Ultrasonic Detection of an Energy Gap Change in the N/S Transition for Trapped H in Nb
For a number of years the properties of low- lying excitations seen in many, amorphous materials have been interpreted in terms of a two-level tunneling model. A large number of measurements of specific heat, neutron scattering, and ultrasonic attenuation and velocity have shown that hydrogen trapped at O or N impurities acts as a tunneling system and can be described with a two-level formalism with the imparities providing an internal strain bias. Recently, measurements in both the normal(N) and superconducting(S) states of ultrasonic attenuation in Nb-N-H, ultrasonic attenuation and velocity in Nb-O-H, and of neutron scattering near 1.5 K and 9 K in Nb-O-H have shown that these systems interact strongly with the conduction electrons of the host material. YU and GRANATO have proposed that the interaction of the conduction electrons with a two-level tunneling system reduces the splitting of the levels in the normal state. The purpose of these ultrasonic velocity measurements was to investigate this predicted effect of the environment on this model tunneling system.
KeywordsNeutron Scattering Ultrasonic Attenuation Tunneling System Modulus Change Ultrasonic Velocity Measurement
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