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Title: Final Technical Report Grant No. DE-FG02-97ER45653 Lance E. De Long, Principal Investigator, University of Kentucky Period of Performance: 09/01/97 to 05/14/15

Prior to 1997, the PI had studied the unusual upper critical magnetic field phase boundaries of several novel or exotic types of superconductors, including charge density wave materials such as NbSe2, organic superconductors such as κ-(ET)2Cu[N(CN)2]Br, high-temperature oxide superconductors such as (Ba,K)BiO3 and the cuprates, heavy fermion superconductors such as U6Fe, UBe13, URu2Si2 and UPt3, and re-entrant Kondo alloys such as (La,Ce)Al2 and ferromagnetic superconductors such as ErRh4B4. Most of these materials exhibited marked positive or negative curvature of HC2(T) which could not be explained by traditional pair-breaking models. It became clear that many of these materials had very short coherence lengths that made quantized vortices highly mobile (depinned) near the phase boundary, and the fundamental, equilibrium HC2(T) difficult to measure using finite field or current drives. These problems made the underlying physics obscure, and led to erroneous interpretations of experimental data in terms of models of exotic superconducting pairing mechanisms. Around 1995, these issues led the PI to take advantage of modern electron beam lithography techniques for patterning superconducting and ferromagnetic thin films on the nanoscale. Primarily due to strong magnetic shape anisotropy effects, EBL patterning has led to enhanced control of the spatial distribution and dynamics of topologicalmore » defects such as domain walls and magnetic vortices, which can create serious energy dissipation and other limitations for modern devices. Moreover, finite size and interface effects also strongly alter phase transition temperatures and phase boundaries of superconducting and magnetic films, as well as introduce barriers to equilibration, enhanced fluctuations and alter magnetic relaxation. Geometrical frustration and spin ice behavior can also be systematically controlled in patterned film media. Film patterning thus provides an excellent tool for conducting highly-controlled, fundamental studies of cooperative phases and interactions in artificially structured condensed matter.« less
  1. Univ. of Kentucky, Lexington, KY (United States)
Publication Date:
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DOE Contract Number:
Resource Type:
Technical Report
Research Org:
Univ. of Kentucky, Lexington, KY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States