Thermodynamics, phonon occupation numbers, and their measurements by helium spin echo

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• Dr Boyao Liu, Cavendish Laboraroty, University of Cambridge
• Tuesday 19 August 2025, 14:00-15:00
• D2.002, Ray Dolby Centre, Cavendish Laboratory.

If you have a question about this talk, please contact Boyao Liu.

In this seminar, we begin with fundamental principles of thermodynamics to establish the energy distribution of a harmonic oscillator at constant temperature, which corresponds to the Bose–Einstein distribution. We then introduce helium spin echo (HeSE) spectroscopy as a powerful technique for probing phonons at surfaces. We will show that HeSE provides access to the differential scattering cross section of helium atoms interacting with a sample surface. From the differential scattering cross section, the Debye–Waller factor of diffuse elastic scattering can be extracted. Furthermore, by comparing the relative intensities of the elastic peak and the one-phonon inelastic peak, the Bose–Einstein distribution of surface phonons can be experimentally determined.

This talk is part of the Surface Physics Seminar series.

This talk is included in these lists:

• D2.002, Ray Dolby Centre, Cavendish Laboratory
• Surface Physics Seminar

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