Gate-Tunable Highly Efficient Spin and Valley Quantum Heat Engine in a Magnetic Tunnel Junction Based on Transition-Metal Dichalcogenides

Abstract

Recently, the nanoscale quantum heat engine (QHE) has become one of the most productive areas of research, due to its role as a conduit for excess heat. Regarding the low thermal conductance and suitable structural properties of transition-metal dichalcogenides (TMDs), here, we design a highly efficient spin and valley QHE in a normal-ferromagnetic-normal TMD-based tunnel junction. Spin splitting caused by the exchange field and the huge spin-orbit coupling (SOC) of TMDs leads to a remarkable spin-valley--dependent Seebeck coefficient with a sharp peak at $E\ensuremath{\approx}{E}_{F}$. Application of the gate voltage changes the bands from conduction to valence; thus, a remarkable spin-valley--dependent Seebeck and conductance are observed, leading to a large gate- and exchange-field-tunable spin- and valley-dependent maximum power, which is greatly enhanced compared to other two-dimensional materials such as silicene- and graphene-based QHEs. Additionally, a enormous gate-controllable figure of merit and, consequently, a high efficiency at maximum power are achieved in this device, which confirms the advantage of using TMD-based junctions for highly efficient QHEs. These findings may open the door to the design of spin-valley caloritronics devices based on TMDs.