C5. Commission on Low Temperature Physics

Report to the 2002 General Assembly for 1999-2002
Berlin, Germany
October 7-12, 2002

COMMISSION ACTIVITIES

The Commission C5 on Low-Temperature Physics is the most important international body which on the worldwide scale attends to the interests of low-temperature physicists. Low temperature physics deals with the properties of matter in condensed forms, which often are unusual and only exist at low temperatures. The most well-known example cases are the superfluid and superconducting phases, which exhibit quantization on macroscopic scales. Central to low temperature physics is the development of new refrigeration techniques and low-noise high-sensitivity measuring methods for the purpose to study matter at low temperatures or to improve measurement sensitivity and resolution.

CONFERENCES

There are a number of established engineering conferences in cryogenics and superconductivity which provide large international platforms for meetings of the low temperature community. However, the most important forum for physicists in basic research is the triennial IUPAP-sponsored International Conference on Low Temperature Physics ("LT-Conferences").

Commission C5 finds the host for this meeting and supervises the conference arrangements.

The LT-Conferences cover several areas of physics: Quantum Gases, Fluids, and Solids; Superconductivity; Magnetism and Properties of Solids; Quantum Electron Transport and Mesoscopic Physics; Applications, Materials, and Techniques. Most of these fields also organize regular specialized meetings, often as satellite-conferences to the LT.

LT22: The conference LT22 took place on August 4-11, 1999 in Helsinki. It was organized by the Low Temperature Laboratory of the Helsinki University of Technology, a leading institution in this field. The number of registered participants was 1381. The conference program consisted of five parallel program lines, including 238 oral and 1250 poster presentations. The printed Proceedings is published in a regular issue of Physica B (2000) and can be accessed by the web at the address http://www.elsevier.nl/locate/physb. IUPAP-sponsored travel grants were attributed to 14 physicists of developing countries of Asia, Africa and South-America.

LT23: The conference LT23 took place on August 20-27 in Hiroshima. It was organized by members of the low temperature community belonging to several outstanding research institutions in Japan. The conference was attended by 1356 registered participants, from 55 countries, who contributed to the scientific program by giving 237 lectures and 1472 poster presentations. The Proceedings will be published in regular issues of Physica (http://www.elsevier.nl). Information about the LT23 conference can be found on the web page http://www.issp.u-tokyo.ac.jp/lt23.

LT24: Commission C5 held a business meeting during LT23 in Hiroshima and decided to accept the proposal from the University of Florida to host the next conference, LT24 in August 2005 in Orlando (USA). The preparations for this meeting are in progress and interest is building up at several places to prepare for a bid to host LT25 in 2008.

The LT conference has demonstrated its vitality and functionality during the last fifty years. New fields of research have been born at regular intervals, sometimes from the midst of traditional low temperature research, sometimes from its fringe areas. Today, as before, the prime concern of C5 is to maintain the LT conference in the forefront of new development in basic research and cryogenic technology.

Fritz LONDON Award

At the LT-Conferences the Fritz London Memorial Award, one of the 9 awards for scientific excellence sponsored by IUPAP, is given to recognize outstanding experimental and theoretical contributions in low temperature physics.

In 1999 at LT22, the prize was received by D. Brewer, for his work on adsorbed helium films, by W. Ketterle for the development of thechniques which allowed the observation of Bose-Einstein condensation, and by M. Krusius for his work on superfluid 3He.

In 2002 at LT23 the prize was received by R.J. Donnelly for his work on turbulence at low temperatures, by W. Hardy for his work on atomic and molecular hydrogen and high critical temperature superconductors, and by A.M. Goldman for his work on the Superconductor-Insulator transition in two dimensions.

FEENBERG Medal

The Eighth Eugene Feenberg Medal has been awarded to Philippe Nozières in recognition of his many pathbreaking contributions to many-body theory, including seminal works on Quantum Fluids (see the article in the Journal of Low Temperature Physics, 124, 411 (2001)). The Feenberg medal Committee has sought the advice of C5 for this nomination.

QFS Conferences:

QFS, Quantum Fluids and Solids, is an international symposium with the traditional central topics of liquid and solid helium four and helium three and their mixtures, applications, and instrumentation. Related topics such as liquid and solid hydrogen and, most recently, the Bose-Einstein condensed phases of alkali atoms and spin-aligned atomic hydrogen gases have been included in these meetings.
The QFS series started at Penn State University (University Park, 1992), followed by meetings at Cornell University (Ithaca, 1995), Ecole Normale Superieure (Paris, 1997), the University of Massachusetts (Amherst, 1998), and the University of Minnesota (Minneapolis, 2000). A number of other similar symposia devoted to the same topics that have been held in the previous two decades. After the Quantum Fluids and Solids conferences QFS97 (Paris) and QFS98 (Amherst), the decision was taken to maintain contact with the C5 commission and to organize a QFS meeting annually in those years when the LT conference does not take place.
The attendance of the QFS conferences is about 200 participants. The Conference Proceedings are published in the Journal of Low Temperature Physics, a well known scientific journal.

The chair of IUPAP C5 is invited to attend the QFS Steering Committee meeting, as decided by a vote of this Committee.

The University of Minnesota hosted the International Symposium on Quantum Fluids and Solids 'QFS2000', June 6 - 11, 2000, on the campus of the University of Minnesota in Minneapolis. The co-chairs were Charles E. Campbell and William Zimmermann, Jr.

QFS2001 took place in July 22-27, 2001 in the University of Konstanz. It was organised by P. Leiderer, G. Eska and D. Reiner. Information can be found on the web page http://www.uni-konstanz.de/qfs2001.

