I was born on April 6, 1949 in a regional hospital in Frankfurt am Main in Germany. Having the umbilical cord wrapped twice tightly around my neck, my parents’ fear for the mental health of their first-born son subsided only gradually.
My forefathers had been farmers, inn-keepers, blacksmiths, carpenters and shop keepers in the region. My mother, an elementary school teacher, and my father, having finished an apprenticeship, had been married during the previous year, shortly after a devastating war. Opening a store for interior decoration in my father’s home town of Sprendlingen, they were trying to build an existence and start a family at the same time. Eighteen months later a brother, Heinz, was born without the umbilical complications.
Sprendlingen, today a part of Dreieich, just south of Frankfurt, was a town of some 15,000 inhabitants. I was raised in the circle of an extended family of four uncles and aunts, who, together with my parents, lived in two houses with barns and sheds and the store surrounding a large yard. It was an ideal playground for two boys growing up with their cousins – this group always extended by a horde of friends. Constructing huge sand castles with moats and bridges, cardboard tents from the shop’s packing material, building elaborate knight’s armour from scrap floor-covering and intricate race tracks for marbles from curtain rails remain fond memories of childhood.
I began kindergarten at age three and was soon after joined by my brother. The kindergarten’s seemingly unlimited amount of toy building blocks must have fascinated me and I soon became somewhat of the establishment’s chief architect. School, at six, was a happy time, complemented in the afternoons by playing soccer in our yard, roaming about the fields surrounding my home town, and building dozens of detailed cardboard model ships and airplanes from “Ausschneidebögen”.
There was never a doubt in my parents’ mind that their sons would receive the best possible education. Although none of my forefathers graduated from high school, my parents regarded highly the merits of a good education as a tool for social advancement. In their value system knowledge always ranked above wealth – although not rejecting a possible fortuitous marriage of both. To enter “Gymnasium”, at ten, required the passing of a test. I was accepted and from then on commuted for eight years, five km each way, to the “Goethe Gymnasium” in the neighboring town of Neu Isenburg.
Gymnasium was hard. I was not a particularly good student. I loved mathematics and the sciences, but I barely scraped by in German and English and French. Receiving an “F” in either of these subjects always loomed over my head and kept me many a year at the brink of having to repeat a level. Luckily there was “Ausgleich”, balancing a bad grade in one subject with a good grade in another. Mathematics and later physics got me through school without repeat performance. I also excelled in sports, particularly in track and field, where I won a school championship in the 50 m dash. But sports could not be used for “Ausgleich”.
One of my teachers stood out, Mr. Nick. He taught math and physics. A new teacher, basically straight out of college, young, open, articulate, fun, he represented what teachers could be like. His love and curiosity for the subjects he was teaching was contagious. As 15 or 16 year-olds, we read sections of Feynman‘s Lecture Notes in Physics in a voluntary afternoon course he offered.
Having mastered wooden building blocks and cardboard models, passed erector sets and toy trains, I had reached the level of “Elektro-Mann” and “Radio-Mann”. Dozens of telephones and light boxes to communicate between the sheds at home were designed, constructed, improved, and mercilessly wrecked, possibly foreshadowing my later employment by a communications company. And then, of course, there was chemistry, a subject I did not appreciate in school, but it held the secrets for making explosives. I built a rocket that propelled a modified car of a toy train into the air. After several exhilarating launches, the rocket exploded in my hand and ripped off half my right thumb. I learned an important lesson: a rocket and a bomb differ only in the exhaust. Affecting me somewhat during adolescence, the missing thumb also relieved me from army duty. Today, it is only an unimportant, physical curiosity.
