Quantum Interference Device Research Articles

Engineering lateral quantum interference devices using electron beam lithography and molecular beam epitaxy

Various new lateral quantum interference devices (QIDs) have been facbricated using high resolution electron beam lithography and molecular beam epitaxy. These QIDs utilize various nanometer scale electrodes to introduce electrostatic potential barriers in the electron gas at an AlGaAs/GaAs heterojunction. At low temperatures, as the electron mean free path approaches the dimensions of the gate electrode, quantum interference of the electron wave with the barriers and wells creates quasibound states that result in conductance oscillations as the gate voltage is scanned. High resolution electron beam lithography is used to define the nanometer gates, readily allowing the definition and alignment of different electrodes on the same wafer. A planar implantation isolation step is used to facilitate the liftoff of the Ti/Au gates patterned in polymethyl methacrylate (PMMA). Several novel QIDs will be described; emphasis will be on a new lateral double barrier resonant tunneling diode formed by two 80 nm gates separated by 100 nm. At 4.2 K, structure in the drain current is seen as the gate voltage is scanned for drain voltages less than 5 mV.

Coherence length in quantum interference devices having periodic potential

A measurement of coherence length in the quantum interference device using drain current oscillation is proposed. The coherence length for a quantum interference device, called the washboard transistor, is measured by the proposed method. The merit of this method is that the quantitative value of the coherence length is measured using only quantum interference phenomena.

Measurement of contact resistance of electric contacts using SQUID galvanometer

AbstractSQUID (Superconducting Quantum Interference Device) is a very powerful tool in the measurement of very small current, voltage, and resistance because it can be used as a high‐sensitivity galvanometer with zero internal resistance. Since the contact resistance of electric contacts of good quality switches or connectors is low in the milliohm range, it cannot be measured without flowing a current in the range of more than milliamperes in the conventional measuring method. Accordingly, so far, no measured data exist in the very small current region below these values and it is not known whether or not the contact resistance will change in the very small current region in the switches or connectors used in the circuits used for very small signals. In this research, the very small current region of nanoamperes and very small voltage region of picovolts can be measured by using a SQUID galvanometer. In the typical examples of measured results obtained so far the contact resistance of new connectors showed a constant resistance independent of the magnitude and direction of the current in almost all cases.