Filling of an optically created phonon void
P. A. van Walree, A. F. M. Arts, and H. W. de Wijn
Faculty of Physics and Astronomy, and Debye Research Institute, Utrecht
University, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands
A local frequency-selective depletion of phonons has been realized in a
single crystal of dilute ruby at 1.8 K by optical pumping into the
Zeeman-split metastable E(2E) doublet. This
phonon void, which is in dynamic balance with the spin system, is filled
by an inward flow of phonons ultimately supplied by the helium bath. A
quartic frequency dependence for phonon transport across the
crystal-helium interface is found, in accord with diffuse phonon
scattering at the crystal surface.