Laudatio for Gerhard Abstreiter

It is certainly a great honour for me to have been invited by his colleagues in Munich to write a laudatio for Gerhard Abstreiter, one of the most eminent and top ranking scientists in the semiconductor physics and nanostructure science communities. My first encounter with Gerhard was in the early 1970's during his PhD thesis. In those days he was working with Jörg Kotthaus on far‐infrared cyclotron resonance in silicon inversion layers together in Fred Koch's group at the Technische Universität München. At that time the determination of the cyclotron masses of the 2D electrons was a very hot topic and the Physical Review B paper based on his doctoral thesis, which appeared in 1976, has been cited more than 150 times. From 1975 onwards he worked as a research staff scientist in Manuel Cardona's group at the Max Planck Institute for Solid State Research (MPI‐FKF) in Stuttgart, mainly on Raman scattering investigations until 1979. During this time he also spent many fruitful periods staying at an outpost of the MPI‐FKF in the High Magnetic Field Facility in Grenoble. This centre was jointly operated with the French CNRS at the time and provided a highly stimulating research atmosphere for fundamental semiconductor physics at the beginning of semiconductor based nanostructure science. During this period, Gerhard was applying inelastic light scattering methods to probe the fundamental properties of quasi‐two‐dimensional electron systems localised at GaAs/Al x Ga 1– x As heterojunctions. A joint publication with Klaus Ploog in Physical Review Letters has become one of the pioneering and most cited papers on low‐dimensional electron systems at heterointerfaces. In 1979 Gerhard moved back to the Technische Universität München as a group leader in the Physics Department, a position which he occupied until he was promoted to the rank of Full Professor (C4) in Munich in 1987 on the basis of his continued achievements in the field of optical properties of low‐dimensional semiconductor systems. Already in 1986 Gerhard had been offered a chair in experimental physics at the University of Innsbruck, which, unfortunately for Austrian semiconductor physics, he did not accept! In 1986 Gerhard was the recipient of the Walter Schottky Prize of the Deutsche Physikalische Gesellschaft, the first in a series of prestigious prizes that were to follow later on. Already as early as 1985, Gerhard and his co‐workers published a paper on “Strain‐induced two‐dimensional electron gas in selectively doped Si/Si x Ge 1– x superlattices” in Physical Review Letters. The observed mobility enhancement in strained silicon inversion layers has since become the basis for advanced CMOS devices and is, nowadays, exploited by all major semiconductor device manufacturers. This paper has been cited nearly 350 times to date and is just one of the many manifestations of Gerhard's ability to identify fascinating problems and to investigate these in great depth. A lot of Gerhard's time in 1987 was invested on establishing the Walter Schottky Institut (WSI), an interdisciplinary central research institute of the Technische Universität München devoted to basic semiconductor physics, microelectronics and nanostructure science. He became the founding director of the WSI in 1988 and, together with his former colleagues G. Weimann and E. Gornik at its inauguration, and later with P. Vogl, M. Stutzmann, and M.‐C. Amann they quickly established the WSI as one of the top research centres world‐wide in semiconductor physics, optoelectronics and nanostructure science. In 1987 Gerhard was awarded the Gottfried Wilhelm Leibniz Prize of the Deutsche Forschungsgemeinschaft, an award for extraordinarily creative scientists which secured funding for his highly ambitious research program for quite some time. In his group at the Walter Schottky Institut, Gerhard rapidly established a cutting edge research program on the structural, electronic and optical properties of heterostructures, and soon, of nanostructures. For providing high quality samples molecular beam epitaxy for III–V compounds and for Si/SiGe structures was established, with a particular emphasis on ultra high purity GaAs/GaAlAs structures. The latter led to the following important contributions in the field of the fractional quantum Hall effect, often in collaboration with von‐Klitzing's group in Stuttgart, of quantum wires based on cleaved edge overgrowth and novel 1D phases in bent quantum Hall junction, together with his co‐workers W. Wegscheider, M. Grayson and many graduate students. Work on group IV based heterostructures, superlattices and SiGe islands which was started in the late 80's has led to quite a number of seminal and highly cited papers from the early 1990's onwards. Together with his co‐workers K. Eberl, H. Brugger, F. Schäffler and others important manuscripts were published on short‐period Si/Ge superlattices, high electron mobility 2D gases, and growth of SiGe islands and their optoelectronic applications. Recently, he has renewed his interest in group IV materials and Gerhard's group has begun to make new and important contributions on ferromagnetic nanostructures based on GeMn. As his research increased and prospered, already in 1994 he turned his focus to quasi‐zero‐dimensional nanostructures, so‐called quantum dots. Here, it quickly became clear that understanding of the electronic and optical properties of such systems required the study of isolated nanostructures and Gerhard's group were pioneers in the field of single dot spectroscopy. Subsequently, the