&Bullet; physics 14, p48
The researchers demonstrate a method for measuring the chemical potential in a many-electron system that can be used to validate numerical calculations.
The answers to many questions in condensed matter physics are hidden in the interactions that occur in quantum many-body systems. Such systems are known to be difficult to simulate, since numerically verifiable solutions exist under very limited circumstances. Unfortunately for physicists, the computable parameters of many-body systems are experimentally inaccessible, making it difficult to test theories empirically. Now, Fangyuan Yang of the University of California at Santa Barbara and colleagues have measured a previously inaccessible quantity – chemical potential – that enables precise benchmarking of numerical techniques  .
In their experiments, the team examined a graphene-based 2D electron gas. The electron chemical potential of a system is the energy required to add or remove an electron. Together with the electron density, the chemical potential determines how the electrons are arranged in the system.
To carry out their measurement, Yang and colleagues created a stacked structure of alternating layers of graphene and boron nitride, which they then exposed to a strong magnetic field. The field caused an electron of a few thousand carbon atoms in the graphene layers to move in circular orbits called Landau levels.
Landau levels are quantized and each houses a finite number of electrons; The abundance of a certain level determines the electron density of the system. The researchers kept the electron density in the upper layer of graphene constant and applied a voltage to the lower layer, changed the chemical potential of this layer and induced an electric field. They then calculated this chemical potential by measuring how the induced electric field affected the conductivity of the other graphene layer. Such measurements have been attempted before, but only recently have nanofabrication techniques reached the precision required for a successful experiment.
Marric Stephens is Corresponding Editor for physics based in Bristol, UK.
- F. Yang et al., “Experimental determination of the energy per particle in partially filled Landau plains” Phys. Rev. Lett.126156802 (2021).