For the first time, physicists have discovered that in an extremely high magnetic field ‘massless’ Dirac electrons can acquire a mass.
A false-color high-resolution transmission electron microscopy image of the zirconium pentatelluride (ZrTe5) with an inset selected area electron diffraction (SAED) pattern, showing the layer normal along the b axis. Scale bar – 2 nm. Image credit: Yanwen Liu et al.
“This is a very exciting breakthrough because until now, nobody has ever discovered an object whose mass can be switched on or off by applying an external stimulus,” said Prof. Stefano Sanvito, a researcher in the Advanced Materials and BioEngineering Research (AMBER) Center and the CRANN Institute at Trinity College Dublin, Ireland.
While the applications of the discovery remain to be seen, this represents a significant breakthrough in fundamental physics.
It could inspire work in high-energy physics, such as the collision experiments carried out in particle accelerators like CERN’s Large Hadron Collider.
“Every physical object has a mass, which is a measure of the object’s resistance to a change in its direction or speed, once a force is applied,” Prof. Sanvito explained.
“While we can easily push a light-mass shopping trolley, we cannot move a heavy-mass six-wheel lorry by simply pushing.”
“However, there are some examples in nature of objects not having a mass. These include photons, the elementary particles discovered by Albert Einstein responsible for carrying light, and neutrinos, produced in the Sun as a result of thermonuclear reactions.”
Prof. Sanvito and his collaborators from Australia, China, Ireland and the United States have demonstrated for the first time one way in which mass can be generated in a material.
“In principle the external stimulus that enabled this, the magnetic field, could be replaced with some other stimulus and perhaps applied long-term in the development of more sophisticated sensors or actuators,” Prof. Sanvito said.
“It is impossible to say what this could mean, but like any fundamental discovery in physics, the importance is in its discovery.”
The research team studied what happened to the current passing through the exotic material zirconium pentatelluride (ZrTe5) when exposed to an extremely high magnetic field.
Measuring a current in a magnetic field is a standard way of characterizing the material’s electronic structure.
In the absence of a magnetic field the current flows easily through ZrTe5. This is because in ZrTe5 the electrons responsible for the current have no mass.
However, when a magnetic field of 60 Tesla (a million times more intense than the magnetic field of our planet) is applied the current is drastically reduced and the electrons acquire a mass.
An intense magnetic field in ZrTe5 transforms slim and fast electrons into fat and slow ones.
The findings were published this month in the journal Nature Communications.
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Yanwen Liu et al. 2016. Zeeman splitting and dynamical mass generation in Dirac semimetal ZrTe5. Nature Communications 7, article number: 12516; doi: 10.1038/ncomms12516