The next QFS conference, organized by R.V. Duncan and D. Goodstein, will take place on August 3-8, 2003 in Albuquerque (USA). Information can be found on the web page http://coffee.phys.unm.edu/QFS.

Onnes temperature: the superconducting transition temperature

Professors B. Goodman, N. Kurti, H.B.G. Casimir, J. de Nobel, R. de Bruyn Outboter, and J. Huiskamp have sought the support of IUPAP-C5 in order to promote their suggestion that the (zero-magnetic-field) superconducting transition temperature be called the "Onnes Temperature", by analogy with the "Curie " and "Néel" temperatures. There is currently a debate in C5 on the practical implementation of this recommendation, which is becoming more timely in view of the approaching centennial anniversary of Kamerlingh Onnes's two most outstanding accomplishments: the liquefaction of helium in 1908 and the discovery of superconductivity in 1911.

NEW DEVELOPMENTS

During the last years several Nobel Prizes in physics have been awarded to discoveries in the field of low temperatures:
    1996: D.M. Lee, D.D. Osheroff,and R.C. Richardson: for the               discovery of superfluidity in liquid helium-3.
    1997: S. Chu, C. Cohen-Tannoudji, and W.D. Phillips: for the               development of methods to cool and trap atoms with laser               light.
    1998: R.B. Laughlin, H.L. Störmer, D.C. Tsui: for the discovery of               a new form of quantum fluid with fractionally charged               excitations ("fractional quantum Hall effect").
    2001: E. Cornell, W. Ketterle and C.E. Wieman: for the               achievement of Bose-Einstein condensation in dilute gases of               alkali atoms, and for early fundamental studies of the               condensates.
While some of these discoveries were made ten to twenty years ago, striking advances have been made in more recent years. Below we describe some of the general trends and list randomly some areas where progress has been fast.

Physics at low temperatures

Ultracold atoms and molecules show extraordinary quantum properties, like condensate interferences, vortex topological defects with exotic properties. It is now possible to induce transitions between the superfluid and the Mott insulator state by using an optical lattice potential. Mixtures of degenerate dilute gases obeying different quantum statistics have been experimentally obtained. Many theorists traditionally linked to the helium community are participating very actively in this new research area.

Superconductivity is an active field of research. The lack of a comprehensive and well accepted model for the non-conventional high-Tc superconductors (charge and magnetic mechanisms have been proposed, among others) as well as the large application potental of these materials has motivated intensive research in this field. New superconducting materials have been discovered, like MgB2 , a high critical current material with a Tc of 39 K. Ferromagnetism and superconductivity are exciting topics, investigated for instance in CuGe2. Perhaps one of the most spectacular results is the direct observation of the different types of vortices predicted and indirectly found experimentally. These topological defects have now been clearly seen by means of a 1 MV field emission electron microscope.

The nature of the ground state of frustrated magnets is a typical low temperature problem. Studies on a large variety of materials characterized by geometrical frustration, like ZnCr2O4, or quantum frustration, like in two-dimensional 3He, have shown the existence of a new state of matter, the spin-liquid phase. Quantum phase transitions are the object of theoretical and experimental studies in a large variety of materials. Playing with frustrated systems has also led to the exciting observation of the "spin-ice" state in Dy2Ti2O7, for example.

New research lines in condensed matter physics, like mesoscopic physics, have had a rapid development in the last three years. The fundamental problem of decoherence has found in low temperature nanophysics an adequate test ground. Mesoscopic superconductivity is one of the topics where low temperature physics has found new research possibilities, for instance on the vortex states of mesoscopic superconductors, Josephson charge or spin Q-bits, or quantum phase slips in superconducting nanowires. These investigations are expected to lead to a new generation of highly sensitive devices and important applications. In this category we could also include carbon nanotubes. The interplay with magnetism offers novel tools, like "spintronics", spin currents being currently manipulated in sophisticated nanodevices.

In Quantum Fluids and Solids, an important area of research is the study of superfluids in the presence of disorder, obtained when He liquids are confined in Aerogel. Randomly oriented strands of Aerogel at low density introduce weak disorder, in analogy with impurities in superconductors, which suppresses correlations and phase transitions. In 3He, the p-wave paired fermionic superfluid, the suppression of the critical temperature and the superfluid density have been measured and are in reasonable agreement with quantitative theoretical interpretation. The role of topological defects and the nature of the phase transitions in the "impure" superfluid are currently a subject of debate. Novel issues on supercooling and the dynamics of the phase transition have been raised. Several proposals have been presented to exploit analogies between superfluid 3He and cosmological models in quantum field theory. Last but not least, hydodynamics has found in helium a working fluid allowing to extend the experimental range towards extremely high Reynolds numbers, and in superfluid helium new exciting phenomena of quantum turbulence.

Some applications of Low Temperatures:

The industrial activity and scientific research in advanced cryogenic technologies has led to advances in several fields. It is worth mentioning the production of cryogenic fluids (Nitrogen, Oxygen, Hydrogen, Helium), the liquefaction of natural gas for transportation purposes, the production of pure gases for the semiconductor industry, the use of cryogenic fuel in space launchers, the design of novel superconducting power equipment (alternators, transformers, motors, current limiters), recent applications in communications (HTc filters), the construction of the CERN Large Hadron Collider (superconducting magnets and superfluid helium technology), the gravitational waves antennas and elementary particle bolometric detection instruments, cold targets for nuclear and particle physics, medical applications (NMR scanners, cryopreservation of organs or cells), the development of more accurate metrology (electrical standards, primary thermometry), high sensitivity electronics (infrared detectors, magnetometers), ultra-low noise devices for physical measurements (SQUIDS, amplifiers, choppers), cryo-pumping and ultra-clean vacuum technology, among others.

Henri Godfrin and Hidetoshi Fukuyama