A new discovery that provides evidence that an electron is composed of two particles

Credits: Catherine Zandonella, Princeton University

A new discovery made by Princeton University can change our entire understanding of how electrons behave as if they are made of two particles, one is a particle that gives a negative charge to the electron and the other provides a magnet-like property called spin. 

Eugene Higgins, a professor of physics at Princeton University and the lead author of a paper published in the journal, nature physics.

The experimental results satisfy the predictions made decades ago to explain quantum spin liquid, which is a phase of matter which is formed during the interaction of quantum spins in certain magnetic materials. For all materials, the electron spin is upward or downward, and under a certain temperature, all the spins are uniform in one direction, but in spin liquid materials, spin cannot establish a uniform pattern, even when cooled very close to absolute temperature, instead the spin is tightly tuned and constantly changing with coordinated and entangled choreography.

To mathematically explain this behaviour, Philip Anderson, who predicted the existence of spin liquid in 1973, proposed as an explanation, of particles which he called spinons, one is negatively charged with an electron and the other contains its spin. In this new study, the team looked for a sign of spinons in spin liquids composed of ruthenium and chlorine atoms. At near absolute zero Kelvin and in presence of a high magnetic field, the ruthenium chloride crystals enter the spin liquid state. 

Graduate students Peter Czajka and Tong Gao, PhD. In 2020, connected three high sensitivity thermometers to a crystal in a bath maintained at a temperature close to absolute zero and then applied the magnetic field and a small amount of heat to one crystal to measure thermal conductivity. If spinons were present, they would appear as an oscillating pattern in a graph of thermal conductivity versus magnetic field. The signals they were searching for were very tiny, a few hundredths of a degree change, so the measurements demanded a precise control of the sample temperature, as well as careful calibrations of the temperatures in a strong magnetic field. 

Thermal conductivity (vertical axis) changes as a function of magnetic field B (horizontal axis) and temperature T (axis to page). Vibration provides evidence of spinon. Credits: Peter Czajka, Princeton University

The team used the purest crystals available, and over three years of experiments, Czajka and Gao detected the temperature oscillations consistent with spinons with increasingly high resolution, providing evidence that electron is composed of two particles, as predicted by Anderson. 

“People have been searching for this signature for four decades,” Ong said. “If this finding and the spinon interpretation are validated, it would significantly advance the field of quantum spin liquids.”

“From the purely experimental side,” Czajka said, “it was exciting to see results that in effect break the rules that you learn in elementary physics classes.”

Reference: DOI: 10.1038 / s41567-021-01243-x

Source: Princeton University