Tribology: Sliding on vacuum

A team of researchers conducted investigations to understand non-contact friction and distinguish the contributions of electrons and lattice vibrations or phonons. Investigations revealed that non-contact friction occurred between bodies in relative motion that were not even in mechanical contact but separated by a vacuum gap. The researchers also investigated another similarly universal but conservative interaction, known as the van der Waals (vdW) force. The conservative vdW force had a dissipative analogue, such as vdW friction, which was understood similarly as the conservative vdW force, except that the back-action photon had a Doppler shift or time delay induced by the relative motion. The researchers also incorporated another experimental approach to understand vdW, electrostatic, and phononic friction, which aimed to distinguish between phononic and electronic dissipation.