Klaus von Klitzing

Surprises From Flatland: When Experiments Rewrite the Rules

Scientific revolutions often begin with simple questions pursued through basic research. This talk retraces an unexpected journey that started with investigations of silicon field-effect transistors and the physics of electrons confined to two dimensions – a world that may be called “flatland.” What began as an effort to understand and improve the properties of microelectronic devices led, in the early hours of 5 February 1980, to an observation that defied conventional expectations: the discovery of the quantum Hall effect.

At approximately 2 a.m., experimental data revealed an astonishingly precise quantization of the Hall resistance. This surprising result challenged established understanding and opened a new chapter in condensed matter physics. The phenomenon demonstrated that under extreme conditions, the collective behaviour of electrons in two dimensions gives rise to fundamentally new quantum states governed by universal constants of nature.

The talk will recount the experimental path to this discovery, the initial skepticism and excitement surrounding the first measurements, and the conceptual insights that emerged as the effect was understood. Beyond its profound significance for basic physics, the quantum Hall effect proved to be far more than a scientific curiosity. Its extraordinary reproducibility and exactness transformed electrical metrology by providing a resistance standard linked directly to fundamental constants.

This development ultimately contributed to a broader revolution in measurement science, culminating in the redefinition of the International System of Units (SI), in which constants of nature now form the foundation of our system of measurement.

Takaaki Kajita

Neutrino Oscillations

Neutrinos have been assumed to have no mass. If neutrinos do have mass, their type may change during the propagation, which is called neutrino oscillation. Neutrino oscillation was discovered about 30 years ago by studying neutrinos produced by cosmic ray interactions in the atmosphere. I will discuss the discovery of neutrino oscillations, its implications and the prospects for neutrino experiments.