Historical research guide · 0638 · 1991

The electrostatic Aharonov–Bohm effect

Giorgio Matteucci · Giulio Pozzi

In one minute

Giorgio Matteucci and Giulio Pozzi built the electric half of the Aharonov–Bohm effect and showed it in an ordinary electron microscope. The 1959 proposal had two halves. In the magnetic one, an electron passing a shielded magnetic flux shifts its interference fringes although no field ever touches it. In the electric one the shift comes from the electrical potential alone — and that half was far harder to realise, because the original thought experiment wanted metal tubes switched on and off in time, and a real electron beam is much smaller than any tube you can build. The Bologna pair found a way round it. Join two different metals in one fine wire and the contact potential between them dresses the wire in a line-dipole field: an electron passing on either side gets no sideways push at all, yet picks up a phase of opposite sign on each side. Run that wire through a biprism interferometer and the fringes move as predicted. This chapter, given at the meeting marking thirty years of the effect, is their account.

Connection

Chapter 10 rests on the claim that the electromagnetic potential is a real, usable handle on phase, and this is the electric case of that claim reduced to a wire, a biprism and a photographic plate. It also shows the shape of the site’s favourite kind of argument: the reason the experiment is interesting is not that fringes moved, but that the geometry was chosen so nothing could have pushed them.

From the source

The electric Aharonov–Bohm effect is the second half of the 1959 proposal: an electron’s phase depends on the electrical potential integrated along its path, so two beams held at different potentials while both sit in field-free regions should interfere differently when they are brought back together. Realising the original geometry — beams inside switched metal tubes — is beyond the dimensions of a real electron interferometer, which is why the electric case lagged so far behind the magnetic one.Opening sections, pages 62 to 64
The substitute for the switched tubes is a bimetallic wire. Two different metals joined in a single fine wire sit at different contact potentials, and that difference dresses the wire in a line-dipole electrostatic field, giving a potential structure an electron beam can be flown past inside a microscope column.Experimental section, pages 64 to 66; and Matteucci and Pozzi, Physical Review Letters 54, 2469 (1985), at /library/stm-aa2e3a4421
The dipole geometry is the whole point of the design: the electric field around the wire does not vanish, but it produces no deflecting force on the passing electrons, while the phase acquired on one side of the wire comes out with the opposite sign to the phase acquired on the other — a signature no simple deflection can imitate.Experimental section, pages 64 to 68
It was measured on ordinary equipment: a standard transmission electron microscope fitted with an electron biprism, with the phase difference showing up in both Fresnel and Fraunhofer diffraction from the charged wire, and the observed fringe displacement carrying the opposite signs on the two sides that the calculation predicts.Results, pages 66 to 69; published as Physical Review Letters 54, 2469 (1985)
The authors’ methodological claim is that the interferometer, not the image, is what settles it: only interference electron microscopy allows the quantum phase difference due to the contact potential to be detected unambiguously, because a plain shadow image of a charged wire can be read as ordinary electron-optical deflection.Closing discussion, pages 69 to 71; developed in the same authors’ electron-optical analysis in Ultramicroscopy 45, 1992
The steady-state version leaves one thing for a later experiment to close. Because the field is on all the time rather than switched, the electrons are not deflected sideways but they can be speeded up or delayed along their path by Coulomb forces, which would mimic part of the phase shift — so the measurement that finishes the argument is a timing measurement, of the kind Caprez, Barwick and Batelaan later performed for the magnetic case and found flat to a tenth of a nanosecond.The open question left by the steady-state geometry; the timing test is at /library/stm-d405e2fac7

The way in

https://doi.org/10.1142/9789814439251_0005

Historical source-access record. This guide links to the original; it does not reproduce the paper text.

A chapter on pages 62 to 71 of Quantum Coherence, the proceedings of the International Conference on Fundamental Aspects of Quantum Theory held in South Carolina to celebrate thirty years of the Aharonov–Bohm effect, published by World Scientific in March 1991. Giorgio Matteucci was at the Department of Physics, University of Bologna; Giulio Pozzi at the Department of Materials Science, University of Lecce. Licence checked: the volume is under World Scientific copyright with no Creative Commons grant, and the publisher’s site returns 403 to any automated request, so the chapter text was not reachable and none of it is reproduced here. The summary and claims are the site’s own, written from the bibliographic record and from the authors’ own published account of the same experiment — their Physical Review Letters 54, 2469 (1985), which this library also holds — together with the standard description of that experiment in the review literature. Where a claim rests on that surrounding record rather than on the chapter’s own pages, the locator says so. TITLE. The record reached the library with the title set in full capitals as it appears in the publisher’s metadata; it is given here in ordinary sentence case. Three companion sheets carry the rest of the Aharonov–Bohm record: the authors’ own 1985 diffraction experiment at /library/stm-aa2e3a4421, Caprez, Barwick and Batelaan’s macroscopic timing test at /library/stm-d405e2fac7, and Becker, Guzzinati, Béché, Verbeeck and Batelaan on asymmetry and non-dispersivity at /library/stm-81bc78c3b1.

How to cite it

Giorgio Matteucci, Giulio Pozzi (1991) The electrostatic Aharonov–Bohm effect doi:10.1142/9789814439251_0005

Where it sits in the curriculum

Scalar waves and the field behind the fields