Biomedical subjects

P M Gehring

Publications and source records attributed to P M Gehring.

3 recordsLinked to original sources

PubMed2004

High-q-resolution neutron scattering technique using triple-axis spectrometers.

A new technique is presented that gives a substantial increase in the wavevector q resolution of triple-axis spectrometers by matching the measurement wavevector q to the reflection taua of a perfect-crystal analyzer. A relative Bragg width of deltaq/Q approximately 10(-4) can be achieved with reasonable collimation settings. This technique is very useful in measuring small structural changes and line broadenings that cannot be accurately measured with conventional set-ups, while keeping all the strengths of a triple-axis spectrometer.

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PubMed2002

Quantum impurities in the two-dimensional spin one-half Heisenberg antiferromagnet.

The study of randomness in low-dimensional quantum antiferromagnets is at the forefront of research in the field of strongly correlated electron systems, yet there have been relatively few experimental model systems. Complementary neutron scattering and numerical experiments demonstrate that the spin-diluted Heisenberg antiferromagnet La2Cu1-z(Zn,Mg)(z)O4 is an excellent model material for square-lattice site percolation in the extreme quantum limit of spin one-half. Measurements of the ordered moment and spin correlations provide important quantitative information for tests of theories for this complex quantum-impurity problem.

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PubMed2001

Soft mode dynamics above and below the Burns temperature in the relaxor Pb(Mg1/3Nb2/3)O3.

We report neutron inelastic scattering measurements of the lowest-energy transverse optic (TO) phonon branch in the relaxor Pb(Mg1/3Nb2/3)O3 from 400 to 1100 K. Far above the Burns temperature T(d) approximately 620 K we observe well-defined propagating TO modes at all wave vectors q, and a zone center TO mode that softens in a manner consistent with that of a ferroelectric soft mode. Below T(d) the zone center TO mode is overdamped. This damping extends up to, but not above, the waterfall wave vector q(wf), which is a measure of the average size of the polar nanoregions.

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