An international research team – including the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) – has discovered a quantum state that could be described in this way. Scientists have succeeded in cooling a special material to almost absolute zero. They discovered that a central property of atoms – their alignment – did not ‘frozen’ as usual, but remained in a ‘liquid’ state.
Within quantum materials, the electrons interact with unusual intensity, both with each other and with the atoms of the crystal lattice. This tight connection produces powerful quantum effects that affect microscopic and macroscopic levels. These phenomena give quantum materials extraordinary properties. At low temperatures, for example, they can transport electricity losslessly. Often even small variations in temperature, pressure or electrical voltage are enough to significantly change the behavior of a material.
prof. Jochen Wosnitza of the Dresden High Field Magnetic Laboratory (HLD) at HZDR said: “In principle, magnets can also be regarded as quantum materials; After all, magnetism is based on the intrinsic Spin of the electrons in the material. In some ways, these spins can behave like a liquid.”
“As the temperature drops, these disordered spins can freeze, just like water freezes into ice.”
“Certain types of magnets, so-called ferromagnets, for example, are non-magnetic above their ‘freezing point’, or rather, ordering point. Only when they fall below can they become permanent magnets.”
In this study, scientists sought to discover a quantum state in which the atomic alignment associated with the spins was not ordered even at ultra-cold temperatures – similar to a liquid that does not solidify even in extreme cold.
To achieve this state, the research team used a unique substance, a mixture of praseodymium, zirconium and oxygen. They believed that the characteristics of the crystal lattice in this material would allow the electron spins to interact uniquely with their orbitals around the atoms.
prof. Satoru Nakatsuji from the University of Tokyo said: “However, the condition was to have crystals of extreme purity and quality. It took several attempts, but in the end the team succeeded in producing crystals pure enough for their experiment: In a cryostat, a kind of super thermos, the experts gradually cooled their sample to 20 millikelvins – just one fiftieth of a degree above absolute zero point. To see how the sample responded to this cooling process and within the magnetic field, they measured how much it changed in length. In another experiment, the group recorded how the crystal reacted to ultrasonic waves passed directly through it.”
Dr. Sergei Zherlitsyn, HLD’s expert in ultrasound examination, describes: “If the spins had been ordered, it would have caused an abrupt change in the behavior of the crystal, such as a sudden change in length. But, as we saw, nothing happened! There were no sudden changes in length or the response to ultrasonic waves.”
“The pronounced interplay of spins and orbitals had prevented ordering, leaving the atoms in their liquid quantum state – the first time such a quantum state had been observed. Further research in magnetic fields confirmed this assumption.”
Jochen Wosnitza speculates, “This basic research result may one day also have practical implications: At some point, we may be able to use the new quantum state to develop susceptible quantum sensors. However, to do this, we still need to figure out how to systematically generate excitations in this state. Quantum sensing is considered a promising technology of the future.Because of their quantum nature they are extremely sensitive to external stimuli, quantum sensors can register magnetic fields or temperatures much more accurately than conventional sensors.”
- Tang, N., Gritsenko, Y., Kimura, K. et al. Spin-orbital liquid state and liquid-gas metamagnetic transition on a pyrochlore lattice. Wet. Physically. (2022). DOI: 10.1038/s41567-022-01816-4