The discovery of a new quantum state similar to water that does not freeze

Cryostat is used to achieve temperatures up to 20 mK. Credit: HZDR/Jürgen Jeibmann

Water that simply won’t freeze, no matter how cold it is – a research group including Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has discovered a quantum state that can be described in this way.

Experts from the Institute of Solid State Physics at the University of Tokyo in Japan, Johns Hopkins University in the United States, and the Max Planck Institute for Physics of Complex Systems (MPI-PKS) in Dresden, Germany, have managed to cool a special sample material to a temperature close to absolute zero.

And they found that the central property of atoms – their alignment – did not “freeze” as usual, but remained in a “liquid” state. The new quantum material can serve as a model system for the development of new, highly sensitive quantum sensors. The team presented its findings in the journal nature physics.

At first glance, quantum materials look no different than ordinary materials — but they certainly do their own thing: Inside, electrons interact with extraordinary intensity, with each other and with the atoms of the crystal lattice. This intimate interaction results in powerful quantum effects that act not only at the microscopic level, but also at the macroscopic scale.

Thanks to these effects, quantum materials exhibit remarkable properties. For example, they can conduct electricity completely losslessly at low temperatures. Small changes in temperature, pressure, or electrical potential are often enough to radically change the behavior of a material.

In principle, magnets can also be considered quantum materials; After all, magnetism depends on the inward spin of the electrons in the material. “In some ways, these spins can behave like a fluid,” explains Professor Jochen Wosnitza of the High-field Magnetic Field (HLD) Dresden Laboratory at the HZDR. “As temperatures drop, these turbulent cycles can freeze, much like a lot of water freezes into ice.”

For example, certain types of magnets, so-called ferromagnets, are non-magnetic above their “freeze”, or more accurately point of order. Only when they fall under it can they become permanent magnets.

High purity materials

The international team intended to create a quantum state in which the atomic alignment associated with spin is not ordered, even at very cold temperatures – similar to a liquid that will not solidify, even in extreme cold. To achieve this state, the research group used a special material — a compound of the elements, praseodymium, zirconium, and oxygen. They hypothesized that in this material, the properties of the crystal lattice would enable the electron’s spin to interact with their orbits around the atoms in a special way.

“The prerequisite, however, was to obtain crystals of very high purity and quality,” explains Professor Satoru Nakatsuji of the University of Tokyo. It took several tries, but eventually the team was able to produce crystals pure enough for their experiment: In a cryostat, a kind of super thermos flask, experts gradually cooled the sample to 20 millicelvin—just fifty degrees above absolute. zero.

To see how the sample responds to this cooling process and within a magnetic field, they measured how its length changed. In another experiment, the group recorded how the crystal reacted to ultrasound being sent directly through it.

intimate interaction

The result: “If the spins had ordered, they should have caused an abrupt change in the behavior of the crystal, such as a sudden change in length,” describes it Dr. Sergey Zerlitsyn, HLD’s expert in ultrasound probes. “However, as we noted, nothing happened! There were no abrupt changes in either height or in response to ultrasound.”

Conclusion: The apparent interaction between spins and orbitals has prevented ordering, which is why atoms remain in their liquid quantum state – the first time such a quantum state has been observed. Further investigations into magnetic fields confirmed this assumption.

These fundamental research findings could also have practical implications one day: “At some point we may be able to use the new quantum state to develop highly sensitive quantum sensors,” speculates Jochen Vosnitza. “To do this, however, we have yet to figure out how to systematically generate excitement in this state.”

Quantum sensing is a promising technology in the future. Because their quantum nature makes them very sensitive to external stimuli, quantum sensors can record magnetic fields or temperatures with much greater accuracy than conventional sensors.

more information:
Satoru Nakatsuji, Rotational Orbital Liquid State and Ferromagnetic Translocation of Gas-Liquid on a Perchlor Lattice, nature physics (2022). DOI: 10.1038/s41567-022-01816-4

Provided by the Helmholtz Association of German Research Centers

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