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Phys. Rev. Lett. 76, 4560 - 4563 (1996)

Direct Spectroscopic Observation of Elementary Excitations in Superfluid He Droplets

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M. Hartmann, F. Mielke, J. P. Toennies, and A. F. Vilesov
Max-Planck-Institut für Strömungsforschung, Bunsenstrasse 10, D-37073 Göttingen, Germany

G. Benedek
Istituto Nazionale di Fisica della Materia, Dipartimento di Fisica dell'Università, via Celoria, I-20133 Milano, Italy

Received 9 February 1996

The absorption spectra of the electronic S1←S0 transition of glyoxal molecules (C2H2O2) embedded in He droplets ( ≈5500 atoms) show well-resolved vibronic bands with a width <0.5 cm-1. The phonon wings at higher frequencies have distinct gaps amounting to ΔE  =  8.1 K followed by a small maximum at 14.8 K. The phonon wing shape agrees with a theoretical simulation based on the dispersion curve of elementary excitations in bulk He II, providing the first evidence for superfluidity in the finite-sized He droplets.


©1996 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevLett.76.4560
DOI: 10.1103/PhysRevLett.76.4560
PACS: 67.40.Yv, 33.20.Kf, 67.40.Db

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