Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na$_2$BaCo(PO$_4$)$_2$

N. Li; Q. Huang; X. Y. Yue; W. J. Chu; Q. Chen; E. S. Choi; X. Zhao; H. D. Zhou; X. F. Sun

doi:10.1038/s41467-020-18041-3

paper

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na $_{2}$ BaCo(PO $_{4}$ ) $_{2}$

arXiv:1911.11107 · doi:10.1038/s41467-020-18041-3

Abstract

The most fascinating feature of certain two-dimensional (2D) gapless quantum spin liquid (QSL) is that their spinon excitations behave like the fermionic carriers of a paramagnetic metal. The spinon Fermi surface is then expected to produce a linear increase of the thermal conductivity with temperature that should manifest via a residual value ( $κ_{0} / T$ ) in the zero-temperature limit. However, this linear in T behavior has been reported for very few QSL candidates. Here, we studied the ultralow-temperature thermal conductivity of an effective spin-1/2 triangular QSL candidate Na $_{2}$ BaCo(PO $_{4}$ ) $_{2}$ , which has an antiferromagnetic order at very low temperature ( $T_{N} \sim$ 148 mK), and observed a finite $κ_{0} / T$ extrapolated from the data above $T_{N}$ . Moreover, while approaching zero temperature, it exhibits series of quantum spin state transitions with applied field along the $c$ axis. These observations indicate that Na $_{2}$ BaCo(PO $_{4}$ ) $_{2}$ possibly behaves as a gapless QSL with itinerant spin excitations above $T_{N}$ and its strong quantum spin fluctuations persist below $T_{N}$ .

24 pages, 5 figures, with Supplementary Information

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na2​BaCo(PO4​)2​

Abstract

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na $_{2}$ BaCo(PO $_{4}$ ) $_{2}$