New study of quantum material proves theoretical predictions

October 8, 2021 – Researchers have discovered a type of spin that is difficult to observe in a quantum mechanical system. In physics, a quantum mechanical system is a set of components that interact at the quantum scale. It is the domain of atoms and subatomic particles such as those defined in the Standard Model of Particle Physics. Spins are magnetic particles in a quantum system. The researchers were able to simulate and measure how spins can exhibit a type of motion known as Kardar-Parisi-Zhang (KPZ) in solid materials at different temperatures. Their results demonstrate that the KPZ motion accurately describes changes over time in spin chains – linear channels of spins that interact with each other – in certain quantum materials.

When quasiparticles come together, they cause a collective twisting motion of spin chains in a quantum system. In this animation, neighboring rotations in red point upward because of this movement, while their counterparts in blue change direction.
Image courtesy of Michelle Lehman, ORNL

This is the first time that scientists have found evidence for KPZ dynamics in quantum materials. Scientists have previously found KPZ dynamics only in soft matter and other classical materials, where conventional forces predominate over quantum mechanics. The new analyzes allowed the team to gain new insight into the properties of fluids and other underlying characteristics of quantum systems. This knowledge could potentially be exploited for real-world applications. For example, it could help improve heat transport capabilities using spinning chains. It could also facilitate future efforts in the field of spintronics, which saves energy and reduces noise that can disrupt quantum processes by manipulating the spin of a material instead of its charge.

Summary

In quantum mechanics, spins proceed from place to place in two ways. In ballistic transport, tendrils travel freely in space. In diffusive transport, the spins bounce off impurities in the magnetic material – or on top of each other – and propagate slowly. But smooth rotations are unpredictable, sometimes displaying unusual movements. An example is KPZ dynamics, an intermediate category between the two standard forms of spin transport. In this case, the quasiparticles move randomly through a material and affect all the other particles they touch. Using resources from the Oak Ridge National Laboratory Computing and data environment for science and Spallation neutron source, the Lawrencium computing cluster at Lawrence Berkeley National Laboratory Computer Research Laboratory center, and the National Center for Scientific Computing for Energy Research, the team first simulated the behavior of KPZ demonstrated by a single spin chain in copper potassium fluoride. Next, they examined a previously unexplored region in a crystal sample of the material to measure the KPZ activity of actual physical spin chains. Both methods revealed evidence for KPZ dynamics at room temperature, a surprising achievement given that quantum systems typically need to be cooled to near absolute zero to display the effects of quantum mechanics.

Funding

This work was funded by the Department of Energy Office of Science. Additional support was provided by the Quantum Science Center, a DOE Office of Science National Quantum Information Science Research Center, and the Simons Foundation’s Investigator program.

Publications

Scheie, A. et al., Detection of Kardar – Parisi – Zhang hydrodynamics in a Heisenberg spin-1/2 quantum chain. Physics of nature 17, 726-730 (2021). [DOI: 10.1038/s41567-021-01191-6]

Related links

ORNL News: Subtle spin behavior of quantum material proves theoretical predictions


Source: Oak Ridge National Laboratory, DOE Science Office

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