Scientists at Princeton University have studied a controversial theory about the structure of the electron. During experiments, they obtained evidence that this familiar building block of matter behaves as if it consists of two particles. One particle gives the electron its negative charge and the other gives it a magnet-like property known as spin.
“We think we have obtained the first hard evidence of spin charge separation,” says Nai Fuang Ong, the Eugene Higgins Professor of Physics at Princeton.
The scientists’ results confirm a prediction made decades ago to explain one of the most complex states of matter, the quantum spin liquid. In all materials, the spin of the electron can be upward or downward. But in the case of quantum spin liquid, spins cannot form a homogeneous pattern even when cooling is very close to absolute zero.
To mathematically describe the amazing behavior of the electron, Nobel Prize-winning physicist Philip Anderson, who first predicted the existence of spin liquids in 1973, proposed his explanation: in quantum mode the electron can be seen as consisting of two particles, one carrying the negative charge of the electron, and the other – its spin. Anderson called the second particle a spinon.
New research – new facts
Scientists at Princeton University looked for signs of a spinon in a spin liquid composed of ruthenium and chlorine atoms. At temperatures a fraction above absolute zero Kelvin (or about -452 degrees Fahrenheit) and in the presence of a strong magnetic field, ruthenium chloride crystals go into spin liquid state.
The experiment was conducted as follows: the experts placed the crystal in a bath with a temperature of 0 degrees Kelvin and connected to it three highly sensitive thermometers. Then they applied a magnetic field and a small amount of heat to one edge of the crystal to measure its thermal conductivity. If spinons were present, they should have appeared as an oscillating pattern on a graph of thermal conductivity versus magnetic field.
The signal they were looking for was incredibly difficult to detect – the readings could vary by only a few hundredths of a degree, so the measurements required extremely precise control of the sample temperature, as well as careful calibration of the thermometers in a strong magnetic field.
Not just one experiment was conducted, but an entire series over nearly three years. As a result, scientists were able to detect temperature fluctuations corresponding to spinons. This indicates that the electron consists of two particles, and confirms Anderson’s controversial theory. According to the researchers, people have been searching for this signature for four decades. The scientists’ observations will be tested more than once. If all goes well, the field of quantum spin liquids will advance considerably.