Structural phase transition in the 2D spin dimer compound SrCu 2 ( BO 3 ) 2

Sparta, Karine; Redhammer, Günther J.; Roussel, Pascal; Heger, G.; Roth, Georg; Lemmens, P.; Ionescu, A.; Grove, M.; Güntherodt, G.; Hüning, Felix; Lueken, Heiko; Kageyama, Hiroshi; Onizuka, Kenzo; Ueda, Yutaka

doi:10.1007/s100510170296

Cited by 41 publications

(56 citation statements)

References 19 publications

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“…[18][19][20] The model contains isotropic couplings 4 and both interdimer 9,12 and intradimer Dzyaloshinskii-Moriya interactions. 14 It reads…”

Section: A General Anisotropic Modelmentioning

confidence: 99%

“…17 All these components are indeed allowed by the symmetry of the crystal structure in the lowtemperature phase of SrCu 2 ͑BO 3 ͒ 2 , 18-20 whose copper planes are slightly buckled. Were it not buckled ͑as in the hightemperature phase 19 ͒, these components would have vanished. It was for this reason that they were neglected in the original interpretation of the neutron inelastic scattering.…”

Section: Introductionmentioning

confidence: 99%

“…We shall not consider them here because, on one hand, no distortions of the crystal structure that would allow them have been reported so far, 19,20 and electric-dipole transitions provide a symmetrypreserving alternative to explain forbidden transitions. 9,29 Although it is not clear whether ESR is of magnetic-dipole or electric-dipole nature, it has been shown that the forbidden transitions observed by far-infrared spectroscopy were clearly electric dipole.…”

Section: Introductionmentioning

confidence: 99%

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Magnon dispersion and anisotropies inSrCu2(BO3)2

et al. 2007

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We study the dispersion of the magnons ͑triplet states͒ in SrCu 2 ͑BO 3 ͒ 2 including all symmetry-allowed Dzyaloshinskii-Moriya interactions ͓J. Phys. Chem. Solids 4, 241 ͑1958͒; Phys. Rev. 120, 91 ͑1960͔͒. We can reduce the complexity of the general Hamiltonian to a simpler form by appropriate rotations of the spin operators. The resulting Hamiltonian is studied by both perturbation theory and exact numerical diagonalization on a 32-site cluster. We argue that the dispersion is dominated by Dzyaloshinskii-Moriya interactions. We point out which combinations of these anisotropies affect the dispersion to linear order, and extract their magnitudes.

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“…[18][19][20] The model contains isotropic couplings 4 and both interdimer 9,12 and intradimer Dzyaloshinskii-Moriya interactions. 14 It reads…”

Section: A General Anisotropic Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Magnon dispersion and anisotropies inSrCu2(BO3)2

et al. 2007

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“…1(a) and 1(b)) and the nonmagnetic Sr layers. 3,4 The magnetic layer containing orthogonal arrays of spin-1/2 Cu 2+ dimers is a realization of the 2D Shastry-Sutherland model, S i · S j + J ′ n.n.n.…”

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confidence: 99%

A Novel Ordered Phase in SrCu₂(BO₃)₂ under High Pressure

et al. 2007

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We report results of 11 B NMR and susceptibility measurements on the quasi 2D frustrated dimer spin system SrCu2(BO3)2 under high pressure. At 2.4 GPa and in a magnetic field of 7 T, NMR lines split with decreasing temperature in two steps. A gradual splitting below T =30 K breaking the four-fold symmetry of magnetic response is followed by a further sudden splitting below 3.6 K. The latter indicates a magnetic phase transition, which is also marked by a kink in the susceptibility at 1.44 GPa. From the magnetic hyperfine shift data, we conclude that the low-T phase has a doubled unit cell containing two types of dimers, one in a nearly singlet state and the other with a finite magnetization down to T =0.KEYWORDS: SrCu2(BO3)2, Shastry-Sutherland model, high pressure, NMR, phase transition A variety of exotic phenomena has been discovered in the quasi two dimensional dimer spin system SrCu 2 (BO 3 ) 2 .1, 2 It has an alternating stack of the magnetic CuBO 3 layers (Figs. 1(a) and 1(b)) and the nonmagnetic Sr layers.3, 4 The magnetic layer containing orthogonal arrays of spin-1/2 Cu 2+ dimers is a realization of the 2D Shastry-Sutherland model,where J (J ′ ) is the intradimer (interdimer) Heisenberg exchange interaction. The ground state of this model is obvious in two limiting cases: the dimer singlet phase for J ′ /J << 1 and the Néel ordered phase for J ′ /J >> 1. The dimer singlet phase is known to be stable up to (J ′ /J) c =0.68. [6][7][8] Various experiments have established that SrCu 2 (BO 3 ) 2 has a dimer singlet ground state at ambient pressure and zero magnetic field 1, 9, 10 with the energy gap of 33 K 11-13 and J ′ /J=0.60-0.64. 14, 15Frustration in the Shastry-Sutherland model strongly suppresses the kinetic energy of triplets.6 Indeed SrCu 2 (BO 3 ) 2 has an extremely small width of the triplet dispersion (∼0.2meV 12,13 scattering. It also leads to the magnetization plateaus at 1/8, 1/4, and 1/3 of the saturated magnetization in high magnetic fields, 19 where triplets crystalize in commensurate superlattices due to mutual repulsion. 20-23Since J ′ /J in SrCu 2 (BO 3 ) 2 is close to the critical value, tuning the exchange parameters, e.g. by applying pressure, might enable us to explore the phase diagram of the Shastry-Sutherland model, which is still an open issue. A plaquette singlet phase was proposed to exist between the dimer singlet and the Néel ordered phase.8, 24 Alternatively, instability of two-triplet bound * E-mail address: twac@issp.u-tokyo.ac.jp † Present address: Hitachi Medical Corporation, Kashiwa, Chiba ‡ E-mail address: masashi@issp.u-tokyo.ac.jp states 25 may lead to a spin nematic phase. Further variation may arise from the Dzyaloshinski-Moriya interaction beyond the Shastry-Sutherland model. 26In spite of such interest, only a few experiments under pressure have been reported to date. Magnetic susceptibility data up to P =0.7 GPa indicates reduction of the energy gap extrapolating to zero near P =2.5-3.0 GPa. 27The X-ray study shows a tetragonal to monoclinic structural transit...

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“…So far the study of phononic excitations has been especially focussed in relation to the structural phase transition at T = 395 K [9,10]. The lattice soft mode of the 2 nd order transition from the I4/mcm to the I42m group can be seen in Fig 3. The phonon which condenses belongs to the B 1u representation of the higher symmetry group and, in terms of Cu atoms, it involves mainly an alternate displacement along the c-axis of the nearest neighbor dimers, see Fig 1. A symmetry analysis of the phononic excitations in SrCu 2 (BO 3 ) 2 is done in the following.…”

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confidence: 99%