Observation of anomalous dissipation in dynamics of vortices in Bi2212 in the region of 3D-2D crossover

Anomalous decrease of the amplitude of Bi 2212 single-crystal vibrations in magnetic field is observed, indicating the existence of strong damping in vortex matter in the region of 3D-2D crossover. This phenomenon occurs in the temperature region 5–35 K and at magnetic fields of 500–1500 Oe where the second-peak effect in magnetization is observed. The results are in qualitative agreement with the Monte Carlo simulation of phase transitions in a vortex system

Small-angle scattering of neutrons on normal and superfluid liquid helium

Experiments on small-angle scattering of neutrons on liquid helium at temperatures of 1.0–5 K at the ISIS pulsed neutron source (England) are reported. Detailed measurements of the angular distribution of the scattered neutrons reveal a significant change in the temperature dependence of the second moment of the pairwise correlation function (the first derivative of the angular distribution for small scattering angles). At high temperatures the angular distribution of the scattered neutrons follows the classical description for small-angle scattering, but at temperatures below the λ-point, quantum mechanical behavior is observed (scattering of neutrons on quantum fluctuations). It is confirmed experimentally that over the entire temperature range the neutron scattering cross section at zero angle is determined by classical thermodynamic fluctuations in the density