****Technical Abstract**** Muon spin relaxation (MuSR) measurements provide unique information on the ordered volume fraction, moment size, slow spin fluctuations, and critical behavior for studies of magnetic ordering, and allow reliable determination of the superfluid density in type-II superconductors. The present project aims to study exotic spin and charge correlations in novel superconducting and magnetic systems by extensive MuSR measurements at TRIUMF (Canada) and PSI (Switzerland). The present research covers: (1) quantum critical behaviors and Skyrmion spin correlations in weak itinerant ferro/helical magnets MnSi and FeGe, (2) novel ferromagnetic system Li(Zn,Mn)As generated by doping charge (with excess Li) and spin (with Mn) into the I-II-V semiconductor LiZnAs, and (3) various FeAs, CuO and heavy fermion superconductors, with a special focus on strange/unexplained behaviors in the overdoped regions. Success of the present project will advance understanding of very strong and unconventional spin-charge couplings found in many of these systems, and possibly contribute to development of new superconducting and spin-tronics systems and devices. The MuSR measurements will be performed in extensive international collaborations, providing opportunities for development of graduate, undergraduate and post-doctoral students and researchers in a unique multi-national environment and facilities. Outreach plans include development of on-line lecture courses, and involvement of high school students.

Nontechnical Abstract

Over the last 30 years, solid state physics has developed with discoveries of many novel and unconventional materials and phenomena. They include high-Tc CuO superconductors, doped ferromagnetic semiconductors, and systems existing in the boundary of magnetically ordered and disordered (or suprconducting) states. The key element of these systems is strong interaction between spins (origin of magnetism) and charges (required for metallic, semiconducting, or superconducting behaviors). Another notable development of modern solid state physics is the use of large accelerator facilities which produce high-intensity beams of X-rays, neutrons and muons. The present project will use positive muons obtained at dedicated high-intensity accelerator facilities in Canada (TRIUMF) and Switzerland (PSI) to elucidate detailed relationship between magnetic (spin) and conductive (charge) phenomena. Rsearch advances may contribute to development of novel materials for superconducting and / or spin-sensitive electronics (spintronics) devices. The muon measurements will be performed in international collaboration including gropus from the US, Canada, Japan, China, Brazil, UK and Switzerland, which will help development of students and researchers in a unique multi-national environment. Educational/outreach activities include the development of on-line lecture courses for solid state physics, associated with text books and lab courses. In cooperation with TRIUMF's outreach activities, the project supports involvements of high school students and physics teachers in forefront experimental research using very large accelerator facilities.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Guebre X. Tessema
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Columbia University
New York
United States
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