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

Abstract

The magnetic field control of quantum matter enables to study of 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 that of the substrate underneath. Here, we unravel a unique 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 0.2 THz 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. NdGaO3 crystals are widely used as substrates in oxide thin film heterostructures; hence, while realizing ultrafast control of magnetic order, specifically in antiferromagnetic spintronics devices, the Kramer’s double mode should be carefully separated from ordered spin resonance mode.

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO3 thin film

“…Terahertz (THz) spectroscopy has proved its efficacy in unraveling the information about the structural and dynamic properties of a condensed matter material. For example, timeaveraged THz spectroscopy has uncovered various low energy carrier dynamics, such as charge-/spin-density wave, magnons/electromagnons, inter-/intra-level transitions, etc, in strongly correlated systems [18][19][20][21][22]. THz spectroscopy measurements also allow precise measurement of scattering rate in a wide range of metals as THz frequency coincides with typical metals' electron momentum scattering rate [23,24].…”