Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na<sub>2</sub>BaCo(PO<sub>4</sub>)<sub>2</sub>.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 32839456.
- Also identified by DOI 10.1038/s41467-020-18041-3 and PMC identifier 7445251.
- Licence recorded as CC BY.
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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<sub>0</sub>/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<sub>2</sub>BaCo(PO<sub>4</sub>)<sub>2</sub>, which has an antiferromagnetic order at very low temperature (T<sub>N</sub> ~ 148 mK), and observed a finite κ<sub>0</sub>/T extrapolated from the data above T<sub>N</sub>. 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<sub>2</sub>BaCo(PO<sub>4</sub>)<sub>2</sub> possibly behaves as a gapless QSL with itinerant spin excitations above T<sub>N</sub> and its strong quantum spin fluctuations persist below T<sub>N</sub>.