Helium

  • Breakthrough in Quantum Physics: Reaction of Quantum Fluid to Photoexcitation of Dissolved Particles

    Markus Koch (3rd from left), Bernhard Thaler (4th fro left), head of institute Wolfgang Ernst (far right) and team in the "Femtosecond-Laser-Lab" at the Institute of Experimental Physics at TU Graz. ©Lunghammer - TU Graz

    Researchers from Graz University of Technology have described for the first time the dynamics which takes place within a trillionth of a second after photoexcitation of a single atom inside a superfluid helium nanodroplet. In his research, Markus Koch, Associate Professor at the Institute of Experimental Physics of Graz University of Technology (TU Graz), concentrates on processes in molecules and clusters which take place on time scales of picoseconds (10⁻¹² seconds) and femtoseconds (10⁻¹⁵ seconds). Now Koch and his team have achieved a breakthrough in the research on completely novel molecular systems.

  • Freiburg Researchers Investigate Ultrafast Reaction of Superfluid Helium Triggerd by Extreme Ultraviolet Laser Pulses

    Excitation of helium nanodroplets by ultra-short laser pulses. Photo: AG Stienkemeier

    A team headed by Professor Frank Stienkemeier at Freiburg’s Institute of Physics and Dr. Marcel Mudrich, professor at the University of Aarhus in Denmark, has observed the ultrafast reaction of nanodroplets of helium after excitation with extreme ultraviolet radiation (XUV) using a free-electron laser in real time. The researchers have published their findings in the latest issue of Nature Communications. Lasers generating high-intensity and ultra-short XUV and X-ray pulses give researchers new options for investigating the fundamental properties of matter in great detail. In many such experiments, material samples in the nanometer range are of particular interest. Some scientists use helium droplets no larger than a few nanometers as a means of transporting and studying embedded molecules and molecular nanostructures.

  • New Manifestation of Magnetic Monopoles Discovered

    A superfluid helium droplet acts as a magnetic monopole. IST Austria/Birgit Rieger

    Significant effort has gone into engineering the long-sought magnetic monopoles. Now scientists have found them in an unexpected place, and revealed that they have been around for a long time. The startling similarity between the physical laws describing electric phenomena and those describing magnetic phenomena has been known since the 19th century. However, one piece that would make the two perfectly symmetric was missing: magnetic monopoles. While magnetic monopoles in the form of elementary particles remain elusive, there have been some recent successes in engineering objects that behave effectively like magnetic monopoles.

  • Partnership at a distance: Deep-frozen helium molecules

    “When two loners are forced to share a bed, they move well beyond its edges to get away from each other.” Peter Evers

    As atomic physicists in Frankfurt have now been able to confirm, over 75 percent of the time helium atoms are so far apart that their bond can be explained only by the quantum-mechanical tunnel effect. Helium atoms are loners. Only if they are cooled down to an extremely low temperature do they form a very weakly bound molecule. In so doing, they can keep a tremendous distance from each other thanks to the quantum-mechanical tunnel effect. As atomic physicists in Frankfurt have now been able to confirm, over 75 percent of the time they are so far apart that their bond can be explained only by the quantum-mechanical tunnel effect.

  • Roton Quasiparticles Observed in Quantum Gas

    A cigar-shaped gas of magnetic atoms can support a roton mode. IQOQI Innsbruck/Harald Ritsch

    An Innsbruck team of experimental physicists, in collaboration with theorists from Innsbruck and Hannover, has for the first time observed so-called roton quasiparticles in a quantum gas. Empirically introduced by Landau to explain the bizarre properties of superfluid liquid Helium, these quasiparticles reflect an "energy softening" in the system as precursor of a crystallization instability. The new work published in Nature Physics demonstrate similar phenomena in the quantum-gas phase thanks to magnetic interactions, paving the way for a novel understanding of paradigmatic states of quantum fluids, such as supersolids.