RUI: NMR Studies of Hidden Order and Quantum Criticality

California State L A University Auxiliary Services Inc., Los Angeles CA

Investigators

Abstract

Non Technical This is an experimental condensed matter project. It concentrates on the investigation of phase transitions and the possibility of discovering new states of matter. The materials used for this investigation are named "electron-correlated systems." These are mostly inter-metallic compounds whose thermal and conductance properties are very different from normal metals such as copper or silver, for instance. Electron-correlated materials are of current interest for science and technology because of the many states in which they can be found. For instance, they can display superconductivity, magnetism, antiferromagnetism, quadrupolar ordering, colossal magnetoresistance, and of particular interest for this project, hidden order and the so-called "non-Fermi liquid behavior." Nuclear-magnetic resonance techniques will be used to study the properties of URu2Si2 and UCu5-xNix with the goal of understanding the nature of their unusual behavior. Undergraduate and masters-level students will be trained in the techniques of magnetic resonance, radio-frequency electronics, cryogenics, and computer interface. One aspect of this project is related to K-12 education. Some Los Angeles area teachers will have a chance to deepen their understanding of the science standards and concepts taught at the elementary school level and will learn about experimental techniques that will enhance instruction around those standards. The collaboration will involve meetings at the elementary school sites and Cal State L.A., as well as curricular trips for the students. Technical This experimental condensed matter project will concentrate on the study of phase transitions and intrinsic inhomogeneous properties in electron-correlated materials. It will aim to characterize the static and dynamic properties of local magnetic and electric-field-gradient distributions in two specific materials and their compounds: URu2Si2 and UCu1-xNix. The former undergoes a phase transition involving an as-yet unknown order parameter. Among the possible ordered states being proposed are quadrupolar, octupolar, spin chiral, and orbital antiferromagnetism. NMR will be used to probe the internal fields and their local distributions with the goal of elucidating the true order parameter. UCu4Ni and other compositions near x=1 are disordered by design and present non-Fermi liquid behavior related to a quantum critical point. NMR will be used to study the magnetic disorder and to elucidate to what extent it or quantum criticality is responsible for the unusual behavior at low temperatures. One main question to address is that of the universality of quantum critical phenomena, since both ordered and disordered non-Fermi liquid systems seem to behave very similarly near absolute zero. This project has a K-12 education component in which Los Angeles area teachers will deepen their understanding of the science standards and concepts taught at the elementary school level and learn experimental techniques that will enhance instruction. Meetings at the elementary school sites and Cal State L.A. as well as curricular trips for the students will be carried out.