= Tsui-Störmer-Gossard fractional Hall experiment
{c}
<Daniel Tsui>, <Horst Störmer> and <Arthur Gossard> reported the effect in 1982. They grew <gallium arsenide>–<aluminium gallium arsenide> layers by <molecular beam epitaxy>, separating the <two-dimensional electron gas> from its <semiconductor doping>. They cut <Hall bars> and made <indium> contacts. Low-field measurements established <number density> and <charge carrier mobility>. A perpendicular <magnetic field> sweep measured transverse and longitudinal <sheet resistivities> at several <temperatures>. Cooling sharpened the plateau near $3h/e^2$ and the longitudinal minimum at <filling factor> $1/3$; integer plateaus provided an internal comparison. The longitudinal minimum remained finite at the lowest <temperature>: zero-temperature vanishing was unresolved. This established anomalous transport, without directly measuring excitation <electric charge>.<Two-Dimensional Magnetotransport in the Extreme Quantum Limit by Daniel Chee Tsui and others>[pp. 1559–1561, sample preparation, Figs. 1–2 and finite longitudinal minimum]{ref}
\Image[/fractional-hall-functional-readout.png]
{title=Separate transverse and longitudinal readouts of a <fractional quantum Hall effect> experiment}
{description=Original functional <Hall bar> schematic, with chosen contact labels and no historical dimensions. The inset separates the <two-dimensional electron gas> from <semiconductor doping>; the two meters distinguish transverse <electrical resistance> from longitudinal dissipation. No trace or measured value is reconstructed.}
The two readouts test different statements. A single intersection with $R_H=3R_K$ would also occur on the smooth classical relation $R_H=B/(n_se)$ at $n_sh/(eB)=1/3$. A <quantum Hall plateau> instead persists over a <magnetic field> interval. Comparing transverse and longitudinal signals helps distinguish that plateau from a contact-placement artefact; the <quantum Hall conductivity tensor inversion> quantifies the contamination when longitudinal <sheet resistivity> is nonzero.
Later, 1997 <shot noise> measurements associated with <quantum tunnelling> at <filling factor> $1/3$ tested the excitation <electric charge> separately, finding $e/3$. That is a different observable from a Hall plateau.<Observation of the e⁄3 Fractionally Charged Laughlin Quasiparticle by L. Saminadayar and others>[Publisher abstract: tunnelling noise and inferred quasiparticle charge]{ref}
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