Magnetic Weyl semimetals with diamond structure realized in spinel compounds

At a Glance

Metadata	Details
Publication Date	2020-03-18
Journal	Physical review. B./Physical review. B
Authors	Wei Jiang, Huaqing Huang, Feng Liu, Jian‐Ping Wang, Tony Low
Institutions	University of Utah, University of Minnesota
Citations	29
Analysis	Full AI Review Included

Technical Documentation: Magnetic Weyl Semimetals in Diamond-Structure Spinels

This document analyzes the research on realizing Magnetic Weyl Semimetals (WSMs) within a diamond lattice structure, specifically in VMg₂O₄ spinel compounds. The findings are highly relevant to engineers and scientists utilizing high-purity CVD diamond platforms for advanced spintronics and quantum material research.

Executive Summary

The research introduces a novel $e_g$-orbital diamond model that hosts complex topological states, demonstrating its realization in spinel compounds, which share the Fd-3m space group symmetry with diamond.

Topological Discovery: Identification of a 3D Nodal Cage (NC) feature and hourglass fermions protected by orbital and sublattice degeneracies within the $e_g$-diamond model.
Material Realization: The model is realized in the 4-2 spinel VMg₂O₄, where the A-site cations form a perfect diamond sublattice structure.
Half-Metallicity: VMg₂O₄ exhibits ideal half-metallicity, crucial for spintronics, characterized by one metallic spin channel and one insulating channel with a large spin gap (up to 6.62 eV).
Magnetic Weyl Semimetal: Inclusion of Spin-Orbit Coupling (SOC) transforms the system into a Magnetic Weyl Semimetal (WSM) state, confirmed by 18 pairs of Weyl points and topological Fermi arcs.
Integration Potential: VMg₂O₄ shows excellent lattice matching (< 0.4% mismatch) with MgO, facilitating integration into industrial spintronics devices (e.g., Magnetic Tunneling Junctions, MTJs).
Application Focus: The findings open pathways for developing low switching energy magnetic devices and utilizing the unique properties of diamond-structure topological materials.

Technical Specifications

The following hard data points were extracted from the first-principles calculations on VMg₂O₄:

Parameter	Value	Unit	Context
Spin Gap (PBE Level)	4.36	eV	Half-metallicity feature (Spin Down Channel)
Spin Gap (HSE Level)	6.62	eV	Enhanced gap using Hybrid Functionals
Magnetic Moment	2	µ_B per UC	Ferromagnetic (FM) state, primarily contributed by V cations
FM/AFM Energy Difference	0.43	eV	Indicates promising room temperature FM stability
Nodal Point Proximity	< 20	meV	Energy dispersion of nodal points relative to the Fermi level
Lattice Mismatch with MgO	< 0.4	%	Critical for epitaxial growth on (001) and (111) planes
Anomalous Hall Conductivity (Peak)	≈ 100	Ω^-1 cm^-1	Intrinsic anomalous Hall conductivity (σ_H^A)
Crystal Structure	Fd-3m	Space Group	Same symmetry as the diamond lattice

Key Methodologies

The research utilized advanced computational techniques to model and confirm the topological states derived from the $e_g$-diamond structure:

Tight-Binding (TB) Model Development: A novel 3D $e_g$-orbital diamond model was constructed, incorporating both nearest-neighbor (NN) and next-nearest-neighbor (NNN) hopping interactions to analyze band structure and degeneracy.
First-Principles DFT Calculations: Density Functional Theory (DFT) calculations were performed on the 4-2 spinel VMg₂O₄ to determine electronic and magnetic ground states (Ferromagnetic).
Half-Metallicity Confirmation: Band structures were calculated without Spin-Orbit Coupling (SOC) to confirm the ideal half-metallic state and the large spin gap in the insulating channel.
Wannier Function Fitting: Maximally Localized Wannier Functions (MLWFs) were used to accurately fit the DFT band structures, confirming the orbital characteristics ($d_{z^2}$ and $d_{x^2-y^2}$) consistent with the $e_g$-diamond model.
Topological State Analysis: 3D band structures and 2D k-plane cuts were analyzed to confirm the formation of the 3D Nodal Cage (NC) feature near the Fermi level.
Magnetic Weyl Semimetal Confirmation: Non-collinear calculations including SOC were performed, demonstrating the breaking of degeneracy and the transition to a Magnetic Weyl Semimetal state characterized by 18 pairs of Weyl points.
Surface State and Transport Calculation: Topological surface states, Fermi arcs, and intrinsic anomalous Hall conductivity (σ_H^A) were calculated using Green’s function methods to verify the WSM phase.

