Kenneth B. Lyons

Spin fluctuations and superconductivity in Ba2YCu

We report observation of spin-pair excitations in Ba/sub 2/YCu/sub 3/O/sub 6+//sub delta/, with delta in the range 0.0--0.9. The frequency of the excitations, and hence the value of the exchange constant, J = 950 cm/sup -1/, is similar to that reported recently for (nonsuperconducting) La/sub 2/CuO/sub 4/. The present observation of magnetic excitations in a superconducting material, and of their evolution as a function of delta, demonstrate a large influence of carrier concentration on the spin-fluctuation dynamics.

K‐dependent Brownian diffusion constant in a critical mixture

The K ‐dependent diffusion constant of 0.3μ Teflon particles in the critical mixture isooctane‐nitroethane has been measured for 0.001 < T − T c < 2 °C. The results are presented along with a simple theory that gives good agreement by considering the surface energy force on the particle due to concentration fluctuations.

Spin fluctuations and superconductivity in Ba/sub 2/YCu/sub 3/O/sub 6+//sub delta/

We report observation of spin-pair excitations in Ba/sub 2/YCu/sub 3/O/sub 6+//sub delta/, with delta in the range 0.0--0.9. The frequency of the excitations, and hence the value of the exchange constant, J = 950 cm/sup -1/, is similar to that reported recently for (nonsuperconducting) La/sub 2/CuO/sub 4/. The present observation of magnetic excitations in a superconducting material, and of their evolution as a function of delta, demonstrate a large influence of carrier concentration on the spin-fluctuation dynamics.

Spin fluctuations and superconductivity inBa2YCu3O6+δ

We report observation of spin-pair excitations in Ba/sub 2/YCu/sub 3/O/sub 6+//sub delta/, with delta in the range 0.0--0.9. The frequency of the excitations, and hence the value of the exchange constant, J = 950 cm/sup -1/, is similar to that reported recently for (nonsuperconducting) La/sub 2/CuO/sub 4/. The present observation of magnetic excitations in a superconducting material, and of their evolution as a function of delta, demonstrate a large influence of carrier concentration on the spin-fluctuation dynamics.