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

量子スピン液体と四十極秩序状態にあるTb$$_{2+x}$$Ti$$_{2-x}$$O$$_{7+y}$$の連続励起帯と擬ギャップ

門脇 広明*; 脇田 美香*; F${aa}$k, B.*; Ollivier, J.*; 河村 聖子; 中島 健次 ; 高津 浩*; 玉井 元健*

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

フラストレートしたパイロクロア酸化物Tb$$_{2+x}$$Ti$$_{2-x}$$O$$_{7+y}$$についての非弾性中性子散乱実験を行った。相転移を示さず量子スピン液体になる系($$x = -0.007 < x_{c} < sim -0.0025$$)と、二つの四重極秩序を起こす系($$x = 0.000, 0.003$$)の単結晶試料を調べた。量子スピン液体の系は弾性散乱の他に0.1meV程度の連続励起を持ち、$$x$$が増加すると連続励起領域から四重極のスピン波が分かれてくる。これは、粉末試料の結果と同じであり、試料の$$x$$の制御がよくできている証拠である。

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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パーセンタイル:14.47

分野:Physics, Multidisciplinary

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