Electrical-Field Modulation of the Charge-Density-Wave Quantum Condensate in h-BN/NbS3_3 Heterostructure Devices

We report on the field-effect modulation of the charge-density-wave quantum condensate in the top-gated heterostructure devices implemented with quasi-one-dimensional NbS$_3$ nanowire channels and quasi-two-dimensional h-BN gate dielectric layers. The charge-density-wave phases and collective current in quasi-1D NbS$_3$ nanowires were verified via temperature dependence of the resistivity, non-linear current-voltage characteristics, and Shapiro steps that appeared in the device response under radio frequency excitation mixed with the DC bias. It was demonstrated that the electric field of the applied gate bias can reversibly modulate the collective current of the sliding charge-density-wave condensate. The collective current reduces with more positive bias suggesting a surface effect on the condensate mobility. The single particle current, at small source-drain biases, shows small amplitude fluctuation behavior, attributed to the variations in the background potential due to the pinned or creeping charge-density-wave condensate. The knowledge of the electric-field effect on the charge density waves in quasi-1D NbS$_3$ nanowires is useful for potential electronic applications of such quantum materials.Comment: 17 pages; 5 figure

Low-Frequency Noise Spectroscopy of Charge-Density-Wave Phase Transitions in Vertical Quasi-2D Devices

We report results regarding the electron transport in vertical quasi-2D layered 1T-TaS2 charge-density-wave devices. The low-frequency noise spectroscopy was used as a tool to study changes in the cross-plane electrical characteristics of the quasi-2D material below room temperature. The noise spectral density revealed strong peaks - changing by more than an order-of-magnitude - at the temperatures closely matching the electrical resistance steps. Some of the noise peaks appeared below the temperature of the commensurate to nearly-commensurate charge-density-wave transition, possibly indicating the presence of the debated "hidden" phase transitions. These results confirm the potential of the noise spectroscopy for investigations of electron transport and phase transitions in novel materials.Comment: 16 pages; 5 figure

Decomposition of Ruthenium Olefin Metathesis Catalysts

The decomposition of a series of ruthenium metathesis catalysts has been examined using methylidene species as model complexes. All of the phosphine-containing methylidene complexes decomposed to generate methylphosphonium salts, and their decomposition routes followed first-order kinetics. The formation of these salts in high conversion, coupled with the observed kinetic behavior for this reaction, suggests that the major decomposition pathway involves nucleophilic attack of a dissociated phosphine on the methylidene carbon. This mechanism also is consistent with decomposition observed in the presence of ethylene as a model olefin substrate. The decomposition of phosphine-free catalyst (H_2IMes)(Cl)_2Ru CH(2-C_6H_4-O-i-Pr) (H_2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) with ethylene was found to generate unidentified ruthenium hydride species. The novel ruthenium complex (H_2IMes)(pyridine)_3(Cl)_2Ru, which was generated during the synthetic attempts to prepare the highly unstable pyridine-based methylidene complex (H_2IMes)(pyridine)_2(Cl)_2Ru CH_2, is also reported

Specifics of the Elemental Excitations in "True One-Dimensional" MoI3_3 van der Waals Nanowires

We report on the temperature evolution of the polarization-dependent Raman spectrum of exfoliated MoI$_3$, a van der Waals material with a "true one-dimensional" crystal structure that can be exfoliated to individual atomic chains. The temperature evolution of several Raman features reveals anomalous behavior suggesting a phase transition of a magnetic origin. Theoretical considerations indicate that MoI$_3$ is an easy-plane antiferromagnet with alternating spins along the dimerized chains and with inter-chain helical spin ordering. The calculated frequencies of the phonons and magnons are consistent with the interpretation of the experimental Raman data. The obtained results shed light on the specifics of the phononic and magnonic states in MoI$_3$ and provide a strong motivation for future study of this unique material with potential for spintronic device applications.Comment: 28 page

Hydrothermal growth of two-dimensional SrMnO3

Nanosheets of the four-layered, hexagonal perovskite 4H-SrMnO3, an end-member in a class of magnetoresistive materials, have been synthesized via a hydrothermal method. MnO2 nanosheets were used as the precursor to act as the Mn source which diverges from the Mn-salt precursors commonly seen. These hydrothermal reactions were carried out over a range of times and temperatures with relatively low concentrations of NaOH. Identification and characterization were accomplished through powder X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The resulting nanosheets were found to possess lateral dimensions ranging from several hundred nanometers to a few microns. During the course of these reactions, the morphology was found to be dependent on the Mn:Sr ratio