Stochastic processes are ubiquitous in nature. Also known as random processes, they can take multiple forms like a random walk, or a game of chance. Their studies have played a pivotal role in the development of modern physics starting with Langevin and the Brownian motion well illustrated by pollen grain floating in water. Recent advances in measurement precision and resolution have extended the framework of Brownian motion to unprecedented space-time scales and to a wider variety of systems, including atomic diffusion in optical lattices and spin diffusion in liquids. Studies of such systems are providing insights into the mechanisms and interactions responsible for stochasticity.
For example, membrane fluctuations are also a purview of Brownian motion. Where it becomes really interesting is when properly understood, the random membrane fluctuations can be usefully exploited for energy harvesting. From a stochastic nanoresonators, it could be possible to harvest the energy of the continuous movement of a massive system. The only condition for that to happen is to be able to control precisely the membrane fluctuations, and this just what a team from the University of Arkansas did!
This simulation illustrates the phenomenon of stochastic resonance. An overdamped particle in a periodically oscillating double-well potential is subjected to Gaussian white noise, which induces transitions between the potential wells.
The team of researchers led by physicist Paul Thibado reported the precise measurements of the motion of atoms in freestanding graphene. By tracking the vertical position over a long time period, they achieved to measure space-time dynamics of atomically thin membranes. They observed anomalous dynamics and long-tail equilibrium distributions like stochastic resonance phenomenon. By measuring the rate and scale of these graphene waves, Thibado figured it might be possible to harness it as an ambient temperature power source. So long as the graphene’s temperature allowed the atoms to shift around uncomfortably, it would continue to ripple and bend. Place electrodes to either side of sections of this buckling graphene, and you’d have a tiny shifting voltage.
Outline of experimental setup in the left. Perspective view of the membrane and height of the central carbon atom in time from simulation in the right.
Our measurements uncover an unexplored spatial and temporal domain in membrane fluctuations with profound implications both for our fundamental understanding and technological applications of membranes. Properly understood, the random membrane fluctuations can be usefully exploited. For example, energy harvesting from the continuous movement of a massive system is an important application of stochastic nanoresonators.