I always wanted to become a physicist. Supposedly, at age six, I had told just that to a technician, who was repairing a TV set in our home. Obviously, I had little clue as to what a physicist did. Nevertheless, the goal persisted all through high school, but suddenly got overthrown during the last year of “Gymnasium” when an art teacher discovered my talent for design. I passed my baccalaureate with average grades – quite good in the sciences but quite poor in the humanities – and started to study architecture at the Technical High School in Darmstadt, about 20 km south of my home town. Being too late at application time, I had to register for “Lehrfach für Bauwesen”, a related subject, that consisted of similar freshmen courses as architecture. I turned out to be very good in making any technical drawing of a bird cage from any requested angle, but very poor in freehand drawing and decided that architecture was not for me. Instead I went on to pursue my true love – physics.
As with architecture in Darmstadt, I was too late for registration in physics at the Goethe University in Frankfurt and took up mathematics instead, transferring to physics the following year. The year was 1968. Student revolts swept the campuses from Berkeley to Berlin. Frankfurt was a major site for riots in the streets and in the lecture halls. For a young student, hardly familiar with university life, largely ignorant of the aim of the different protests, these were uncertain times. Legitimate educational reform requests became confused with larger political issues leading to absurd happenings around campus. Damage was done to the institution of the university and its teaching staff but, at the same time, 1968 marked the beginning of a gradual and rational reform.
Studying physics and mathematics was wonderful. It was a far cry from Gymnasium. I loved the rigor of mathematics. In physics we had fascinating beginners lectures by two descendants of the famous “Pohl School” of Göttingen, Prof. Martienssen and Prof. Queisser. I had joined a group of likeminded students that studied together and hung out in “Café Bauer” for relaxation. Life was good, until I took the “Vordiplom”, the major exam in all courses at the end of the fourth semester.
All physics and math exams – some six to eight written or verbal tests – went very well. They went so well, that I thought I needn’t study at all for the dreaded verbal chemistry test. With straight “A”s in physics and mathematics, what was the chemistry professor to do but let me pass? I was mistaken and flunked badly, requiring all tests to be taken again, six months, later. Thankfully, physics and math professors – some having had experiences of their own with chemistry tests – conspired and promised to maintain my grades in those subjects. It gave me six months, to study nothing but chemistry. I never felt more confident walking into an exam and succeeded getting an “A” in chemistry. I had been wary of the field of chemistry throughout high school and during much of my studies. Counting valences and bonds, memorizing dozens of exceptions to the rules and hundreds of arcane compounds never made much sense to me. I came to revise my attitude towards chemistry once I had grasped quantum mechanics and the origin of the chemical bond.
The thesis work for my Diploma – in Germany a required step towards the Ph.D. – was performed in Professor Werner Martienssen’s Physical Institute under the supervision of a young assistant professor Eckhardt Hoenig. Professor Hoenig had just returned from the United States, where he had worked on highly-sensitive superconducting detectors, so-called SQUIDS. The aim was to use these new devices to study the magnetic properties of hemoglobin to derive the geometry of its bond with oxygen. It was a time of immense joy paired with intense learning of intricate low-temperature techniques. Hoenig was a wizard in inventing and building sophisticated instrumentation to attack physics questions. Gerd Binnig, who later shared the Nobel Prize for the invention of the Scanning Tunneling Microscope, was another student of a total of four working with Hoenig at this time in the same lab. It is probably coincidental, nevertheless, I believe our education in experimental physics down in this basement of the “Neubau” was second to none and strongly affected our experimental approaches throughout our careers. Hemoglobin did not bow to our instruments, at least over the course of a year, and I quickly performed some measurements on iron impurities in magnesium. I wrote an unimpressive diploma thesis on the magnetic anisotrophy of their susceptibility and received the necessary license to start with a Ph. D. thesis.
