Interaction of vortices with ultrasound and the acoustic Faraday effect in type-II superconductors

Abstract

We study the interaction of sound waves with vortices in type-II superconductors, taking into account pinning and electrodynamic forces between vortices and crystal displacements. We propose ultrasound techniques as a method for obtaining information about vortex dynamics. This is particularly appropiate at low temperatures where transport measurements are ineffective. The changes in sound velocity and attenuation due to vortices, can provide information on the elastic constants of the vortex system and on vortex dissipation, respectively. At low temperatures the Magnus force acting on vortices leads to the acoustic Faraday effect: there is a rotation of the polarization plane of tranverse sound waves propagating along the magnetic field. This effect is linear in the Magnus force and magnetic field in crystals with equivalent a and b axes for a field parallel to the c axis. We discuss how this effect can be measured by means of either pulse-echo techniques or standing sound waves. Also, we show that an ac electromagnetic field acting on the vortex system can generate ultrasound. We calculate the amplitude of the generated sound waves in the linear regime and compare with recent experiments.

High-field state of the flux-line lattice in the unconventional superconductorCeCoIn5

“…1(a), the transverse polarization of the sound has the FLL undergo a long-wavelength ( | k | λ ≪ 1 ) bending mode, limited by the FLL tilt modulus in the limit | k |→ 0, c f 44 (| k |→ 0) = B 2 /µ 0 . The FLL contribution can then be written as [17] …”

Acoustic attenuation in a type-II superconductor at high magnetic fields

“…This simplifies our calculations since the coupling between the collective modes associated with fluctuations of the order parameter and the longitudinal phonons can be neglected to a good approximation. 9,10 The attenuation of sound waves is given by the imaginary part of the retarded phonon self energy. To lowest order in the electron-phonon coupling we get for the attenuation α(ω): 11…”

Vortex bending and avalanche in a type-II superconductor observed with contactless ultrasonics

“…2 One recently reported contactless ultrasonic method makes use of the mutual conversion between an electromagnetic field and ultrasonic waves. [3][4][5] However, this method is not totally contactless since a quartz transducer and a delay rod are used either to detect or generate ultrasonic waves. A totally contactless ultrasonic method using two coils that can simultaneously generate and detect ultrasonic waves in a superconductor is reported here.…”

“…Such phenomena have never been observed before. [3][4][5][6][7][8][9][10][11] An abrupt disappearance of the longitudinal waves, a sudden appearance of shear waves, and some more unusual phenomena followed as the field strength was varied. Equations describing the conversion efficiency between an ac magnetic field and ultrasonic waves are derived and changes of the near surface vortex bending angle and the vortex density with applied field are calculated using the ultrasonic data.…”