Phase Transitions and Disorder Effects in Pure and Doped Frustrated Quantum Antiferromagnet Cs<sub>2</sub>CuBr<sub>4</sub>

Ono, Toshio; Tanaka, Hidekazu; Nakagomi, T.; Kolomiyets, O.; Mitamura, Hiroyuki; Ishikawa, Fumihiro; Goto, T.; Nakajima, Kenji; Oosawa, Akira; Koike, Yasuhiro; Kakurai, Kazuhisa; Klenke, J.; Smeibidle, P.; Meißner, Michael; Katori, Hiroko Aruga

doi:10.1143/jpsjs.74s.135

Cited by 56 publications

(80 citation statements)

References 24 publications

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“…For even stronger alternation and by introducing frustration due to next-nearest-neighbor interactions, T χ max /T C max further increases slightly to 3.6. On the other hand, for 2D strongly frustrated triangular-lattice spin-1/2 Heisenberg antiferromagnets, such as Cs 2 CuBr 4 with a ratio J /J = 0.74 [18] or the spin-liquid candidate κ-(BEDT-TTF) 2 Cu 2 (CN) 3 with J /J = 0.64-0.74 [19], one obtains a ratio T χ max /T C max close to one [12,20,21].…”

Section: Resultsmentioning

confidence: 99%

Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe3P[Pd(dmit)2]2

et al. 2014

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The organic charge-transfer salt EtMe 3 P[Pd(dmit) 2 ] 2 is a quasi-two-dimensional Mott insulator with localized spins S = 1/2 residing on a distorted triangular lattice. Here we report measurements of the uniaxial thermal expansion coefficients α i along the in-plane i = a and c axis as well as along the out-of-plane b axis for temperatures 1.4 K T 200 K. Particular attention is paid to the lattice effects around the phase transition at T VBS = 25 K into a low-temperature valence-bond-solid phase and the paramagnetic regime above where effects of short-range antiferromagnetic correlations can be expected. The salient results of our study include (i) the observation of strongly anisotropic lattice distortions accompanying the formation of the valence-bond-solid phase, and (ii) a distinct anomaly in the thermal expansion coefficients in the paramagnetic regime around 40 K. Our results demonstrate that upon cooling through T VBS the in-plane c axis, along which the valence bonds form, contracts while the second in-plane a axis elongates by the same relative amount. Surprisingly, the dominant effect is observed for the out-of-plane b axis which shrinks significantly upon cooling through T VBS . The pronounced anomaly in α i around 40 K is attributed to short-range magnetic correlations. It is argued that the position of this maximum, relative to that in the magnetic susceptibility around 70 K, speaks in favor of a more anisotropic triangular-lattice scenario for this compound than previously thought.

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Section: Resultsmentioning

confidence: 99%

Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe3P[Pd(dmit)2]2

et al. 2014

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“…In experiments, the quantum magnetization plateau at 1 3 M s was actually observed in Cs 2 CuBr 4 , [11][12][13][14][15][16] 12,13) Furthermore, precise thermodynamic measurements revealed the cascade of field-induced quantum phase transitions.…”

Section: )mentioning

confidence: 90%

“…In Cs 2 CuBr 4 , an additional quantum plateau was also observed at 2 3 M s . 12,13) Furthermore, precise thermodynamic measurements revealed the cascade of field-induced quantum phase transitions.…”

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confidence: 99%

Quantum Magnetization Plateau in Spin-1 Triangular-Lattice Antiferromagnet Ba₃NiSb₂O₉

