An international research team composed of scientists from the United States, Germany and Canada wrote in the latest issue of Physical Review X that they have observed the "ground state of quantum spin liquid" for the first time on the magnetic material ce2zr2o7. The latest research is expected to open up a new direction for quantum computer design.
Spin is the internal property of electrons related to rotation. It is spin that makes the materials in the magnet magnetic. In some materials, spin can lead to structural disorder, similar to molecules in liquid, so there is the term "spin liquid". The main feature of spin liquids is that they remain disordered even when cooled to absolute zero degrees (minus 273 degrees Celsius), because the spin direction fluctuates continuously as the material cools, rather than stabilizing in the solid state like traditional magnets (in which all spins are aligned).
Think of an electron as a small compass pointing up or down, the researchers explained. In traditional magnets, the electron spins point in the same direction, up or down, forming the so-called "ferromagnetic phase". However, in quantum spin liquid, electrons are placed in a triangular lattice to form triangles, which is characterized by strong turbulence interfering with their order. The result is an entangled wave function without magnetic order.
Andrea Bianchi, a professor of physics at the University of Montreal and the head of the latest research, explained: "when a third electron is added, the electron spins cannot be aligned because the spins of two adjacent electrons are opposite, which produces what we call magnetoresistance frustration. This ground state will generate excitation, which can maintain the disorder of spins even at very low temperatures, thus maintaining the liquid state."
Bianchi said that ce2zr2o7 is a magnetic cerium based material. Previously, scientists have made this compound. The new research is to make it in a unique and pure form. They use samples melted in an optical furnace to create a nearly perfect triangular atomic arrangement, and then check the quantum state. The results show that it is this almost perfect triangle that makes them produce magnetoresistive frustration in ce2zr2o7.
"Our measurements show that the particle functions overlap, so there is no obvious sign of classical magnetic order. In addition, we also observed the distribution of fluctuating spin direction, which is the characteristic of spin liquid and magnetoresistance frustration, indicating that the materials we created behave like real spin liquid at low temperature," Bianchi said
After confirming these observations through computer simulation, the research team concluded that they did observe an unprecedented quantum state - the ground state of quantum spin liquid.