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Title:X-ray scattering studies of charge density waves in cuprate and pnictide superconductors
Author(s):Lee, Sangjun
Director of Research:Abbamonte, Peter
Doctoral Committee Chair(s):Madhavan, Vidya
Doctoral Committee Member(s):Fradkin, Eduardo; Filippini, Jeffrey
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Unconventional superconductors
Charge density wave
X-ray scattering
Resonant soft x-ray scattering
Abstract:The phase diagrams of unconventional superconductors exhibit many different broken-symmetry phases near superconductivity, such as antiferromagnetism, charge density wave, spin density wave, and nematic order. The proximity and similar temperature scales of these orders suggest superconductivity and other order parameters are intertwined, and how they intertwine is a longstanding problem in condensed matter physics. Among the phases found in the vicinity of superconductivity, charge density wave (CDW) has been found in nearly all cuprate superconductors and observed to have an intimate relationship with superconductivity. Thus, characterizing the nature of CDWs is crucial for understanding the mechanism of unconventional superconductivity. Here, we studied CDWs in cuprate and pnictide superconductors using various x-ray scattering techniques. We discovered new CDW phases in BaNi2As2 and Co-, Sr-doped systems, confirming a generic presence of CDW in the phase diagram of unconventional superconductors, and the nature of the superconductivity in these systems are closely related to the presence of CDW. We also precisely measured the temperature and doping evolution of the CDW wave vector in La1.8-xEu0.2SrxCuO4, revealing the effect of the finite charge compressibility and the coupling of charge and spin order on the wave vector change. Furthermore, energy- and time-resolved resonant soft x-ray scattering experiments on the CDW in La2-xBaxCuO4 were performed to reveal a previously unidentified fluctuating nature of the CDW.
Issue Date:2020-12-17
Rights Information:Copyright 2021 Sangjun Lee
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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