Repulsive Tomonaga-Luttinger liquid in the quasi-one-dimensional alternating spin-1/2 antiferromagnet NaVOPO4

S. S. Islam, Prashanta K. Mukharjee, P. K. Biswas, Mark Telling, Y. Skourski, K. M. Ranjith, M. Baenitz, Y. Inagaki, Y. Furukawa, A. A. Tsirlin, and R. Nath

We probe the magnetic field-induced Tomonaga-Luttinger liquid (TLL) state in the bond-alternating spin-
1/2 antiferromagnetic (AFM) chain compound NaVOPO4 using thermodynamic as well as local μSR and 31P
NMR probes down to mK temperatures in magnetic fields up to 14 T. The μSR and NMR relaxation rates
in the gapless TLL regime decay slowly following characteristic power-law behavior, enabling us to directly
determine the interaction parameter K as a function of the magnetic field. These estimates are crosschecked
using magnetization and specific heat data. The field-dependent K lies in the range of 0.4 < K < 1 and indicates
the repulsive nature of interactions between the spinless fermions, in line with the theoretical predictions. This
renders NaVOPO4 the first experimental realization of TLL with repulsive fermionic interactions in hitherto
studied S = 1/2 bond-alternating AFM-AFM chain compounds.

Phys. Rev. B 109, L060406(2024)

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