Measurement of Conduction and Valence Bands g-factors in a Transition Metal Dichalcogenide Monolayer

The electron valley and spin degree of freedom in monolayer transition metal dichalcogenides can be manipulated in optical and transport measurements performed in magnetic fields. The key parameter for determining the Zeeman splitting, namely the separate contribution of the electron and hole g-factor, is inaccessible in most measurements. Here we present an original method that gives access to the respective contribution of the conduction and valence band to the measured Zeeman splitting. It exploits the optical selection rules of exciton complexes, in particular the ones involving inter-valley phonons, avoiding strong renormalization effects that compromise single particle g-factor determination in transport. These studies yield a direct determination of single band g factors. We measure g_c1= 3.84±0.1, g_c2=0.86±0.1 for the top (bottom) conduction band and g_v=6.1±0.1 for the valence band of monolayer WSe₂. These measurements are helpful for more quantitative interpretation of optical and transport measurements performed in magnetic fields. The measured g-factor values are also valuable input parameters for optimizing band structure calculations of these 2D materials.