Regensburg 2022 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 28: Correlated Electrons: Theory 1

TT 28.4: Vortrag

Donnerstag, 8. September 2022, 10:15–10:30, H23

Field-tunable Berezinskii-Kosterlitz-Thouless correlations in a quasi-2d spin-1/2 Heisenberg lattice — D. Opherden¹, M.S.J. Tepaske^2,3, F. Bärtl^1,4, M. Weber³, M.M. Turnbull⁵, T. Lancaster⁶, S.J. Blundell⁷, M. Baenitz⁸, J. Wosnitza^1,4, C.P. Landee⁹, R. Moessner³, D.J. Luitz^2,3, and •H. Kühne¹ — ¹Hochfeld-Magnetlabor Dresden, HZDR — ²Physikalisches Institut, Univ. Bonn — ³MPI PKS, Dresden — ⁴IFMP, TU Dresden — ⁵Carlson School of Chemistry, Clark Univ. — ⁶Durham Univ., Centre for Materials Physics — ⁷Clarendon Laboratory, Univ. of Oxford — ⁸MPI CPfS, Dresden — ⁹Department of Physics, Clark Univ.

We discuss the manifestation of field-induced Berezinskii-Kosterlitz-Thouless (BKT) correlations in the weakly-coupled spin-1/2 Heisenberg layers of the material [Cu(pz)₂(2-HOpy)₂](PF₆)₂ (CuPOF). Due to the moderate intralayer exchange coupling of J/k_B = 6.8 K, laboratory magnetic fields induce a substantial XY anisotropy of the spin correlations. This provides a significant BKT regime, as the tiny interlayer exchange J^′/ k_B ≈ 1 mK only induces 3d correlations upon close approach to the BKT transition. We employed NMR and µ⁺SR measurements to probe the spin correlations that determine the critical temperatures of the long-range order and the BKT transition. Further, we performed stochastic series expansion QMC simulations based on the experimentally determined model parameters. Finite-size scaling of the spin stiffness yields an excellent agreement of the critical temperatures between theory and experiment.