Quasi-Homoepitaxial Growth of Highly Strained Alkali-Metal Ultrathin Films on Kagome Superconductors.

Applying lattice strain to thin films, a critical factor to tailor their properties such as stabilizing a structural phase unstable at ambient pressure, generally necessitates heteroepitaxial growth to control the lattice mismatch with substrate. Therefore, while homoepitaxy, the growth of thin film on a substrate made of the same material, is a useful method to fabricate high-quality thin films, its application to studying strain-induced structural phases is limited. Contrary to this general belief, here the quasi-homoepitaxial growth of Cs and Rb thin films is reported with substantial in-plane compressive strain.

Moiré-Assisted Realization of Octahedral MoTe Monolayer.

A current key challenge in 2D materials is the realization of emergent quantum phenomena in hetero structures via controlling the moiré potential created by the periodicity mismatch between adjacent layers, as highlighted by the discovery of superconductivity in twisted bilayer graphene. Generally, the lattice structure of the original host material remains unchanged even after the moiré superlattice is formed. However, much less attention is paid for the possibility that the moiré potential can also modify the original crystal structure itself.

Fermiology and Origin of T_{c} Enhancement in a Kagome Superconductor Cs(V_{1-x}Nb_{x})_{3}Sb_{5}.

Kagome metals AV_{3}Sb_{5} (A=K, Rb, and Cs) exhibit a characteristic superconducting ground state coexisting with a charge density wave (CDW), whereas the mechanisms of the superconductivity and CDW have yet to be clarified. Here we report a systematic angle-resolved photoemission spectroscopy (ARPES) study of Cs(V_{1-x}Nb_{x})_{3}Sb_{5} as a function of Nb content x, where isovalent Nb substitution causes an enhancement of superconducting transition temperature (T_{c}) and the reduction of CDW temperature (T_{CDW}). We found that the Nb substitution shifts the Sb-derived electron band at the Γ point downward and simultaneously moves the V-derived band around the M point upward to lift up the saddle point (SP) away from the Fermi level, leading to the reduction of the CDW-gap magnitude and T_{CDW}.

Selective Fabrication of Bismuthene and α-Bi on Hydrogen-Terminated SiC(0001).

Nanomaterials based on monoatomic bismuth (Bi) are attracting particular attention because they are candidates of two-dimensional (2D) topological insulators and Rashba metals useful for spintronic applications. We report convenient selective fabrication of two different types of ultrathin Bi films, bismuthene and α-Bi on hydrogen-terminated SiC(0001), by combining the molecular-beam-epitaxy (MBE) method and the low-temperature and low-pressure hydrogen chemical etching of SiC. We have succeeded in selectively fabricating these two different Bi phases by simply tuning the substrate temperature during the MBE process.

Dirac semimetal phase and switching of band inversion in XMgBi (X = Ba and Sr).

Topological Dirac semimetals (TDSs) offer an excellent opportunity to realize outstanding physical properties distinct from those of topological insulators. Since TDSs verified so far have their own problems such as high reactivity in the atmosphere and difficulty in controlling topological phases via chemical substitution, it is highly desirable to find a new material platform of TDSs. By angle-resolved photoemission spectroscopy combined with first-principles band-structure calculations, we show that ternary compound BaMgBi is a TDS with a simple Dirac-band crossing around the Brillouin-zone center protected by the C symmetry of crystal.