A dynamic view of frozen excitons
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Controlling Coulomb correlations and fine structure of quasi-one-dimensional excitons by magnetic order
Many surprising properties of quantum materials result from Coulomb correlations defining electronic quasiparticles and their interaction chains. In van der Waals layered crystals, enhanced correlations have been tailored in reduced dimensions, enabling excitons with giant binding energies and emergent phases including ferroelectric, ferromagnetic and multiferroic orders. Yet, correlation design has primarily relied on structural engineering. Here we present quantitative experiment–theory proof that excitonic correlations can be switched through magnetic order. By probing internal Rydberg-like transitions of excitons in the magnetic semiconductor CrSBr, we reveal their binding energy and a dramatic anisotropy of their quasi-one-dimensional orbitals manifesting in strong fine-structure splitting. We switch the internal structure from strongly bound, monolayer-localized states to weakly bound, interlayer-delocalized states by pushing the system from antiferromagnetic to paramagnetic phases. Our analysis connects this transition to the exciton’s spin-controlled effective quantum confinement, supported by the exciton’s dynamics. In future applications, excitons or even condensates may be interfaced with spintronics; extrinsically switchable Coulomb correlations could shape phase transitions on demand.
Bottom-up fabrication of 2D Rydberg exciton arrays in cuprous oxide
Solid-state platforms provide exceptional opportunities for advancing on-chip quantum technologies by enhancing interaction strengths through coupling, scalability, and robustness. Cuprous oxide (Cu2O) has recently emerged as a promising medium for scalable quantum technology due to its high-lying Rydberg excitonic states, akin to those in hydrogen atoms. To harness these nonlinearities for quantum applications, the confinement dimensions must match the Rydberg blockade size, which can reach several microns in Cu2O. Using a CMOS-compatible growth technique, this study demonstrates the bottom-up fabrication of site-selective arrays of Cu2O microparticles. We observed Rydberg excitons up to the principal quantum number n = 5 within these Cu2O arrays on a quartz substrate and analyzed the spatial variation of their spectrum across the array, showing robustness and reproducibility on a large chip. These results lay the groundwork for the deterministic growth of Cu2O around photonic structures, enabling substantial light-matter interaction on integrated photonic platforms and paving the way for scalable, on-chip quantum devices.
Static and dynamic Raman excitation mapping of chirality-pure carbon nanotube films
Raman spectroscopy is a powerful method for probing electronic and vibrational properties of materials, particularly nanomaterials such as single-wall carbon nanotubes. Typically, Raman spectroscopy is conducted at a single, or few, excitation wavelengths, but that provides limited information about excitation resonance structure, and their dynamical evolution. Here, we extend a sensitive full-spectrum technique to rapidly obtain two-dimensional Raman excitation maps both statically and dynamically for chirality-pure single-wall carbon nanotube films. We demonstrate sensitive evaluation of structured resonance profiles even from weak vibrational modes, and sub-second time resolution of the dynamics of photo-driven defect production. Findings include the direct observation of bands and their profiles – including bands which could be missed in conventional Raman spectroscopy – and demonstration of differences for odd vs. even defect band combinations. This opens up possibilities to investigate the coupling of electronic states with vibrational modes in nanomaterials and track their dynamical evolution subject to intentional modulation.
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Understanding the performance of perovskite solar cells is critical for advancing sustainable energy solutions. Hot-drop casted quasi-2D Ruddlesden-Popper perovskites (RPPs) exhibit remarkable efficiency and stability, making them promising for commercial applications. However, the ultrafast energy transfer and exciton-phonon interactions in these materials remain unclear. Here, we show that using advanced techniques like two-dimensional electronic spectroscopy (2DES) and transient grating (TG), we can unravel energy dynamics in hot-drop casted RPP films. Our study reveals rapid energy transfer between perovskite layers occurring within 100–220 femtoseconds and highlights how exciton-phonon coupling drives structural changes in the material. Coherent vibrational signals identify key lattice and organic cation modes, providing insights into their role in energy dissipation. These findings deepen our understanding of how 2D perovskites work and pave the way for improving the efficiency and stability of next-generation optoelectronic devices.
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