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In metallic transition metal dichalcogenides (TMDs), which remain superconducting down to single-layer thickness, the critical temperature T c decreases for Nb-based, and increases for Ta-based materials. This contradicting trend is puzzling, impeding the development of a unified theory. Here we study the thickness-evolution of superconducting tunneling spectra in TaS 2  heterostructures. The upper critical field H c2 is strongly enhanced towards the single-layer limit - following H c 2 ∝ T c 2 . The same ratio holds for the entire family of intrinsically metallic 2H-TMDs, covering 4 orders of magnitude in H c2 . Using Gor'kov's theory, we calculate the suppression of T c by the competing charge density wave (CDW) order, which affects the quasiparticle density of states and the resulting T c and H c2 . The latter is found to be universally enhanced by two orders of magnitude. Our results substantiate CDW as the key determinant factor limiting T c across the TMD family., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Colloidal semiconductor quantum dots are robust emitters implemented in numerous prototype and commercial optoelectronic devices. However, active fluorescence colour tuning, achieved so far by electric-field-induced Stark effect, has been limited to a small spectral range, and accompanied by intensity reduction due to the electron-hole charge separation effect. Utilizing quantum dot molecules that manifest two coupled emission centres, we present a unique electric-field-induced instantaneous colour-switching effect. Reversible emission colour switching without intensity loss is achieved on a single-particle level, as corroborated by correlated electron microscopy imaging. Simulations establish that this is due to the electron wavefunction toggling between the two centres, induced by the electric field, and affected by the coupling strength. Quantum dot molecules manifesting two coupled emission centres may be tailored to emit distinct colours, opening the path for sensitive field sensing and colour-switchable devices such as a novel pixel design for displays or an electric-field-induced colour-tunable single-photon source., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Coupling of atoms is the basis of chemistry, yielding the beauty and richness of molecules. We utilize semiconductor nanocrystals as artificial atoms to form nanocrystal molecules that are structurally and electronically coupled. CdSe/CdS core/shell nanocrystals are linked to form dimers which are then fused via constrained oriented attachment. The possible nanocrystal facets in which such fusion takes place are analyzed with atomic resolution revealing the distribution of possible crystal fusion scenarios. Coherent coupling and wave-function hybridization are manifested by a redshift of the band gap, in agreement with quantum mechanical simulations. Single nanoparticle spectroscopy unravels the attributes of coupled nanocrystal dimers related to the unique combination of quantum mechanical tunneling and energy transfer mechanisms. This sets the stage for nanocrystal chemistry to yield a diverse selection of coupled nanocrystal molecules constructed from controlled core/shell nanocrystal building blocks. These are of direct relevance for numerous applications in displays, sensing, biological tagging and emerging quantum technologies.

Semiconductor heterostructure nanocrystals, especially with core/shell architectures, are important for numerous applications. Here we show that by decreasing the shell growth rate the morphology of ZnS shells on ZnSe quantum rods can be tuned from flat to islands-like, which decreases the interfacial strain energy. Further reduced growth speed, approaching the thermodynamic limit, leads to coherent shell growth forming unique helical-shell morphology. This reveals a template-free mechanism for induced chirality at the nanoscale. The helical morphology minimizes the sum of the strain and surface energy and maintains band gap emission due to its coherent core/shell interface without traps, unlike the other morphologies. Reaching the thermodynamic controlled growth regime for colloidal semiconductor core/shell nanocrystals thus offers morphologies with clear impact on their applicative potential.