{"id":37,"date":"2020-02-03T10:56:10","date_gmt":"2020-02-03T10:56:10","guid":{"rendered":"http:\/\/127.0.0.1\/wordpress\/?page_id=36"},"modified":"2026-07-17T20:24:28","modified_gmt":"2026-07-17T14:54:28","slug":"moire-physics-interfaces","status":"publish","type":"page","link":"https:\/\/physics.iisc.ac.in\/~aksy\/moire-physics-interfaces\/","title":{"rendered":"Moir\u00e9 Physics"},"content":{"rendered":"

Optical spectroscopy of Moir\u00e9 homo and heterostructures<\/h3>\t\t\t

Vertical homo and heterostructures are thought to be van der Waals bound (weak binding), but recent studies suggest that layers may be coupled more strongly, and may also go beyond the rigid lattice picture. Further, the twist angle between layers imparts a tunable moir\u00e9 period, scaling as (unit cell length)\/(twist angle), leading to a modified potential landscape. These moir\u00e9 heterostructures emerge as an ideal platform to realise new properties and functionalities that are not present in the individual layers. Additionally, the moir\u00e9 potentials give rise to well defined localized moir\u00e9 excitons (interlayer and intralayer excitons), that are protected against disorder, and can be tuned with external fields revealing interesting topological phases, many-body interactions, and quantum phase transitions. Optical techniques are ideal to explore these systems due to their strong interaction with light. Using both steady-state and time-resolved optical spectroscopies such as steady-state and time-resolved photoluminescence (TRPL) and transient absorption (Pump-Probe) spectroscopy, we study inter-layer coupling, spin-valley information and fundamental carrier dynamics, which occur over timescales of femtoseconds-nanoseconds.<\/p>\n

In reconstructed MoSe\u2082\/WSe\u2082 heterostructures, atomic reconstruction creates mesoscopic domains with uniform atomic registry that dramatically alter the local potential landscape. Using time-resolved photoluminescence, we reveal that quantum confinement persists in these flat reconstructed regions, uncovering multiple finely-spaced interlayer exciton states (~1 meV separation) with enormous lifetime variations spanning sub-nanosecond to over 100 nanoseconds across a 10 meV energy window. At high excitation rates, we observe a novel effect we term “quantum siphoning” \u2014 a transient suppression of emission followed by gradual recovery \u2014 demonstrating that nonlinear excitonic dynamics persist well beyond the ideal moir\u00e9 paradigm.<\/p>\n

In WSe\u2082\/WS\u2082 moir\u00e9 heterostructures, by optically suppressing ultrafast charge transfer to interlayer excitons, we uncover long-lived moir\u00e9 intralayer excitons (lifetimes >1000 ps) arising from their localized Wannier and in-plane charge-transfer character. We observe moir\u00e9 intralayer intervalley biexcitons with a binding energy of ~16 meV \u2014 stabilised by moir\u00e9 confinement \u2014 and find time-domain signatures of strong coupling between these excitons and ultralow-energy phasons (~10 \u03bceV), evidenced as twist-angle-dependent GHz oscillations in the exciton dynamics.<\/p>\n

 
\nUseful references<\/strong>:
\nMondal et al., Quantum siphoning of finely spaced interlayer excitons in reconstructed MoSe\u2082\/WSe\u2082 heterostructures, Nano Letters 26, 5162 (2026)
\nDalal et al., Signatures of moir\u00e9 intralayer biexcitons and exciton-phason coupling in WSe\u2082\/WS\u2082<\/em>, arXiv:2601.03045 (2026)
\nMondal et al., Quantification of 2D Interfaces: Quality of heterostructures, and what is inside a nanobubble<\/em>, ACS Applied Materials and Interfaces 16 42608 (2024)
\nDebnath et al., \u201cTuning exciton complexes in twisted bilayer WSe2 at intermediate misorientation<\/em>\u201d, Physical Review B 106 125409 (2022)
\nTran et al., \u201cMoir\u00e9<\/em> and beyond in transition metal dichalcogenide twisted bilayers<\/em>\u201d, 2DMater. 8 022002 (2021)
\nTran et al., \u201cEvidence for moir\u00e9 excitons in van der Waals heterostructures<\/em>\u201d, Nature 567, 71-75 (2019)<\/p>\n<\/div>\n\t\t<\/div><\/div>

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