Exploiting the Quantum Entangled State between Muon Spin and ⁵¹V Nuclear Spin (I = 7/2) in A15 Compounds by using Muon Spin Spectroscopy

We study the quantum interaction between the muon spin (S = 1/2) and nuclei with spin I > 1/2 and with electric quadrupole moment Q. It is well known that muon μ can form a quantum entangled state when implanted between two nuclear spins I = 1/2 (Q=0), which give rise to coherent oscillations in the μ spin polarization function measured by muon spectroscopy, e.g. in F-μ-F [1, 2]. We have recently observed coherent oscillations of the μ polarization in the V₃Si system with A15 structure. A correct description for large nuclear spin I = 7/2 of ⁵¹V should include also the quadrupolar interaction. We have developed an open-source program, UNDI [3], to simulate the muon spin polarization function by both exact and approximated estimates in presence of dipolar and quadrupolar interactions. By comparing the experimental and simulated results we provide a detailed description of the quantum V-μ-V interaction. The results suggest that this interaction might be informative about charge and structural related phenomenon occurring in quantum materials by using muon spin spectroscopy.
[1] J. H. Brewer et al., Phys. Rev. B 33, 7381 (1986).
[2] J. M. Wilkinson and S. J. Blundell, Phys. Rev. Lett. 125, 087201 (2020)
[3] P. Bonfà et al., accepted for publication in Comp. Phys. Comm.