Phenomenon thought to occur only in exotic, high-energy physics environments seen in quantum material.
By Philip Bell
An exotic effect in particle physics that’s theorized to occur in immense gravitational fields — near a black hole, or in conditions just after the Big Bang — has been seen in a lump of material in a laboratory, physicists report.
A team led by physicist Johannes Gooth at IBM Research near Zurich, Switzerland, say they have seen evidence for a long-predicted effect called the axial–gravitational anomaly. It states that huge gravitational fields — which general relativity describes as the result of enormous masses curving space-time — should destroy the symmetry of particular kinds of particles that usually come in mirror-image pairs, creating more of one particle and less of another.
The kinds of conditions needed to prove this unusual breakdown of a fundamental ‘conservation law’ can’t be created in a laboratory. But the researchers exploited a peculiar parallel between gravity and temperature to create a lab analogue of the anomaly in niobium phosphide crystals. “This anomaly is so hard to measure that even indirect evidence is a major breakthrough,” says team member Adolfo Grushin of the University of California, Berkeley.
Inside the crystal, the effect is as if a drawerful of pairs of gloves were suddenly to acquire an excess of right-handed gloves because some of the left-handed ones had switched handedness. The result, published in Nature2, bolsters an emerging view that quantum materials — crystals whose properties are dominated by quantum-mechanical effects – can act as experimental test-beds for physics effects that could only otherwise be seen under exotic circumstances.
Not everyone is persuaded that the researchers have observed what they claim. Boris Spivak, a physicist at the University of Washington in Seattle, insists that the axial–gravitational anomaly simply doesn’t exist in Weyl semimetals. A temperature gradient, he says, can’t induce electrons to convert between the two quasiparticles of different handedness. “There are many other mechanisms which can explain their data,” Spivak says. He thinks the researchers are just measuring the impact of a magnetic field on the well-known thermoelectric effect, in which electrical currents are produced by temperature gradients.
But Gooth and his colleagues disagree. They say that the existence of the temperature-induced chiral anomaly is strongly supported by theory. And Subir Sachdev, a specialist on quantum effects in solid-state materials at Harvard University in Cambridge, Massachusetts, says the researchers have “compelling evidence for the physical consequences of the axial–gravitational anomaly”.
The existence of the anomaly was not really in doubt, Sachdev adds, but “it is nice to see it appear in real materials”. He says it confirms that gravity interacts with quantum fields in the manner indicated by Einstein’s theories of relativity.
Grushin suspects that understanding how this anomaly manifests in these materials should lead to new physics. And IBM also hopes that the finding might be exploited in electronics, because it generates an electrical current inside the niobium phosphide crystal. Devices that expoit the anomaly might improve the efficiency of materials that can generate electrical energy from temperature gradients, Gooth says.
- Nature doi:10.1038/nature.2017.22338
This article (Big Bang gravitational effect observed in lab crystal – Resonance Science Foundation) was originally published on Nature and syndicated by The Event Chronicle. Found via Resonance Science Foundation.