et al. 2011

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We report the results of magnetization and specific heat measurements on Ba 3 NiSb 2 O 9 , which is a quasi-twodimensional spin-1 triangular-lattice antiferromagnet. We observed a nonclassical magnetization plateau at one-third of the saturation magnetization that is driven by spin frustration and quantum fluctuation. Exact diagonalization for a 21-site rhombic cluster was performed to analyze the magnetization process. Experimental and calculated results agree well.KEYWORDS: Ba 3 NiSb 2 O 9 , triangular-lattice antiferromagnet, magnetization plateau Triangular-lattice antiferromagnet (TLAF), which is one of the simplest frustrated systems, exhibits a rich variety of physics.1-3) A symbolic quantum effect predicted for smallspin Heisenberg TLAF is that magnetization is quantized at one-third of the saturation magnetization M s in magnetic fields. [4][5][6][7][8] For classical spin, the equilibrium condition in a magnetic field H is given by S 1 þ S 2 þ S 3 ¼ g B H=ð3JÞ with the sublattice spins S i . Because the number of the equations is smaller than the number of parameters to determine the spin configuration, the stable state is not uniquely determined; thus, the ground state is infinitely degenerate. This classical degeneracy can be lifted by the quantum fluctuation that is remarkable for small spin, and a specific spin state is selected as the ground state. Consequently, the up-up-down state is stabilized in a finite field range, which can be observed as a magnetization plateau at 1 3 M s . 9)In experiments, the quantum magnetization plateau at 1 3 M s was actually observed in Cs 2 CuBr 4 , [11][12][13][14][15][16] 12,13) Furthermore, precise thermodynamic measurements revealed the cascade of field-induced quantum phase transitions.17) These unusual observations should be attributed to the spatially anisotropic triangular lattice and the Dzyaloshinsky-Moriya interaction, [18][19][20][21][22] but the overall explanation is still an open question.The motivation of this study comes from a question on whether the ground states for Heisenberg TLAFs with integer and half-integer spins are qualitatively the same. It is known that in the case of kagome-lattice Heisenberg antiferromagnet that is closely related to Heisenberg TLAF, the ground states for spin-1 2 and spin-1 are qualitatively different.23) For spin-1 Heisenberg TLAF, the ground states in zero and finite magnetic fields have not been well understood. NiGa 2 S 4 is known as spin-1 Heisenberg TLAF with incommensurate spin correlation. [24][25][26] In this nickel compound, no clear magnetization plateau has been observed, although the magnetization shows a tiny undulate anomaly at around 1 3 M s .27) To investigate the magnetization process of spin-1 Heisenberg TLAF, we have performed high-field magnetization measurements on Ba 3 NiSb 2 O 9 . As shown below, a nonclassical magnetization plateau was observed at 1 3 M s . Ba 3 NiSb 2 O 9 crystallizes in a high symmetric hexagonal structure, P6 3 =mmc, 28,29) which is the same as the hexagonal BaTiO 3 struct...

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“…Another route to the random-singlet state of S = 1/2 triangular AFs might be an insulating mixed crystal Cs 2 Cu(Br 1−x Cl x ) 4 . Experiments suggest that this compound might exhibit a non-magnetic ground state in the range x > 0.17 80 , at which the system possesses a considerable amount of randomness associated with the random arrangement of Cl − and Br − . Interestingly, in this QSLlike regime, the gapless behavior including the T -linear low-temperature specific heat is observed 81 .…”

Section: Summary and Discussionmentioning

confidence: 99%

Static and dynamical spin correlations of theS=12random-bond antiferromagnetic Heisenberg model on the triangular and kagome lattices

Shimokawa¹,

Watanabe²,

Kawamura³

2015

Phys. Rev. B

105

146

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Inspired by the recent theoretical suggestion that the random-bond S = 1/2 antiferromagnetic Heisenberg model on the triangular and the kagome lattices might exhibit a randomness-induced quantum spin liquid (QSL) behavior when the strength of the randomness exceeds a critical value, and that this "random-singlet state" might be relevant to the QSL behaviors experimentally observed in triangular organic salts κ−(ET)2Cu2(CN)3and EtMe3Sb[Pd(dmit)2]2 and in kagome herbertsmithite ZnCu3(OH)6Cl2, we further investigate the nature of the static and the dynamical spin correlations of these models. We compute the static and the dynamical spin structure factors, S(q) and S(q, ω), by means of an exact diagonalization method. In both triangular and kagome models, the computed S(q, ω) in the random-singlet state depends on the wavevector q only weakly, robustly exhibiting gapless behaviors accompnied by the broad distribution extending to higher energy ω. Especially in the strongly random kagome model, S(q, ω) hardly depends on q, and exhibits an almost flat distribution for a wide range of ω, together with a ω = 0 peak. These features agree semi-quantitatively with the recent neutron-scattering data on a single-crystal herbertsmithite. Furthermore, the computed magnetization curve agrees almost quantitatively with the experimental one recently measured on a single-crystal herbertsmithite. These results suggest that the QSL state observed in herbersmithite might indeed be the randomness-induced QSL state, i.e., the random-singlet state.

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Phase Transitions and Disorder Effects in Pure and Doped Frustrated Quantum Antiferromagnet Cs₂CuBr₄

Cited by 56 publications

References 24 publications

Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe3P[Pd(dmit)2]2

Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe3P[Pd(dmit)2]2

Quantum Magnetization Plateau in Spin-1 Triangular-Lattice Antiferromagnet Ba₃NiSb₂O₉

Static and dynamical spin correlations of theS=12random-bond antiferromagnetic Heisenberg model on the triangular and kagome lattices

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Phase Transitions and Disorder Effects in Pure and Doped Frustrated Quantum Antiferromagnet Cs2CuBr4

Cited by 56 publications

References 24 publications

Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe3P[Pd(dmit)2]2

Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe3P[Pd(dmit)2]2

Quantum Magnetization Plateau in Spin-1 Triangular-Lattice Antiferromagnet Ba3NiSb2O9

Static and dynamical spin correlations of theS=12random-bond antiferromagnetic Heisenberg model on the triangular and kagome lattices

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Phase Transitions and Disorder Effects in Pure and Doped Frustrated Quantum Antiferromagnet Cs₂CuBr₄

Quantum Magnetization Plateau in Spin-1 Triangular-Lattice Antiferromagnet Ba₃NiSb₂O₉