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...
We have investigated the topography and the local electronic structure of compact Aus5 cluster pellets by scanning tunnelling microscopy (STM) at room temperature. Surface topography and differential conductivity (aZ/av) were measured simultaneously. Additionally, I(V) curves were taken at particular locations on the surface. The topographies generally show largely ideally arranged individual clusters, while also a few agglomerates of several clusters could be observed. The surfaces exhibit a nearly homogeneous differential conductivity, whereby some clusters produce a striking <
Articles you may be interested inStudies of low coverage adsorption of Li on Si(001): Observation of negative differential resistance and electron trapping J.Using some sophisticated modes of scanning tunneling spectroscopy the local density of states on two superconducting compounds in the superconductive state at 4.2 K were analyzed. On NbSe 2 which is a type-II low-T c material, the Abrikosov flux line lattice was imaged for various external magnetic fields up to B C2 . The field-induced decrease of the vortex core radius for increasing magnetic field, which was recently predicted by a microscopic theory, could be clearly verified. On sputtered YBa 2 Cu 3 O 7Ϫ␦ films the measurements yielded some distinct types of the surface density of states involving gaps, being in accordance to the Bardeen-Cooper-Schrieffer theory, unexpectedly large gaps, Coulomb staircases, and zero-bias peaks.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.