Spin-relaxation times exceeding seconds for color centers with strong spin–orbit coupling in SiC

Abstract

Spin-active color centers in solids show good performance for quantum technologies. Several transition-metal defects in SiC offer compatibility with telecom and semiconductor industries. However, whether their strong spin–orbit coupling degrades their spin lifetimes is not clear. We show that a combination of a crystal-field with axial symmetry and spin–orbit coupling leads to a suppression of spin–lattice and spin–spin interactions, resulting in remarkably slow spin relaxation. Our optical measurements on an ensemble of Mo impurities in SiC show a spin lifetime T 1 of 2.4 s at 2 K.

Hyperfine-mediated transitions between electronic spin-1/2 levels of transition metal defects in SiC

“…Group theory predicts limited possibilities for driving spin transitions in these defect centers at moderate magnetic fields, compatible with the long spin lifetimes observed for Mo defects [17][18][19]. Nevertheless, experimental results [14,15,21,22] demonstrate efficient electron spin resonance on V defects with an oscillating magnetic field parallel to the symmetry axis.…”

“…These spectral features can in good approximation be explained as a defect center in a Si-substitutional site that, after bonding to the lattice (and ionization in the case of Mo), is left with one unpaired electron spin in the d-orbitals of the TM core. In this case, the strongly anisotropic Zeeman spectrum is a consequence of a combination of the defect three-fold rotational symmetry and spin-orbit coupling [12,[17][18][19]22], which gives rise to two ground-state KDs transforming as the Γ 4 and Γ 5,6 irreducible representations of the double group C3v , and separated in energy due to spin-orbit coupling.…”

“…Their spin properties arise from electrons strongly localized at the d-orbitals of the TM core, subject to the relevant point-group symmetries. The V and Mo defects in hexagonal SiC have been extensively investigated recently, motivated by the fact that their optical transitions are near or at telecom-standard wavelengths, and that SiC is an industrially mature semiconductor platform [12,[17][18][19][20][21]. When these defect centers are in a charge state with one localized d-electron, they are largely analogous to each other, both having ground states with electronic spin-1/2 behavior.…”

Hyperfine Structure of Transition Metal Defects in SiC

“…Transition metal (TM) defects in silicon carbide (SiC) constitute a similar familiy of systems that have the benefit of being based on a well established host material as well as having accessible transitions in the telecommunication bands [19][20][21][22][23]. Recent studies made the first steps towards control of nuclear spins via transition metal defects in SiC [22].…”

“…The prime examples for TM defects in SiC are created by neutral vanadium (V) and positively charged molybdenum (Mo) atoms substituting a Si atom in 6H-or 4H-SiC [19][20][21][22][23][24][25]. These defects have one active electron in the atomic D-shell and are invariant under the transformations of the C 3v point group imposed by the crystal structure surrounding the defect.…”