Electron Spectroscopy Studies of Quantum Emergence in Low Dimensional Systems

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*****NON-TECHNICAL ABSTRACT****Electrical, magnetic and mechanical properties of materials are ?emergent collective behaviors? of the underlying quantum mechanics of their electrons and constituent atoms. A principal goal of solid state physics and materials science is to elucidate this emergence. A full achievement of this goal would imply the ability to engineer a material that is optimum for any particular application. The mainstay of the current understanding of electrons in solids is a set of deep ideas known as the "Fermi liquid theory." This theory explains why electrons in solids can often be described in a simplified picture which appears to ignore the large repulsive forces that electrons are known to exert on one another. There is a growing appreciation that this theory probably fails for entire classes of possibly useful materials and there is the suspicion that the failure has to do with unresolved competition between different possible emergent behaviors. This research grant supports an experimental program aimed at using a technique called electron spectroscopy to measure and quantify the underlying quantum mechanical behaviors of electrons in materials which manifest this unresolved competition because their crystal structures are quasi-one or quasi-two dimensional. If successful the work will pinpoint essential ideas that must be combined to take the goal of engineering materials to the next level of sophistication. The experiments are performed both in a home laboratory at the University of Michigan, and at various national and international synchrotron facilities. The program relies on strong collaborations with other groups around the world for the providing of well characterized samples to measure, for determining electrical, thermal and magnetic properties of new materials, and for expert theoretical advice and advanced calculations. It thus builds human bridges across geographic, institutional and disciplinary boundaries. It also brings program personnel, including students, into close contact with scientists in a variety of professional roles at a variety of institutions, and trains them in the techniques of collaborative work. Thereby it contributes to our country?s human scientific resources. Program personnel are also encouraged to seek opportunities to explain their work to the public in settings such as public lectures or science cafes. *****TECHNICAL ABSTRACT****Strongly correlated electron materials manifest emergent phenomena by the remarkable range of quantum ground states that they display, e.g., insulating, metallic, magnetic, superconducting, with apparently trivial, or modest changes in chemical composition, temperature or pressure. Of great recent interest are the behaviors of a system poised between two stable zero temperature ground states, i.e. at a quantum critical point. These behaviors intrinsically support non-Fermi liquid (NFL) phenomena, including the electron fractionalization that is characteristic of thwarted ordering in a one-dimensional interacting electron gas. This research program uses the techniques of photoemission and inverse photoemission spectroscopies to measure the single-particle electronic structures of selected low dimensional materials and seeks to identify emergent quantum structures and their relation to the underlying electronic structure. If fully successful, the work could provide a sharp answer to the question of whether or not there are new quantum states of matter associated with the stabilization in higher than one dimension of properties associated with purely one dimensional theory models. The experiments are performed both in a home laboratory at the University of Michigan, and at various national and international synchrotron facilities. The experimental data are analyzed by comparison to theories which treat the Coulomb interactions in different ways, and which provide a link between the spectra and the electrical or magnetic properties. The program relies on strong collaborations with other groups around the world for the providing of well characterized samples to measure, for determining electrical, thermal and magnetic properties of new materials, and for expert theoretical advice and advanced calculations. It thus builds human bridges across geographic, institutional and disciplinary boundaries. It also brings program personnel, including students, into close contact with scientists in a variety of professional roles at a variety of institutions and trains them in the techniques of collaborative work. Program personnel are also encouraged to seek opportunities to explain their work to the public in settings such as public lectures or science cafe?s.