Unconventional Field-Induced Spin Gap in an $S=1/2$ Chiral Staggered Chain

Unconventional Field-Induced Spin Gap in an $S = 1 / 2$ Chiral Staggered Chain

J. Liu, S. Kittaka, R. D. Johnson, T. Lancaster, J. Singleton, T. Sakakibara, Y. Kohama, J. van Tol, A. Ardavan, B. H. Williams, S. J. Blundell, Z. E. Manson, J. L. Manson, and P. A. Goddard

Phys. Rev. Lett. 122, 057207 – Published 8 February 2019

Abstract

We investigate the low-temperature magnetic properties of the molecule-based chiral spin chain $[Cu (pym) (H_{2} O)_{4}] Si F_{6} \cdot H_{2} O$ ( $pym = pyrimidine$ ). Electron-spin resonance, magnetometry and heat capacity measurements reveal the presence of staggered $g$ tensors, a rich low-temperature excitation spectrum, a staggered susceptibility, and a spin gap that opens on the application of a magnetic field. These phenomena are reminiscent of those previously observed in nonchiral staggered chains, which are explicable within the sine-Gordon quantum-field theory. In the present case, however, although the sine-Gordon model accounts well for the form of the temperature dependence of the heat capacity, the size of the gap and its measured linear field dependence do not fit with the sine-Gordon theory as it stands. We propose that the differences arise due to additional terms in the Hamiltonian resulting from the chiral structure of $[Cu (pym) (H_{2} O)_{4}] Si F_{6} \cdot H_{2} O$ , particularly a uniform Dzyaloshinskii-Moriya coupling and a fourfold periodic staggered field.

Received 30 August 2018

DOI:https://doi.org/10.1103/PhysRevLett.122.057207

Physics Subject Headings (PhySH)

Antiferromagnetism Magnetism

1-dimensional spin chains

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

J. Liu¹, S. Kittaka², R. D. Johnson¹, T. Lancaster³, J. Singleton⁴, T. Sakakibara², Y. Kohama², J. van Tol⁵, A. Ardavan¹, B. H. Williams¹, S. J. Blundell¹, Z. E. Manson⁶, J. L. Manson^6,*, and P. A. Goddard^7,†

¹Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
²Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
³Centre for Materials Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom
⁴National High Magnetic Field Laboratory, Los Alamos National Laboratory, MS-E536, Los Alamos, New Mexico 87545, USA
⁵National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
⁶Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, Washington 99004, USA
⁷Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom