A sheet of graphene one atom thick hangs in the air like a taut bedsheet. Heat waves, vibrations of atoms that physicists call phonons, ripple across it. Previously, it was thought that these waves quickly scatter due to strong interactions, and heat transfer is poor. But experiments showed the opposite: heat flows better than old calculations predicted.
In the new work, the explanation lies in how the sheet's bends are coupled to its plane. When atoms vibrate up and down, they slightly change the bending stiffness of the entire sheet. This effect, called stiffness renormalization, makes bending vibrations more stable. Heat waves no longer damp out quickly and can travel farther, like ripples on water after a stone is thrown.
Thanks to this, heat in suspended graphene flows almost like a liquid — scientists call this phonon hydrodynamics. The discovery links the macroscopic elasticity of the sheet to microscopic atomic vibrations. It paves the way for controlling heat in future electronics, where every nanometer counts.
Graphene is the thinnest material in the world: a sheet the size of a football field would weigh less than one gram.