Publication Date

2007-12-14

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Physics (Arts and Sciences)

Date of Defense

2007-11-23

First Committee Member

Fulin Zuo - Committee Chair

Second Committee Member

Stweart Barnes - Committee Member

Third Committee Member

Massimiliano Galeazzi - Committee Member

Fourth Committee Member

Michael Wang - Committee Member

Abstract

The I-V characteristics of Tin films in the superconducting transition have been measured when ac current was applied. The experimental results suggest that the electrical response in ac is not satisfied with the I-V equation in dc. A new equation was suggested to describe the vortex motion and the vortex pair separation in the two dimensional superconducting transition with ac current, which is satisfied with our experimental results. The excess noises of Tin films in the superconducting transition have been found to depend strongly on the temperature and ac current. An empirical expression of voltage noise density in term of resistance has been used to fit the data. The peak of voltage noise density follows closely but always shifted down from dR/dT. Comparison with the dc noise measurement shows the voltage noise density with ac current is much larger than with dc current. The excess noises with ac appear earlier than the noises with dc. The difference of excess noises between ac and dc can be explained by the fluctuation of vortex pair separation process which dominates the noises generation in ac. I-V characteristics and voltage noises are measured simultaneously to reveal the nature of the excess noises. The coincidence of the excess noise and the third harmonic voltage suggests that the fluctuation of vortex pair separation process is one of the main contributions to excess noises in the two dimensional superconducting transition.

Keywords

K-T Transition; TES Microcalorimeter

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