Penetrating the quantum nature of magnetism

Penetrating the quantum nature of magnetism: he LQM scientists, led by Henrik M. Rønnow, cooled down a copper sulfate crystal close to absolute zero (about 0.01 K) to turn it into a quantum spin liquid and then used inelastic neutron scattering to investigate the motion of electrons' spins. The experiments reveal that the magnetic properties of copper sulfate can no longer be described by the individual behavior of the magnetic moments carried by each individual electron in the sample. Instead, flipping the magnetic moment of one single electron creates two spatially separated quantum objects called spinons.

New physics in iridium compounds

New physics in iridium compounds: The researchers looked at the electronic structure of Sr3CuIrO6, a compound in which the iridium atoms are surrounded by oxygen atoms in a slightly distorted octahedron.

Such a system is typically modeled by assuming that the octahedron is perfectly regular and thus the orbital degree of freedom is being quenched in certain ways. If the shape is not perfect, then the layout of the electron cloud is deformed, but previous research groups have assumed that minor irregularities made little difference and could be ignored. In this case, the structure of Sr3CuIrO6 is close to the ideal.

When the Brookhaven-led group gathered data on the actual structure, however, they found that the irregularity makes a noticeable and important change to the wave function, which thus deforms the orbitals of the active electrons, as shown in the graphic. When the spin couples to the orbitals, the effect cannot be ignored.

Spin liquids: an exotic quantum state of matter | KurzweilAI

Spin liquids: an exotic quantum state of matter | KurzweilAI: The researchers found a “kaleidoscope” of phases that represent the lowest-energy states that are allowed given the magnetic interactions... a change in the strengths of the interactions among the spins (the J1 and J2 parameters) results in different phases. For example, one simple solution is an antiferromagnet, where the spins are anti-aligned.

But one phase turns out to be a true quantum spin liquid having no order at all. When J2 is between about 21% and 36% of the value of J1, frustration coaxes the spins into disorder; the entire sample co-exists in millions of quantum states simultaneously.

Ultrathin copper-oxide layers behave like quantum spin liquid

Ultrathin copper-oxide layers behave like quantum spin liquid: The magnetic measurements revealed that when the slabs contained four or more copper-oxide layers, they showed anti-ferromagnetic ordering - just like thick, bulk crystals of the same materials, and even up to the same temperature. However, thinner slabs that contained just one or two copper-oxide layers showed an unexpected result: "While the magnetic moments, or spins, were still present and had about the same magnitude, there was no long-range static anti-ferromagnetic order, not even on the scale of a few nanometers. Rather, the spins were fluctuating wildly, changing their direction very fast," Bozovic said.
Even more telling, this effect was stronger the lower the temperature of the sample. "That means these fluctuations could not be of thermal origin and must be of quantum origin - quantum objects fluctuate even at zero temperature," Bozovic explained.

Quantum mapmakers complete first voyage through spin liquid

Quantum mapmakers complete first voyage through spin liquid: The scientists mapped quantum spin liquid by implanting muons – sub-atomic particles which come from space but can also be produced in particle accelerators – into the spin liquid in order to measure the microscopic magnetism...

The quantum spin liquid state that has been mapped by the team is found in 70 milligrams of tiny black crystals of the layered organic material κ-(BEDT-TTF)2Cu2(CN)3 cooled to just a couple of hundredths of a degree above absolute zero. Despite it being extremely difficult to make the tiny plate-like crystals, the material is perfect for these experiments since it is on the border between being an insulator and a metal, a key requirement for the existence of the quantum spin liquid state...

Inside the material, magnetic atoms are arranged on triangular grids and behave as ‘quantum spins’. The interactions between these spins make them liquid-like, so they never freeze into one configuration.

A new spin on superconductivity?

A new spin on superconductivity?: The crystal, known as herbertsmithite, is part of a family of crystals called Zn-paratacamites, which were first discovered in 1906. Physicists started paying more attention to quantum spin liquids in 1987, when Nobel laureate Philip W. Anderson theorized that quantum spin liquid theory may relate to the phenomenon of high-temperature superconductivity, which allows materials to conduct electricity with no resistance at temperatures above 20 degrees Kelvin (-253 degrees Celsius).

To test this theory, scientists have been looking for materials that preserve quantum spin (a measure of angular momentum) dynamics down to milli Kelvin temperatures (those below -273 degrees Celsius). Almost all ordinary materials lose their spin dynamics at such low temperatures, just as they lose all of their kinetic energy.

Probing spin liquids with a new pulsed-magnet system

Probing spin liquids with a new pulsed-magnet system: "Entirely new experimental vistas could be opened by a device called a precursor pulsed-magnet system developed by an international team of scientists. This system can generate magnetic fields as high as 30 Tesla for synchrotron x-ray scattering experiments. The researchers recently completed the first practical work using the system at the U.S. Department of Energy’s Advanced Photon Source (APS) at Argonne National Laboratory to study magnetoelastic effects in the rare-earth pyrochlore terbium titanate (Tb2Ti2O7)."