Heinrich Rohrer

Heinrich Rohrer was born on June 6, 1933 in Buchs, a quiet town in the Swiss canton of St. Gallen, half an hour after his twin sister. He often said that those thirty minutes of seniority were the only ones he ever lost to anybody. The family stayed in the countryside through the war years, and Rohrer later described his childhood as carefree, full of cold rivers, long bicycle rides, and the kind of mountain silence that, he claimed, taught him to listen for very small signals long before he knew what a signal was. In 1949 the family moved to Zürich, and two years later, in 1951, the seventeen-year-old Rohrer enrolled at the Eidgenössische Technische Hochschule, the ETH, where Einstein had once been a student and where Wolfgang Pauli was now lecturing on quantum mechanics.

Rohrer took courses from Pauli and from Paul Scherrer, the experimentalist who had given his name to the Debye-Scherrer X-ray method a generation earlier. His doctoral work, supervised by P. Grassmann, was in cryogenic engineering. The project, inherited from a previous student named Jørgen Lykke Olsen, was to measure how a superconductor changes its length by a few parts per million when a magnetic field destroys its superconductivity. The signals were so faint that Zürich’s daytime traffic drowned them in vibration. Rohrer reorganized his life around the city’s pulse, sleeping during the morning and arriving in the lab after midnight. He later said that the habit of working only when the world was quiet stayed with him. It was the single most important technical lesson of his career, more important than any equation he learned at ETH, because it told him what an instrument really needs in order to see something small.

Heinrich Rohrer (6 June 1933 – 16 May 2013) was a Swiss physicist who shared half of the 1986 Nobel Prize in Physics with Gerd Binnig for the design of the scanning tunneling microscope (STM). The other half of the Prize was awarded to Ernst Ruska. The Heinrich Rohrer Medal is presented triennially by the Surface Science Society of Japan with IBM Research – Zurich, Swiss…

His studies were briefly interrupted by service in the Swiss mountain infantry, the same alpine regiments his grandfather had served in. In 1961 he married Rose-Marie Egger, and they spent their honeymoon driving across the United States. The trip ended at Rutgers University in New Jersey, where Rohrer stayed for a postdoctoral year measuring the thermal conductivity of type-II superconductors with Bernie Serin. He liked the American style of doing physics, fast, informal, generous with equipment, and he carried it back to Zürich when, in 1963, he joined the IBM Research Laboratory in Rüschlikon under Ambros Speiser. He would remain at IBM for the rest of his working life.

The Rüschlikon lab, perched above Lake Zürich, gave Rohrer a long leash. For nearly two decades he worked on magnetic phase transitions, on Kondo systems in pulsed magnetic fields, on critical phenomena near the points where matter changes its state. In 1974 he took a sabbatical year at the University of California, Santa Barbara, studying nuclear magnetic resonance with Vince Jaccarino and Alan King. It was steady, careful, well-respected work, but it was not the kind of work that wins prizes.

Everything changed in 1978, when a young German physicist named Gerd Binnig arrived at the lab. Rohrer was forty-five, Binnig twenty-nine. They wanted to study very thin oxide layers on surfaces, the inhomogeneities that made integrated circuits fail, and they realized that no existing technique could resolve a single atom on a surface in real space. Electron microscopes could, but only by destroying the sample. The two of them began to ask whether the quantum mechanical tunneling current that flows between two electrodes separated by a vacuum gap, a current that Gamow had first analyzed for alpha decay in 1928, could be used as a ruler. Tunneling current depends exponentially on distance: shrink the gap by a single atomic diameter and the current jumps by a factor of about ten. That exponential is the world’s most sensitive height gauge, if only one could hold the tip steady enough to use it.

For the next four years Rohrer and Binnig fought vibration. They built a microscope that floated on superconducting magnets, then on rubber feet stacked on lead blocks, then in a chamber inside a chamber inside the basement. Rohrer’s old habit of working at night came back. They needed the lab quiet, the city asleep, the trams stopped. On a March night in 1981 the first reproducible tunneling signal appeared on their oscilloscope. By 1982 they were imaging single atoms on a silicon surface, the famous 7×7 reconstruction of the (111) face that surface scientists had argued about for twenty years and that the scanning tunneling microscope solved in a single afternoon.

The 1986 Nobel Prize in Physics was awarded that October. Half went jointly to Rohrer and Binnig for the design of the scanning tunneling microscope; the other half went to Ernst Ruska, then eighty-year-old, for the original 1933 electron microscope. Ruska had waited fifty-three years for his prize. Rohrer had waited four. He was made an IBM Fellow that same year and ran the lab’s physics department from 1986 to 1988. Within a year of the Nobel, Binnig invented the atomic force microscope, a cousin of the STM that could image insulators as well as conductors, and Rohrer’s group helped shepherd that instrument from prototype into a research tool that now sits in nearly every nanoscience laboratory in the world.

Rohrer remained at IBM Rüschlikon until his formal retirement in 1997 and stayed close to the lab afterwards. He was elected an honorary member of the Swiss Physical Society in 1990 and an honorary academician of Academia Sinica in 2008. He died of natural causes on May 16, 2013 at his home in Wollerau, on the shore of Lake Zürich, aged seventy-nine. The Heinrich Rohrer Medal, presented every three years by the Surface Science Society of Japan together with IBM Research Zürich and the Swiss Embassy in Japan, now recognizes the kind of patient surface-science work that he and Binnig had spent four nights a week protecting from passing streetcars.

What Rohrer means to the quantum story is concrete and small. Before 1981, an atom was an inference. After 1981, it was a thing you could photograph.