By Josh Perry, Editor
[email protected]

Researchers from the Weizmann Institute of Science (Rehovot, Israel), the University of Toronto (Canada), and the University of Tel Aviv (Israel) have discovered a new type of electronic noise, called delta-T noise, which is created when two sides of an electrical junction are held at different temperatures.

Researchers have found a new thermal noise that could impact electronics.
(Wikimedia Commons)

As described in an article from Physics World, the researchers believe that this delta-T noise could cause problems as electronic components become smaller, but that it also could solve the challenge of trying to measure temperature at the nano-scale.

“In an electrode near absolute zero, almost all the electrons are in the lowest possible energy level,” the article explained. “Therefore, almost all the states up to a particular energy (the Fermi energy) are filled, whereas the higher energy levels are empty. In a warmer electrode, however, thermal excitation allows some electrons to jump to higher energy levels, leading to empty states below the Fermi energy and filled states above it.”

In junctions that have warm and cold electrodes, electrons will be moving in both directions. Above the Fermi energy layer, electrons will move from hot to cold but below that level they will move in the opposite direction. “Each current, however, experiences shot noise and, being uncorrelated, the random fluctuations do not cancel each other,” the article added.

Researchers needed to develop a method for measuring delta-T noise that included electrical heaters and thermometers in the system while keeping the system isolated from ambient noise signals that could cause fluctuations in the results.

The research was recently published in Nature. The abstract stated:

“Since the discovery a century ago of electronic thermal noise and shot noise, these forms of fundamental noise have had an enormous impact on science and technology research and applications. They can be used to probe quantum effects and thermodynamic quantities, but they are also regarded as undesirable in electronic devices because they obscure the target signal.

“Electronic thermal noise is generated at equilibrium at finite (non-zero) temperature, whereas electronic shot noise is a non-equilibrium current noise that is generated by partial transmission and reflection (partition) of the incoming electrons. Until now, shot noise has been stimulated by a voltage, either applied directly or activated by radiation.

“Here we report measurements of a fundamental electronic noise that is generated by temperature differences across nanoscale conductors, which we term ‘delta-T noise’. We experimentally demonstrate this noise in atomic and molecular junctions, and analyse it theoretically using the Landauer formalism.

“Our findings show that delta-T noise is distinct from thermal noise and voltage-activated shot noise8. Like thermal noise, it has a purely thermal origin, but delta-T noise is generated only out of equilibrium. Delta-T noise and standard shot noise have the same partition origin, but are activated by different stimuli.

“We infer that delta-T noise in combination with thermal noise can be used to detect temperature differences across nanoscale conductors without the need to fabricate sophisticated local probes.

“Thus it can greatly facilitate the study of heat transport at the nanoscale. In the context of modern electronics, temperature differences are often generated unintentionally across electronic components. Taking into account the contribution of delta-T noise in these cases is likely to be essential for the design of efficient nanoscale electronics at the quantum limit.”