Paul Thibado

Paul M. Thibado is Professor of Physics at the University of Arkansas. His work on the intrinsic motion of freestanding graphene is the most frequently cited scientific reference point of neutrinovoltaic technology.

The initial puzzle

A single sheet of graphene is not flat. It ripples in the third dimension — and these ripples are the reason a strictly two-dimensional crystal can be stable at room temperature at all. Without them, thermal motion would destroy it.

Thibado's group investigated this motion with a scanning tunnelling microscope observing individual regions a few nanometres across over long periods.

The surprising finding

One would have expected an even trembling of the kind ordinary thermal motion produces — many small, random displacements about a mean position.

What was found was something else. The membrane remains for a longer time in one curved shape and then suddenly snaps into the opposite one. Between these jumps lie many small oscillations.

Motions of this kind, with rare large excursions, are called Lévy motion in statistics. They differ mathematically from ordinary Brownian motion, and the group published this finding in 2016 in Physical Review Letters.

The step to energy

When a charged surface moves, the electric field in its surroundings changes. If a counter-electrode is placed nearby, an alternating current arises.

That alone is of no use — an alternating current from random motion averages to zero. A rectification is needed, that is, the ratchet effect.

Thibado's group coupled freestanding graphene through diodes into a circuit and published in 2020 in Physical Review E the measurement of a current obtained from it.

The objection and how it is handled

This is exactly where the technical discussion begins, and it has a venerable starting point.

Richard Feynman treated in his lectures a thought experiment going back to Marian Smoluchowski: a paddle wheel, nudged by molecules, connected to a ratchet that permits rotation in only one direction. Feynman showed that it does not work — the pawl is itself so small that it too is nudged by thermal motion and slips back exactly often enough to cancel the gain. As long as everything is at the same temperature, nothing remains.

Transferred to Thibado's setup, the objection reads: the diodes also have a temperature and they too make noise. A clean demonstration must show that the measured current does not stem from this intrinsic noise.

The group has presented several papers on this and argues that the motion of the graphene, because of its Lévy character, does not correspond to the simple equilibrium case Feynman treated.

The question remains open to this day. What was measured is undisputed; what it goes back to is still being investigated.

Why the group refers to it

The Neutrino® Energy Group cites Thibado's work as one of several building blocks. The connection is plain: if directed current can be obtained from the intrinsic motion of a graphene lattice, then that is in miniature exactly the process the multilayer film of graphene and silicon is meant to perform at scale.

The master equation describes this contribution as one channel among several — alongside particle momenta, cosmic muons and electromagnetic fluctuations.

Assessment

Thibado's papers appeared in peer-reviewed journals and continue to be discussed there — neither ignored nor refuted.

That is precisely the situation basic research is often in, and it can be described without exaggeration in both directions: a measured effect, a contested interpretation, open questions. Anyone wanting to place neutrinovoltaic technology will find here the most honest starting point.

Sources

  • P. Thibado et al.: Fluctuation-induced current from freestanding graphene, Physical Review E 102, 042101 (2020).
  • M. L. Ackerman et al.: Anomalous Dynamical Behavior of Freestanding Graphene Membranes, Physical Review Letters 117, 126801 (2016).