The kagome lattice provides a fertile platform to explore novel symmetry-breaking states. Charge-density wave (CDW) instabilities have been recently discovered in a new kagome metal family, commonly considered to arise from Fermi-surface instabilities. Here we report the observation of Raman-active CDW amplitude modes in CsV3Sb5, which are collective excitations typically thought to emerge out of frozen soft phonons, although phonon softening is elusive experimentally. The amplitude modes strongly hybridize with other superlattice modes, imparting them with clear temperature-dependent frequency shift and broadening, rarely seen in other known CDW materials. Both the mode mixing and the large amplitude mode frequencies suggest that the CDW exhibits the character of strong electron-phonon coupling, a regime in which phonon softening can cease to exist. Our work highlights the importance of the lattice degree of freedom in the CDW formation and points to the complex nature of the mechanism.

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Hysteretic switching of domain states is a salient character of all ferroic materials and the foundation for their multifunctional applications. Ferro-rotational order is emerging as a new type of ferroic order featuring structural rotations, but its controlled switching remains elusive due to its invariance under both time reversal and spatial inversion. Here, we demonstrate electrical switching of ferro-rotational domain states in nanometer-thick 1T -TaS 2 crystals in its charge-density-wave phases. Cooling from the high-symmetry phase to the ferrorotational phase under an external electric field induces domain state switching and domain wall formation, realized in a simple two-terminal configuration using a volt-scale voltage. Although the electric field does not couple with the order due to symmetry mismatch, it drives domain wall propagation to give rise to reversible, durable, and nonvolatile isothermal state switching at room temperature. These results pave the path for manipulation of the ferro-rotational order and its nanoelectronic applications. MainFerroic orders arise from symmetry-breaking phase transitions, finding applications in wide-ranging advanced technologies [1]. Symmetry therefore provides a powerful guide to the identification of conjugate fields that couple with and even switch the orders -a prerequisite for utilizing the associated multi-stable domain states [2]. This principle is well applicable to three out of the four types of ferroics with a vector order parameter [2]: ferromagnets (ferroelectrics) feature time-reversal (spatial-inversion) symmetry breaking spontaneous magnetization (electric polarization) that is switchable by a magnetic (electric) field, whereas the ferro-toroidal order breaks both symmetries and can be switched using composite magnetic and electric fields [3][4][5]. The remaining type -the ferro-rotational (also known as ferroaxial) order -stands out, as it is both time-reversal and spatial-inversion invariant, hence insensitive to electromagnetic fields [2,6]. The lack of external fields that hysteretically switch the ferro-rotational order casts doubts on its ferroic nature [7] and limits its potential applications.

There is a lack of deep understanding of hydrogen intercalation into graphite due to many challenges faced during characterization of the systems. Therefore, a suitable route to trap isolated hydrogen molecules (H 2 ) between the perfect graphite lattices needs to be found. Here we realize the formation of hydrogen bubbles in graphite with controllable density, size, and layer number. We find that the molecular H 2 cannot be diffused between nor escape from the defect-free graphene lattices, and it remains stable in the pressurized bubbles up to 400 °C. The internal pressure of H 2 inside the bubbles is strongly temperature dependent, and it decreases as the temperature rises. The proton permeation rate can be estimated at a specific plasma power. The producing method of H 2 bubbles offers a useful way for storing hydrogen in layered materials, and these materials provide a prospective research platform for studying nontrivial quantum effects in confined H 2 .