Controlling how electrons zip through a material is of central importance to build novel electronic devices. How the electronic motion is affected by magnetic fields is an old problem that has not been fully solved, yet has already led to multiple physics Nobel prizes. Now researchers at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg have solved one of the long-standing problems in the field, namely how a certain symmetry can be restored. Their results were just published in Physical Review Letters.
Electrons moving in a strong magnetic field perform a circular motion due to the Lorentz force, on which electromagnetic induction and the electric motor are based.
In the quantum flatland of atomically thin two-dimensional materials, this leads to weird quantum effects like the integer and the fractional quantized Hall effects, which state that the number of Lorentz-deflected charges are not arbitrary but increase in discrete (quantized) steps.
Despite much progress in the field, the fundamental description of how electrons behave in magnetic fields has remained somewhat incomplete.
"There is a deep problem here. Let’s say I have a giant magnetic coil and generate a field that is the same everywhere in space, the electrons in my quantum sheet should feel the same force everywhere," says Vasil Rokaj, PhD student in the MPSD Theory Department and lead author of the study. "But standard textbooks treating the magnetic field classically, fail to account for this physical requirement," he adds.
With a team of researchers led by MPSD Theory Director Angel Rubio and group leaders Michael Ruggenthaler and Michael Sentef, Rokaj and co-author Markus Penz set out to derive new equations that would cure this shortcoming.
"We did not know originally what to expect," adds Ruggenthaler. "In fact, we were interested in a different problem, namely how a quantized rather than classical field in a so-called cavity affects the electronic motion."
To achieve this, Rokaj had to use the formalism of quantum electrodynamics, which was first developed in the 1930s and 1940s to describe how electrons and photons interact. When Rokaj wrote down the equations for the electrons in the solid, the team realized that something interesting happened.
"The magnetic field in a coil is composed of photons, so in principle we should be able to also describe the old problem with our new approach," says Ruggenthaler. "Surprisingly, the quantum uncertainty (or fluctuations) of the field, which is usually not taken into account, helps to restore the fundamental symmetry - that everything should be the same no matter where in space we look."
Angel Rubio adds: "These efforts prove that we are on the right track by tackling the problem in a fully quantum way." In his Theory Department, many researchers work on the large-scale problem of how photons change the properties of matter - from novel chemical reactions to materials that might help build future quantum computers.
"This work proves that it is always worthwhile to take a fresh look at old problems, and to start from the basic principles," says Rubio. "I am sure that further surprises are just waiting to be discovered."
Vasil Rokaj, M.Sc.
Phone: +49 (0)40 8998 88331
Dr. Michael Ruggenthaler
Phone: +49 (0)40 8998-88319
Quantum Electrodynamical Bloch Theory with Homogeneous Magnetic Fields
Vasil Rokaj, Markus Penz, Michael A. Sentef, Michael Ruggenthaler, and Angel Rubio
Phys. Rev. Lett. 123, 047202 – Published 23 July 2019
https://doi.org/10.1103/PhysRevLett.123.047202 original publication
Dr. Joerg Harms | Max-Planck-Institut für Struktur und Dynamik der Materie
Newfound superconductor material could be the 'silicon of quantum computers'
16.08.2019 | National Institute of Standards and Technology (NIST)
Moon glows brighter than sun in images from NASA's Fermi
16.08.2019 | NASA/Goddard Space Flight Center
Soft robots have a distinct advantage over their rigid forebears: they can adapt to complex environments, handle fragile objects and interact safely with humans. Made from silicone, rubber or other stretchable polymers, they are ideal for use in rehabilitation exoskeletons and robotic clothing. Soft bio-inspired robots could one day be deployed to explore remote or dangerous environments.
Most soft robots are actuated by rigid, noisy pumps that push fluids into the machines' moving parts. Because they are connected to these bulky pumps by tubes,...
Researchers at TU Graz are working together with European partners on new possibilities of measuring vehicle emissions.
Today, air pollution is one of the biggest challenges facing European cities. As part of the Horizon 2020 research project CARES (City Air Remote Emission...
Over the next three years, researchers from the Vrije Universiteit Brussel, University of Cambridge, École Supérieure de Physique et de Chimie Industrielles de la ville de Paris (ESPCI-Paris) and Empa will be working together with the Dutch Polymer manufacturer SupraPolix on the next generation of robots: (soft) robots that ‘feel pain’ and heal themselves. The partners can count on 3 million Euro in support from the European Commission.
Soon robots will not only be found in factories and laboratories, but will be assisting us in our immediate environment. They will help us in the household, to...
Scientists at the University of Leeds have created a new form of gold which is just two atoms thick - the thinnest unsupported gold ever created.
The researchers measured the thickness of the gold to be 0.47 nanometres - that is one million times thinner than a human finger nail. The material is regarded...
An international team of scientists involving the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg has unraveled the light-induced electron-localization dynamics in transition metals at the attosecond timescale. The team investigated for the first time the many-body electron dynamics in transition metals before thermalization sets in. Their work has now appeared in Nature Physics.
The researchers from ETH Zurich (Switzerland), the MPSD (Germany), the Center for Computational Sciences of University of Tsukuba (Japan) and the Center for...
16.08.2019 | Event News
14.08.2019 | Event News
12.08.2019 | Event News
16.08.2019 | Life Sciences
16.08.2019 | Physics and Astronomy
16.08.2019 | Medical Engineering