208 research outputs found
Time relaxation of microwave second order response of superconductors in the critical state
Relaxation of the microwave second order response of YBa2Cu3O7 and
Ba0.6K0.4BiO3 crystals in the critical state is studied. The samples are
exposed to static and pulsed microwave magnetic fields. The second harmonic
signals decay during the time in which the microwave pulse endures. The decay
times depend on the supercon-ductor investigated and on the way the value of
the static field has been reached.Comment: 2 pages, 1 figur
Electron Spin-Lattice Relaxation of Er3+ ions in Er0.01Y0.99Ba2Cu3Ox
The temperature dependence of the electron spin-lattice relaxation SLR was
studied in Er0.01Y0.99Ba2Cu3Ox compounds. The data derived from the electron
spin resonance ESR and SLR measurements were compared to those from inelastic
neutron scattering studies. SLR of Er3+ ions in the temperature range from 20 K
to 65 K can be explained by the resonant phonon relaxation process with the
involvement of the lowest excited crystalline-electric-field electronic states
of Er3+. These results are consistent with a local phase separation effects.
Possible mechanisms of the ESR line broadening at lower temperatures are
discussed. Keywords: YBCO; EPR; ESR; Electron spin-lattice relaxation time, T ;
Crystalline-electric-fieldComment: 6 pages, 4 figure
Spin dynamic simulations of solid effect DNP: the role of the relaxation superoperator
Relaxation plays a crucial role in the spin dynamics of dynamic nuclear polarisation. We review here two different strategies that have recently been used to incorporate relaxation in models to predict the spin dynamics of solid effect dynamic nuclear polarisation. A detailed explanation is provided how the Lindblad-Kossakowski form of the master equation can be used to describe relaxation in a spin system. Fluctuations of the spin interactions with the environment as a cause of relaxation are discussed and it is demonstrated how the relaxation superoperator acting in Liouville space on the density operator can be derived in the Lindblad-Kossakowski form by averaging out non-secular terms in an appropriate interaction frame. Furthermore we provide a formalism for the derivation of the relaxation superoperator starting with a choice of a basis set in Hilbert space. We show that the differences in the prediction of the nuclear polarisation dynamics that are found for certain parameter choices arise from the use of different interaction frames in the two different strategies. In addition we provide a summary of different relaxation mechanism that need to be considered to obtain more realistic spin dynamic simulations of solid effect dynamic nuclear polarisation
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
Dynamic nuclear polarisation by thermal mixing: quantum theory and macroscopic simulations
A theory of dynamic nuclear polarisation (DNP) by thermal mixing is suggested based on purely quantum considerations. A minimal 6-level microscopic model is developed to test the theory and link it to the well known thermodynamic model. Optimal conditions for the nuclear polarization enhancement and effects of inhomogeneous broadening of the electron resonance are discussed. Macroscopic simulations of nuclear polarization spectra displaying good agreement with experiments, involving BDPA and trityl free radicals, are presented
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
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