Research Projects

The discovery of the quantum spin Hall effect (QSHE), characterized by spin-polarized edge states where electrons with opposite spins travel in opposite directions along the edges while the bulk remains insulating, marked a major milestone in condensed matter physics. Unlike the non-quantized spin Hall effect (SHE), the QSHE is robust against disorder and scattering due to the topological protection of its edge states, enabling dissipation-less spin transport. This is crucial for energy-efficient spintronics and quantum computing applications, where minimizing energy loss and maximizing stability are essential. Beyond spintronics, a new field—orbitronics—has emerged, focusing on the orbital motion of electrons rather than their spin for information transport. The orbital Hall effect (OHE) offers advantages over the SHE, as it does not rely on spin-orbit coupling, which opens up the possibility of using a broader range of materials. Similar to the QSHE, a quantized version of the OHE could enable dissipation-less orbital current, which forms the central focus of this proposal. The primary objective of this proposal is to explore the existence of the quantum orbital Hall effect (QOHE) in topological materials. Specifically, we will investigate if topological skyrmion-like magnetic textures and electronic band topology drive the QOHE using theoretical approaches. Our work will combine numerical calculations based on model Hamiltonians with density functional theory (DFT)-based methods. DFT will be particularly valuable in bridging theoretical models with real materials, allowing us to identify materials that exhibit QOHE, and guiding future experimental validation. Building on ongoing research on the orbital Hall effect, which attributes the generation of orbital moments to crystal symmetries, we propose two novel mechanisms: (i) the breaking of inversion symmetry through complex spin arrangements in topological spin textures, and (ii) the breaking of time-reversal symmetry in Chern insulators. We will investigate how the skyrmion index and Chern number—quantities that define the topology of magnetic textures and electronic bands, respectively—impact the orbital magnetization in these materials and lead to quantized orbital Hall conductivity. Furthermore, we will explore the origin of QOHE by studying its orbitally polarized edge states. Using DFT, we will propose candidate materials that host QOHE, which could serve as a starting point for experimental investigations. To date, only one proposal has suggested the existence of QOHE in quantum Hall systems. Thus, this proposal holds significant potential to contribute to fundamental understanding by connecting seemingly distinct fields: orbitronics, topological spin textures, and Chern insulators. Demonstrating QOHE in these systems highlights the importance of orbital degrees of freedom and opens new possibilities for applications beyond spintronics, broadening the scope of research in orbitronics.