Abstract
Quantum spin systems such as magnetic insulators usually show magnetic order, but such classical states can give way to quantum liquids with exotic entanglement through two known mechanisms of frustration: geometric frustration in lattices with triangle motifs, and spin-orbit-coupling frustration in the exactly solvable quantum liquid of Kitaev’s honeycomb lattice. Here we present the experimental observation of a new kind of frustrated quantum liquid arising in an unlikely place: the magnetic insulator Ba4Ir3O10 where Ir3O12 trimers form an unfrustrated square lattice. The crystal structure shows no apparent spin chains. Experimentally we find a quantum liquid state persisting down to 0.2 K that is stabilized by strong antiferromagnetic interaction with Curie–Weiss temperature ranging from −766 to −169 K due to magnetic anisotropy. The anisotropy-averaged frustration parameter is 2000, seldom seen in iridates. Heat capacity and thermal conductivity are both linear at low temperatures, a familiar feature in metals but here in an insulator pointing to an exotic quantum liquid state; a mere 2% Sr substitution for Ba produces long-range order at 130 K and destroys the linear-T features. Although the Ir4+(5d5) ions in Ba4Ir3O10 appear to form Ir3O12 trimers of face-sharing IrO6 octahedra, we propose that intra-trimer exchange is reduced and the lattice recombines into an array of coupled 1D chains with additional spins. An extreme limit of decoupled 1D chains can explain most but not all of the striking experimental observations, indicating that the inter-chain coupling plays an important role in the frustration mechanism leading to this quantum liquid.
| Original language | English |
|---|---|
| Article number | 26 |
| Journal | npj Quantum Materials |
| Volume | 5 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 1 2020 |
Funding
We acknowledge very useful discussions with Drs. Daniel Khomskii, Sergey Streltsove, Igor Mazin, Leon Balents and Bernd Buchner. The experimental work conducted in G. C.’s group was supported by NSF grants DMR-1712101 and 1903888. Thermal conductivity data were obtained in the National High Magnetic Field Laboratory, which is supported by NSF Cooperative Agreements No. DMR-1157490 and the State of Florida. M.H. was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (BES) under Award number DE-SC0014415. I.K. was supported as follows: until 12/10/2018, in part by a Simons Investigator Award to Leo Radzihovsky from the James Simons Foundation, and in part by the Army Research Office under Grant Number W911NF-17-1-0482; after 12/10/2018, by a National Research Council Fellowship through the National Institute of Standards and Technology. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein. The work at ORNL was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. C. A. P was partially supported by Colorado Energy Research Collaboratory.