Terahertz electron paramagnetic resonance generalized spectroscopic ellipsometry: The magnetic response of the nitrogen defect in 4H-SiC

Abstract

We report on terahertz (THz) electron paramagnetic resonance generalized spectroscopic ellipsometry (THz-EPR-GSE). Measurements of the field and frequency dependencies of the magnetic response due to the spin transitions associated with the nitrogen defect in 4H-SiC are shown as an example. THz-EPR-GSE dispenses with the need of a cavity, permits independently scanning field and frequency parameters, and does not require field or frequency modulation. We investigate spin transitions of hexagonal (h) and cubic (k) coordinated nitrogen including coupling with its nuclear spin (I=1), and we propose a model approach for the magnetic susceptibility to account for the spin transitions. From the THz-EPR-GSE measurements we can fully determine the polarization properties of the spin transitions and we obtain g and hyperfine splitting parameters using magnetic field and frequency dependent Lorentzian oscillator lineshape functions. We propose frequency-scanning THz-EPR-GSE as a new and versatile method to study properties of spins in solid state materials.Electron paramagnetic resonance (EPR) is ubiquitous in science. 1 Traditional EPR instruments operate in the lower Gigahertz (GHz) range limited to one or a few frequencies only. 2 The possibility to access electron spin dynamics at much higher, i.e., Terahertz (THz) frequencies is attractive. Large energies permit better understanding of spin dynamics in single-molecule magnets, for example, 3,4 and allow investigation of systems with large zero-field splitting such as in transition metal complexes, 5,6 or in ultrawide-bandgap semiconductors, e.g., SiC 7-9 and group-III nitrides 10,11 for quantum technologies, or the recently emerging monoclinic gallium oxide for high voltage electronic applications. [12][13][14][15][16][17][18][19] To bring spin resonances into the THz range, superconducting magnets reaching large magnetic fields are necessary. The emergence of closed-cycle dry magnet systems and novel superconducting materials have made 20 T fieldflattened single-solenoid EPR magnets possible. 20 In the THz spectral range one can employ optical methods such as reflectance and transmittance measurements using free space plane wave propagation. Advantages of large-field frequency-scanning far-field THz EPR are manifold. The need for a fixed cavity and fixed frequency tied to the cavity is dispensed with. Furthermore, frequency scana) Electronic mail: