BENEDEK GIORGIO

A short biography of Giorgio Benedek

(see also J. Phys.: Cond. Matter 24, 100402 (2012))

Education and career.

Giorgio Benedek (GB) was born in Bologna, Italy, in 1941. He is married with Carmen Lavarini. Their single daughter is professor of Italian literature at the Orsoline art high school in Milano. GB has been until 2011 full professor (presently Emeritus professor) of Structure of Matter at the University of Milano-Bicocca. He graduated in Physics in 1965 at the University of Milano and earned the university teaching qualification (LD) in Solid State Physics in 1970. He obtained very early a permanent position at the National Research Council (CNR) as a researcher. This position, which he held from 1967 to 1984, allowed him to teach at the University of Milano as a Lecturer of Physics for Biological Sciences (1970-84) and also to take fairly long leaves as a visiting scientist abroad.

He spent one year (1974-75) in Belgium as a research fellow within the ESIS project at the University of Liège. Then he was a visiting scientist at the Max Planck Institut für Festkörperforschung in Stuttgart, Germany (1978-79, followed by short periods every year until 1987), the University of Virginia, USA (1981), and as a Franqui International Chair awardee at the Facultés Universitaires Notre Dame de la Paix in Namur (1985). From 1981 until present he has been a regular visiting scientist at the Max-Planck Institut für Strömungsforschung (now für Dynamik und Selbstorganisation)  in Göttingen with Prof. J. Peter Toennies (JPT); in the years 1990 to 1993 he spent there longer periods as a recepient of an Alexander von Humboldt Award and a co-recipient (with JPT) of the Max-Planck Prize. From 2003 until present he is also a regular visiting scientist of the Donostia International Physics Center (DIPC) in San Sebastian, Basque Country, Spain. Also visiting professot at EPFL in Lausanne, Switzerland in 2011.

In 1984 he got a call as associate professor and soon after as a full professor at the University of Milano. In 1998 he moved with a group of condensed matter physicists and chemists to establish the Department of Materials Science at the newborn University of Milano-Bicocca. 

Scientific activity (for the list of publication see CV)

GB’s first scientific interest was for the theory of the vibrational and optical properties of point defects in crystals, which he developed in his thesis work. Relevant new results were: (a) the concepts of effective force constant, accounting for the long range forces in ionic crystals, and of local elastic constants; (b) the prediction of giant frequency shifts of defect resonances under pressure, a fact soon after proved experimentally at Cornell; (c) the theory of Raman scattering from colour centres with application to ordinary and Jahn-Teller defects.

            In the seventies GB transferred the powerful Green’s function methods, first used for defective crystals, to the theory of surface phonons and inelastic atom surface scattering, predicting the feasibility of surface-phonon spectroscopy with inelastic atom scattering. In 1975, besides showing that van Hove singularities of surface phonon spectra can be detected already in angular distributions of helium scattering, he devised the theoretical tools for the analysis of the future time-of-flight (TOF) spectroscopy.

            When in the late seventies JPT at the Max Planck Institut für Strömungforschung (now Dynamik und Selbstorganisation) in Göttingen, obtained the first inelastic scattering spectra of helium atoms from solid surfaces using a high-resolution TOF technique, GB started with JPT a long and very exciting (still running) collaboration. As normally happens when a novel technique becomes available, for many years they worked (JPT on the experimental side, GB on the theory) on the surface phonon spectroscopy with He atom scattering (HAS), exploring a wide range of systems and problems made accessible to the four new TOF spectrometers operating at Göttingen. Unlike neutron scattering, HAS bears a rich and complex information about surface dynamics, which made initially the theoretical analysis essential to the development of the HAS technique. The dispersion curves of surface phonons were measured in all classes of solids (insulators, semiconductors, layered crystals, metals, charge-density-wave systems, superconductors, etc.). It was soon recognized that HAS carries information on surface electron-phonon interaction, thought it took many years to reach a first-principle demonstration of the mechanism. This joint work has been awarded with the 1992 Max Planck Prize to JPT and GB. Moreover JPT was awarded the 1992 HP-EPS prize together with H. Ibach and G. Ertl for the experimental achievements in surface dynamics. The recent progress of first-principle methods in surface dynamics is at the basis of GB’s recent activity in a broad network with colleagues in Milano, Göteborg, San Sebastián and, of course, Göttingen. A breakthrough in this area was the demonstration that the mode-selected electron-phonon interaction of conducting surfaces can be directly measured with inelastic He atom scattering (quantum sonar effect), and similarly the electron-phonon interaction at the interfaces of topological insulators with Brillouin light scattering.

The collaboration with JPT extended to other applications of He supersonic beams superfluid, notably the study of helium droplets and solid helium vacuum expansion. In a work with JPT and coworkers, GB developed a theory of the phonon and roton sidebands in the absorption spectrum of chromophores in 4He droplets which confirmed the droplet superfluidity previously established by JPT et al with a landmark nanoscale Andronikashvili experiment. A recently extension to fermion (3He) droplets led to the first evidence of localized collective excitations. With regard to the vacuum expansion of solid helium, the theoretical interest of GB was motivated by the intriguing observation, made in 2001 by JPT and R. Grisenti of the so-called geyser effect, which led to some recent joint papers.

In another long collaboration with the late Heinz Bilz at the MPI für Festkörperforschung in Stuttgart (1978-1987), GB was involved in three different projects: (a) a new theory of ferroelectricity, based on nonlinear polarizability and in contrast to the old anharmonic model, which led to the prediction of several non-linear excitations possibly carried by ferroelectrics; (b) the dynamics of magnetic layered crystals, notably 3d-metal halides, with a study on the spin-induced Raman activity; and (c) the surface dynamics of noble metals and compound superconductors, with the foundation of the multipole expansion (pseudo-charge) model for metal surface dynamics and the theory of shifted Kohn anomalies.

Consistently with the work on non-linearities in ferroelectrics, GB and Heinz Bilz organized in 1983 at the Ettore Majorana Centre in Erice the workshop “Statics and Dynamics of Non-linear Systems” which was, according to K.-Alex Müller, the source of inspiration of the work which led to the discovery of high Tc superconductivity (HTS) by Müller and Bednoz in 1986. This was indeed the start of a series of Erice worksops on HTS at the initiative of Alex Müller and GB.

The interest in supersonic He beams was also the main motivation for establishing in Milano, together with Paolo Milani (cluster-beam expert) and Ricardo Broglia (nuclear theory), a laboratory for supersonic cluster-beam deposition (SCBD). This was again a joint theory-experiment enterprise, the first aim being predicting exotic carbon structures by large-scale simulations and producing them via SCBD. Among many predictions (a triclinic diamond, superconducting or luminescent doped clathrates, etc.), the joint work lead in 1998 to the first preparation of carbon schwarzites, or carbon foams (as highlighted by Ed Gestner in Nature), the fourth allotropic form of sp2 carbon after fullerenes, nanotubes and graphene.

            GB is the author (actually the co-author in most) of over 400 papers in the fields of defects in solids, surface physics, cluster physics and cluster assembled materials, and the co-editor of ten volumes. GB and JPT are authors of a book on surface phonon spectroscopy, to appear soon with Springer Verlag.

Duties and honours (see CV)