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

Abstract

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 $2{\Delta }_1$ and $2{\Delta }_2$ obtained from photo-emission. These results can be explained by assuming CDW-CDW tunneling in the presence of an energy gap corrugation ${\epsilon }_2$ comparable to ${\Delta }_2$, which eliminates expected peak at ${\Delta }_1+{\Delta }_2$. The nanometer length-scales our experiments imply indicate that an alternative explanation based on tunneling through back-to-back CDW-normal junctions is unlikely.

5 pages, 3 figures, submitted to physical review letters