Progress In Realizing Quantum Spin Liquids and Quantum Spin Ice

Tb₂Ti₂O₇ has remained an enigma in condensed matter physics, and more specifically in the field of frustrated magnetism, for more than twenty-five years [1]. This material evades long-range order down to temperature as low as 20 mK and its ground state exhibits puzzling diffuse magnetic scattering [2,3]. Its low energy spin dynamics includes, on the one hand, an exciton located at about D = 1.5 meV, which shows a significant dispersion [4]; on the other hand, Tb₂Ti₂O₇ also hosts exotic low energy collective dynamics (≈ 0.3 meV), which is believed to be hybrid dipolar-quadrupolar excitations [5,6].

 

Using polarized inelastic neutron scattering measurements, I will present a review of the characteristics of these low-energy modes, including their dispersion and evolution of spectral weight in the Brillouin zone. I will then describe RPA simulations, based on a Hamiltonian, which includes both dipolar and quadrupolar couplings [7], yielding spin dynamics, which compare quite well with those data. The best set of couplings suggest that Tb₂Ti₂O₇ is one of the very rare examples of quantum spin ice, yet very close to several ordered phases, especially a planar antiferromagnetic dipolar phase and a purely quadrupolar one [8,9].

 

 

[1]  M. J. P. Gingras and P. A. McClarty. Rep. Prog. Phys., 77, 056501 (2014).

[2]  T.Fennell et al. Phys. Rev. Lett., 109(1), 017201 (2012).

[3]  T.Fennell et al. Phys. Rev. Lett., 112(1), 017203 (2014).

[4]  M.Ruminy et al.Phys. Rev. B, 224431 (2019).

[5]  S.Guitteny et al. Phys. Rev. Lett., 111(8), 087201 (2013).

[6]  H.Takatsu et al. Phys. Rev. Lett., 116, 217201 (2016).

[7]  A. M. Hallas et al. arXiv:2009.05036 (2020).

[8] A. Roll et al, PRR 6 043011 (2024)

[9] A Roll et al, in preparation.