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Direct programming of functional metasurfaces is demonstrated by locally crystallizing the phase-change material In₃SbTe₂ via laser irradiation. In₃SbTe₂ is established as a versatile nanophotonic platform for beam steering, lensing, and holography.

Here, the authors experimentally demonstrate a platform for tunable polariton refractive and meta-optics based on hexagonal boron nitride and phase change Ge₃Sb₂Te₆. This combination has the advantage of the long-lived phonon-polariton with switchable refractive index of the phase change material.

Phase-change materials are widely used as non-volatile memories, for example in optical data storage, but the search for improved phase-change materials has proved difficult. Based on a fundamental understanding of their bonding characteristics, a systematic prediction of phase-change properties has now become possible.

Although phase-change materials are of significant importance for optical and electronic information storage applications, the search for new materials so far has been based on empirical methods. Now, the discovery that their crystalline phase shows resonant bonding opens the way to a deterministic search for new phase-change materials.

The occupied anti-bonding states at the Fermi level in metavalently bonded systems stems from the interplay between metavalent bonds and the phase of orbitals. This provides a recipe for identifying superior dopants to improve the thermoelectric performance of metavalently bonded materials.

The authors find chemical bonding mechanisms play a key role in tailoring the solubility of dopants and improving the thermoelectric performance of metavalently bonded materials.

Doping is a common strategy to improve thermoelectric performance yet limited to the solid solubility of dopants. Here, the authors find that forming metavalently bonded precipitates is key to property enhancement in Te rather than modifying the matrix lattice.

The pronounced temperature dependence of crystal-growth speed in phase-change materials not only rationalizes their favourable characteristics for non-volatile memory applications, but also suggests a profound new insight into their fundamental properties.

Studying the charge transport across individual grain boundaries is challenging yet important for materials design. Here, the authors find that metavalent bonding collapses at grain boundaries, increasing the barrier height for charge transport.

The crystallization of phase-change materials is relevant to their applications in memory and neuromorphic computing devices. Cheng et al. show that the β-relaxation in Ge₁₅Sb₈₅ can be controlled by thermal annealing, leading to the tunability in its crystallization kinetics by one order of magnitude.

Phase-change materials are a route to high-density data storage, but changes in their properties in time are a limiting factor. Here, the authors combine numerical simulations, photothermal deflection spectroscopy and impedance spectroscopy experiments to investigate the aging process in germanium telluride.

Tailoring the crystallization kinetics of materials is important for targeting applications. Here the authors observe a remarkable dependence of crystallization and vitrification kinetics and attribute it to systematic bonding changes for a class of materials between metallic and covalent bonding.

Tailored light-matter interaction can be achieved with surface phonon polaritons (SPhPs). Here, Conrads et al. employ the plasmonic phase-change material In₃SbTe₂ on the polar crystal SiC for direct programming of confined SPhP resonators and study their resonance modes via near-field microscopy.

Materials that undergo a structural transformation between amorphous and crystalline phases under the influence of an electrical current have been known for decades. But with the discovery of new phase-change materials and new device configurations to make them switch, interest in them is being rejuvenated.

Fundamental understanding of the kinetics of phase transitions in phase-change materials has been hindered by challenges in the experimental quantification. Via an in situ laser reflectivity technique, Salinga et al.measure the crystal growth kinetics, revealing an extremely high fragility in the supercooled liquid.

The authors demonstrate an efficient platform for electrically driven reconfigurable metasurfaces by using Ge₂Sb₂Te₅ to realize non-volatile, reversible, multilevel, and fast optical modulation and wavefront engineering in the near-infrared spectral range.

Here, the authors introduce In3SbTe2 (IST) as a programmable material platform for plasmonics and nanophotonics in the infrared. They demonstrate direct optical writing, modifying and erasing of metallic crystalline IST nanoantennas, tuning their resonances, as well as nanoscale screening and soldering.

SnSe has a very high thermoelectric figure of merit ZT, but uncommonly polycrystalline samples have higher lattice thermal conductivity than single crystals. Here, by controlling Sn reagent purity and removing SnO_x impurities, a lower thermal conductivity is achieved, enabling ZT of 3.1 at 783 K.

Quantitative imaging on the doping in phase-change materials for data storage remains scarce. Here, the authors combine electron microscopy, atom probe tomography, and simulations to determine the role of indium and silver dopants during recrystallization.

Optically rewritable surface phonon–polariton resonators are demonstrated in a system combining phase-change materials that can reversibly switch between amorphous and crystalline phases, with polar crystals that support surface phonon–polaritons.

Chalcogenide phase-change materials (PCMs) are leading candidates for non-volatile memory and neuro-inspired computing devices. This Review focuses on the crystallization mechanisms of PCMs as well as the design principles to achieve PCMs with high switching speeds and good data retention, which will aid the development of PCM-based universal memory and neuro-inspired devices.

Initially formed amorphous GeTe layer crystallizes during growth by molecular beam epitaxy, as critical film thickness is reached. A remarkable change in bonding mechanism and improvement in atomic order are observed, in striking contrast to conventional lattice-matched epitaxial systems. Supported by density function theory calculations, resonant bonding is shown to be less favorable in an ultrathin GeTe film.