Search for: All records

The molecule-based ferrimagnetic semiconductor vanadium tetracyanoethylene (V[TCNE] x , x [Formula: see text] 2) has garnered interest from the quantum information community due to its excellent coherent magnonic properties and ease of on-chip integration. Despite these attractive properties, a detailed understanding of the electronic structure and mechanism for long-range magnetic ordering have remained elusive due to a lack of detailed atomic and electronic structural information. Previous studies via x-ray absorption near edge spectroscopy and the extended x-ray absorption fine structure have led to various proposed structures, and in general, V[TCNE] x is believed to be a three-dimensional network of octahedrally coordinated V 2+ , each bonded to six TCNE molecules. Here, we elucidate the electronic structure, structural ordering, and degradation pathways of V[TCNE] x films by correlating calculations of density functional theory (DFT) with scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) of V[TCNE] x films. Low-loss EELS measurements reveal a bandgap and an excited state structure that agree quantitatively with DFT modeling, including an energy splitting between apical and equatorial TCNE ligands within the structure, providing experimental results directly backed by theoretical descriptions of the electronic structure driving the robust magnetic ordering in these films. Core-loss EELS confirms the presence of octahedrally coordinated V +2 atoms. Upon oxidation, changes in the C1s- π* peak indicate that C=C of TCNE is preferentially attacked. Furthermore, we identify a relaxation of the structural ordering as the films age. These results lay the foundation for a more comprehensive and fundamental understanding of magnetic ordering and dynamics in these classes of metal–ligand compounds. 

The interface between 2D topological Dirac states and ans‐wave superconductor is expected to support Majorana‐bound states (MBS) that can be used for quantum computing applications. Realizing these novel states of matter and their applications requires control over superconductivity and spin‐orbit coupling to achieve spin‐momentum‐locked topological interface states (TIS) which are simultaneously superconducting. While signatures of MBS have been observed in the magnetic vortex cores of bulk FeTe_0.55Se_0.45, inhomogeneity and disorder from doping make these signatures unclear and inconsistent between vortices. Here superconductivity is reported in monolayer (ML) FeTe_1–ySe_y(Fe(Te,Se)) grown on Bi₂Te₃by molecular beam epitaxy (MBE). Spin and angle‐resolved photoemission spectroscopy (SARPES) directly resolve the interfacial spin and electronic structure of Fe(Te,Se)/Bi₂Te₃heterostructures. Fory = 0.25, the Fe(Te,Se) electronic structure is found to overlap with the Bi₂Te₃TIS and the desired spin‐momentum locking is not observed. In contrast, fory = 0.1, reduced inhomogeneity measured by scanning tunneling microscopy (STM) and a smaller Fe(Te,Se) Fermi surface with clear spin‐momentum locking in the topological states are found. Hence, it is demonstrated that the Fe(Te,Se)/Bi₂Te₃system is a highly tunable platform for realizing MBS where reduced doping can improve characteristics important for Majorana interrogation and potential applications.