The metastable heterostructure, (BiSe) 0.97 MoSe 2 , containing alternating bilayers of BiSe and MoSe 2 trilayers was synthesized using the modulated elemental reactant method to determine if charge transfer from BiSe to MoSe 2 would stabilize the metallic 1T polymorph of MoSe 2 . Optimum synthesis conditions were determined by following the structural evolution as a function of temperature. The structure of the product contained distorted rock salt-structured BiSe layers alternating with hexagonal MoSe 2 layers. High-angle annular dark field scanning transmission electron microscopy images revealed that two different polymorphs of MoSe 2 coexisted in (BiSe) 0.97 MoSe 2 . Raman spectroscopy confirmed the presence of 1T MoSe 2 layers. X-ray photoelectron spectroscopy (XPS) indicated that there were two different electronic states for both Mo and Bi. The Mo states are consistent with having octahedral and trigonal prismatic coordination of molybdenum as found in the 1T and 2H polymorphs of MoSe 2 . The two different electronic states for Bi are consistent with the presence of antiphase boundaries in the BiSe layers. Estimating the relative amount of each electronic state from the XPS spectra indicates that the percentage of 1T MoSe 2 is about 40%, whereas the amount of Bi 3+ in the BiSe is approximately 60%. The measured resistivity increases as temperature is decreased, consistent with an activated conduction mechanism with a small activation energy (∼0.05 eV). The temperature stability and low resistivity of (BiSe) 0.97 MoSe 2 make it potentially interesting as a means of improving electrical contacts to MoSe 2 .

UTe2 is a newly-discovered unconventional superconductor wherein multicomponent topological superconductivity is anticipated based on the presence of two superconducting transitions and time-reversal symmetry breaking in the superconducting state. The observation of two superconducting transitions, however, remains controversial. Here we demonstrate that UTe2 single crystals displaying an optimal superconducting transition temperature at 2 K exhibit a single transition and remarkably high quality supported by their large residual resistance ratio and small residual heat capacity in the superconducting state. Our results shed light on the intrinsic superconducting properties of UTe2 and bring into question whether UTe2 is a multicomponent superconductor at ambient pressure.

Understanding structure−function relationships is essential to guide the designed synthesis of novel materials with emergent properties. In this work, we targeted the metastable heterostructures [(PbSe) 1+δ ] m (VSe 2 ) 1 , where m = 1−4, to test if the charge density wave (CDW) transition temperature increases as the layer thickness separating the VSe 2 monolayers increases, as was observed when SnSe was the separating layer. The modulated elemental reactant approach was used to make the targeted products. This approach involves depositing elemental layers in which the number of atoms of each element per square angstrom in Pb|Se and V| Se bilayers equals the number calculated for a rock salt-structured PbSe bilayer and a CdI 2 -structured VSe 2 slab, respectively. Layered elemental precursors with the correct composition and nanoarchitecture for each of the targeted compounds were prepared by repeatedly depositing a single V|Se bilayer followed by m Pb|Se bilayers. Precursors close to the targeted number of atoms per unit area were determined via X-ray fluorescence and the correct nanoarchitecture self-assembled to the targeted compounds during a low-temperature anneal. Resistivity measurements show that the number of PbSe layers per repeat unit (m) does not change the charge density transition onset temperature as previously reported for the analogous [(SnSe) 1+δ ] m (VSe 2 ) 1 compounds. The temperature dependence and absolute values of the resistivity of the m = 3 and 4 heterostructures scale as expected for composite behavior. The difference in the thickness dependence of the CDW transition between the PbSe-and SnSe-containing compounds highlights that the identity of the intervening rock salt layer plays a more important role in modifying the CDW onset temperature than the separation of the VSe 2 layers.

Newly-discovered superconductor UTe2 is a strong contender for a topological spin-triplet state wherein a multi-component order parameter arises from two nearly-degenerate superconducting states. A key issue is whether both of these states intrinsically exist at ambient pressure. Through thermal expansion and calorimetry, we show that UTe2 at ambient conditions exhibits two detectable transitions only in some samples, and the size of the thermal expansion jump at each transition varies when the measurement is performed in different regions of the sample. This result indicates that the two transitions arise from two spatially separated regions that are inhomogeneously mixed throughout the volume of the sample, each with a discrete superconducting transition temperature (Tc). Notably, samples with higher Tc only show a single transition at ambient pressure. Above 0.3 GPa, however, two transitions are invariably observed in ac calorimetry. Our results not only point to a nearly vertical line (constant pressure) in the pressure-temperature phase diagram but also provide a consistent scenario for the sample dependence of UTe2.

The interaction between a rock salt compound, PbSe, and the surface of a dichalcogenide (VSe2) is probed by making PbSe, VSe2, [(PbSe)1.11]1(VSe2)1 and PbSe on VSe2 films. PbSe precursors deposited on SiO2 form rough films with randomly oriented PbSe crystallites. VSe2 precursors deposited on a SiO2 surface form crystallographically aligned films. The precursor to the metastable misfit layer compound [(PbSe)1.11]1(VSe2)1 deposited on SiO2 forms a crystallographically aligned film. PbSe precursors deposited on VSe2 are very crystallographically aligned relative to PbSe deposited on SiO2. This reflects the strong interaction between PbSe and VSe2 at the interface. The results suggest that comparing the degree of crystallographic alignment of films of precursors of prospective constituents on SiO2 relative to depositing them on each other may be a simple test to show if a misfit layer compound will form between the two constituents.