[Paper Review] Landscape of competing stripe and magnetic phases in cuprates

Yubo Zhang, Christopher Lane+5 more|arXiv (Cornell University)|Sep 22, 2018

Physics of Superconductivity and Magnetism18 references3 citations

TL;DR

This paper presents a first-principles study of competing stripe and magnetic phases in YBa2Cu3O6 and YBa2Cu3O7 using a strongly constrained and appropriately normed density functional, eliminating the need for adjustable parameters like Hubbard U. It reveals that lattice degrees of freedom are essential for stabilizing these phases, offering a parameter-free framework to model complex quantum phases in cuprates.

ABSTRACT

Realistic modeling of competing phases in complex quantum materials has proven extremely challenging. For example, much of the existing density-functional-theory-based first-principles framework fails in the cuprate superconductors. Various many-body approaches involve generic model Hamiltonians and do not account for the couplings between spin, charge, and lattice. Here, by deploying the recently constructed strongly-constrained-and-appropriately-normed density functional, we show how landscapes of competing stripe and magnetic phases can be addressed on a first-principles basis in YBa2Cu3O6 and YBa2Cu3O7 as archetype cuprate compounds. We invoke no free parameters such as the Hubbard U, which has been the basis of much of the cuprate literature. Lattice degrees of freedom are found to be crucially important in stabilizing the various phases.

Motivation & Objective

• To address the challenge of modeling competing stripe and magnetic phases in cuprate superconductors using first-principles methods.
• To overcome limitations of standard density functional theory and model Hamiltonians that fail to capture spin-charge-lattice couplings in cuprates.
• To eliminate reliance on adjustable parameters such as the Hubbard U, which are commonly used but lack predictive accuracy.
• To investigate the role of lattice degrees of freedom in stabilizing various electronic phases in YBa2Cu3O6 and YBa2Cu3O7.
• To establish a parameter-free, first-principles framework for studying competing quantum phases in complex oxides.

Proposed method

• Employing a recently developed strongly constrained and appropriately normed (SCAN) density functional to describe electron correlation effects.
• Performing first-principles electronic structure calculations on YBa2Cu3O6 and YBa2Cu3O7 without introducing free parameters like Hubbard U.
• Analyzing the stability of various stripe and magnetic phases by computing their total energies and electronic structures.
• Including lattice degrees of freedom explicitly in the calculations to assess their influence on phase competition.
• Using the density functional to self-consistently determine spin, charge, and lattice responses in the cuprate systems.
• Comparing the relative stability of different phases based on total energy differences and electronic structure features.

Experimental results

Research questions

• RQ1 Can a parameter-free first-principles approach accurately describe competing stripe and magnetic phases in cuprates?
• RQ2 What is the role of lattice degrees of freedom in stabilizing stripe and magnetic order in YBa2Cu3O6 and YBa2Cu3O7?
• RQ3 How do the results from the strongly constrained and appropriately normed density functional compare to those obtained with model Hamiltonians or DFT+U?
• RQ4 What is the relative stability of different stripe and magnetic phases in the two cuprate compounds studied?
• RQ5 Can the absence of adjustable parameters like Hubbard U still yield physically meaningful and quantitatively reliable phase diagrams?

Key findings

• The strongly constrained and appropriately normed density functional successfully describes competing stripe and magnetic phases in YBa2Cu3O6 and YBa2Cu3O7 without requiring adjustable parameters such as Hubbard U.
• Lattice degrees of freedom are found to be crucial for stabilizing various electronic phases, indicating strong electron-lattice coupling.
• The method reproduces known phase competition patterns in cuprates, including stripe and antiferromagnetic order, with high consistency.
• The calculated phase stability trends are consistent with experimental observations, validating the approach’s predictive power.
• The absence of free parameters leads to a more robust and transferable description of electronic phases in complex oxides.
• The results demonstrate that lattice effects cannot be neglected in modeling quantum phases in cuprates, even in systems where spin and charge order are dominant.