Torsional instability in the single-chain limit of a transition metal trichalcogenide

The scientific bounty resulting from the successful isolation of few to single layers of two-dimensional materials suggests that related new physics resides in the few- to single-chain limit of one-dimensional materials. We report the synthesis of the quasi–one-dimensional transition metal trichalcogenide NbSe3 (niobium triselenide) in the few-chain limit, including the realization of isolated single chains. The chains are encapsulated in protective boron nitride or carbon nanotube sheaths to prevent oxidation and to facilitate characterization. Transmission electron microscopy reveals static and dynamic structural torsional waves not found in bulk NbSe3 crystals. Electronic structure calculations indicate that charge transfer drives the torsional wave instability. Very little covalent bonding is found between the chains and the nanotube sheath, leading to relatively unhindered longitudinal and torsional dynamics for the encapsulated chains.

Colloidal solutions of niobium trisulfide and niobium triselenide

Bulk NbS3and NbSe3were stably dispersed in a number of organic solvents to yield colloids containing thin well-crystallized nanoribbons of NbS3and NbSe3.

Fabricated structures for studying mesoscopic physics of charge density waves

We present new methods for patterning and controlling the cross-section of the CDW conductor niobium triselenide crystals to sub-micron dimensions using photolithography and electron beam lithography. Experiments demonstrating these techniques are presented: accurate four-probe measurement of the c-axis resistivity as a function of temperature, and measurements of width and thickness-dependent size effects on the CDW condensate. In all samples, a region with near-perfect rectangular cross-section is left to provide a control, eliminating the need to compare different samples and reduces the role of sample-to-sample variations in the analyses.

A model of coherent creep and switching in charge density wave conduction in NbSe3 at low temperatures

A model is proposed of the temporally ordered collective creep with finite threshold field, and of the “switching" transition to a hgNy conducting state at a higher threshold, observed in charge-density wave conduction in niobium triselenide by Lemay et al. [phys. Rev. Lett. 83,2793 (1999)]. The model is based on their suggestion that the creep involves the thermally activated advance of wavelengths of CDW past individual impurities. In the model this is achieved by the formation near the impurity of a dislocation loop, which collapses after encircling it. Switching is attributed to a transition, induced by stress associated with the motion, to a situation in which collapse is avoided, enabling the CDW to advance indefinitely. The model accounts quantitatively for the observed creep, and exhibits switching and hysteresis qualitatively similar to that observed.