Unconventional magnetic excitations and spin dynamics of exotic quantum spin systems BaCo2V2O8 and Ba3CuSb2O9

• Published in: Applied magnetic resonance Vol. 52; no. 4; pp. 349 - 362
• Main Authors: Han, Yibo, Kimura, Shojiro, Okunishi, Kouichi, Hagiwara, Masayuki
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.04.2021; Springer Nature B.V
• Subjects: Antiferromagnetism; Atoms and Molecules in Strong Fields; Critical point; Distortion; Electron paramagnetic resonance; Electron spin; Electrons; Excitation; Ising model; Jahn-Teller effect; Laser Matter Interaction; Magnetic fields; Neutrons; Organic Chemistry; Phase transitions; Physical Chemistry; Physics; Physics and Astronomy; Quantum tunnelling; Review; Single crystals; Solid State Physics; Spectroscopy/Spectrometry; Spectrum analysis; Spin dynamics; Spin liquid; Spin resonance; Symmetry; Temperature; Terahertz Spectroscopy
• ISSN: 0937-9347; 1613-7507
• DOI: 10.1007/s00723-020-01296-w

We review terahertz (THz) electron spin resonance studies of two types of exotic quantum spin systems, namely, the spin( S )-1/2 one-dimensional (1D) Ising-like antiferromagnet BaCo 2 V 2 O 8 and the S =1/2 two-dimensional (2D) honeycomb-like antiferromagnet Ba 3 CuSb 2 O 9 in magnetic fields of up to 50 T. For the former subject, unconventional magnetic excitations were identified below a critical magnetic field H c ( ∼ 4 T), where the exotic field-induced order-to-disorder transition occurs, and magnetic excitations in a Tomonaga-Luttinger liquid state were observed above H c . The novel magnetic excitations were analyzed with an S =1/2 1D XXZ model by considering the peculiar structure of this compound. For the latter subject, the orbital quantum dynamics of the spin liquid candidate Ba 3 CuSb 2 O 9 was revealed using multifrequency electron spin resonance ranging from 9.3 GHz to 0.73 THz. The g -factor of the hexagonal Ba 3 CuSb 2 O 9 single crystal possesses a weak six-fold symmetry at low frequencies, while two-fold symmetry is manifested at high frequencies. From the critical point between the two frequency regions, the frequency of the dynamic Jahn-Teller distortion is determined to be approximately 10 GHz. This dynamic distortion, accompanied by orbital quantum tunneling, proves the spin-orbital liquid state in Ba 3 CuSb 2 O 9 .