PHONONS 2007

Observation of chiral phonons.

Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of cl...

Photons refrigerating phonons

Phonons as Goldstone bosons

The implications of the hidden, spontaneously broken symmetry for the properties of the sound waves of a solid are analyzed. Although the discussion does not go beyond standard wisdom, it presents some of the known results from a different perspective. In particular, I argue that, as a consequence of the hidden symmetry, the equations of motion for a sound wave necessarily contain nonlinear ter...

Gaussian superlattice for phonons

A recently developed long-wavelength continuum phenomenological model is employed to study the phonon tunneling through semiconductor heterostructures where the barrier parameters are varied gradually according to a Gaussian function. The optical modes of a Si/SixGe1Kx Gaussian superlattice are considered. Such structures allow the incident phonons to be nearly totally transmitted when the inci...

Phonons in Nanocrystalline 57Fe

We measured the phonon density of states (DOS) of nanocrystalline Fe by resonant inelastic nuclear g-ray scattering. The nanophase material shows large distortions in its phonon DOS. We attribute the high energy distortion to lifetime broadening. A damped harmonic oscillator model for the phonons provides a low quality factor, Qu, averaging about 5, but the longitudinal modes may have been broa...