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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.

Geochemistry of lithospheric aqueous fluids modified by nanoconfinement

Water is a principal component of Earth’s fluids, and its interaction with rocks governs lithospheric geochemical and geodynamic processes. Water–rock interactions are crucial in societally relevant resource management, including subsurface extraction and storage of energy, the deep carbon cycle and generating critical metal deposits. The prevailing view is that fluids navigate through the lithosphere without being influenced by the distinct properties that arise from matter confined at the nanoscale. Here we use electron microscopy and neutron scattering data to show that a diverse range of lithospheric rocks, including sandstones, peridotites and serpentinites, consistently show nanoporosity, predominantly with pore sizes < 100 nanometres. Using molecular dynamics simulations, we demonstrate that water’s dielectric permittivity—a fundamental property that governs its geochemical behaviour—diverges in nanoconfinement from its bulk counterpart under conditions ranging from ambient to extremes of 700 °C and 5 GPa. Our geochemical simulations suggest that changes in water permittivity due to confinement will decrease mineral solubility, a process that is not currently considered in models of fluid–rock interactions. Given that permittivity is also intimately linked to ion speciation, pore-size-dependent properties should be expected to exert a primary influence on rock reactivity and the geochemical evolution of fluids during fluid–rock interactions.

Ultrafast exciton-phonon coupling and energy transfer dynamics in quasi-2D layered Ruddlesden-Popper perovskites

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.

ToF-SIMS sputter depth profiling of interphases and coatings on lithium metal surfaces

Lithium metal as a negative electrode material offers ten times the specific capacity of graphitic electrodes, but its rechargeable operation poses challenges like excessive and continuous interphase formation, high surface area lithium deposits and safety issues. Improving the lithium | electrolyte interface and interphase requires powerful surface analysis techniques, such as ToF-SIMS sputter depth profiling.This study investigates lithium metal sections with an SEI layer by ToF-SIMS using different sputter ions. An optimal sputter ion is chosen based on the measured ToF-SIMS sputter depth profiles and SEM analysis of the surface damage. Further, this method is adapted to lithium metal foil with an intermetallic coating. ToF-SIMS sputter depth profiles in both polarities provide comprehensive insights into the coating structure. Both investigations highlight the value of ToF-SIMS sputter depth profiling in lithium metal battery research and offer guidance for future studies.

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