THz probing of non-trivial topological states in Co2MnGe Heusler alloy thin films

Co2MnGe (CMG) has been demonstrated recently as a half-metallic ferromagnetic Heusler alloy, which possesses a topologically non-trivial band structure. This behavior is unique to such systems and hence warrants extensive experimental exploration for potential spintronic and chirality sensitive optoelectronic applications. Here, we demonstrate that an epitaxial thin film of CMG acts as a source of terahertz (THz) radiation upon photoexcitation by optical femtosecond laser pulses. Detailed experiments have revealed that a large contribution to THz emission occurs due to nonmagnetic or spin-independent origin; however, a significant contribution in the THz generation is evidenced through an excitation light helicity-dependent circular photogalvanic effect confirming the presence of topologically non-trivial carriers in the epitaxial CMG thin films. Furthermore, we show that not only the topological contribution is easily suppressed but also the overall THz generation efficiency is also affected adversely for the epitaxial films grown at high substrate temperatures.