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TT: Fachverband Tiefe Temperaturen

TT 3: Focus Session: Entanglement as a Probe for Correlated Quantum Matter

TT 3.7: Vortrag

Montag, 27. September 2021, 16:00–16:15, H6

Structural and thermodynamic properties of the spin-liquid candidate Na₂BaCo(PO₄)₂ — •Vera P. Bader¹, Alexander A. Tsirlin¹, Ivo Heinmaa², Raivo Stern², Noah Winterhalter-Stocker¹, and Philipp Gegenwart¹ — ¹Center for Electronic Correlations and Magnetism, University of Augsburg — ²National Institute of Chemical Physics and Biophysics, Tallinn

The first report of Na₂BaCo(PO₄)₂ as a spin liquid candidate [1] brought the compound to the fore. One structural prerequisite is fulfilled as the Co²⁺ ions with an effective spin 1/2 form a frustrated triangular lattice. The low temperature properties found in the literature are rather controversial. On the one hand a clear transition is observed in the heat capacity data in zero magnetic field at 140 mK [2]. One the other hand AC magnetic susceptibility data and ZF-µSR measurements indicate a dynamically fluctuating ground state down to 80 mK [3]. The spin-liquid state is highly sensitive to details of the crystal structure and may be suppressed upon structural disorder. Here, we revise both crystal structure and low-T temperature-field phase diagram of Na₂BaCo(PO₄)₂. Using high-resolution synchrotron XRD and NMR, we show symmetry lowering and signatures of structural disorder. Moreover, our milli-K heat capacity, thermal expansion and magnetostriction measurements confirm magnetic order in zero field and reveal field-induced phases expected from a nearest-neighbor triangular antiferromagnet.
[1] Zhong et al., PNAS 116 29 (2019)
[2] Li et al., Nat. Commun 11 4216 (2020)
[3] Lee et al., Phys. Rev B 103 024413 (2021)