At this time, my horizon unexpectedly widened. It had never occurred to me, nor to many of my town’s youngsters, to go to university anywhere else but Frankfurt or Darmstadt. We went to the closest one and lived at home, where our families had been based for generations. However, in the fall of 1974, a former student from Frankfurt, Wolfgang Kottler, visited. He had since moved to Grenoble, France, where the Max-Planck-Institute for Solid State Research in Stuttgart was operating a high-magnetic field facility together with the French National Center for Scientific Research, CNRS. He was just finishing his Ph.D. thesis under Professor Hans-Joachim Queisser and was beating the bushes for his own replacement in Grenoble. Initially hesitant to make such a big step, moreover to a foreign country, the mastery of whose language I largely failed in school, I visited Grenoble and asked myself: Why not?
Going to Grenoble was the single most important step in my life. Leaving the familiar surroundings of home, diving into another culture, another language, meeting new people, making new friends was initially frightening, but eventually immensely educational and gratifying. Meeting my wife, Dominique Parchet, in Grenoble certainly added to the city’s attractions. Grenoble, at the edge of the Alps, not far from Switzerland was the French Science City. The magnet lab had been established only a few years back. Professor Klaus Dransfeld was the local director. There existed a frontier atmosphere with an exhilarating “can do” sentiment. It was an international place. Many famous scientists passed through and, due to the informality surrounding the lab, even the students were able to meet them on a very personal basis. This was quite different from other, more hierarchically structured research institutes. In a certain sense, students were kings at the magnet lab. They knew all the ins and outs of the magnets and the visiting collaborators were willing to share their scientific knowledge with them in return. It also was there, I first met Daniel Tsui from Bell Labs.
My thesis project was to work on the properties of electron hole droplets in high magnetic fields, a subject that had been proposed by Dieter Bimberg of the magnet lab. I was joined by Rolf Martin, who had just received his Ph.D. from the University of Stuttgart. Together we spent hundreds of immensely enjoyable and very productive research hours – daytime or nighttime – around the colossal magnets. Sharing a French “villa” with Ronald Ranvaud, where many distinguished visitors from abroad were often guests, life revolved totally around science. I finished my thesis in just over two years and received my Ph.D. from the University of Stuttgart, where my thesis advisor, Prof. Queisser, now a director at the Max-Planck-Institute in Stuttgart, held the position of an honorary professor. Instead of the usual dedication, my thesis had started with a cartoon. I learned only recently, that this had been a major cause of irritation and that removal of the cartoon as well as cutting my shoulder-length hair could barely be warded off.
All through my Ph.D. years, Prof. Queisser had urged me to finish my thesis swiftly and move on to the United States. He himself had been in the US, working at Bell Labs and later with Shockley, one of the inventors of the transistor. Bell Labs, the research arm of American Telephone and Telegraph (AT&T), was the “Mecca” of solid state research. Strongly encouraged and supported by my thesis advisor, I had visited Bell Labs and worked with John Hensel on electron hole droplets for several weeks during the spring of 1976. The visit was also intended to make contact with Raymond Dingle of Bell Labs. At the time, he was working on semiconductor quantum wells, an exciting new area of research made possible by the invention of molecular beam epitaxy (MBE) in the late ’60s by Alfred Cho, also of Bell Labs. I had heard Dingle speaking on the topic at the 1975 March meeting of the German Physical Society and had decided that this was the subject I wanted to pursue. As it turned out Queisser knew Dingle personally and with partial financial support from the Max-Planck-Institute in Stuttgart I was accepted into a consultant position in Venky Narayanamurti’s Department, working effectively as a postdoc with Ray Dingle. I moved to Bell Labs in June 1977.
Modulation-doping, the technique to generate ultra-high mobility two-dimensional electron systems, instrumental for practically all of my later research, was conceived about two weeks after my arrival at Bell Labs in a conversation with Ray Dingle. In his office, he had outlined their recent efforts to introduce free carriers into semiconductor superlattices and had sketched the positions of band edges, impurities and electrons on his white-board. It occurred to me that by placing impurities exclusively into the potential barriers, while keeping them out of the potential wells, the scattering of electrons by impurities should be reduced, thus increasing mobilities. It was a casual, almost trivial observation, which, however, turned out to have big impact.
