Abstract

We report a direct measurement of the low-energy optical conductivity of large-area single crystal YbMgGaO4, a newly found spin-liquid candidate material, by means of time domain terahertz spectroscopy. No magnetic resonance absorption was observed in polarization dependent measurement down to 1.5K indicating absence of magnetic order. From magneto-terahertz measurement up to 7T within Faraday geometry, we observed an absorption feature which is linearly proportional to the applied magnetic field, yielding evidence for a Zeeman splitting of magnetic moment, from which we extract the value of in-plane g-factors g_‖~4.2. Furthermore, we measure reflectivity and transmittance spectra between 10000cm⁻¹ and 20000cm⁻¹ using FTIR, our measurement reveal that the fine structure spectrum of YbMgGaO4 is similar to a single ion Yb³⁺ absorption features arising from ground state ²F_7/2to ²F_5/2 excitations in trigonal CEF. From optical measurement, we suggest that YbMgGaO4 is a nonmagnetic insulator and long range order do not develop down to 1.5K.

© 2016 Optical Society of America