Measurement of Phonon Angular Momentum via the Einstein-deHaas Effect, Fiber-Optic Interferometry, and a High-Q Oscillator
ORAL
Abstract
We report the design and use of a fiber-optic-interferometer
system to measure the predicted1 macroscopic phonon angular
momentum. An oscillating magnetic field is applied to an
insulating ferromagnet attached to our single-crystal high-Q
double torsional oscillator. By the Einstein-de Haas effect,
oscillator displacement measurements between low
temperatures and those closer to the Debye temperature allow
extraction of the changing phonon angular momentum. A force
change of 5 x 10-8 N was detected between 77 K and 300 K for a
1 mm3 MgZn ferrite sample. Our oscillator, with a resonance at
1.3 kHz, has a thermal noise limit on the order of 10-14 N/√Hz,
allowing the possibility of high-accuracy detection. Competing
effects are being minimized; for example, induced eddy current
momentum can overwhelm the phonon effect for metallic
ferromagnets, and careful temperature-dependent studies are
required for force calibrations.
system to measure the predicted1 macroscopic phonon angular
momentum. An oscillating magnetic field is applied to an
insulating ferromagnet attached to our single-crystal high-Q
double torsional oscillator. By the Einstein-de Haas effect,
oscillator displacement measurements between low
temperatures and those closer to the Debye temperature allow
extraction of the changing phonon angular momentum. A force
change of 5 x 10-8 N was detected between 77 K and 300 K for a
1 mm3 MgZn ferrite sample. Our oscillator, with a resonance at
1.3 kHz, has a thermal noise limit on the order of 10-14 N/√Hz,
allowing the possibility of high-accuracy detection. Competing
effects are being minimized; for example, induced eddy current
momentum can overwhelm the phonon effect for metallic
ferromagnets, and careful temperature-dependent studies are
required for force calibrations.
* Supported by the University of Texas College of Natural SciencesFreshman Research Initiative
–
Publication: L. Zhang, Q. Niu, Phys. Rev. Lett. 112, 085503 (2014)
Presenters
-
Matthew Dwyer
Department of Physics, University of Texas at Austin
Authors
-
Matthew Dwyer
Department of Physics, University of Texas at Austin
-
Devan Shoemaker
Department of Electrical and Computer Engineering, University of Texas at Austin
-
John T Markert
University of Texas at Austin