Heat breaks the rules at the nanoscale and scientists used it to their advantage

Heat is something we encounter every day. A steaming cup of coffee gradually cools, a laptop warms up during use, and sunlight heats the Earth's surface. Yet when heat is examined at distances far smaller than the width of a human hair, it can behave in unexpected ways.

Researchers from Carnegie Mellon University, working with collaborators at Stanford University and Purdue University, have now demonstrated a powerful new method for controlling heat at the nanoscale. Their findings, published in Nature, provide strong experimental evidence that heat transfer can be intentionally engineered and significantly enhanced using specially designed metamaterials.

The research centers on a phenomenon known as near-field radiative heat transfer. When two objects are separated by an extremely small distance, only a few hundred nanometers, heat can travel between them much more efficiently than it does under ordinary conditions.

Instead of simply radiating outward, thermal energy can effectively tunnel across the narrow gap through electromagnetic waves. This process allows far more heat to flow from one object to another than would normally be expected.

Scientists have understood this effect for years, but experimentally demonstrating how to dramatically strengthen it has remained a challenge.

To accomplish this, the researchers turned to metamaterials, engineered materials that contain microscopic repeating structures designed to interact with energy in highly controlled ways.

"Unlike conventional materials, metamaterials are built with tiny, repeating patterns that interact with energy in precise ways," said Sheng Shen, a professor of mechanical engineering at Carnegie Mellon University and senior author of the study. "We patterned microscopic gold structures onto thin membranes and positioned them face-to-face across a nanoscale gap. This increased heat transfer by as much as four times compared to similar setups without metamaterials which is far beyond what traditional physics would predict at larger distances."

The team's experiments showed that the gold-patterned structures substantially increased the amount of heat moving across the gap, achieving heat transfer rates up to four times greater than comparable systems lacking the engineered patterns.

The enhancement is not simply the result of adding more routes for heat to travel.

"Rather than simply adding more pathways for heat, the gold structures interact with naturally occurring energy waves in the material, known as surface phonon polaritons, creating a resonance effect," said Zexiao Wang, a Ph