First-principles prediction of optical second-order harmonic generation in the endohedralN@C60compound

Abstract

Non-linear-optical properties in C 60 have attracted enormous attention for over two decades. The endohedral complex N@C 60 , with its remarkable thermal stability and spin-quartet ground state, is a candidate for future room-temperature quantum computing, but there has been no investigation of its non-linear-optical properties.Here, a first-principles calculation shows that N@C 60 is a promising material for nanoscale and ultrafast modulations. Excitation by a pump laser pulse of the nitrogen-atom vibration inside the C 60 cage transiently breaks inversion symmetry and can enable second-harmonic generation (SHG) from a probe pulse. Unlike the SHG observed in C 60 thin films, this harmonic signal is switched on and off periodically every 345 fs. For an fcc crystal of N@C 60 , the second-order susceptibility χ (2) is on the order of 10 −8 esu, similar to commercially used nonlinear materials.

BerkeleyGW: A massively parallel computer package for the calculation of the quasiparticle and optical properties of materials and nanostructures

“…For example, an excitation that should have zero oscillator strength by symmetry, due to interference between transitions to two degenerate states, may not be dark if only one of those transitions is included. This issue is quite general and applies to the choice of active spaces in other theories as well, such as configuration interaction [50]. Breaking degeneracy in either the coarse or fine grid can also cause trouble in interpolation of the kernel and quasiparticle energies.…”

Proposed Coherent Trapping of a Population of Electrons in aC60Molecule Induced by Laser Excitation

“…For clarity, other energy levels are not shown. Just based on the symmetry argument, one immediately realizes that this system resembles a Λ system, a result that remains true even if we consider the many-body states [26].…”

Generation and propagation of high-order harmonics in crystals

“…One important way the periodic potential manifests itself is in the linear scaling of the high energy cutoff of the HHG with field [13]. It has also been predicted that the HHG spectrum would have a imprint of the electronic states in solids [13,23,24] .…”