researchers from tu wien (vienna, austria) have published new ideas about quantum critical points where phase transitions happen at absolute zero without the change in temperature that is typically needed for those type of changes.

alessandro toschi, thomas schäfer and karsten held worked on the research.
(tu wien)

according to a report from the university, researchers have been puzzling over theoretical models for quantum critical points, such as with high-temperature superconductivity, but there is no conclusive model despite years of research.

the tu wien scientists explored thermal fluctuations in which individual particles shake or rotate at random. these fluctuations become more pronounced at higher temperatures and can lead to phase transitions, but at absolute zero, where it would be assumed that there is no motion in the atoms, motion still exists without thermal fluctuations.

“so, when it is too cold for classic shaking movements, quantum physics ensures that physically interesting things can still happen,” the article explained. “and that is exactly why phase transitions at absolute zero are so endlessly fascinating.”

researchers are particularly interested in what this motion means for energy. they demonstrated that the shape of fermi surfaces, which shows the 3-d shapes of particles in a solid, have to be taken into account to calculate a material’s properties as it approaches absolute zero.

“now the researchers hope to use this new tool to better describe quantum critical materials – and maybe shed light on some of the great mysteries that materials science has been working so hard to solve for so many years,” the article concluded.

the research was recently published in physical review letters. the abstract read:

“a general understanding of quantum phase transitions in strongly correlated materials is still lacking. by exploiting a cutting-edge quantum many-body approach, the dynamical vertex approximation, we make important progress, determining the quantum critical properties of the antiferromagnetic transition in the fundamental model for correlated electrons, the hubbard model in three dimensions.

“in particular, we demonstrate that—in contradiction to the conventional hertz-millis-moriya theory—its quantum critical behavior is driven by the kohn anomalies of the fermi surface, even when electronic correlations become strong.”