Modifications to the MBE crystal growth instrumentation of Arthur Gossard and his assistant William Wiegmann to allow for such a selective doping were made over the course of a few months, and they demonstrated the anticipated gains in mobilities. Initially, mobilities improved by a mere factor two or three over conventionally doped superlattices, but they have since grown by another factor of ~1000. Loren Pfeiffer and Ken West, both from Bell Labs, have led this effort and have consistently provided the most exquisite samples for research. Much of our experimental success rests on our direct access to their “candy store”.
Modulation-doping gained me a permanent position at Bell Labs in the fall 1978, and I was soon joined by my long-time assistant, Kirk Baldwin. With such high-quality material available, many physics experiments – previously conducted on two-dimensional electron systems in silicon – became feasible in gallium arsenide. It also opened the door to many optical experiments on two-dimensional electron systems, largely performed by Aron Pinczuk and his colleagues at Bell Labs in Holmdel.
At the time, Dan Tsui of Bell Labs was already recognized as one of the world’s leading experts on two-dimensional electron systems in silicon. He quickly recognized the potential of the new material for research and invited him on his frequent trips to the MIT Francis Bitter High Magnetic Field Lab in Cambridge, Massachusetts. It was the beginning of a scientific collaboration and personal friendship, which has lasted now for almost 20 years.
The quantum Hall effect, having just been discovered in 1980 by Klaus von Klitzing, was a major topic of our research. Another topic was the electron crystal, which was theoretically predicted to form in very low electron density samples in very high magnetic field. An exceptionally high quality, low electron density specimen had just been fabricated by Art Gossard and Willy Wiegmann. Dan Tsui had succeeded in contacting it electrically, and in October 1981 we took it to the Magnet Lab to look for signs of an electron crystal. What we discovered instead, during the evening of October 6, was the fractional quantum Hall effect.
Since this discovery, many outstanding graduate students (Gregory Boebinger, Robert Willett, Andrew Yeh, Wei Pan), postdocs (Albert Chang, Hong-Wen Jiang, Rui Du, Woowon Kang) and colleagues (James Eisenstein, Peter Berglund) joined us and made discoveries of their own in this fascinating research area. Other postdocs working with me (Edwin Batke, Rick Hall, Joe Spector, Ray Ashoori, and Amir Yacoby) have performed research in neighboring areas, but affected our thinking in lower-dimensional physics in general.
In 1983, I was promoted to head the department for Electronic and Optical Properties of Solids. Administration was a minor chore during those days, and I could continue to pursue my own research, practically full time. They were very exciting and intense research days during which the fractional quantum Hall effect and its implications were established in many laboratories around the world. Theoretical progress was rapid and exhilarating.
In 1991, I was promoted to director of the Physical Research Laboratory, heading some 100 researchers in eight departments in William Brinkman’s Physics Research Division at Bell Labs. The time available for my own research dwindled, but I was compensated by becoming exposed to a wide range of exciting research topics. The initial satisfaction faded when the physical sciences at Bell Labs came under strong pressure from management to contract. These were difficult years, not just for me, but much more so for many of my friends and colleagues at Bell Labs. I was reminded of Gymnasium and the power of teachers. With the split-up of AT&T in 1996, the creation of Lucent Technologies, which subsumed Bell Labs, and a change of leadership, the physical sciences at Bell Labs are blossoming again today.
I always had thought of becoming a teacher one day. Being totally immersed in exciting research at Bell Labs, the idea had faded. It was resurfacing. I stepped down from my position in the Summer of 1997 and joined Columbia University in January of 1998 as a Professor of Physics and Applied Physics, while remaining Adjunct Physics Director at Bell Labs, part-time.
This autobiography/biography was written at the time of the award and later published in the book series Les Prix Nobel/ Nobel Lectures/The Nobel Prizes. The information is sometimes updated with an addendum submitted by the Laureate.