit
We have investigated the lowest binding-energy electronic structure of the
model cuprate Sr_2CuO_2Cl_2 using angle resolved photoemission spectroscopy
(ARPES). Our data from about 80 cleavages of Sr_2CuO_2Cl_2 single crystals give
a comprehensive, self-consistent picture of the nature of the first
electron-removal state in this model undoped CuO_2-plane cuprate. Firstly, we
show a strong dependence on the polarization of the excitation light which is
understandable in the context of the matrix element governing the photoemission
process, which gives a state with the symmetry of a Zhang-Rice singlet.
Secondly, the strong, oscillatory dependence of the intensity of the Zhang-Rice
singlet on the exciting photon-energy is shown to be consistent with
interference effects connected with the periodicity of the crystal structure in
the crystallographic c-direction. Thirdly, we measured the dispersion of the
first electron-removal states along G->(pi,pi) and G->(pi,0), the latter being
controversial in the literature, and have shown that the data are best fitted
using an extended t-J-model, and extract the relevant model parameters. An
analysis of the spectral weight of the first ionization states for different
excitation energies within the approach used by Leung et al. (Phys. Rev. B56,
6320 (1997)) results in a strongly photon-energy dependent ratio between the
coherent and incoherent spectral weight. The possible reasons for this
observation and its physical implications are discussed.Comment: 10 pages, 8 figure
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