Physicists discover the first possible 3D quantum spin liquid

There is no known way to prove that a three-dimensional "quantum spin liquid" exists. Rice University physicists and their collaborators have therefore taken the following step: they have shown that their single crystals of cerium, zirconium pyrochlore have the qualities required to be considered as the first possible. -D version of the state of the long sought after material.

Despite its name, a quantum spin liquid is a solid material in which the strange property of quantum mechanics – entanglement – ensures a magnetic state similar to a liquid.

In a newspaper this week Physical Nature, the researchers offered a host of experimental evidence – including crucial neutron scattering experiments at the Oak Ridge National Laboratory (ORNL) and muon spin relaxation experiments at the Paul Scherrer Institute (PSI) in Switzerland – to support their thesis that cerium zirconium pyrochlore crystalline form, is the first material that can be called 3D quantum spin liquid.

"Scientists are defining a quantum spin liquid based on what you do not see," said Rice's Pengcheng Dai, corresponding author of the study and a member of Rice's Quantum Materials Center (RCQM). "You do not see any long-term order in the arrangement of the towers, you do not see a mess, and a variety of other things, that's not it, it's not that there is no conclusive positive identification. "

The samples from the research team are considered the first of its kind: Pyrochlores because of their ratio of cerium, zirconium and oxygen from 2 to 7, and single crystals because their atoms are arranged from continuously and continuously. mesh.

"We did all the experiments we could think of on this compound," said Dai. "(Co-author of the study), Emilia Morosan's group at Rice performed a work on thermal capacity to show that the material undergoes no phase transition up to 50 millikelvins. We carried out a very detailed crystallography to show that there was no disorder in the crystal.We performed a relaxation of the spin of the muon, experiments demonstrating a lack of order. long-range magnetic order up to 20 millikelvins and diffraction experiments showing that the sample showed no oxygen deficiency nor any other known defect, then an inelastic neutron scattering highlighting the presence of ## EQU1 ## 39, a spin continuum excitation – which can be a quantum spin liquid quantum punch – up to 35 millikelvin ".

Dai, professor of physics and astronomy, attributed the success of the study to his colleagues, including co-authors Bin Gao and Tong Chen and co-author David Tam. Gao, a Rice postdoctoral research associate, created the monocrystalline samples in a floating zone laser furnace in the laboratory of Rutgers University's co-author, Sang-Wook Cheong. Tong, a student rice doctorate, helped Bin to conduct ORNL experiments that produced a spin-excited continuum indicating the presence of spin entanglement producing short-range order, and Tam, who also holds a doctorate in rice. student, directed muon spin rotation experiments at PSI.

Despite the team's efforts, Dai said that it was impossible to say with certainty that cerium-zirconium 227 was a spin liquid, in part because physicists do not have to worry about it. were not yet agreed on the experimental evidence needed to make this statement, and partly because the definition of a quantum spin the liquid is a state that exists at the absolute zero temperature, an ideal out of scope of any experience.

Quantum spin liquids are thought to occur in solid materials composed of magnetic atoms in particular crystal arrangements. The inherent property of electrons that leads to magnetism is spin, and electronic spins can only point up or down. In most materials, the tricks are randomly mixed, like a deck of cards, but the magnetic materials are different. In the magnets of refrigerators and MRI devices, spins detect their neighbors and collectively organize themselves in one direction. Physicists call this "long-range ferromagnetic order", and another important example of long-range magnetic order is antiferromagnetism, in which spins collectively arrange according to a scheme repetitive, up-down, up-down.

"In a solid with a periodic arrangement of spins, if you know what a spin is here, you can know what a spin is doing a lot, a lot of repetitions because of the long order term, "said the theoretical physicist of Rice – Andriy Nevidomskyy, associate professor of physics and astronomy and member of the RCQM. "In a liquid, on the other hand, there is no order at long range.If you look at two molecules of water a millimeter away, for example, there is no However, because of their hydrogen-hydrogen bonds, they may still have an orderly arrangement at very short distances with nearby molecules, which would be an example of short range order. "

In 1973, the Nobel laureate physicist Philip Anderson proposed the idea of ​​quantum spin liquids, starting from the observation that this geometric arrangement of atoms in certain crystals could prevent the tangled spins from moving collectively in stable arrangements.

As noted by science writer Philip Ball, aptly described in 2017, "Imagine an antiferromagnetic – in which adjacent spins prefer to be oriented in opposite directions – on a triangular lattice.Each spin has two closest neighbors in a triangle, but Antiparallel alignment can not be satisfied for all One of the possibilities is that the spin lattice freezes in a messy "vitreous" state, but Anderson has shown that quantum mechanics allows the possibility of fluctuating variations even at absolute zero (temperature) This state is called spin quantum liquid Anderson later suggested that it could be connected to superconductivity at high temperature. "

The possibility that quantum spin liquids can explain high-temperature superconductivity has attracted widespread interest among condensed-matter physicists since the 1980s. Nevidomskyy added that this interest was further increasing when it was suggested that "some Examples of topological quantum spin liquids could be developed "qubits" for quantum computing.

"But I think part of the curiosity about quantum spin liquids is that they have resurfaced in many incarnations and theoretical propositions," he said. "And although we have theoretical models where we know, in fact, that the result will be a spin liquid, the search for a physical material that would respond to these properties has proved very difficult until it reaches the end of its life. Now there is no consensus in the field, so far any material – 2D or 3D – is a quantum spin liquid. "