Magnetic-field–induced Zeeman excitation mode in paramagnetic NdGaO3single-crystal probed by magneto-terahertz spectroscopy

Abstract

Abstract The magnetic field control of quantum matter enables to study various exotic phenomena which emerge in complex oxide materials. The thin film heterostructures of these systems, potentially relevant in oxide electronics, require a great deal of care in distinguishing the properties of the film from those of the substrate underneath. Here, we unravel a low-energy excitation mode in NdGaO3 crystals which is an important constituent of oxide thin film heterostructures. Employing terahertz (THz) time-domain spectroscopy with control of the external magnetic field, an excitation mode resonating at a frequency of 0.2THz was observed along two key (001) and (110) crystallographic orientations. The mode develops and strengthens with an application of increasing magnetic field and weakens with increasing temperature; all attributes conforming to the predictions for the energetics of Zeeman splitting and intra-level transition within Kramer's doublet ground state. A dominance of the magnetic field control of this mode along (110) compared to that along (001) orientation also further unveils a structural control. NdGaO3crystals are widely used as substrates in oxide thin film heterostructures; hence, while realizing ultrafast control of magnetic order, specifically in oxide thin films, the Kramer crystal field splitting mode should be carefully separated from ordered spin resonance mode.