Non-linear conductance of a short quantum point contact

We have measured non-linear conductance $G$ of a very short, less than 80 nm in lithographic length, quantum point contact as a function of the source-drain voltage $V_{sd}$ and gate voltage $V_g$ at the device lattice temperature T$<$20 mK. The width/length ratio of the QPC is approximately 2.5. We observe several well-resolved plateaus in $G$ at $V_{ds}$=0, but find no prominent zero-bias peak in $G(V_{ds})$ reported by several groups in longer, lower aspect ratio contacts at near-opening gate voltage [1,2]. The peak is believed to arise due to Kondo-like correlations between a quasi-local magnetic state in the constriction [1,3] and the device leads. Our data suggest that the quasi-bound spin state does not form in short QPCs and agree qualitatively with the recent predictions [3]. [1] S.M. Cronenwett~et. al. {\em Physical Review Letters}, 88(226805), 2002. [2] E.J.~Koop et. al. {\em J Supercond Nov Magn}, 20:433, 2007.[3]Tomaz Rejec and Yigal Meir. {\em Nature}, 442:900, 2006.