Crystal-field Paschen-Back effect on ruby in ultrahigh magnetic fields

Abstract

Zeeman spectra of the R lines of ruby (Cr3+: α-Al2O3) were studied in ultrahigh magnetic fields up to 230 T by magnetophotoluminescence measurements. The observed Zeeman patterns exhibit nonlinear behaviors above 100 T, evidencing the breakdown of the previously reported Paschen-Back effect for BâŠ1c geometry. We adopted the crystal-field multiplet theory including the cubic crystal field (Hcubic), the trigonal crystal field (Htrig), the spin-orbit interaction (HSO), and the Zeeman interaction (HZ). It is found that the nonlinear splitting of the R lines is owing to the hybridization between the E2 and T12 states, which leads to the quantization of these Zeeman levels with the orbital angular momentum. Our results suggest that the exquisite energy balance among Hcubic, Htrig, HSO, and HZ realized in ruby offers a unique opportunity to observe the onset of the crystal-field Paschen-Back effect toward the high-field extreme.