Predicted strong spin-phonon interactions in Li-doped diamond

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Chemistry

Background:

• Understanding point defects in diamond is crucial for quantum technologies.
• Lithium (Li) as a substitutional defect in diamond presents unique electronic and spin properties.
• Spin-phonon coupling in defects can significantly influence material properties and spectroscopic signatures.

Purpose of the Study:

• To investigate the electronic structure and spin properties of the Li substitutional defect in diamond using DFT.
• To explore the impact of spin states on the vibrational properties and Raman spectra of the Li defect.
• To elucidate the role of spin-phonon coupling in observed spectral differences.

Main Methods:

• Density Functional Theory (DFT) calculations employing the B3LYP functional.
• Utilized a 64-atom supercell model for simulating the Li substitutional defect in diamond.
• Calculated static structures, included zero-point vibrations, and analyzed effective charges and spin distributions.

Main Results:

• The quartet (Sz = 3/2) spin state is energetically favored over the doublet (Sz = 1/2) state by 0.07-0.09 eV.
• While effective charges are similar, significant differences in spin distributions exist between spin states.
• Unprecedented, large differences in Raman spectra (frequency and intensity) were observed, attributed to strong spin-phonon coupling.

Conclusions:

• Strong spin-phonon coupling is identified as the primary cause for the distinct Raman spectra of different Li defect spin states.
• The calculated spectral differences are orders of magnitude larger than those in previously studied transition metal or rare-earth compounds.
• The findings suggest that Raman spectroscopy can be a sensitive probe for spin states in Li-defected diamond.