First ever images of Landau levels

Landau Levels – the quantum levels that determine electron behaviour in a strong magnetic field – have been imaged for the first time by physicists at the University of Warwick and Tohoku University. The researchers used scanning tunnelling spectroscopy, a technique involving a spatially resolved probe that directly interacts with electrons. The results have revealed the internal ring-like structure of these Landau Levels at the surface of a semiconductor. The findings are published in Physical Review Letters.

Professor Rudolf Roemer of the Department of Physics at the University of Warwick said: “This is an exciting step for us, we are really seeing for the first time individual quantum mechanical wave functions of electrons in real materials.”

The experimental challenge was to have sufficient spatial resolution in order to overcome the intrinsic disorder in the material that usually allows only the observation of smeared out “drift” states.

Landau Levels were first proposed by Nobel prize winner Lev Landau in 1930. The resulting images from this research show clearly that Landau was right when he predicted that, in a clean system, the electrons would take on the form of concentric rings, the number of which would increase according to their energy level. This forms of the basis of the quantum Hall effect.

The quantum Hall effect was originally of mostly fundamental interest but has been used in recent years to define the standard for what we mean by electrical resistance and could soon be used to define to kilogram.

“On the face of it this might seem far removed from everyday life. “However the question of what defines a kilogram is currently being debated, with the spacing between the rings of these Landau levels acting as a kind of marker for a universal weight. So next time you measure out your sugar to bake a cake, you might unknowingly be making use of these quantum rings,” Roemer added.