Research Projects

Traditional semiconductor technology based on charge manipulation is limited by Joule heating leading to decreased efficiency. Spin and valleytronics offer alternatives by utilizing internal degrees of freedom of electron—spin and valley index— thus overcoming major limitations of conventional electronics for next-generation information processing. While spintronics demands complex interfaces, valleytronics exploits the degenerate but inequivalent valley ‘states’ that can encode, process, and store information. The isolation of 2D materials such as graphene and transition metal dichalcogenides (TMDs) has facilitated the exploration of valleytronics since these 2D materials host readily available valley index allowing dynamic control of valley degree of freedom. Monolayer molybdenum disulfide (MoS₂), is an ideal candidate with inequivalent but energetically degenerate valleys at K and K’ points of the Brillouin zone which function as unique two-level system. Broken inversion symmetry and strong spin–orbit coupling yield valley-contrasting selection rules with circularly polarized light. The time-reversal symmetry is broken by an out-of-plane magnetic field which lifts the valley degeneracy via the valley Zeeman effect, an imperative phenomenon for future valleytronic application. We propose that proximity-induced exchange interaction from a 2D ferromagnet can effectively lift the valley degeneracy in MoS₂ without an external magnetic field, enabling helicity-sensitive photocurrent generation. Usually, all optical methods are employed for detection of the valley index. However, excitonic response to valley polarization in electrical transport will enable spin detection in device architecture. While recent studies have demonstrated Zeeman-induced photocurrents under strong magnetic fields, this work proposes to achieve electrical detection of valley-polarized excitons using ferromagnetic van der Waals (vdW) heterostructures, under zero external magnetic field. We implement an all-2D route with vdW heterostructure—stacking MoS₂ with a ferromagnetic layer like CrI3—to generate Zeeman-induced photocurrent. With photon energy near A exciton resonance, circularly polarized laser radiation will be used to excite the system. Proximity-induced large effective magnetic field from the ferromagnetic 2D layer will lift the valley degeneracy and spin information will be detected with spin-selective contacts (Co/Ni) fabricated via electron beam lithography. This allows experimental access of valley-sensitive optoelectronic response arising due to valley-Zeeman induced charged excitons complementing the standard all-optical route. Low-temperature and field-dependent measurements will enable deeper insight into the nature of excitons, trions, and other quasiparticles. Such a study will advance our understanding of how symmetry, topology, and correlations shape the valley landscape, laying the groundwork for both novel quantum phenomena and future device concepts.