The high temperature superconductors which were discovered in 1986 still continue to pose major challenges to scientists. Not only is the mechanism for superconductivity not known, but the nature of the superconducting state and the motion of vortices continue to be debated intensely. We study the microwave response of superconductors, both for understanding the nature of superconductivity, the dynamics of vortices and for practical applications in microwave devices.

The principal areas of our research are:

  • Fundamental measurements and analysis of the penetration depth and surface impedance of superconductors, with a view to understanding the pairing state, the quasiparticle spectrum and the gap parameter
  • Vortex dynamics at high (rf and microwave) frequencies to obtain quantiative measurements of parameters such as pinning force constants, vortex viscosity, critical fields, melting and vortex glass transitions
  • Flux penetration and critical state dynamics
  • Josephson type nonlinear phenomena at microwave frequencies
  • Development of novel measurement techniques, such as the “hot finger” cavity method to measure surface impedance, tunnel diode technique of measuring penetration depth, patterned film structures to study vortex dynamics, modulated microwave absorption

The materials we study are the cuprate High Tc superconductors, borocarbides, and organic superconductors.

Our work in Superconductivity is supported by:

  • National Science Foundation
  • Division of Materials Research and Division of Electrical and Communications Systems, Rome Laboratory, Hanscom AFB (an AFOSR lab)

Related Publications

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Wei, Yan-Zhen; Kumbharkhane, AC; Sadeghi, M; Sage, JT; Tian, WD; Champion, PM; Sridhar, S; McDonald, MJ

Protein hydration investigations with high-frequency dielectric spectroscopy Journal Article

In: The Journal of Physical Chemistry, vol. 98, no. 26, pp. 6644–6651, 1994.

Abstract | Tags: Chemical & Biological Physics

Wei, Yan-Zhen; Sridhar, S

A new graphical representation for dielectric data Journal Article

In: The Journal of chemical physics, vol. 99, no. 4, pp. 3119–3124, 1993.

Abstract | Tags: Chemical & Biological Physics

Wei, Yan-Zhen; Sridhar, S

Relationships between the dielectric and structural properties of supercooled LiCl: RH2O solutions Journal Article

In: Journal of Molecular Liquids, vol. 56, pp. 259–273, 1993.

Abstract | Tags: Chemical & Biological Physics

Wei, Yan-Zhen; Chiang, Ping; Sridhar, S

Ion size effects on the dynamic and static dielectric properties of aqueous alkali solutions Journal Article

In: The Journal of chemical physics, vol. 96, no. 6, pp. 4569–4573, 1992.

Abstract | Tags: Chemical & Biological Physics

Wei, Yanzhen; Sridhar, S

Biological applications of a technique for broadband complex permittivity measurements Inproceedings

In: 1992 IEEE MTT-S Microwave Symposium Digest, pp. 1271–1274, IEEE 1992.

Abstract | Tags: Chemical & Biological Physics

Liu, Ping; Rappaport, Carey M; Wei, Yan-zhen; Sridhar, S

Simulated biological materials at microwave frequencies for the study of electromagnetic hyperthermia Inproceedings

In: 1992 14th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, pp. 272–273, IEEE 1992.

Abstract | Tags: Chemical & Biological Physics

Sridhar, S

Experimental observation of scarred eigenfunctions of chaotic microwave cavities Journal Article

In: Physical review letters, vol. 67, no. 7, pp. 785, 1991.

Abstract | Tags: Chemical & Biological Physics

Wei, Yan-Zhen; Sridhar, S

Dielectric spectroscopy up to 20 GHz of LiCl/H2O solutions Journal Article

In: The Journal of chemical physics, vol. 92, no. 2, pp. 923–928, 1990.

Abstract | Tags: Chemical & Biological Physics

Wei, Yan-Zhen; Sridhar, S

Technique for measuring the frequency-dependent complex dielectric constants of liquids up to 20 GHz Journal Article

In: Review of scientific instruments, vol. 60, no. 9, pp. 3041–3046, 1989.

Tags: Chemical & Biological Physics

Sridhar, S; Taborek, P

High-frequency structural relaxation in supercooled liquids Journal Article

In: The Journal of chemical physics, vol. 88, no. 2, pp. 1170–1176, 1988.

Tags: Chemical & Biological Physics

SRIDHAR, SPP; KUMAR, R

Hemato-biochemical changes in calves during neonatal life Journal Article

In: Indian Journal Animal Health, pp. 105–109, 1988.

Tags: Chemical & Biological Physics

WEI, YAN-ZHEN; SRIDHAR, S

PROPERTIES OF SUPERCOOLED LiCl RH O SOLUTIONS Journal Article

In: 0000.

Abstract | Tags: Chemical & Biological Physics