Nontrivial thermoelectric behavior in cubic SnSe driven by spin-orbit coupling

Highlights: • By alloying with AgSbSe₂, SnSe undergoes a phase transition from the orthorhombic structure to a cubic phase. • Cubic SnSe is a nontrivial band semiconductor driven by spin-orbit coupling. • In cubic SnSe, the two competing factors, Seebeck coefficient and electrical conductivity, are decoupled by SOC. This study reveals that such spin-orbit semiconductors are a new class of promising thermoelectric materials. Recently, tin selenide SnSe has attracted extensive attention for the reported excellent thermoelectric performance. By alloying with AgSbSe₂, we observed that SnSe undergoes a phase transition from the orthorhombic structure to a cubic phase. The cubic SnSe exhibits some anomalous thermoelectric properties compared with common IV-VI cubic semiconductors, such as PbTe and SnTe. It is proven that cubic SnSe is not a trivial band semiconductor, whereas its band gap originates in the spin-orbit coupling effects. In this nontrivial semiconductor, the competing factors, Seebeck coefficient and electrical conductivity, can be simultaneously optimized. The peak ZT reaches 0.82 at 842 K in Sn_0.4(AgSb)_0.3Se. This study reveals that such spin-orbit semiconductors are a new class of promising thermoelectric materials, in which the thermoelectric performance strongly depends on the local spin-orbit coupling, besides the overall chemical bonding.