New evidence for Electron’s dual nature found in a Quantum Spin fluid.
Results from a Princeton-led experiment support a controversial theory that the electron is composed of two particles.
A new discovery led by Princeton University could improve our understanding of how electrons behave in quantum materials under extreme conditions.
The finding provides experimental evidence that this familiar building block of matter behaves as if it were made up of two particles: one that gives the electron its negative charge and another that provides its magnet-like property, known as spin.
“We believe this is the first hard evidence of spin charge separation,” said Nai Phuan Ong, Prince’s Eugene Higgins professor of physics and senior author of the paper published this week in the journal Nature Physics.
The experimental results fulfill a prediction made decades ago to explain one of the most mind-altering states of matter, the quantum spin fluid. In all materials the spin of an electron can point up or down.
In the known magnet, all spins uniformly point in one direction through the sample when the temperature drops below a critical temperature.
However, in liquid spinning materials, the spins are unable to establish a uniform pattern even when cooled very close to absolute zero. Instead, the spins constantly turn into a tightly coordinated, jumbled choreography.
The result is one of the most entangled quantum states ever conceived, a state of great interest to researchers in the growing field of quantum computing.
To describe this behavior mathematically, Nobel laureate Princeton physicist Philip Anderson (1923-2020), who first predicted the existence of spinning liquids in 1973, proposed an explanation:
In the quantum regime, an electron can be thought of as composed of two particles, one with the electron’s negative charge and the other with its spin. Anderson called the spin-containing particle a spinon.
In this new study, the team looked for signs of the spinon in a spinning fluid composed of ruthenium and chlorine atoms. At temperatures a fraction of a Kelvin above absolute zero (or roughly -452 degrees Fahrenheit) and in the presence of a high magnetic field, ruthenium chloride crystals enter the liquid spin state.
Graduate student Peter Czajka and Tong Gao, Ph.D. 2020, three highly sensitive thermometers connected to the crystal that was in a bath kept at temperatures near absolute zero degrees Kelvin. They then applied the magnetic field and a small amount of heat to a crystal rim to measure its thermal conductivity, an amount that indicates how well it conducts a heat flow.
If spinons were present, they should appear as an oscillating pattern on a graph of thermal conductivity versus magnetic field.
The oscillating signal they were looking for was small – only a few hundredths of a degree change – so the measurements required extremely precise control of the sample temperature and careful calibrations of the thermometers in the strong magnetic field.
The team used the purest crystals available, grown at the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL) led by David Mandrus, a professor of materials science at the University of Tennessee-Knoxville, and Stephen Nagler, corporate research fellow at ORNL’s Neutron Scattering Division.
The ORNL team has extensively studied the quantum spinning fluid properties of ruthenium chloride.
In a series of experiments conducted over nearly three years, Czajka and Gao found temperature swings consistent with increasingly higher-resolution spinons, providing evidence that the electron is composed of two particles consistent with Anderson’s prediction.
“Humans have been looking for this signature for four decades,” said Ong, “if this finding and the spinon interpretation are validated, it would significantly improve the field of quantum spin fluids.
” Czajka and Gao confirmed the experiments last summer while falling under COVID restrictions, requiring them to wear masks and maintain social distance.
“From the purely experimental side,” said Czajka, “it was exciting to see results that actually break the rules you learn in elementary physics classes.
” Reference: “Thermal conductivity oscillations in the spin-liquid state of α-RuCl3” by Peter Czajka, Tong Gao, Max Hirschberger, Paula Lampen-Kelley, Arnab Banerjee, Jiaqiang Yan, David G. Mandrus, Stephen E. Nagler and NP Ong, May 13, 2021, Nature Physics.