THz magnetic resonance ellipsometry: Bloch equations, paramagnetic Lyddane-Sachs-Teller relation, and magnetic susceptibility sum rules

Mathias Schubert

A new optical technique is presented to detect the signatures of magnetic resonances in materials at terahertz frequencies and high magnetic fields using generalized spectroscopic ellipsometry. Measurements dispense with the need for modulation techniques and resonance cavities in traditional NMR and EPR methods. The elements of the normalized Mueller matrix are determined, which contain hitherto undetected information about the polarization, frequency, and field response, e.g., of unpaired electron spin moments including nuclear magnetic coupling. Approaches to model analysis of the frequency dependent magnetic susceptibility tensor are discussed, Bloch equations are revisited, and an analogue to the Lyddane-Sachs-Teller relationship is shown from theory and experiment. Magnetic sum rules are derived from the Kramers Kronig relations and discussed. The new method permits detailed defect characterization in emerging semiconductor materials, demonstrated for low-symmetry ultrawideband gap metal oxides and group-III nitrides.