6CCVD Solutions & Capabilities

The realization of complex topological states based on the diamond lattice structure presents a unique opportunity for 6CCVD to supply high-purity CVD diamond materials as foundational platforms for next-generation spintronics research.

Applicable Materials for Topological Research

The research relies on the structural perfection inherent in the diamond lattice. 6CCVD provides materials that serve as ideal templates, substrates, or functional components for replicating and extending this work:

Optical Grade Single Crystal Diamond (SCD): Required for applications demanding the highest structural integrity and lowest defect density. SCD provides a perfect crystalline platform (Ra < 1 nm polishing) necessary for studying subtle topological effects and integrating high-quality epitaxial films like VMg₂O₄.
Boron-Doped Diamond (BDD): Ideal for use as robust, conductive electrodes or substrates in transport experiments (e.g., measuring the anomalous Hall conductivity, σ_H^A). BDD offers tunable conductivity without compromising chemical inertness.

Customization Potential for Device Integration

The proposed application involves complex stacking (e.g., VMg₂O₄/MgO/VMg₂O₄ MTJs). 6CCVD’s custom manufacturing capabilities directly address the needs of device fabrication:

Research Requirement	6CCVD Capability	Technical Specification
Custom Substrate Dimensions	Custom plates and wafers up to 125 mm in diameter (PCD) or large-area SCD.	Plates/wafers up to 125 mm (PCD). Substrates up to 10 mm thick.
Precise Film Thickness	SCD and PCD materials available in ultra-thin film formats.	Thickness range: 0.1 µm to 500 µm (SCD/PCD).
Electrical Contact Integration	In-house metalization services for electrode deposition.	Custom metal stacks including Au, Pt, Pd, Ti, W, and Cu.
Surface Quality	Ultra-low roughness polishing essential for epitaxial growth.	Polishing: Ra < 1 nm (SCD), Ra < 5 nm (Inch-size PCD).

Engineering Support

The theoretical discovery of the $e_g$-diamond model and its realization in VMg₂O₄ requires specialized material knowledge for experimental validation.

Material Selection for Spintronics: 6CCVD’s in-house PhD team can assist researchers in selecting the optimal diamond material (SCD vs. PCD vs. BDD) and surface orientation required for the epitaxial growth of spinel compounds and subsequent measurement of topological properties (e.g., Fermi arcs and anomalous Hall effect).
Interface Optimization: We provide consultation on surface preparation and metalization schemes necessary to create low-resistance contacts for high-frequency or quantum transport measurements in these novel magnetic Weyl semimetal systems.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Diamond-structure materials have been extensively studied for decades, which\nform the foundation for most semiconductors and their modern day electronic\ndevices. Here, we discover a e$g$-orbital ($d{z^2}$,$d_{x^2-y^2}$ ) model\nwithin the diamond lattice (e$_g$-diamond model) that hosts novel topological\nstates. Specifically, the e$_g$-diamond model yields a 3D nodal cage (3D-NC),\nwhich is characterized by a $d$-$d$ band inversion protected by two types of\ndegenerate states (i.e., e$_g$-orbital and diamond-sublattice degeneracies). We\ndemonstrate materials realization of this model in the well-known spinel\ncompounds (AB$_2$X$_4$), where the tetrahedron-site cations (A) form the\ndiamond sub-lattice. An ideal half metal with one metallic spin channel formed\nby well-isolated and half-filled e$_g$-diamond bands, accompanied by a large\nspin gap (4.36 eV) is discovered in one 4-2 spinel compound (VMg$_2$O$_4$),\nwhich becomes a magnetic Weyl semimetal when spin-orbit coupling effect is\nfurther considered. Our discovery greatly enriches the physics of diamond\nstructure and spinel compounds, opening a door to their application in\nspintronics.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevb.101.121113