Field evolution of low-energy excitations in the magnet β − Li2 3

• Published in: Physical review. B 2020-06, Vol.101 (21)
• Main Authors: Majumder, M, Prinz-Zwick, M, Reschke, S, Zubtsovskii, A, Dey, T, Freund, F, Büttgen, N, Jesche, A, Kézsmárki, I, Tsirlin, A Tsirlin, Gegenwart, P
• Format: Article
• Language: English
• Subjects: Electrons; Excitation; Magnetism; Magnons; NMR; Nuclear magnetic resonance; Ruthenium trichloride; Spin-lattice relaxation
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.101.214417

7Li nuclear magnetic resonance and terahertz (THz) spectroscopies are used to probe magnetic excitations and their field dependence in the hyperhoneycomb Kitaev magnet β − Li2 IrO3 . Spin-lattice relaxation rate (1 / T1) measured down to 100 mK indicates the gapless nature of the excitations at low fields (below Hc ≃ 2.8 T), in contrast to the gapped magnon excitations found in the honeycomb Kitaev magnet α − RuCl3 at zero applied magnetic field. At higher temperatures in β − Li2 IrO3 , 1 / T1 passes through a broad maximum without any clear anomaly at the Néel temperature TN ≃ 38 K, suggesting the abundance of low-energy excitations that are indeed observed as two peaks in the THz spectra; botHcorrespond to zone-center magnon excitations. At higher fields (above Hc ), an excitation gap opens, and a redistribution of the THz spectral weight is observed without any indication of an excitation continuum, in contrast to α − RuCl3 where an excitation continuum was reported.