Enhanced Spin Seebeck Effect in Monolayer Tungsten Diselenide Due to Strong Spin Current Injection at Interface

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 (WSe2) between Pt and YIG layers. A comparative study of longitudinal spin Seebeck effect (LSSE) measurements is conducted. Two types of ML WSe2(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/Delta Tby 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 WSe2/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.