Xuecong Wang | Searcharxiv

arXiv2026

Magnetic quantum defects in a uniaxial antiferromagnetic insulator

Point defects have been successfully utilized in various quantum technologies, serving as quantum qubits for quantum computation, single-photon emitters for quantum communication, and nanoscale sensors for quantum metrology. However, their further development faces key challenges, particularly in discovering and exploring suitable defect-host systems that meet the necessary criteria for quantum applications. Here, using polarization-resolved Raman spectroscopy and terahertz absorption spectroscopy, we discover three distinct chromium-vacancy-induced excitations in the uniaxial antiferromagnetic insulator, Cr$_2$O$_3$. These vacancy-induced excitations have an energy scale of a few tens of millielectronvolts and are twofold degenerate, and the lowest one at 64 $cm^{-1}$ is sharp and sensitive to the external magnetic field along the easy-axis direction, particularly close to the spin-flop regime around 6T, where the mode softens from 64 to 27$cm^{-1}$. Based on the defect supercell first-principles calculations, we interpret the mode at 64 $cm^{-1}$ as a local magnetic excitation of the local moment within the chromium vacancy state. Our results establish that the magnetic defect states in Cr$_2$O$_3$ have potential for quantum applications.

cond-mat.mtrl-sci↗

arXiv2025

Intrinsic defects and 4d/5d transition metal defects in Cr$_2$O$_3$: pathways to enhance the Néel temperature

First-principles calculations are employed to explore avenues to increase the Néel temperature ($T_{\mathrm{N}}$) of the magnetoelectric antiferromagnet Cr$_2$O$_3$ through doping. Employing the hybrid functional method, we calculate the formation energy of intrinsic defects and transition metal dopants (Mo, W, Nb, Ta, Zr, and Hf) to assess their likelihood of formation. Intrinsic defect calculations indicate that Cr interstitials and oxygen vacancies dominate under Cr-rich conditions, whereas Cr vacancies prevail under O-rich conditions. Notably, under Cr-rich conditions, the Fermi level can be pinned slightly above mid-gap due to the formation of Cr interstitials and oxygen vacancies. To assess the influence of dopant on $T_{\mathrm{N}}$ of Cr$_2$O$_3$, we calculate the enhancement of the exchange energy for the spin on the dopant site or on adjacent Cr site using the supercell method. Our study identifies isovalent Mo and W substitution on Cr site as the most promising candidates to increase Néel temperature due to the impurity-mediated enhanced exchange interaction for half-filled bands. Formation energy calculations indicate that Mo and W substitution on Cr are easier to form under Cr-rich conditions and a Fermi level near or slightly above the midgap renders a desirable neutral Mo and W defect. This is assisted by the formation of intrinsic Cr interstitial and O vacancy under Cr-rich conditions. These findings offer a route to utilize defects for higher $T_{\mathrm{N}}$ and enhanced performance of Cr$_2$O$_3$ in magnetoelectric devices and furnish invaluable insights for directing subsequent experimental endeavors.

cond-mat.mtrl-sci↗