Inselhalle

Main Hall

Donna Strickland

Laser Acceleration for Medical Applications

Lasers can now deliver ultrashort pulses with over Petawatt peak powers. Efforts are ongoing to accelerate charged particles with high-power pulses that could lead to new radiation treatments. We are now starting to study acceleration with less powerful ultrashort pulses to deliver energetic electrons at the end of an optical fiber that can be placed inside a body. If this is possible, the lower energy electrons could irradiate the remains of a surgically removed tumor without collateral damage

J. Michael Kosterlitz

Phase Transitions and Dimensional Crossover in Layered Systems

This is a numerical study of the structure and melting of layered systems with realistic interatomic potentials. The layers are confined between uniform flat plates separated by a width w and subject to a lateral pressure. The atoms studied are Helium and Neon. The structures and melting of these layered systems of up to 2 million particles are studied and we find that a single confined layer melts by the Halperin-Nelson-Young scenario while multilayer systems all undergo first order melting. The existence of a hexatic fluid phase is confirmed but it exists for a narrow temperature range which decreases with increasing number of layers and vanishes at a critical number.

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.