Giant bipolar unidirectional photomagnetoresistance.

Positive magnetoresistance (PMR) and negative magnetoresistance (NMR) describe two opposite responses of resistance induced by a magnetic field. Materials with giant PMR are usually distinct from those with giant NMR due to different physical natures. Here, we report the unusual photomagnetoresistance in the van der Waals heterojunctions of WSe/quasi-two-dimensional electron gas, showing the coexistence of giant PMR and giant NMR. The PMR and NMR reach 1,007.5% at 9 T and 93.5% at 2.2 T in a single device, respectively. The magnetoresistance spans over two orders of magnitude on inversion of field direction, implying a giant unidirectional magnetoresistance (UMR). By adjusting the thickness of the WSe layer, we achieve the maxima of PMR and NMR, which are 4,900,000% and 99.8%, respectively. The unique magnetooptical transport shows the unity of giant UMR, PMR, and NMR, referred to as giant bipolar unidirectional photomagnetoresistance. These features originate from strong out-of-plane spin splitting, magnetic field-enhanced recombination of photocarriers, and the Zeeman effect through our experimental and theoretical investigations. This work offers directions for high-performance light-tunable spintronic devices.NMR).