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First experimental verification of a phononic frequency comb

A theoretical prediction by CUI scientist Prof. Peter Schmelcher (Universität Hamburg) has just been impressively confirmed: Investigating the behavior of phonons in a rectangular wafer of silicon, Prof. Ashwin Seshia and his colleagues at the University of Cambridge observed a phononic frequency comb. The team reports its findings in Physical Review Letters.


Frequency combs may occur as a result of nonlinear vibrational resonances. Credit: Schmelcher

Optical frequency combs are an important tool for precision measurements in modern physics with diverging applications in various fields such as metrology, atomic clocks, and spectroscopy. In the year 2014 Schmelcher and his team had described the possible emergence of such frequency combs as a result of nonlinear vibrational resonances. The phononic frequency comb, which was also predicted in Physical Review Letters, is based on the excitation of only two or three eigenmodes and manifests itself as the splitting of the intrinsic frequency of each excited mode into a series of equidistant spectral lines.

As the Cambridge scientists now report, their observations can be explained very well by Schmelcher’s model. They investigated the vibrations in a wafer covered by a thin layer of aluminum nitride, which occurred in response to an oscillating applied voltage. When they applied the oscillating voltage at certain frequencies, the researchers were surprised to find a vibrational spectrum of equidistant lines as in a frequency comb. Thus the development of the comb can be explained by the nonlinear interaction of phonons.

“We are very excited that the new experiments verify our proposals,” Schmelcher says. It will be possible now to use phononic frequency combs in nanoelectronic sensors for precise measurements among others. Text: Adler/Behringer

Ganesan A., Do C., and Seshia A.
Phononic Frequency Comb via Intrinsic Three-Wave Mixing
Phys. Rev. Lett. 118, 033903 (2017)

Cao L.S., Qi D.X., Peng R.W., Wang M. and Schmelcher P.
Phononic Frequency Combs via Nonlinear Resonances
Physical Review Letters 112, 075505 (2014)
DOI: 10.1103/PhysRevLett.112.075505