Enhanced Spin Seebeck Effect in Monolayer Tungsten Diselenide Due to Strong Spin Current Injection at Interface
Sang‐Kwon Lee, Won‐Yong Lee, Takashi Kikkawa, Chinh Tam Le, Min‐Sung Kang, Gil‐Sung Kim, Anh D. Nguyen, Yong Soo Kim, No‐Won Park, Eiji Saitoh
Abstract
Abstract The spin current is significantly limited by the spin‐orbit interaction strength, material quality, and spin‐mixing conductance at material interfaces. Such limitations lead to spin current decay at the interfaces, which severely hinders potential applications in spin‐current‐generating thermoelectric devices. Thus, methodical studies on the enhancement of spin currents are indispensable. Herein, a novel approach for enhancing the spin current injected into a normal metal, Pt, using interface effects with a ferromagnetic insulator, yttrium iron garnet (YIG), is demonstrated. This is accomplished by inserting atomically thin monolayer (ML), tungsten diselenide (WSe 2 ) between Pt and YIG layers. A comparative study of longitudinal spin Seebeck effect (LSSE) measurements is conducted. Two types of ML WSe 2 (continuous and large‐area ML WSe 2 and isolated ML WSe 2 flakes) are used as intermediate layers on YIG film. Notably, the insertion of ML WSe 2 between the Pt and YIG layers significantly enhances the thermopower, V LSSE /Δ T by a factor of approximately 5.6 compared with that of the Pt/YIG reference sample. This enhancement in the measured LSSE voltages in the Pt/ML WSe 2 /YIG trilayer can be explained by the increased spin‐to‐charge conversion at the interface owing to the large spin‐orbit coupling and improved spin mixing conductance with the ML WSe 2 intermediate layer.