Monday, September 14, 2015
APL accepted: Liquid-induced damping of mechanical feedback effects in single electron tunneling through a suspended carbon nanotube
One of the surprises that suspended, clean carbon nanotubes have in store is that they can start vibrating strongly at millikelvin temperatures without any applied radio-frequency driving signal. This was proposed theoretically several years ago by Usmani et al., as a strong feedback between the transversal vibration of the nanotube and the single electron tunneling through it. The effect was identified in measurements, and for example in a previous publication we have shown that damping induced by a magnetic field can suppress it.
Here, we demonstrate how one and the same device behaves distinctly different depending on the environment medium (or lack of the latter): we compare measurements made at the same temperature in a conventional dilution refrigerator, where the chip is placed into a vacuum chamber, and in a so-called top-loading dilution refrigerator, where the chip is inserted into the 3He/4He liquid of the mixing chamber. The overall electronic properties of the device do not change much, even though the thermal cycling could cause a lot of damage and has done so in the past for other devices. We can here even extract a rough estimate of the liquid helium dielectric constant by comparing the slightly shifted Coulomb oscillation positions of the two measurements.
However, a striking difference appears when looking at finite bias conductance and the mechanical feedback effects. In the viscous helium liquid, the resonator is damped and the vibrations are suppressed, and the unperturbed electronic transport spectrum emerges. Such an inert, liquid environment can thus be used to do transport spectroscopy at high transparency of the tunnel barriers and high applied bias voltages - parameter regions interesting for e.g. non-equilibrium Kondo phenomena, where otherwise mechanically-induced features would make data evaluation highly challenging.
"Liquid-induced damping of mechanical feedback effects in single electron tunneling through a suspended carbon nanotube"
D. R. Schmid, P. L. Stiller, Ch. Strunk, and A. K. Hüttel
Applied Physics Letters 107, 123110 (2015); arXiv:1407.2114 (PDF)