Spectroscopy of Impurities in Correlated Electron Systems
Creators: name: University Of California Office Of The President
Publisher: name: University of California Office of the President
publisherIdentifier: https://ror.org/00dmfq477
publisherIdentifierScheme: ROR
Year: 2024

description: Impurities have played an important role in the development of applications of condensed matter, such as in the case of doped silicon in semiconducting devices. In contrast to silicon, where electrons are essentially non-interacting, electrons in strongly correlated materials exhibit unexpected behaviors and emergent phenomena which can not be predicted a priori. A theoretical understanding of the ground state and excited states of these materials is one of the grand challenges of condensed matter physics, and is the focus of a tremendous international research effort. Our hypothesis is that the added impurity locally modifies the ordered state and it opens a window to probe the ordered state of the strongly correlated host through its local interaction with the impurity. These modifications of the ordered state hence can be probed locally by variety of techniques. The probe we will use is Nuclear Magnetic Resonance. In this proposal, we address the fundamental puzzle of heavy fermion state and hidden order in the heavy fermion URu2Si2 system by introducing impurities to change the ordered state locally. The nature of the hidden order in URu2Si2 has remained a puzzle since it was discovered in mid 80's, and identifying the nature of the order parameter continues to be hotly debated to this day. There is a growing realization that novel emergent properties of correlated materials have several common features that are crosscutting between different classes. With this realization URu2Si2 is coming back to the center of attention as an example of a novel emergent state. We will monitor the effects with Nuclear Magnetic Resonance (NMR) as a spectroscopic tool to probe the low energy states that emerge in the vicinity of these impurities. NMR is real-space probe that provides detailed microscopic information about the local physics of the impurities in bulk, and complements real-space surface probes such as scanning tunneling microscopy (STM). By studying the response of these systems to "dirt" we will shed important light on the underlying behavior of the host material. Our team's efforts will be guided by two main objectives: (1) to carry out systematic studies of the nature of the Kondo coherence and hidden order in URu2Si2 using NMR as a local probe; and (2) to train graduate students and postdoctoral researchers at UC Davis and LANL within a multidisciplinary program aimed at addressing the Grand Challenges identified by DOE BES. We will pursue this goal by combining experimental and theoretical efforts that are strongly coupled. On experimental side we will focus on NMR measurements of effects of Rh dopants in URu2Si2. We will investigate locally induced competing magnetic order near Rh. On theory side we will focus on the Ginzburg-Landau approach at first and subsequently on a microscopic description of the induced magnetic order. The current team of researchers has a proven track record of collaboration and high impact publications, e.g. Nature, v 434, p 622, (2005). This research addresses the DOE Grand Challenges on emergent properties of correlated matter and on superconductivity. If successful this research will impact fundamental understanding of emergent properties and hidden order of URu2Si2, a puzzle that defied understanding despite 20 years of research.