Scattering and thermodynamic studies of effects of hole- and electron-doping in selected antiferromagnetic Mott Insulators

Zakrzewski, Alexander V

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https://hdl.handle.net/2142/115487 Copy

Description

Title

Scattering and thermodynamic studies of effects of hole- and electron-doping in selected antiferromagnetic Mott Insulators

Author(s)

Zakrzewski, Alexander V

Issue Date

2022-04-22

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

MacDougall, Gregory J

Doctoral Committee Chair(s)

Abbamonte, Peter

Committee Member(s)

• Fradkin, Eduardo
• Ricker, Paul

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• condensed matter physics
• solid state physics
• magnetism
• superconductivity
• unconventional superconductivity
• x-ray scattering
• neutron scattering
• spin density waves
• charge density waves
• percolation
• Mott insulators

Abstract

The following Thesis is dedicated to a series of studies on two distinct families of antiferromagnetic Mott insulators which, upon doping, are either known or suspected to exhibit unconventional superconducting states. The underlying motivation for these studies is the presence of high-temperature superconductivity within layered cuprate compounds when hole-doped from a parent state which contains antiferromagnetism. In this Thesis, I present a detailed study of magnetic order in a specific family of cuprate superconductors, LaEu(2−x)Sr(x)CuO4 (LESCO). Specifically, I focus on a range of dopings that exhibit quasi-one dimensional stripe-like correlations. In addition, I present studies of magnetic order in the electron-doped spinel antiferromagnet Cu(1−x)Zn(x)Rh2O4. The parent compound CuRh2O4 is an oxide analogue to the superconducting chalcogenide compounds CuRh2S4 and CuRh2Se4. Original work is presented in Chapter 3. I present our results on the cuprate superconductor LESCO in Chapter 3. This includes single crystal growth, characterization, and neutron scattering measurements of magnetic order within this material. I begin by describing methods I used to grow large single crystals of this compound with isotopically-enriched Europium to facilitate neutron scattering experiments, as well as characterization activities carried out at the University of Illinois. I then describe our comprehensive neutron scattering study on LESCO, which firmly establishes the presence of static spin stripe order within this compound at intermediate dopings. This result brings LESCO in line with other layered cuprates, namely La(1.6−x)Nd(0.4)Sr(x)CuO4 and La(2−x)Ba(x)CuO4, which contain similar order. Additionally, I present the results of magnetization measurements which demonstrate the presence of anisotropic superconductivity, a key signature of predictions made by pair density wave theory. In Chapter 4, I present scattering and thermodynamic studies of the effects of magnetic dilution on the Asite spinel CuRh2O4 with non-magnetic Zn2+ ions. In studying the physics of spinel antiferromagnets, dilution with non-magnetic ions can be a powerful strategy for probing unconventional spin states or uncovering interesting phenomena. The data presented in this chapter confirm the helical spin order recently identified at low-temperatures in this material, and further demonstrate a systematic suppression of the associated N´eel temperature with increasing site dilution towards a continuous critical doping of xspin ∼ 0.44. We demonstrate that this critical doping is distinct from a second structural critical point at xJT ∼ 0.6, which is consistent with the suppression of orbital order on the A-site through a classical percolative mechanism. Both the anomalously low value for x_spin and observed critical exponents at this doping are inconsistent with predictions of classical percolation theory, and suggests rather that the spin transition in this material is driven by an enhancement of pre-existing spin fluctuations with weak dilution. Chapter 1 presents an introduction to the physical concepts relevant to these studies. A description of experimental methods used to carry out this work is presented in Chapter 2. Chapter 5 summarizes the main conclusions and presents relevant discussion.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Alexander V. Zakrzewski

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