When the universe was just a few microseconds old, it existed as a strange soupy substance called quark-gluon plasma (QGP), which exhibits a whole host of unusual quantum effects. Now, for the first time, IBM researchers have observed a gravitational anomaly in earthly materials, which was previously only thought to occur in QGP in deep space or just after the Big Bang.
The world of classical physics is governed by the laws of conservation, stating that a measurement like energy or mass in a system cannot change quantity, although it may change form. But exotic types of matter, like QGP, can exhibit quantum effects that throw those laws out the window.
These exotic materials, forged in the crucible of the Big Bang or high energy particle accelerators, were thought to be the only places such quantum phenomena could occur. But now IBM scientists have observed a quantum effect called an axial-gravitational anomaly in recently-discovered materials called Weyl semimetals.
The electrons in these crystals are divided into two groups according to the direction of their spin, and normally there are equal numbers of each type of electron. But when the researchers mimicked a gravitational field by imposing a temperature gradient, they found that quantum anomalies mess with this symmetry by changing electrons from one type to the other, and vice versa. This is the first time that this gravitational anomaly has been observed under normal circumstances here on Earth.
"This is an incredibly exciting discovery," says Karl Landsteiner, co-author of the paper. "We can clearly conclude that the same breaking of symmetry can be observed in any physical system, whether it occurred at the beginning of the universe or is happening today, right here on Earth."
Weyl semimetals are solid state crystals, so to find these anomalies at work inside them has implications for electronics built on solid state physics.
"For the first time, we have experimentally observed this fundamental quantum anomaly on Earth which is extremely important towards our understanding of the universe," says Johannes Gooth, lead author of the paper. "We can now build novel solid-state devices based on this anomaly that have never been considered before to potentially circumvent some of the problems inherent in classical electronic devices, such as transistors."
The research was published in the journal Nature.