523 research outputs found
Direct Observation of High-Spin States in Manganese Dimer and Trimer Cations by X-ray Magnetic Circular Dichroism Spectroscopy in an Ion Trap
The electronic structure and magnetic moments of free Mn and Mn
are characterized by x-ray absorption and x-ray magnetic circular
dichroism spectroscopy in a cryogenic ion trap that is coupled to a synchrotron
radiation beamline. Our results show directly that localized magnetic moments
of 5 are created by states at each ionic core,
which are coupled in parallel to form molecular high-spin states via indirect
exchange that is mediated in both cases by a delocalized valence electron in a
singly-occupied derived orbital with an unpaired spin. This leads to total
magnetic moments of 11 for Mn and 16 for Mn, with
no contribution of orbital angular momentum
Soft landing of size selected clusters in rare gas matrices
Soft landing of mass selected clusters in rare gas matrices is a technique used to preserve mass selection in cluster deposition. To prevent fragmentation upon deposition, the substrate is covered with rare gas matrices to dissipate the cluster kinetic energy upon impact. Theoretical and experimental studies demonstrate the power of this technique. Besides STM, optical absorption, excitation, and fluorescence experiments, x-ray absorption at core levels can be used as a tool to study soft landing conditions, as will be shown here. X-ray absorption spectroscopy is also well suited to follow diffusion and agglomeration of clusters on surfaces via energy shifts in core level absorption
External validity of a prediction rule for residual mass histology in testicular cancer: An evaluation for good prognosis patients
We assessed the external validity of a prediction rule for nonseminomatous testicular cancer patients. The rule was developed to predict the probability of retroperitoneal metastases being benign (only necrosis/fibrosis) after chemotherapy treatment. Patients with a high probability of benign residual masses might be offered surveillance as opp
Spin relaxation in (110) and (001) InAs/GaSb superlattices
We report an enhancement of the electron spin relaxation time (T1) in a (110)
InAs/GaSb superlattice by more than an order of magnitude (25 times) relative
to the corresponding (001) structure. The spin dynamics were measured using
polarization sensitive pump probe techniques and a mid-infrared, subpicosecond
PPLN OPO. Longer T1 times in (110) superlattices are attributed to the
suppression of the native interface asymmetry and bulk inversion asymmetry
contributions to the precessional D'yakonov Perel spin relaxation process.
Calculations using a nonperturbative 14-band nanostructure model give good
agreement with experiment and indicate that possible structural inversion
asymmetry contributions to T1 associated with compositional mixing at the
superlattice interfaces may limit the observed spin lifetime in (110)
superlattices. Our findings have implications for potential spintronics
applications using InAs/GaSb heterostructures.Comment: 4 pages, 2 figure
Electron Spin Decoherence in Bulk and Quantum Well Zincblende Semiconductors
A theory for longitudinal (T1) and transverse (T2) electron spin coherence
times in zincblende semiconductor quantum wells is developed based on a
non-perturbative nanostructure model solved in a fourteen-band restricted basis
set. Distinctly different dependences of coherence times on mobility,
quantization energy, and temperature are found from previous calculations.
Quantitative agreement between our calculations and measurements is found for
GaAs/AlGaAs, InGaAs/InP, and GaSb/AlSb quantum wells.Comment: 11 pages, 3 figure
Intersubband spin-density excitations in quantum wells with Rashba spin splitting
In inversion-asymmetric semiconductors, spin-orbit coupling induces a
k-dependent spin splitting of valence and conduction bands, which is a
well-known cause for spin decoherence in bulk and heterostructures.
Manipulating nonequilibrium spin coherence in device applications thus requires
understanding how valence and conduction band spin splitting affects carrier
spin dynamics. This paper studies the relevance of this decoherence mechanism
for collective intersubband spin-density excitations (SDEs) in quantum wells. A
density-functional formalism for the linear spin-density matrix response is
presented that describes SDEs in the conduction band of quantum wells with
subbands that may be non-parabolic and spin-split due to bulk or structural
inversion asymmetry (Rashba effect). As an example, we consider a 40 nm
GaAs/AlGaAs quantum well, including Rashba spin splitting of the conduction
subbands. We find a coupling and wavevector-dependent splitting of the
longitudinal and transverse SDEs. However, decoherence of the SDEs is not
determined by subband spin splitting, due to collective effects arising from
dynamical exchange and correlation.Comment: 10 pages, 4 figure
Experimental and theoretical near edge x ray absorption fine structure studies of NO
Experimental near edge x ray absorption fine structure NEXAFS spectra of the nitrosonium NO ion are presented and theoretically analyzed. While neutral NO has an open shell, the cation is a closed shell species, which for NEXAFS leads to the simplicity of a closed shell spectrum. Compared to neutral NO, the electrons in the cation experience a stronger Coulomb potential, which introduces a shift of the ionization potential towards higher energies, a depletion of intensity in a large interval above the amp; 960; amp; 8727; resonance, and a shift of the amp; 963; amp; 8727; resonance from the continuum to below the ionization threshold. NEXAFS features at the nitrogen and oxygen K edges of NO are compared, as well as NEXAFS features at the nitrogen edges of the isoelectronic closed shell species NO , N2, and N2
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares
We review basic theoretical concepts in particle acceleration, with
particular emphasis on processes likely to occur in regions of magnetic
reconnection. Several new developments are discussed, including detailed
studies of reconnection in three-dimensional magnetic field configurations
(e.g., current sheets, collapsing traps, separatrix regions) and stochastic
acceleration in a turbulent environment. Fluid, test-particle, and
particle-in-cell approaches are used and results compared. While these studies
show considerable promise in accounting for the various observational
manifestations of solar flares, they are limited by a number of factors, mostly
relating to available computational power. Not the least of these issues is the
need to explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A brief
prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
- …