Spin dynamics in the high-field phases of volborthite

• Published in: Physical review. B, Condensed matter and materials physics Vol. 96; no. 18
• Main Authors: Yoshida, M., Nawa, K., Ishikawa, H., Takigawa, M., Jeong, M., Berthier, C., Matsui, K., Goto, T., Kimura, S., Sasaki, T., Yamaura, J., Yoshida, H., Okamoto, Y., Hiroi, Z., Krämer, S., Horvatić, M.
• Format: Journal Article
• Language: English
• Published: American Physical Society 27-11-2017
• Subjects: Condensed Matter; Physics; Strongly Correlated Electrons
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/PhysRevB.96.180413

We report single-crystal 51V NMR studies on volborthite Cu3V2O7(OH)2 2H2O, which is regarded as a quasi-two-dimensional frustrated magnet with competing ferromagnetic and antiferromagnetic interactions. In the 1/3 magnetization plateau above 28 T, the nuclear spin-lattice relaxation rate 1/T1 indicates an excitation gap with a large effective g factor in the range of 4.6-5.9, pointing to magnon bound states. Below 26 T where the gap has closed, the NMR spectra indicate small internal fields with a Gaussian-like distribution, whereas 1/T1 shows a power-law-like temperature dependence in the paramagnetic state, which resembles a slowing down of spin fluctuations associated with magnetic order. We discuss the possibility of an exotic spin state caused by the condensation of magnon bound states below the magnetization plateau.