arXiv subjects

K. O'Neill

Publications and source records attributed to K. O'Neill.

4 recordsLinked to original sources

arXiv2007

Self-breaking in planar few-atom Au constrictions for nm-spaced electrodes

We present results on electromigrated Au nanojunctions broken near the conductance quantum $77.5 μ$S. At room temperature we find that wires, initially narrowed by an actively-controlled electromigration technique down to a few conductance quanta, continue to narrow after removing the applied voltage. Separate electrodes form as mobile gold atoms continuously reconfigure the constriction. We find, from results obtained on over 300 samples, no evidence for gold cluster formation in junctions broken without an applied voltage, implying that gold clusters may be avoided by using this self-breaking technique.

cond-mat.mtrl-sci↗

arXiv2006

In-Chain Tunneling Through Charge-Density Wave Nanoconstrictions and Break-Junctions

We have fabricated longitudinal nanoconstrictions in the charge-density wave conductor (CDW) NbSe$_{3}$ using a focused ion beam and using a mechanically controlled break-junction technique. Conductance peaks are observed below the T$_{P1}$$=145 $K and T$_{P2}$$=59 $K CDW transitions, which correspond closely with previous values of the full CDW gaps $2Δ_{1}$ and $2Δ_{2}$ obtained from photo-emission. These results can be explained by assuming CDW-CDW tunneling in the presence of an energy gap corrugation $ε_{2}$ comparable to $Δ_{2}$, which eliminates expected peak at $Δ_{1}+Δ_{2}$. The nanometer length-scales our experiments imply indicate that an alternative explanation based on tunneling through back-to-back CDW-normal junctions is unlikely.

cond-mat.str-el↗

arXiv2004

Measurement of the shear strength of a charge-density wave

We have explored the shear plasticity of charge density waves (CDWs) in niobium triselenide samples with cross-sections having a single micro-fabricated thickness step. Shear stresses along the step result from thickness-dependent CDW pinning. For small thickness differences the CDW depins elastically at the volume average depinning field. For large thickness differences the thicker, more weakly pinned side depins first via plastic shear. A simple model describes the qualitative features of our data, and yields a value for the CDW's shear strength of approximately 9.5*10^3 N/m^2 and a lower bound for the elastic shear modulus of 2.1*10^4 N/m^2. These values are orders of magnitude smaller than the CDW's longitudinal modulus but are much larger than corresponding values for flux-line lattices, and may explain the relative coherence of the CDW response.

cond-mat.str-el↗

arXiv2003

Crossover from 2-dimensional to 1-dimensional collective pinning in NbSe3

We have fabricated NbSe$_3$ structures with widths comparable to the Fukuyama-Lee-Rice phase-coherence length. For samples already in the 2-dimensional pinning limit, we observe a crossover from 2-dimensional to 1-dimensional collective pinning when the crystal width is less than 1.6 $μ$m, corresponding to the phase-coherence length in this direction. Our results show that surface pinning is negligible in our samples, and provide a means to probe the dynamics of single domains giving access to a new regime in charge-density wave physics.

cond-mat.str-el↗