Measurement of Phonon Angular Momentum via the Einstein-de Haas 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.
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Publication: L. Zhang, Q. Niu, Phys. Rev. Lett. 112, 085503 (2014)
Presenters
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Matthew Dwyer
Department of Physics, University of Texas at Austin
Authors
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Matthew Dwyer
Department of Physics, University of Texas at Austin
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Devan Shoemaker
Department of Electrical and Computer Engineering, University of Texas at Austin, University of Texas at Austin
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John T Markert
Department of Physics, University of Texas at Austin, Department of Physics, The University of Texas at Austin, University of Texas at Austin