On the Effect of Resonance in the Exchange of Excitation Energy

O. K. Rice

Herbert C. Cheung

Antoine Klauser, Jorn Mossel, Jean-Sébastien Caux +1 more

We determine the spin-exchange dynamical structure factor of the Heisenberg spin chain, as is measured by indirect resonant inelastic x-ray scattering (RIXS). We find that two-spin RIXS excitations nearly entirely fractionalize into two-spinon states. These share the same continuum lower bound as single-spin neutron scattering excitations, even if the relevant final states belong to orthogonal symmetry sectors. The RIXS spectral weight is mainly carried by higher-energy excitations, and is beyond the reach of the low-energy effective theories of Luttinger liquid type.

J. Cooper, Derek N. Stacey

Peter L. Hagelstein, Irfan U. Chaudhary

We consider a generalization of the spin-boson model in which two different two-level systems are coupled to an oscillator, under conditions where the oscillator energy is much less than the two-level system energies, and where the oscillator is highly excited. We find that the two-level system transition energy is shifted, producing a Bloch-Siegert shift in each two-level system similar to what would be obtained if the other were absent. At resonances associated with energy exchange between a two-level system and the oscillator, the level splitting is about the same as would be obtained in the spin-boson model at a Bloch-Siegert resonance. However, there occur resonances associated with the transfer of excitation between one two-level system and the other, an effect not present in the spin-boson model. We use a unitary transformation leading to a rotated system in which terms responsible for the shift and splittings can be identified. The level splittings at the anticrossings associated with both energy exchange and excitation transfer resonances are accounted for with simple two-state models and degenerate perturbation theory using operators that appear in the rotated Hamiltonian.

Tomoyuki Maruyama, Satoshi Chiba

We study the excitation energy of the isoscalar giant quadrupole resonance by the scaling method in the relativistic many-body framework with the momentum dependent parts of the Dirac self-energies arising from the one-pion exchange. It is shown that this momentum dependence enhances the Landau mass significantly and thus suppresses the quadrupole resonance energy while the Dirac effective mass is kept to a reasonable value.