Regulation of Rashba properties in Janus van der Waals TeSSe/PtSe 2 heterostructures with external electric field

Pristine Janus TeSSe monolayers exhibit weak intrinsic Rashba spin splitting, which severely restricts their practical applications in spintronics. Herein, we construct Janus TeSSe/PtSe₂ van der Waals heterostructures and systematically investigate their structural stability, electronic properties, and electric-field-modulated Rashba effect via density functional theory calculations. Structural screening confirms that the AA-Se-0 stacking configuration with vertical Te–Te interfacial alignment is thermodynamically stable, serving as a valid structural model for further property analysis. Electronic calculations identify the heterostructure as an indirect-bandgap semiconductor, with band gaps of 0.75 eV and 0.553 eV in the absence and presence of spin–orbit coupling, respectively. Significant Rashba spin splitting is observed at the Γ-point conduction band minimum. The equilibrium conduction-band Rashba coefficient is 1.163 eV·Å, 4.7 times that of pristine TeSSe monolayers and comparable to that of the typical strong Rashba material BiTeI, while the valence-band Rashba coefficient is 0.257 eV·Å. The applied vertical electric field enables efficient, reversible, and linear modulation of the Rashba effect while maintaining the semiconducting nature of the system. A positive electric field reinforces the intrinsic interfacial built-in electric field, boosting the conduction-band Rashba coefficient by 31% to 1.52 eV·Å at +0.6 V/Å, whereas a negative electric field suppresses the Rashba response. Charge density difference and electrostatic potential analyses demonstrate that interfacial electron transfer from TeSSe to PtSe₂ generates the built-in electric field and accounts for the enhanced Rashba splitting. External electric fields precisely regulate spin splitting by superposing or counteracting the built-in interfacial field. This study reveals the underlying mechanism of the electric-field-tunable Rashba effect in two-dimensional van der Waals heterostructures, overcomes the spin-modulation bottleneck of primitive Janus monolayers, and provides valuable theoretical insights for the design of low-power, electrically controlled high-performance spintronic devices.