Field-induced bound-state condensation and spin-nematic phase in SrCu<sub>2</sub>(BO<sub>3</sub>)<sub>2</sub> revealed by neutron scattering up to 25.9 T.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38200029.
- Also identified by DOI 10.1038/s41467-023-44115-z and PMC identifier 10781965.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
In quantum magnetic materials, ordered phases induced by an applied magnetic field can be described as the Bose-Einstein condensation (BEC) of magnon excitations. In the strongly frustrated system SrCu<sub>2</sub>(BO<sub>3</sub>)<sub>2</sub>, no clear magnon BEC could be observed, pointing to an alternative mechanism, but the high fields required to probe this physics have remained a barrier to detailed investigation. Here we exploit the first purpose-built high-field neutron scattering facility to measure the spin excitations of SrCu<sub>2</sub>(BO<sub>3</sub>)<sub>2</sub> up to 25.9 T and use cylinder matrix-product-states (MPS) calculations to reproduce the experimental spectra with high accuracy. Multiple unconventional features point to a condensation of S = 2 bound states into a spin-nematic phase, including the gradients of the one-magnon branches and the persistence of a one-magnon spin gap. This gap reflects a direct analogy with superconductivity, suggesting that the spin-nematic phase in SrCu<sub>2</sub>(BO<sub>3</sub>)<sub>2</sub> is best understood as a condensate of bosonic Cooper pairs.