Quantum Coupling of Two Atomic Defects in a Carbon Nanotube Semiconductor.

Chemical defects can create organic color centers in the graphitic lattice of single-walled carbon nanotubes. However, the underlying physics remains somewhat of a mystery. Here we show that two sp atomic defects can interact with each other in a way reminiscent of atoms bonding to form molecules. Each defect creates an atom-like mid-gap state within the band gap of the nanotube semiconductor. Two such defects, when brought close to each other, interact to form a split pair of orbitals akin to two hydrogen atoms covalently bonding to form a H molecule. This unexpected finding may help in understanding the nature of atomic defects in solids and provide a fresh perspective to the engineering of these color centers.