Quantum Science

Dual nature of electrons

A new discovery could upend our understanding of how electrons behave under extreme conditions

June 29, 2021
The Scitech

A new discovery led by Princeton University researchers provides experimental evidence that electrons often behave as if they are made of two particles — one particle that gives the electron its negative charge and another that gives it a magnet-like property known as spin. “We think this is the first hard evidence of spin-charge separation,” said Nai Phuan Ong, Eugene Higgins Professor of Physics, the senior author on a study published this week in the journal Nature Physics. The experimental results fulfill a prediction made decades ago to explain one of the most mind-bending states of matter, the quantum spin liquid. In all materials, the spin of an electron can point either up or down. In the familiar magnet, the spins uniformly point in one direction throughout the sample when the temperature drops below a critical temperature. However, in spin liquid materials, the spins are unable to establish a uniform pattern even when cooled very close to absolute zero. The result is one of the most entangled quantum states ever conceived, a state of great interest to researchers in the nascent field of quantum computing.

In this new study, the team searched for signs of the spinon in a spin liquid composed of ruthenium and chlorine atoms. At temperatures a fraction of a Kelvin above absolute zero (or roughly –452 degrees Fahrenheit), ruthenium chloride crystals enter a spin liquid state in the presence of a high magnetic field. Physics graduate student Peter Czajka and Tong Gao, a 2020 Ph.D. graduate, connected three highly sensitive thermometers to the crystal as it sat in a bath maintained at temperatures close to absolute zero Kelvin. They then applied the magnetic field and a small amount of heat to one crystal edge to measure its thermal conductivity, a quantity that expresses how well it conducts a heat current. If spinons were present, they should appear as an oscillating pattern in a graph of the thermal conductivity versus magnetic field. The oscillating signal they were searching for was tiny, so the measurements demanded an extraordinarily precise control of the sample temperature as well as careful calibrations of the thermometers in a strong magnetic field. In a series of experiments extending over nearly three years, Czajka and Gao detected the temperature oscillations consistent with spinons with increasingly higher resolution, providing evidence that the electron is composed of two particles, consistent with Anderson’s prediction.

Source: Princeton University news release