ability to control and study single artificial atoms has enabled the control of single charges, spins, and photons in semiconductor quantum structures. In 1994, his seminal contribution on the first single dot spectroscopy in photoluminescence and two photon absorption of biexcitons in GaAs/GaAlAs by K. Brunner et al. appeared in Physical Review Letters. This paper had an enormous impact on the development of the entire field and still contains much of the essence of zero‐dimensional nanostructures and their current applications in the field of quantum information science. Based on self‐assembled GaInAs quantum dots in p–i–n junctions, single quantum dot photodiodes were realized in 2002 by A. Zrenner et al. in Gerhard's group in Munich. For the first time coherent optical excitations in the quantum dot two level system could be converted into deterministic photocurrents, i.e., it was shown that such a device can work as an optically triggered single electron turnstile. This work, published in Nature in 2002, certainly provides a firm basis for possible applications of self‐organized quantum dots in future quantum cryptography and quantum information technologies. Similarly important for this field was a paper published in 2004 in Nature, together with J. J. Finley and co‐workers on an “Optically programmable electron spin memory using semiconductor quantum dots”. This paper demonstrated very long spin lifetimes of charge carriers in quantum dots and has subsequently been followed in 2006 by the optical probing of spin and charge interactions in quantum dot molecules in a series of two papers in Physical Review Letters. To date Gerhard is author and co‐author of more than 500 publications which span areas from basic semiconductor physics to semiconductor materials science and technology of novel devices. For several years now he has also been involved in biophysical semiconductor applications, e.g. in the manipulation of single and double stranded DNA and the development of biosensors. The large number of publications demonstrate his remarkable creativity and productivity, the impact of his research is demonstrated by the fact 20 of his publications have been cited more than 100 times. For many years, his students and postdocs in Munich have been exposed to research at the fore‐front of semiconductor physics. The success of his approach is manifested by a large number of prizes like IUPAP young author awards won by his students at the International Conferences on the Physics of Semiconductors, through habilitation degrees, via the appointment of many of his former co‐workers as full professors at several universities and by scientists working successfully in industry. So far he has supervised 82 PhD theses, 65 of which are now completed and 17 of which are still in process. Among the international recognitions which Gerhard received for his remarkable achievements are the following: in 1992 he was appointed a Fellow of the American Physical Society, he was the recipient of the Max Born Prize of the Institute of Physics and the Deutsche Physikalische Gesellschaft in 1998, and in 2000 he received a Senior Fellowship of the Japanese Society for the Promotion of Science. In addition to his work in Munich Gerhard had appointments as a visiting professor at the University of Innsbruck, the University of California in Santa Barbara, at Columbia University in New York, and at the University of Tokyo, Japan which show that Gerhard is acknowledged as one of the most prominent scientists in the field of semiconductor physics. He has also served the semiconductor physics community as a member and chairperson of program and advisory committees at numerous international conferences and his advice has been often decisive. My own interaction with Gerhard became very strong during the series of winter schools on low‐dimensional systems which were started in 1980 in Maria Pfarr, Salzburg and moved in 1982 to Mauterndorf and which he was attending ever since with an increasing number of his co‐workers and students. From his first contribution in 1980 on “Light scattering experiments on surface space charge layers” to the most recent one on “Manipulating and controlling spin and charge in semiconductor quantum dots” in 2006 his talks were always lucid presentations of important up‐to‐date work, often breakthroughs, and his presence has contributed enormously to the success of this winter school series. His ambition and his aspirations to be always in the top league, irrespective of the field, might be illustrated by the following: In Mauterndorf a ski race is always held at the end of the meeting with teams consisting of four members racing against each other. The rule was, and still is, that all four members, among them a senior person as a group leader, have to finish the race in order to appear in the final list of results. During such a race Gerhard unfortunately had an accident resulting in a complicated fracture of a leg which made immediate surgery in a local hospital necessary. This did not prevent him from participating in the ski race in subsequent years and his teams entitled “Raman Express”, “WSI‐1”, “Sharp Edge Overtakers” actually won the competition in the years 1994, 1996 and 1998, and were second as “Bio dot's” in 2004. Gerhard is undoubtedly one of the most creative scientists working in semiconductor physics, his achievements are admired and have found world‐wide recognition. We are all looking forward to his further contributions and wish him all the best for his future. Linz, October 2006