TEM micrograph of the ultrathin nanowires showing them to be ~2nm in diameter. (Right) A four-probe nanowire device, with electrical contacts made via a modified device fabrication route.
Above: The normalised linear response resistance (R) as a function of temperature for four ultra-thin gold nanowire bunches with different number of wires is shown. In all cases R increases with decreasing T in a power law such that R ∝ T−a, which means that that a gold nanorire become insulating when its diameter is reduced to nanomenter scales.
We have investigated the electrical transport on molecular scale single crystalline wires of gold, with diameter of about 2nm (see above), which forms the thinnest freestanding noble metal wire ever measured. The wires are grown via a wet chemical route based on oriented attachment process, by Prof. N. Ravishankar’s group (http://mrc.iisc.ernet.in/~nravi/) at the Materials Research Center in IISc.
Our most striking finding is an insulating behavior in these wires, and emergence of a gap in the density of states, either of which are not expected in a simple transition metal system, such as gold. Our analysis provides very strong evidence for strong electron correlations and the emergence of collective behaviour that bear evidence of the Tomonaga-Luttinger Liquid state, in a metallic system. The linear response electrical resistance exhibits a power-law dependence on temperature (see above). In addition, the variation of current over a wide range of temperature and voltage obeys a universal scaling relation that provides compelling evidence for a non-Fermi liquid behaviour. The study demonstrates that the quantum ground state at the nanoscale can be radically different from the bulk, even in a simple metal. (For Reference, see Chandni et al. ACS Nano 2011, Chandni et al. Advanced Materials 2013)