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arXiv · 1809.00311

Spin correlations of quantum-spin-liquid and quadrupole-ordered states of Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$

Hiroaki Kadowaki·Mika Wakita·Björn Fåk·Jacques Ollivier·Seiko Ohira-Kawamura·Kenji Nakajima·Jeffrey W. Lynn
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Abstract

Spin correlations of the frustrated pyrochlore oxide Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$ have been investigated by using inelastic neutron scattering on single crystalline samples ($x=-0.007, 0.000,$ and $0.003$), which have the putative quantum-spin-liquid (QSL) or electric-quadrupolar ground states. Spin correlations, which are notably observed in nominally elastic scattering, show short-ranged correlations around $L$ points [$q = (\tfrac{1}{2},\tfrac{1}{2},\tfrac{1}{2})$], tiny antiferromagnetic Bragg scattering at $L$ and $Γ$ points, and pinch-point type structures around $Γ$ points. The short-ranged spin correlations were analyzed using a random phase approximation (RPA) assuming the paramagnetic state and two-spin interactions among Ising spins. These analyses have shown that the RPA scattering intensity well reproduces the experimental data using temperature and $x$ dependent coupling constants of up to 10-th neighbor site pairs. This suggests that no symmetry breaking occurs in the QSL sample, and that a quantum treatment beyond the semi-classical RPA approach is required. Implications of the experimental data and the RPA analyses are discussed.

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Hiroaki Kadowaki, Mika Wakita, Björn Fåk, Jacques Ollivier, Seiko Ohira-Kawamura, Kenji Nakajima, Jeffrey W. Lynn. 2018-12-21. Spin correlations of quantum-spin-liquid and quadrupole-ordered states of Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$. https://doi.org/10.1103/physrevb.99.014406

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