110 research outputs found
Nuclear spin diffusion in the semiconductor TlTaS3
We report on a 203Tl and 205Tl nuclear magnetic resonance study of the chain
ternary semiconductor TlTaS3. We show that spin-lattice relaxation in this
compound is driven by two contributions, namely by interactions of nuclear
spins with thermally activated carriers and with localized electron spins. The
latter mechanism dominates at lower temperature; at that, our measurements
provide striking manifestation of the spin-diffusion-limited relaxation regime.
The experimental data obtained allow us to estimate the spin diffusion
coefficient.Comment: 15 pages, 5 figure
Testing T Invariance in the Interaction of Slow Neutrons with Aligned Nuclei
The study of five-fold (P even, T odd) correlation in the interaction of slow
polarized neutrons with aligned nuclei is a possible way of testing the time
reversal invariance due to the expected enhancement of T violating effects in
compound resonances. Possible nuclear targets are discussed which can be
aligned both dynamically as well as by the "brute force" method at low
temperature. A statistical estimation is performed of the five-fold correlation
for low lying p wave compound resonances of the Sb, Sb and
I nuclei. It is shown that a significant improvement can be achieved
for the bound on the intensity of the fundamental parity conserving time
violating (PCTV) interaction.Comment: 22 pages, 5 figures, published versio
Obituary: Professor Alexander Kessenikh (1932-2021)
On September 15, 2021, professor Alexander V. Kessenikh died. He was known for his works on nuclear magnetic resonance (NMR) and history of science
Dynamic nuclear polarization and spin-diffusion in non-conducting solids
There has been much renewed interest in dynamic nuclear polarization (DNP),
particularly in the context of solid state biomolecular NMR and more recently
dissolution DNP techniques for liquids. This paper reviews the role of spin
diffusion in polarizing nuclear spins and discusses the role of the spin
diffusion barrier, before going on to discuss some recent results.Comment: submitted to Applied Magnetic Resonance. The article should appear in
a special issue that is being published in connection with the DNP Symposium
help in Nottingham in August 200
Enhancement of the Electron Spin Resonance of Single-Walled Carbon Nanotubes by Oxygen Removal
We have observed a nearly fourfold increase in the electron spin resonance
(ESR) signal from an ensemble of single-walled carbon nanotubes (SWCNTs) due to
oxygen desorption. By performing temperature-dependent ESR spectroscopy both
before and after thermal annealing, we found that the ESR in SWCNTs can be
reversibly altered via the molecular oxygen content in the samples. Independent
of the presence of adsorbed oxygen, a Curie-law (spin susceptibility ) is seen from 4 K to 300 K, indicating that the probed spins are
finite-level species. For both the pre-annealed and post-annealed sample
conditions, the ESR linewidth decreased as the temperature was increased, a
phenomenon we identify as motional narrowing. From the temperature dependence
of the linewidth, we extracted an estimate of the intertube hopping frequency;
for both sample conditions, we found this hopping frequency to be 100
GHz. Since the spin hopping frequency changes only slightly when oxygen is
desorbed, we conclude that only the spin susceptibility, not spin transport, is
affected by the presence of physisorbed molecular oxygen in SWCNT ensembles.
Surprisingly, no linewidth change is observed when the amount of oxygen in the
SWCNT sample is altered, contrary to other carbonaceous systems and certain 1D
conducting polymers. We hypothesize that physisorbed molecular oxygen acts as
an acceptor (-type), compensating the donor-like (-type) defects that are
responsible for the ESR signal in bulk SWCNTs.Comment: 14 pages, 7 figure
The Flux-Line Lattice in Superconductors
Magnetic flux can penetrate a type-II superconductor in form of Abrikosov
vortices. These tend to arrange in a triangular flux-line lattice (FLL) which
is more or less perturbed by material inhomogeneities that pin the flux lines,
and in high- supercon- ductors (HTSC's) also by thermal fluctuations. Many
properties of the FLL are well described by the phenomenological
Ginzburg-Landau theory or by the electromagnetic London theory, which treats
the vortex core as a singularity. In Nb alloys and HTSC's the FLL is very soft
mainly because of the large magnetic penetration depth: The shear modulus of
the FLL is thus small and the tilt modulus is dispersive and becomes very small
for short distortion wavelength. This softness of the FLL is enhanced further
by the pronounced anisotropy and layered structure of HTSC's, which strongly
increases the penetration depth for currents along the c-axis of these uniaxial
crystals and may even cause a decoupling of two-dimensional vortex lattices in
the Cu-O layers. Thermal fluctuations and softening may melt the FLL and cause
thermally activated depinning of the flux lines or of the 2D pancake vortices
in the layers. Various phase transitions are predicted for the FLL in layered
HTSC's. The linear and nonlinear magnetic response of HTSC's gives rise to
interesting effects which strongly depend on the geometry of the experiment.Comment: Review paper for Rep.Prog.Phys., 124 narrow pages. The 30 figures do
not exist as postscript file
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