Coulomb-blockade oscillations in disordered quantum wires

Abstract

The conductance of narrow wires, defined by a split-gate technique in the two-dimensional electron gas in a modulation-doped GaAs-Al^Gai-^As heterostructure, is studied experimentally äs a function of gate voltage, temperature, and magnetic field. Both intentionally (Be doped) and unintentionally disordered wires are investigated. Periodic conductance oscillations äs a function of gate voltage are found in both Systems, in the regime where only a few hundred electrons are present in the wire. The dominant oscillations are very regularly spaced, with a period that is quite insensitive to a strong magnetic field, and persist up to a few kelvin. A strong magnetic field is found to enhance the amplitude of the oscillations up to values approaching e 2 //«. The experimental data are analyzed in terrns of a theory for Coulomb-blockade oscillations in the conductance of a quantum dot in the regime of comparable level spacing Δ-Ε and charging energy e 2 /C, based on the assumed presence of a conductance-limiting segment in the wire. Good agreement with the experiment is obtained for the temperatuie dependence of the oscillations, using physically reasonable parameter values. At low temperatures, a crossover from the classical regime kßT > Δ£ to the quantum regime ksT < AE is found. The appeaiance of additional periodicities and the onset of irregulär oscillations at very low temperatures in some of the wires are attributed to the presence of multiple segments. No magnetoconductance oscillations are observed, in support of the recently predicted Coulomb blockade of the Aharonov-Bohm effect.

Wigner and Kondo physics in quantum point contacts revealed by scanning gate microscopy

“…However, the fact that approaching the tip towards the QPC results in four successive splittings of the ZBA indicates that this impurity should contain at least eight charges, which is unlikely for a single impurity. Nevertheless, one could imagine that a shallow quantum dot has formed in the QPC due to potential fluctuations induced by residual disorder 44 and giving Coulomb blockade oscillations as often observed in long 1D wires 45 . The major argument to exclude this scenario is that the split-gate has a larger capacitive coupling to the channel than the tip has (that is, a larger lever-arm parameter), so the split-gate should induce more charging events than the tip, but we observe the opposite: approaching the tip by 600 nm produces four successive splittings of the ZBA and sweeping the gate voltage produces only one splitting.…”

Cotunneling and one-dimensional localization in individual disordered single-wall carbon nanotubes: Temperature dependence of the intrinsic resistance

“…The conduction is then thermally activated R͑T͒Ϸexp͑T −1 ͒. [1][2][3][4] Measurements of 2D or 3D arrays of quantum dots can show a slower than thermally activated dependence of the conduction R͑T͒Ϸexp͑T −0.5 ͒. 5,6 This has been recently attributed to cotunneling processes, which allow charge transfer between nonadjacent quantum dots.…”

Single-electron transistor based on modulation-doped SiGe heterostructures

“…[1][2][3][4] However, despite the large improvements that SiGe technology has brought about in Si electronics, only one paper has recently reported on a Coulomb blockade device based on modulation-doped SiGe heterostructures. 5 As a matter of fact, these authors point out the difficulty of observing single-charge effects in this system, in which high leakage currents can bypass any Coulomb blockade effect.…”