Experimental condensed matter · PHYS 440 · UMass Amherst
Quantized conductance
in gold nanojunctions.
I built a measurement circuit and investigated mechanically formed gold nanojunctions, connecting features in laboratory traces to the quantum description of electrical transport.
- My work
- Measurement circuit, trace analysis & technical manuscript
- Course
- Intermediate Laboratory · Spring 2026
- Analyzed evidence
- Eight conductance traces
- Reported observation
- Plateau structure near 1–3 G0
Theoretical scale
G0 = 2e2/h
The conductance quantum sets the scale for comparing the observed plateaus. The equation is a theoretical reference, not a fitted result from the experiment.
01 / The physics question
What changes when a contact becomes extremely small?
A macroscopic wire is described by a smoothly varying resistance. At a sufficiently small contact, a useful description is transport through discrete quantum channels.
Gold nanojunctions provide a way to investigate that transition. As a mechanically formed contact changes, its conductance can develop short plateaus rather than varying smoothly throughout the trace. The experiment asks how those features compare with integer multiples of the conductance quantum.
How channels connect to conductance
In a simple channel picture, conductance is related to the sum of the transmission probabilities of the available channels:
G = G0 ∑n Tn
A fully transmitting channel contributes one conductance quantum. Partially transmitting channels, changing contact geometry, and the measurement circuit can complicate the relationship between a measured plateau and an integer multiple of G0.
Further reading: quantum transport in atomic-size contacts (opens in a new tab)02 / Experimental method
Build the circuit, then make the contact.
I built a circuit to measure the conductance of mechanically formed gold junctions. The work combined hands-on circuit assembly with acquisition and interpretation of the resulting electrical traces.
The contact changes mechanically, so the useful evidence is a sequence of electrical measurements through its evolution. The task is to distinguish plateau-like behavior from changes introduced by the measurement setup or by an unstable contact.
- Form a gold junction
Create and mechanically vary a conducting contact.
- Acquire electrical traces
Use the measurement circuit to follow changes in the junction.
- Analyze the conductance
Compare plateau structure with the scale set by G0 and document the interpretation.
03 / Data interpretation
A step is useful evidence. It still needs context.
I analyzed eight traces and documented plateau structure near 1–3 G0 in a technical manuscript. The analysis connects features in individual measurements to the expected conductance scale.
The important distinction is between an observed feature and a complete statistical characterization. A plateau close to an integer multiple is consistent with the channel picture; it does not, by itself, establish that every contact followed an ideal sequence.
What I looked for
Regions where conductance stays approximately level, changes between those regions, and their positions relative to G0. The interpretation has to account for the limited number of traces and the behavior of the measurement circuit.
This project was practice in explaining a physical result from the apparatus upward: what the circuit measures, what the trace shows, and what the model allows me to conclude.
04 / Observations & limits
Keep the conclusion as specific as the evidence.
- Experimental work
- A built measurement circuit and mechanically formed gold junctions.
- Analysis
- Eight analyzed traces with plateau structure near 1–3 conductance quanta.
- Research communication
- Methods and interpretation documented in a technical manuscript.
The reported plateau structure is the result summarized here. This page does not claim a fitted conductance value, a statistical plateau distribution, or a precision test of the conductance quantum.
Original traces and the manuscript are not currently published on this page. The presentation therefore uses the documented observation and the theoretical scale, without reconstructed data or an illustrative histogram that could be mistaken for a measurement.