Field-tunable BKT and quantum phase transitions in spin-$\frac{1}{2}$ triangular lattice antiferromagnet

Zhang, Dechen [Univ. of Michigan, Ann Arbor, MI (United States)]; Zhu, Yuan [Univ. of Michigan, Ann Arbor, MI (United States)]; Zheng, Guoxin [Univ. of Michigan, Ann Arbor, MI (United States)]; Chen, Kuan-Wen [Univ. of Michigan, Ann Arbor, MI (United States)]; Huang, Qing [Univ. of Tennessee, Knoxville, TN (United States)]; Zhou, Lingxiao [Univ. of Michigan, Ann Arbor, MI (United States)]; Liu, Yujie [Univ. of Michigan, Ann Arbor, MI (United States)]; Jenkins, Kaila [Univ. of Michigan, Ann Arbor, MI (United States)]; Chan, Aaron [Univ. of Michigan, Ann Arbor, MI (United States)]; Zhou, Haidong [Univ. of Tennessee, Knoxville, TN (United States)]; Li, Lu [Univ. of Michigan, Ann Arbor, MI (United States); Univ. of Tennessee, Knoxville, TN (United States)] (ORCID:0000000280547406)

doi:10.1016/j.newton.2025.100256

DOE OSTI · 2957479

Field-tunable BKT and quantum phase transitions in spin-$\frac{1}{2}$ triangular lattice antiferromagnet

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Abstract

Quantum magnetism is one of the most active fields for exploring exotic phases and phase transitions. The recently synthesized Na 2 BaCo(PO 4 ) 2 (NBCP) is an ideal material incarnation of the spin-$\frac{1}{2}$ easy-axis triangular lattice antiferromagnet (TLAF). Experimental evidence shows that NBCP hosts the spin supersolid state with a giant magnetocaloric effect. Theory further predicts that magnetic fields can drive NBCP through Berezinskii-Kosterlitz-Thouless (BKT) and other richer quantum phase transitions. However, detecting these transitions is challenging, as they onset at ultralow temperatures near 60 mK and require high magnetization sensitivity. Using a newly developed gradient force magnetometer in a dilution refrigerator, we mapped the magnetic susceptibility phase diagram down to 30 mK. Our results provide a more comprehensive and accurate understanding of BKT melting of spin supersolidity and several field-tunable quantum phase transitions, which establish NBCP as a model platform for frustrated magnetism and highlight potential applications of its giant magnetocaloric effects.

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BKT transition magnetization plateau magnetocaloric effect magnetometry quantum phase transition spin supersolid symmetry breaking triangular lattice antiferromagnet

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Zhang, Dechen [Univ. of Michigan, Ann Arbor, MI (United States)], Zhu, Yuan [Univ. of Michigan, Ann Arbor, MI (United States)], Zheng, Guoxin [Univ. of Michigan, Ann Arbor, MI (United States)], Chen, Kuan-Wen [Univ. of Michigan, Ann Arbor, MI (United States)], Huang, Qing [Univ. of Tennessee, Knoxville, TN (United States)], Zhou, Lingxiao [Univ. of Michigan, Ann Arbor, MI (United States)], Liu, Yujie [Univ. of Michigan, Ann Arbor, MI (United States)], Jenkins, Kaila [Univ. of Michigan, Ann Arbor, MI (United States)], Chan, Aaron [Univ. of Michigan, Ann Arbor, MI (United States)], Zhou, Haidong [Univ. of Tennessee, Knoxville, TN (United States)], Li, Lu [Univ. of Michigan, Ann Arbor, MI (United States); Univ. of Tennessee, Knoxville, TN (United States)] (ORCID:0000000280547406). 2025-10-10. Field-tunable BKT and quantum phase transitions in spin-$\frac{1}{2}$ triangular lattice antiferromagnet. https://doi.org/10.1016/j.newton.2025.100256

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