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Journal Articles

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

Kadowaki, Hiroaki*; Wakita, Mika*; F${aa}$k, B.*; Ollivier, J.*; Kawamura, Seiko; Nakajima, Kenji; Lynn, J. W.*

Physical Review B, 99(1), p.014406_1 - 014406_12, 2019/01

 Times Cited Count:9 Percentile:46.67(Materials Science, Multidisciplinary)

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-range correlations around $$Gamma$$ points, tiny antiferromagnetic Bragg scattering at L and $$Gamma$$ points, and pinch-point-type structures around $$Gamma$$ points. The short-range 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 tenth-neighbor site pairs. This suggests that no symmetry breaking occurs in the QSL sample and that a quantum treatment beyond the semiclassical RPA approach is required. Implications of the experimental data and the RPA analyses are discussed.

Journal Articles

Continuum excitation and pseudospin wave in quantum spin-liquid and quadrupole ordered states of Tb$$_{2+x}$$Ti$$_{2-x}$$O$$_{7+y}$$

Kadowaki, Hiroaki*; Wakita, Mika*; F${aa}$k, B.*; Ollivier, J.*; Kawamura, Seiko; Nakajima, Kenji; Takatsu, Hiroshi*; Tamai, Mototake*

Journal of the Physical Society of Japan, 87(6), p.064704_1 - 064704_6, 2018/06

 Times Cited Count:9 Percentile:57.76(Physics, Multidisciplinary)

The ground states of the frustrated pyrochlore oxide Tb$$_{2+x}$$Ti$$_{2-x}$$O$$_{7+y}$$ have been studied by inelastic neutron scattering experiments. Three single-crystal samples are investigated; one shows no phase transition ($$x = -0.007 < x_{c} < sim -0.0025$$), being a putative quantum spin-liquid (QSL), and the other two ($$x = 0.000, 0.003$$) show electric quadrupole ordering (QO) below $$T_{c} sim 0.5$$ K. The QSL sample shows continuum excitation spectra with an energy scale 0.1 meV as well as energy-resolution-limited (nominally) elastic scattering. As $$x$$ is increased, pseudospin wave of the QO state emerges from this continuum excitation, which agrees with that of powder samples and consequently verifies good $$x$$ control for the present single crystal samples.

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