Inter-American Materials Collaboration (CIAM): Probing Quantum Phase Transitions by MuSR and Complementary Methods in Applied Pressure

Columbia University, New York NY

Investigators

Abstract

This Inter-American Materials Collaboration (CIAM) project aims to study quantum phase transitions and quantum critical behaviors of correlated electron systems by developing a new spectrometer for high-pressure measurements and performing collaborative muon spin relaxation (mSR) experiments at TRIUMF (Vancouver), together with complementary studies of transport (Toronto), magnetization (Kentucky), and Moessbauer and Perturbed Angular Correlation (PAC) (CBPF-Brazil). mSR has advantages over other microscopic methods (neutron scattering and NMR), in measurements of (1) volume fraction of magnetically ordered regions; (2) magnetic orderof very small / random / dilute moments; and (3) the absolute values of the magnetic field penetration depth in superconducting systems. With these unique capabilities, this project would elucidate: (a) the crossover from itinerant electron ferromagnetism to correlated paramagnetism in MnSi and ZrZn2; (b) interplay of magnetism and superconductivity in CeCu2Si2; (c) competition between the "hidden order" and antiferromagnetic states in URu2Si2; (d) magnetic-ordering systematics of intermetallic Ce compounds; and (e) pressure-induced Mott transition in Ca2RuO4. This project would also promote the participation of experienced as well as young scientists from the US, Canada, Brazil, and Argentina, including several scientists from under-represented groups, in extensive international collaboration. The proposed work will be performed at unique facilities in Vancouver, Kentucky, and Rio de Janeiro, while enriching graduate and undergraduate teaching resources of Columbia Univesity, University of Kentucky, and other participating institutions in Canada, Brazil, and Argentina. Muon Spin Relaxation (mSR), Moessbauer effect, and Perturbed Angular Correlations (PAC) are powerful methods based on technologies and principles from particle/nuclear physics applied to the study of magnetism and superconductivity in solid state physics. The present project is an Inter-American Materials Collaboration (CIAM) in which scientists and students from the US, Canada, Brazil, and Argentina work together. A team of researchers from Columbia University and University of Kentucky will develop capabilities for measuring mSR signals at high applied pressure and perform mSR experiments using TRIUMF, a Canadian accelerator facility in Vancouver. The project also involves Moessbauer and PAC measurements at CBPF-Rio in Brazil, and other complementary studies in Argentina, Toronto, New York, and Kentucky. These techniques will be applied to topical subjects of modern solid-state physics. The goal is to understand novel phenomena exhibited by materials systems in which strong electron correlations play a major role in determining the superconducting and magnetic properties. This project will support senior, junior scientists and students from the US, Canada, Brazil, and Argentina, including several scientists from under-represented groups, while enriching graduate and undergraduate teaching resources of the involved institutions.