Materials World Network: Studies of Quantum Phase Transitions by MuSR in Ambient and Applied Pressure

Columbia University, New York NY

Investigators

Abstract

This Materials-World-Network project aims to support studies of quantum phase transitions (QPTs) by the muon spin relaxation (MuSR) measurements to be performed at high-intensity accelerator facilities, such as TRIUMF in Vancouver, Canada and Paul Scherrer Institut (PSI) in Villigen, Switzerland, by an international team of researchers. The team includes senior and junior scientists from Columbia University (USA), McMaster University and TRIUMF (Canada), PSI (Switzerland), Kyoto and Tohoku Universities (Japan), Brazilian Center for Research in Physics (CBPF, Brazil) and Centro Atomico Bariloche (CAB, Argentina). For many decades, studies of phase transitions have been performed exclusively by varying temperatures (thermal phase transitions). Recent developments of materials and technologies have opened a new window to investigate quantum evolutions of phases at low temperatures by varying pressure or composition as a tuning parameter. Many novel concepts and unexplored features of QPTs are being revealed in studies of heavy-fermion systems, frustrated / low-dimensional magnets and exotic superconductors. Taking advantage of unique capability of MuSR to detect magnetic order of even very small / random magnetic moments, to estimate volume fraction of magnetically ordered regions in a situation involving phase separation, and to characterize dynamic spin fluctuations in a very wide time window complementary to other techniques, the present project will elucidate magnetic QPT's in frustrated square-lattice J1-J2 spin systems, doped magnetic semiconductors (Ga,Mn)As and (Fe,Co)Si, novel ruthenium oxide compounds, quasi one-dimensional spin system which exhibits Bose Condensation of magnons, as well as UGe2 and other heavy-fermion systems. Extensive collaboration of leading researchers in materials development (Kyoto, Tohoku), MuSR measurements (Columbia, McMaster), MuSR instrumentation (TRIUMF, PSI), Moessbauer effect (CBPF), and heavy-fermion physics (CAB), at the world's strongest meson facilities (TRIUMF and PSI) with close involvement of leading theorist team members (Affleck, Maekawa, Millis), will advance basic understandings of the role of competing states and soft dynamic modes near quantum phase boundaries. Such progress could contribute to long-awaited determination of mechanisms for novel superconductors as well as to development of ideal magnetic semiconductors suitable for application to spin-sensitive transistors. Involvement of students and postdoctoral researchers from all participating institutions provides valuable training and international research experience to young scientists in a challenging area of cutting-edge research in condensed matter physics. This project uses large accelerator facilities and principles from particle/nuclear physics to study a variety of materials including novel superconductors to understand properties related to magnetism and quantum physics not accessible to other techniques in this research area. An international team of researchers will conduct the main part of their measurements at TRIUMF, a Canadian accelerator facility in Vancouver, British Columbia. The research is focused on understanding novel condensed matter phenomena in a variety of materials systems including semiconductors and oxide compounds that exhibit interesting magnetic behavior. Students and junior scientists from the US, Canada, Brazil, Argentina, Switzerland and Japan work together in this project and gain valuable international research experience. In addition, web-based courses and seminars for graduate, undergraduate students are planned to be developed and shared among all participating institutions using the technology already available at Columbia University. This award is jointly funded by the Division of Materials Research and the Office of Multidisciplinary Activities in the Mathematical and Physical Sciences Directorate and by the Office of International Science and Engineering ?East Asia and pacific Program.