Research highlights:

Rutgers University:

Investigated the relationship between superconductivity and the metal-insulator transition in disordered and percolating systems (granular Al-Al₂O₃ and granular Mg-MgO). First experiments showing the absence of superconductivity within a 3-D metallic regime (PRL 59, 1232), the occurrence of 3-D quasireentrant superconductivity (PRB 36, 4062), and the shift of the superconductor-normal transition through suppression of localization by spin-orbit scattering (PRL 61,2717).

University of Virginia & Dupont:

Investigated magnetization and flux creep in high-temperature superconductors (HTS). One of the first works to correctly interpret and demonstrate anisotropic flux entry and critical-state magnetization in HTS crystals (PRB 39, 7309; 83 citations). Proposed and verified a new type of memory effect arising from flux creep (PRB 41, 4089). Investigated the isotope effect in the LSCCO system-this work provided the first experimental evidence of large BCS like isotope shifts in any HTS (PRB 41, 282; 164 citations). Work on demagnetization and its influence on threshold flux entry (PRB 43, 2916).

Oak Ridge National Lab and Wright Patterson AFB:

Investigated fundamental phenomena associated with dissipative processes in superconductors and explored the role of the dissipative regime in practical conductors and applications. Provided the first experimental demonstration of free flux flow in any superconductor (PRL 70, 998). Elucidated the nature of the mixed-state Hall effect in YBCO in the free-flow limit (PRL 72 , 2259). Demonstrated current-induced pair-breaking in a high-temperature superconductor (PRL 72 , 752; review article in Mod. Phys. Lett. B 9, 399). Studied the supercritical (J >> J_C) characteristics of prototype HTS wires, tapes and magnet coils from several manufacturers to evaluate their operation in the dissipative regime; found that r_HTS ~ 1% of r_Ag at J values 10 to 100 times higher than J_C (APL 67, 848).

University of South Carolina:

Continued investigation of fundamental behavior in superconductors (high and low-T_C) under high dissipative current densities, and the evaluation and characterization of HTS conductors for practical current-lead and fusion-energy applications. Developed a self-consistent model for solving internal demagnetization and current patterns in HTS ceramics (JAP 84, 6863). Model for the decomposition of the mixed-state Hall effect (Physica C 307, 241 + book chapter in ISBN 81-224-1125-8). Developed and refined apparatus for measuring transport characteristics with pulse rise times ~ 100 ns and power dissipation densities up to 50 billion watts/cm³. Observation of temporal effects in flux motion at short pulse durations (book chapter in ISBN 81-7023-848-X). Observation of flux flow and vortex instability at T<<T_C, and elucidation of the normal state r_n at low temperatures (PRL 84, 5204; Physica C, in press). Theory and preliminary evidence of Cherenkov resonances by vortices as they cross the sound barrier (PRB 60, 12419). Observation of a novel regime in flux motion where the lifetime of vortices (transit time to cross the sample, between nucleation and annihilation) is less than the vortex formation time. Theory and observation of a new effect involving domain formation and "staircase IV" in the regime of negative differential resistivity (in preparation for submission to Nature). Ongoing applied projects include the use of combination lithography (electron-beam plus optical-projection lithography) for deducing the intra- and inter-granular transport behavior in RABiTS tapes (TSF, submitted)and the evaluation of the in-field high-dissipation characteristics of BSCCO/Ag tapes for use in pulsed magnets for fusion energy applications (both projects are funded by Lockheed Martin Energy Research Corporation).

Technical experience:

Cryogenic equipment including He³ & dilution refrigerators. SQUID magnetometers. Ultrahigh vacuum systems. Preparation and characterization of thin films. AES, TEM, SEM, & RBS. Operation of a tandem Van de Graaff accelerator. Data-acquisition and control systems. Measurement of resistances >10¹² W. Design and construction of a high-speed 50 kW pulsed-current apparatus. Computer: BASIC, FORTRAN, C/C++, TeX/LaTeX and HTML languages. RMB, WIN95/98, WINNT, VAX/VMS, UNIX, and LINUX operating systems. Algorithm analysis and database modeling. CVI application development.