Who
Long Yang, Columbia University
Abstract
Quantum materials have strong electron correlation effects. According to the “structure-property” relationship, it is crucial to study the structure of quantum materials to better understand and manipulate the physical properties. The quantum effects are significant at the atomic microscopic length scale, which is not feasible to be studied by the average long-range structure measurement from conventional diffraction methods. Instead the local structure probe, pair distribution function (PDF) analysis, can effectively reveal the mystery of local structure. In this talk, the joint neutron and x-ray PDF (NXPDF) method is used for studying the exotic electronic states in a series of different quantum materials. A new methodology, called structure-mining, is developed to obtain candidate atomic structures from NXPDF in a highly automated way. First, the local structure behavior of praseodymium oxide semiconductor nanoparticles is studied, accompanied by the loss of electrical conductivity when temperature changes. Second, the iron doped barium titanate BaFe x Ti 1−x O 3 system is also investigated using PDF methods for studying the multiferroic behavior in the nanocrystals. In addition, the NXPDF analysis is also performed on the MgTi 2 O 4 spinel system to track the evolution of the local atomic structure across the temperature-dependent metal-insulator transition, and a local fluctuating t 2g orbital-degeneracy-lifted (ODL) precursor state is proposed to explain the high temperature abnormal metallic behavior revealed by PDF.
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