Length dependence of conductance fluctuations in metallic nanobridges

Abstract

Magnetoconductance experiments on metallic nanobridges were performed in a mesoscopic twoprobe con6guration. In our samples a short wire of length L = 100 nm to L = 1 p,m and cross section 30 x 30 nm connected two funnel-shaped contacts. The contacts served as both voltage and current leads. The dependence of conductance Suctuations (CF's) on the length of the mesoscopic wires was measured at temperatures T ( 100 mK. In this temperature range the rms amplitude bG of the CF equals its low-temperature value for all investigated devices. Magnetoconductance Suctuations are caused by the interference of electrons within a phase coherent area I"~. In short bridges F~e ncloses the nanometer wire and parts of the funnel-shaped contacts. Quantuxn diffusion of conduction electrons into the contacts leads to high-frequency magneto-CF. The diffusion in the wide contact regions becomes more and more important with decreasing wire length. This results in a decreasing correlation 6eld B, with decreasing wire length. We observed a weak dependence of the rms amplitude bG of the CF on the wire length, which we attribute to a dimensional crossover from a one-dimensional (1D) to a 2D systexn. Besides the saturation value of bG we studied the temperature dependence of CF's in the range 280 mK to 10 K for a L = 200 nm wire. The decrease of the magnitude of the CF starts only at T ) 500 mK. For higher temperatures it follows a T law.

Geometry dependence of the conductance fluctuations in metallic nanostructures

“…The main difference to the samples investigated in Refs. [8,9] is that in our case l is smaller than w, i.e. the transport is diffusive also in the transverse direction, whereas w ~ 1/2 in Ref.…”

“…the transport is diffusive also in the transverse direction, whereas w ~ 1/2 in Ref. [8]. This quasi-ballistic character of the samples in the transverse direction may cause the observed reduction of the rms-amplitude to 8G ,-~ O.…”

“…This quasi-ballistic character of the samples in the transverse direction may cause the observed reduction of the rms-amplitude to 8G ,-~ O. 12e2/h [6,8,9].…”

“…Experiments on long one-dimensional gold wires with two wide probes [8] and silver wires with two wide current probes and two narrow voltage probes [9] show ~G O.12e2/h. The reduction is attributed to the reduced backscattering probability from the wide probes into the narrow wires and is in qualitative agreement with the all reduction of the UCF amplitude in quasi-ballistic point contacts with diameter a [6,7].…”

The effect of a non‐uniform scattering potential on conductance fluctuations in a quantum wire

“…The calculated value of B crit is shown in the figure, and its close proximity to the experimental maximum is further evidence for scattering at the boundaries of the wire. The symmetry exhibited by the fluctuations upon reversal of the field shows that they are confined to the wire [10] and that the measurement is effectively a two-terminal one [11]. In the magnetic field ranges ∆B low and ∆B high , respectively below and above the critical field B crit , the fluctuations are different.…”