8,365 research outputs found
Probing 5f-state configurations in URu2Si2 with U L3-edge resonant x-ray emission spectroscopy
Resonant x-ray emission spectroscopy (RXES) was employed at the U L3
absorption edge and the La1 emission line to explore the 5f occupancy, nf, and
the degree of 5f orbital delocalization in the hidden order compound URu2Si2.
By comparing to suitable reference materials such as UF4, UCd11, and alpha-U,
we conclude that the 5f orbital in URu2Si2 is at least partially delocalized
with nf = 2.87 +/- 0.08, and does not change with temperature down to 10 K
within the estimated error. These results place further constraints on
theoretical explanations of the hidden order, especially those requiring a
localized f2 ground state.Comment: 11 pages,7 figure
Spin dynamics in high-mobility two-dimensional electron systems
Understanding the spin dynamics in semiconductor heterostructures is highly
important for future semiconductor spintronic devices. In high-mobility
two-dimensional electron systems (2DES), the spin lifetime strongly depends on
the initial degree of spin polarization due to the electron-electron
interaction. The Hartree-Fock (HF) term of the Coulomb interaction acts like an
effective out-of-plane magnetic field and thus reduces the spin-flip rate. By
time-resolved Faraday rotation (TRFR) techniques, we demonstrate that the spin
lifetime is increased by an order of magnitude as the initial spin polarization
degree is raised from the low-polarization limit to several percent. We perform
control experiments to decouple the excitation density in the sample from the
spin polarization degree and investigate the interplay of the internal HF field
and an external perpendicular magnetic field. The lifetime of spins oriented in
the plane of a [001]-grown 2DES is strongly anisotropic if the Rashba and
Dresselhaus spin-orbit fields are of the same order of magnitude. This
anisotropy, which stems from the interference of the Rashba and the Dresselhaus
spin-orbit fields, is highly density-dependent: as the electron density is
increased, the kubic Dresselhaus term becomes dominant and reduces the
anisotropy.Comment: 13 pages, 6 figure
Site Index Prediction for Willow and Cherrybark Oaks in East Texas Bottomland Forests
Estimating site quality for a specific tree species is an important tool in forest management. While intensively managed pine species are often the focus of site quality studies using site index, hardwood species found in bottomland hardwood sites are often lacking in quality growth prediction equations. Two valuable hardwood species, willow oak (Quercus phellos) and cherrybark oak (Q. pagoda), are of interest for forest managers of east Texas bottomland sites. The objective of this study was to develop site index prediction equations and curves for these two species. Using height and age data from 267 cherrybark oaks and 460 willow oaks collected from sites across east Texas, remarkably similar equations were developed, with coefficient of determination (R2 ) of 0.63 for cherrybark oak and 0.52 for willow oak
Mean-Field Description of Phase String Effect in the Model
A mean-field treatment of the phase string effect in the model is
presented. Such a theory is able to unite the antiferromagnetic (AF) phase at
half-filling and metallic phase at finite doping within a single theoretical
framework. We find that the low-temperature occurrence of the AF long range
ordering (AFLRO) at half-filling and superconducting condensation in metallic
phase are all due to Bose condensations of spinons and holons, respectively, on
the top of a spin background described by bosonic resonating-valence-bond (RVB)
pairing. The fact that both spinon and holon here are bosonic objects, as the
result of the phase string effect, represents a crucial difference from the
conventional slave-boson and slave-fermion approaches. This theory also allows
an underdoped metallic regime where the Bose condensation of spinons can still
exist. Even though the AFLRO is gone here, such a regime corresponds to a
microscopic charge inhomogeneity with short-ranged spin ordering. We discuss
some characteristic experimental consequences for those different metallic
regimes. A perspective on broader issues based on the phase string theory is
also discussed.Comment: 18 pages, five figure
Spin-charge separation in the single hole doped Mott antiferromagnet
The motion of a single hole in a Mott antiferromagnet is investigated based
on the t-J model. An exact expression of the energy spectrum is obtained, in
which the irreparable phase string effect [Phys. Rev. Lett. 77, 5102 (1996)] is
explicitly present. By identifying the phase string effect with spin backflow,
we point out that spin-charge separation must exist in such a system: the doped
hole has to decay into a neutral spinon and a spinless holon, together with the
phase string. We show that while the spinon remains coherent, the holon motion
is deterred by the phase string, resulting in its localization in space. We
calculate the electron spectral function which explains the line shape of the
spectral function as well as the ``quasiparticle'' spectrum observed in
angle-resolved photoemission experiments. Other analytic and numerical
approaches are discussed based on the present framework.Comment: 16 pages, 9 figures; references updated; to appear in Phys. Rev.
Multi-subband effect in spin dephasing in semiconductor quantum wells
Multi-subband effect on spin precession and spin dephasing in -type GaAs
quantum wells is studied with electron-electron and electron-phonon scattering
explicitly included. The effects of temperature, well width and applied
electric field (in hot-electron regime) on the spin kinetics are thoroughly
investigated. It is shown that due to the strong inter-subband scattering, the
spin procession and the spin dephasing rate of electrons in different subbands
are almost identical despite the large difference in the D'yakonov-Perel' (DP)
terms of different subbands. It is also shown that for quantum wells with small
well width at temperatures where only the lowest subband is occupied, the spin
dephasing time increases with the temperature as well as the applied in-plane
electric field until the contribution from the second subband is no longer
negligible. For wide quantum wells the spin dephasing time tends to decrease
with the temperature and the electric field.Comment: 6 pages, 4 figures in eps forma
Mott physics, sign structure, ground state wavefunction, and high-Tc superconductivity
In this article I give a pedagogical illustration of why the essential
problem of high-Tc superconductivity in the cuprates is about how an
antiferromagnetically ordered state can be turned into a short-range state by
doping. I will start with half-filling where the antiferromagnetic ground state
is accurately described by the Liang-Doucot-Anderson (LDA) wavefunction. Here
the effect of the Fermi statistics becomes completely irrelevant due to the no
double occupancy constraint. Upon doping, the statistical signs reemerge,
albeit much reduced as compared to the original Fermi statistical signs. By
precisely incorporating this altered statistical sign structure at finite
doping, the LDA ground state can be recast into a short-range antiferromagnetic
state. Superconducting phase coherence arises after the spin correlations
become short-ranged, and the superconducting phase transition is controlled by
spin excitations. I will stress that the pseudogap phenomenon naturally emerges
as a crossover between the antiferromagnetic and superconducting phases. As a
characteristic of non Fermi liquid, the mutual statistical interaction between
the spin and charge degrees of freedom will reach a maximum in a
high-temperature "strange metal phase" of the doped Mott insulator.Comment: 12 pages, 12 figure
Entanglement renormalization of anisotropic XY model
The renormalization group flows of the one-dimensional anisotropic XY model
and quantum Ising model under a transverse field are obtained by different
multiscale entanglement renormalization ansatz schemes. It is shown that the
optimized disentangler removes the short-range entanglement by rotating the
system in the parameter space spanned by the anisotropy and the magnetic field.
It is understood from the study that the disentangler reduces the entanglement
by mapping the system to another one in the same universality class but with
smaller short range entanglement. The phase boundary and corresponding critical
exponents are calculated using different schemes with different block sizes,
look-ahead steps and truncation dimensions. It is shown that larger truncation
dimension leads to more accurate results and that using larger block size or
look-ahead step improve the overall calculation consistency.Comment: 5 pages, 3 figure
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