Photoinduced Topological Phase Transition in 1T-MoS₂ Enables Light-Controlled Quantum Hall States

The quest for materials exhibiting exotic electronic properties has taken a significant step forward with new research into the behaviour of monolayer 1T-MoS, a material poised to revolutionise nanoscale electronics. Mohammad Mortezaei Nobahari from Ferdowsi University of Mashhad, and colleagues, demonstrate how shining light onto this material induces a dramatic shift in its electronic state, triggering a transition between different topological phases. This research establishes 1T-MoS as a uniquely tunable platform where light selectively controls both spin and valley properties, opening up possibilities for designing novel devices that harness these quantum characteristics. The team’s findings reveal a sequence of light-controlled topological states, including spin-polarized and valley-based Hall insulators, offering unprecedented control over electron behaviour in two-dimensional materials.

The study identifies light-controlled transitions, marked by distinct changes in the material’s electronic structure. Depending on the light’s intensity and electric field, the material evolves between various quantum states, including the quantum spin Hall state, spin-polarized quantum Hall insulator, quantum valley Hall, and photo-induced quantum Hall insulator regimes. These results establish 1T′-MoS2 as a versatile platform where circular light selectively manipulates spin and valley degrees of freedom, enabling control over topological states of matter. This precise control allows transitions between distinct quantum phases, offering potential for novel spintronic and valleytronic devices. The observed phenomena demonstrate the capability to engineer topological properties using light, opening avenues for exploring new quantum materials and functionalities.

Topological States in Two-Dimensional Materials

This collection of research explores the fascinating world of topological insulators and 2D materials, particularly transition metal dichalcogenides like MoS2. Researchers are investigating materials that exhibit topologically protected surface states, meaning electrons can conduct on the surface even if the bulk material is insulating. A significant focus lies on manipulating the quantum spin Hall effect in 2D materials, with studies exploring ways to induce and control this effect through electric fields, mechanical strain, and the creation of layered heterostructures. Introducing magnetic materials also plays a role in modifying these surface states.

Transition metal dichalcogenides, such as MoS2 and WSe2, are central to much of this research due to their 2D nature and tunable electronic properties. Janus monolayers, where the top and bottom layers have different chemical compositions, are also investigated for their unique characteristics. Combining different 2D materials into van der Waals heterostructures allows researchers to tailor the material’s properties. Another key area explores Floquet topological insulators, where materials are subjected to periodic driving, such as by light. This driving force can modify the topology of the electronic bands, offering a new way to control electronic properties and induce topological phases. Researchers are also investigating the effects of energy loss in these driven systems.

Advanced concepts under investigation include the quantum anomalous Hall effect, where a quantized Hall effect occurs without an external magnetic field. Studies also explore the formation of magnetic skyrmions in heterostructures combining topological insulators and ferromagnets. Utilizing the valley degree of freedom in 2D materials for information storage and processing, known as valleytronics, is another active area of research. Investigations into quantum phenomena like retroreflection and Klein tunneling in 2D materials further expand the understanding of these materials. Overall, this research represents a strong interdisciplinary effort spanning physics, materials science, chemistry, and engineering, with a focus on designing and fabricating materials with specific topological properties for potential applications in spintronics, valleytronics, and low-power electronics. The dynamic control of topological properties using light and other external stimuli is a growing trend, highlighting the complexity and potential of this field.

Light Drives Topological Phase Transitions in MoS2

Researchers have demonstrated a new method for manipulating the topological phases of monolayer 1T′, MoS2 using high-frequency, circularly polarized light. By applying this light, the team observed transitions between different quantum states, including spin Hall, valley-polarized, spin-polarized, and Chern insulating regimes. These transitions are characterized by changes in the material’s electronic structure and are tunable through both the light’s intensity and electric field. The findings establish 1T′, MoS2 as a platform where spin and valley degrees of freedom can be selectively controlled, allowing reconfiguration of its topological transport properties.

Importantly, the researchers found that the response of individual spin and valley sectors can be tuned independently, originating from light-induced changes to the material’s internal electronic structure. This ability to continuously and reversibly reconfigure the material’s properties highlights its potential for developing light-programmable topological functionalities. Future research could explore the effects of different driving frequencies and polarization states, as well as investigate the potential for extending these findings to other two-dimensional materials. The team’s work provides a foundational understanding of light-matter interactions in topological materials and opens avenues for designing novel optoelectronic devices.