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Laughlin, Robert B

quantum physics electrons observed

(1950–) US physicist: co-discoverer of a new form of quantum fluid.

As a reclusive boy growing up in out-going California, Laughlin’s interest in physics began when his parents gave him a colour TV in kit form. He constructed it, but to learn something of how it worked he experimented with discarded TV sets (and gave himself some severe electric shocks). Undeterred, he made sodium by electrolysis of fused sodium hydroxide, and was severely burned by it in the process. More safely, he taught himself some higher mathematics, and entered Berkeley in 1968 to study electrical engineering, but soon moved to physics, and graduated best in maths. Military service in a missile training school ended in Europe, which he celebrated in traditional fashion by burning his boots (but non-traditionally he filled them first with 3 of nitrate mixed with sugar, giving a 10 m high flameshow).

At MIT as a postgraduate from 1974 he focused on solid state physics, which led on to work at Bell Labs and then at the Livermore lab, where his Nobel Prize work began. From 1984 he worked at Stanford. Quantum fluids are those in which particles combine and form a condensed fluid with unusual properties. Aside from high-energy colliders, they form a crucial arena in which the quantum behaviour of matter can be observed. Liquid helium, superconductors and superfluids are examples, as is the Hall effect. This originated in 1879, when electrons moving through a gold film were observed to be deflected by a perpendicular magnetic field. The quantum version of this was discovered by a century later. At low temperatures and very high field strengths the electrons move as if on a single surface, and the Hall resistance changes in integral quantum steps (rather than linearly) with field strength. This effect occurs because of the selected quantized circular paths which the electrons may move along. One of the biggest surprises in modern physics occurred in 1982 when Horst Störmer (1949–) and Daniel Tsui (1939–) observed fractional values in addition to the integer quanta seen by von Klitzing. A year later Laughlin set out the theoretical explanation, predicting fractionally charged quasiparticles as being responsible. These have now been seen directly, confirming his model. The electrons (as fermions with spin one half) do not condense easily, however they combine with magnetic field flux quanta. Together they form bosons (particles of integer spin) which combine much more readily. When an electron is added it excites the fluid of condensed bosons, and quasiparticles are created within it. Laughlin predicted these effects theoretically, and they have exactly the fractional charge observed in Störmer and Tsui’s experiments. These three people shared the Nobel Prize for physics in 1998.

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