Nonequilibrium-controlled charge-carrier transitions in SnSe single crystals

Single-crystal tin selenide (SnSe) is a promising thermoelectric material with the current record figure of merit at 923 K. To improve the thermoelectric performance of SnSe at ambient conditions, manipulating the charge-carrier transition process has attracted great interest recently. Here, different from static strategies of carrier doping or band engineering, we propose and report a nonequilibrium and complete switching of charge-carrier transitions in SnSe between the interband process and the intraband process. In a broad range of 420–520 nm, the transient absorption (TA) spectroscopy confirms the intraband/interband transition switching with an ultrafast picosecond optical modulation speed and a near-unity degree of completeness, achieved solely by changing the probe pulse polarization. The theoretical analysis of transition dipole moments and transition selection rules links this nonequilibrium-controlled carrier transition with the anisotropic electronic structure and glide-mirror symmetry of SnSe. These results offer insights and raise attractive possibilities to enhance the power factor by exploiting the dynamical electronic anisotropy of thermoelectric materials.