A research group at the University of Tokyo, in collaboration with RIKEN, discovered the quantum phase transition of valences and the associated quantum critical phenomena for the first time in the world.
The change in the state of matter, just as water turns into ice or water vapor, is called the phase transition.The liquid-gas phase transition of water occurs at 100 ° C at normal pressure, but when pressurized, the phase transition temperature rises and becomes a supercritical fluid in which liquid and gas cannot be distinguished under certain conditions of high temperature and high pressure.Since supercritical fluids have both gas diffusivity and liquid solubility, they are widely applied in the industrial field.
In contrast to the phase transition caused by temperature changes such as the phase transition of water, the phase transition when the pressure or magnetic field is changed at absolute zero is called the quantum phase transition.It has been interesting for many years what kind of properties the critical fluctuations before and after the quantum phase transition produce, but it has been difficult to cause the quantum phase transition by making a fluid such as water at absolute zero.
Therefore, in this research, we focused on the phase transition in which the number of electrons (valence) of ions in a substance changes as a candidate that has properties similar to supercritical fluids and is capable of quantum phase transition.We succeeded in observing a crossover in which the valence changes sharply by utilizing the fact that adding a small amount of iron to a ytterbium compound, which has the property of fluctuating the valence with pressure, produces an effect similar to pressure.
At the same time as the valence crossover, we discovered an abnormal metallic state that does not show magnetic order even though the magnetization is very large.This shows that fluctuations between a high valence state showing magnetic properties and a low valence state showing non-magnetic properties are realized, and the quantum phase transition of valences is experimental. It was the first example in the world established in Japan.
This critical fluctuation of valence can be said to be an electronic version of supercritical fluid, and is expected to promote the discovery of new "quantum" supercritical fluids.
Paper information:[Science Advances] Quantum Valence Criticality in a Correlated Metal
