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

Bose-Einstein condensation of electron-hole pairs, exciton condensation, has been effortfully investigated since predicted 60 years ago. Irrefutable evidence has still been lacking due to experimental difficulties in verifying the condensation of the charge neutral and non-magnetic spin-singlet excitons. Whilst, condensation of spin-triplet excitons is a promising frontier because spin supercurrent and spin-Seebeck effects will be observable. A canonical cobaltite LaCoO3 under very high magnetic fields is a propitious candidate, yet to be verified. Here, we unveil the exotic phase diagram of LaCoO3 up to 600 T generated using the electromagnetic flux compression method and the state-of-the-art magnetostriction gauge. We found the continuous magnetostriction curves and a bending structure, which suggest the emergence of two distinct spin-triplet exciton condensates. By constructing a phenomenological model, we showed that quantum fluctuations of excitons are crucial for the field-induced successive transitions. The spin-triplet exciton condensation in a cobaltite, which is three-dimensional and thermally equilibrated, opens up a novel venue for spintronics technologies with spin-supercurrent such as a spin Josephson junction. Spin-triplet exciton condensation has been predicted in perovskite cobaltites in high magnetic fields. Here, the authors report the magnetic phase diagram of LaCoO3 from magnetostriction measurements in ultrahigh magnetic fields and reveal new high-field phases with signatures of the exciton condensate.

Automated summary

This study unveils the exotic phase diagram of LaCoO3 under ultrahigh magnetic fields and reveals the emergence of two distinct spin-triplet exciton condensates. The continuous magnetostriction curves and bending structure are found, indicating the field-induced successive transitions. Quantum fluctuations of excitons are shown to be crucial for these transitions. The spin-triplet exciton condensation in a cobaltite provides a novel venue for spintronics technologies.