Ultrafast Laser Excitation Achieves Nonvolatile Mott Transition in 1T-TaSe2

Controlling the behaviour of materials exhibiting strong interactions between electrons, known as Mott materials, represents a significant challenge in modern physics and holds promise for future technologies. Junde Liu, Liwen Su, and Pei Liu, alongside colleagues at various institutions, now demonstrate a method for achieving a lasting, non-volatile switch between insulating and metallic states in a layered material. The team achieves this transition using precisely timed pulses of light, inducing a rearrangement of the material’s internal structure without requiring large-scale atomic movement. This research establishes a new principle for manipulating correlated electron systems, offering a pathway to create reconfigurable electronic devices and explore previously inaccessible quantum states, and importantly, provides a robust and reversible method for optical control of the Mott state.

Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, China, 2I. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany, Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing, China.

Ultrafast Optics Control Mott Transition in 1T-TaSe2

Scientists have pioneered a method for nonvolatile control of the Mott transition, a change in electronic behaviour, using ultrafast optical excitation in the layered material 1T-TaSe2. Employing angle-resolved photoemission spectroscopy, the team observed a reversible transition from an insulating state to a metallic state following laser pulses, revealing a lasting change in the material’s electronic properties. Experiments utilized femtosecond laser pulses to excite the material, targeting the interlayer stacking to induce this change, bypassing the need for large-scale atomic movement. Theoretical calculations confirmed that this interlayer rearrangement introduces a significant in-plane component to electron hopping, altering the balance between electron interactions and bandwidth, and reducing the ratio of on-site Coulomb interaction to bandwidth.

This suppression of the Mott state stabilizes the metallic phase, delivering a nonvolatile transition where the metallic state persists even after the laser pulse ceases. Building on previous studies of layered materials, the team harnessed the surface sensitivity of ARPES to probe the electronic structure and confirm the induced transition, providing insight into the mechanism driving the nonvolatile behaviour. By optically controlling the interlayer stacking, scientists establish a versatile strategy for tailoring correlated electronic phases and potentially creating reconfigurable high-frequency devices, opening new avenues for exploring and manipulating quantum materials. This approach offers a pathway to control the electronic properties of materials with light, potentially leading to new optoelectronic devices.

Laser Pulses Induce Metallic State Transition

Researchers have demonstrated that laser pulses can induce a transition from a Mott insulating state to a metallic state in a layered material, offering a way to control its electronic properties with light. Mott insulators, which should be metallic according to conventional theory, exhibit localized electrons due to strong electron-electron interactions, and the laser pulse provides energy to overcome these interactions. The transition is reversible, allowing the material to be switched back to the insulating state with further laser pulses, crucial for potential applications in optoelectronic devices. The stacking arrangement of the material’s layers plays a critical role in determining the electronic structure and the ease of inducing the transition, with specific stacking configurations favouring either the insulating or metallic state.

The electronic structure is also strongly influenced by the orbital character of the electrons, and the team used calculations to show how these orbitals contribute to the band structure in different layers and stacking configurations. They determined a laser fluence threshold required to initiate the transition, demonstrating that the energy per unit area is more important than the number of laser pulses. Density Functional Theory calculations, including corrections for electron-electron interactions, support the experimental findings, showing that the Mott gap opens when electron correlations are considered. This research provides a deeper understanding of the physics of Mott insulators and the mechanisms governing the Mott transition, with implications for both fundamental physics and materials science.

Light Switches Material Between Insulator and Metal

Researchers have demonstrated a method for reliably switching a material between an insulating and a metallic state using light, achieving a nonvolatile phase transition in the layered material 1T-TaSe2. This transition stems from a change in how the layers of the material align, specifically the stacking order of charge density waves, following excitation with an ultrafast laser pulse. The team observed that the light induces a rearrangement of these layers, creating new pathways for electrons to move and effectively reducing the tendency for electrons to become localized, a key characteristic of insulating materials. This work establishes that subtle alterations to the interlayer stacking within layered materials can dramatically influence their electronic properties, providing a new way to control correlated electron systems. By manipulating this stacking geometry, scientists can tune the balance between electron localization and bandwidth, suppressing the insulating Mott state and stabilizing a metallic phase, and providing direct spectroscopic evidence for a photo-stabilized correlated state. Further investigation is needed to explore the full potential of this approach across different materials systems, potentially leading to the discovery of new quantum phases and the development of ultrafast, reconfigurable devices.