X-ray scattering studies of charge density waves in cuprate and pnictide superconductors

Lee, Sangjun

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https://hdl.handle.net/2142/110401 Copy

Description

Title

X-ray scattering studies of charge density waves in cuprate and pnictide superconductors

Author(s)

Lee, Sangjun

Issue Date

2020-12-17

Director of Research (if dissertation) or Advisor (if thesis)

Abbamonte, Peter

Doctoral Committee Chair(s)

Madhavan, Vidya

Committee Member(s)

• Fradkin, Eduardo
• Filippini, Jeffrey

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Superconductor
• 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.

Graduation Semester

2021-05

Type of Resource

Thesis

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http://hdl.handle.net/2142/110401

Copyright and License Information

Copyright 2021 Sangjun Lee

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