On the mechanistic understanding of transition between quantized conductance plateaus under strain perturbation
Huntington, Mark D.
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The quantum of electronic conductance is 2e 2 /h (G ° ) corresponding to a fully open transmission channel. Non-quantized conductance values or transition between conductance plateaus in non-integral values of G ° are observed when the available channels are partially transmitting or when the system is subjected to a perturbation. In this work a simple method based on differential in coefficient of thermal expansion between the electrodes of a metal point contact and its underlying substrate is developed. As the sample is cooled a controlled amount of strain is applied to the system. This allows for the observation of the complete and contiguous mechanistic structure of transition between adjacent conductance plateaus under strain perturbation. Using gold as a model system, results reveal three distinct stages during the controlled extraction of a single atom from a given point contact -- two stages where the conductance fluctuates due to partially open channels, separated by an intermediate stage of random telegraphic noise characterizing mechanical instability of the contact. Whereas random telegraphic noise in larger contacts was previously attributed to fluctuations of metastable defects between discrete configurations [K. S. Ralls and R. A. Buhrman, Phys. Rev. Lett. 60, 2434 (1988); Phys. Rev. B 44, 5800 (1991)], its appearance in the present study is attributed to the fluctuations of a metastable contact between discrete configurations having slightly different transmission probabilities. In addition to Au, preliminary studies on Cu and Ni show similar behavior, pointing to the universal nature of the transition. The technique can be easily applied to study multivalent elements, magnetic atoms, as well as molecular electronics and mechanics.