Odd Product Breaks a Typical Rule of Physics

A simple tenet of college or university physics is that as stress will increase, thermal conductivity—a material’s ability to perform heat—increases, much too, simply because atoms that are squeezed alongside one another interact extra.

Much more than a century of investigation has confirmed this rule. But engineers have now uncovered an exception: when they used rigorous force to boron arsenide, a recently identified semiconductor material, thermal conductivity reduced. The acquiring, explained in Mother nature, difficulties established idea and most likely upends recent products of how substances behave beneath excessive problems.

“Now that we have produced this to start with discovery, we believe this can not be the only product with abnormal behavior,” states research senior author Yongjie Hu, a chemist and mechanical engineer at the College of California, Los Angeles. If other substances display this home, “the proven understanding of thermal conductivity could not be accurate.”

In prior scientific studies, Hu and other scientists identified boron arsenide as owning extremely substantial thermal conductivity. The scientists also calculated that regular thermal conductivity principles may well not utilize to it in specified situation.

To check people predictions, Hu and his colleagues positioned a little piece of boron arsenide less than 100 microns thick in the hole among two diamonds. They utilized force to the diamond sandwich to make a power on the boron arsenide hundreds of moments higher than that at the bottom of the ocean. The scientists applied ultrafast optics, spectroscopy and x-rays to document how boron arsenide’s thermal conductivity begins to reduce as heat propagates throughout the sample and it is subjected to rigorous tension. They observed that the lower comes from related kinds of warmth waves overlapping and canceling a single a different out—a phenomenon predicted by quantum mechanics.

If Hu and his colleagues can present this conduct generalizes to other components, he states, physicists could have to revise recognized types for environments this kind of as outer place or planetary interiors, which include Earth’s. The latter could alter predictions about weather improve due to the fact terrain temperatures are afflicted by what takes place within the earth.

The new study presents “the very first and most effective experimental proof that I know of to clearly show that thermal conductivity can be tuned,” states College of California, Berkeley, geophysicist Raymond Jeanloz, who was not included in the investigation. The discovering, he adds, “opens up the possibility” of superior technologies that conserve vitality and amazing electronics by managing thermal conductivity.