Signature of spin-triplet exciton condensations in LaCoO3 at ultrahigh magnetic fields up to 600 T

A research group at the University of Electro-Communications has successfully measured the "stretch and shrinkage" of crystals under an ultra-high magnetic field of 600 Tesla (Figure 1) utilizing an original high-speed strain gauge (Figure 2) and found signs of a new magnetic (spin) superfluid state (Figure 3) in a transition metal oxide, cobalt oxide (LaCoO₃). This achievement is expected to lead to novel devices based on spin superfluidity and applications in spintronics technology and quantum computers.

These results were published in Nature Communications, an open-access international journal, on April 4.

Figures captions

Figure 1

Conceptual diagram of the new electromagnetic compression system used for 1000 Tesla generation. First, electrical energy is stored in a 5-megajoule capacitor power supply. Next, it is discharged into the electromagnetic flux compression coil. The electromagnetic compression coil uses the received energy to compress the metallic liner (cylinder) at high speed. The initial magnetic flux in the metal liner (about 3 Tesla) rapidly densifies to generate a 1000 Tesla class ultra-high magnetic field. Immediately after the super-strong magnetic field is generated, the coil explodes. This explosion is caused by the reaction force when the metal liner is contracted and the repulsive force of the generated super-strong magnetic field itself.

Figure 2

Schematic diagram of the ultrafast strain measurement system utilized to measure the "stretch and shrinkage" in a single instant during the generation of an ultrahigh magnetic field accompanied by an explosion. An optical fiber is bonded to the side of the crystal to be measured. The optical fiber is a fiber Bragg grating, which functions as a strain gauge. The "shrinkage" is detected at a distance through the fiber. Using a specially developed 100 megahertz ultra-high-speed measurement method, the strain is measured in a single shot in an instant.

Figure 3

Schematic of how applying an ultra-high magnetic field to a cobalt oxide induces the magnetic "super" states. LaCoO₃ has a "vacuum" (low-spin) and a "magnetic exciton" (high-spin) state. Before applying a magnetic field, all cobalt ions are in the vacuum state; when a magnetic field of up to 600 Tesla is applied, a change occurs and a magnetic superfluid or magnetic supersolid state develops. Since magnetic excitons have the property of pushing the crystal lattice apart, we observed signs of these changes with this "shrinkage" measurement. Eventually, all cobalt oxides are expected to reach a fully magnetized state, but this has not been observed in this study.