High resolution Raman study of the two-roton bound state

Murray, Cherry A.; Woerner, R.; Greytak, Thomas J.

doi:10.1088/0022-3719/8/6/003

Cited by 37 publications

(5 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The weak second maximum in the experimental spectrum at E 14.8 K can hardly be interpreted as a two-roton process because this would imply a binding energy with respect to the two-roton energy of E 17.3 K in the bulk of 2.5 K which is greater than the accepted value of 0.22 K [10]. More likely it can be assigned to the maxon.…”

Section: Direct Spectroscopic Observation Of Elementary Excitations Imentioning

confidence: 83%

“…This critical velocity could so far only be observed for negative ions which were found to move without friction in liquid helium at P 25 atm and T 0.4 K [9]. Two-phonon Raman spectroscopy in bulk helium also has been shown to provide information on the elementary excitations [10]. In the quest for more direct spectroscopic probes of superfluidity several groups have developed sophisticated techniques to levitate atoms in liquid helium [11][12][13][14].…”

Section: Direct Spectroscopic Observation Of Elementary Excitations Imentioning

confidence: 99%

See 1 more Smart Citation

Direct Spectroscopic Observation of Elementary Excitations in Superfluid He Droplets

Hartmann¹,

Mielke²,

Toennies³

et al. 1996

Phys. Rev. Lett.

245

257

View full text Add to dashboard Cite

The absorption spectra of the electronic S 1 √ S 0 transition of glyoxal molecules (C 2 H 2 O 2 ) embedded in He droplets (ഠ5500 atoms) show well-resolved vibronic bands with a width , 0.5 cm 21 . The phonon wings at higher frequencies have distinct gaps amounting to DE 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. [S0031-9007(96)00383-3] PACS numbers: 67.40.Yv, 33.20.Kf, 67.40.Db A number of recent theoretical studies predict that 4 He clusters with more than about 64 atoms are superfluid with a transition temperature which is somewhat lower than the bulk l-point temperature T l 2.2 K [1-3]. So far, however, there is no direct experimental evidence for superfluidity in these nanosize liquid particles. Recently it has been possible to observe a very sharp rovibrational spectrum of single SF 6 molecules located in the interior of He droplets ͑N . 1000 atoms͒ which were produced in free jet expansions [4,5]. From this the rotational temperature was found to be T 0.37 6 0.05 K [5] in good agreement with theoretical predictions [6]. In addition, infrared spectra of SF 6 dimers indicate that these larger entities can also rotate freely in the He droplets [7].In the bulk the most direct evidence for superfluidity comes from neutron diffraction experiments which indicate sharp elementary excitations with a dispersion characterized by a maximum at E max 13.7 K ͑Q max 1.10 Å 21 ͒ called a maxon and the well known roton minimum at E rot 8.65 K ͑Q rot 1.91 Å 21 ͒ [8]. As first pointed out by Landau the sharp excitations at the roton minimum enable the fluid to flow unhindered at velocities below about 58 m͞s which is the most prominent manifestation of superfluidity. This critical velocity could so far only be observed for negative ions which were found to move without friction in liquid helium at P 25 atm and T 0.4 K [9]. Two-phonon Raman spectroscopy in bulk helium also has been shown to provide information on the elementary excitations [10]. In the quest for more direct spectroscopic probes of superfluidity several groups have developed sophisticated techniques to levitate atoms in liquid helium [11][12][13][14]. Up to now only broad lines of several cm 21 width could be observed. A recent study of the electronic spectra of Na 2 attached to the surface of He droplets reveals vibronic bands consisting of a sharp zero phonon line (ZPL) and an intense broad phonon wing (PW) [15]. In this system multiphonon processes appear to dominate the spectra and conceal the elementary excitations of the droplet.To circumvent these difficulties we have undertaken the first spectroscopic experiments with a simple organic molecule. Glyoxal (C 2 H 2 O 2 ) was chosen since its visible spectroscopy has been studied both as a free molecule and in cryomatrices [16,17]. Compared to the alkali metals glyoxal is readily solvated by helium...

show abstract

Section: Direct Spectroscopic Observation Of Elementary Excitations Imentioning

confidence: 83%

Section: Direct Spectroscopic Observation Of Elementary Excitations Imentioning

confidence: 99%

Direct Spectroscopic Observation of Elementary Excitations in Superfluid He Droplets

Hartmann¹,

Mielke²,

Toennies³

et al. 1996

Phys. Rev. Lett.

245

257

View full text Add to dashboard Cite

show abstract

“…Scattering (unbound) orbits in a classical theory (Roberts & Donnelly 1973 have an average critical impact parameter of about 6.7 8, in good agreement with experiments determining the roton viscosity. The binding energy is known experimentally to be (-0.22f0.07) K (Murray, Woerner & Greytak 1975). This quantity was calculated classically by Roberts & Donnelly (1973 and they obtained a value of about -18.4 K with a stable separation of about 1.05 8.…”

Section: Is Quantum Turbulence Really Quantum Mechanics ?mentioning

confidence: 99%

Quantum turbulence

Donnelly

Swanson

1986

J. Fluid Mech.

View full text Add to dashboard Cite

We present a review of quantum turbulence, that is, the turbulent motion of quantized vortex lines in superfluid helium. Our discussion concentrates on the turbulence produced by steady, uniform heat flow in a pipe, but touches on other turbulent flows as well. We have attempted to motivate the study of quantum turbulence and discuss briefly its connection with classical turbulence. We include background on the two-fluid model and mutual friction theory, examples of modern experimental techniques, and a brief survey of the phenomenology. We discuss the important recent insights that vortex dynamics has provided to the understanding of quantum turbulence, from simple scaling arguments to detailed numerical simulations. We conclude with a discussion of open questions in this field.

show abstract

“…[9,82]). Measurements [34,54] showed a peak in the Raman scattering at an energy, 2R = 16.97 ± 0.03, K = 1.462 ± 0.003 meV. The energy of the peak was interpreted as the energy required to create two interacting rotons of equal and opposite wave vector so that the total wave vector of the pair, Q = k 1 + k 2 , is zero.…”

Section: Liquid 4 He Collective Modesmentioning

confidence: 99%