Large thermomagnetic effects in weakly disordered Heisenberg chains

Shimshoni, Efrat; Rasch, David; Jung, P.; Sologubenko, A. V.; Rosch, Achim

doi:10.1103/physrevb.79.064406

Cited by 8 publications

(12 citation statements)

References 26 publications

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“…As discussed in Ref. 28, spinon umklapp scattering in the presence of weak disorder can lead to minima in the field dependence of the spin thermal conductivity s ͑B͒. However, the minima discussed in the present paper are observed in the phonon part of the heat conductivity ph .…”

contrasting

confidence: 52%

Evidence for spinon localization in the heat transport of the spin-12ladder compound(C5<

et al. 2009

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We present experiments on the magnetic-field-dependent thermal transport in the spin-1 2 ladder system ͑C 5 H 12 N͒ 2 CuBr 4 . The thermal conductivity ͑B͒ is only weakly affected by the field-induced transitions between the gapless Luttinger-liquid state realized for B c1 Ͻ B Ͻ B c2 and the gapped states, suggesting the absence of a direct contribution of the spin excitations to the heat transport. We observe, however, that the thermal conductivity is strongly suppressed by the magnetic field deeply within the Luttinger-liquid state. These surprising observations are discussed in terms of localization of spinons within finite ladder segments and spinon-phonon umklapp scattering of the predominantly phononic heat transport. DOI: 10.1103/PhysRevB.80.220411 PACS number͑s͒: 75.40.Gb, 05.60.Gg, 75.47.Ϫm Studies of the heat transport in one-dimensional ͑1D͒ spin systems are of strong current interest. 1-3 From the theoretical side, there is consensus that the intrinsic spin-mediated heat transport of integrable spin models is ballistic, while the situation in nonintegrable spin models is less clear. Experimentally, such studies were stimulated by the observation of a strong anisotropy of the thermal conductivity ͑T͒ in the spin-1 2 ladder compound ͑Sr, Ca, La͒ 14 Cu 24 O 41 , which has been explained by a large spin contribution s along the ladder direction. [4][5][6] In order to relate model calculations to experimental data, theory has to incorporate the coupling between spin excitations and the underlying lattice, while experimentally it is necessary to separate s from the measured total . Here, studies of the magnetic-field dependent ͑B , T͒ can provide much more information than just the zero field ͑T͒ since strong enough magnetic fields change the spin excitation spectra and cause transitions between different quantum phases. Yet, the above-mentioned ͑Sr, Ca, La͒ 14 Cu 24 O 41 is unsuitable for such studies due to the strong exchange interaction ͑ϳ2000 K͒ in the ladders that require magnetic fields far above typical laboratory magnets. Piperidinium copper bromide ͑C 5 H 12 N͒ 2 CuBr 4 ͑Ref. 7͒ is one of the best spin-1 2 ladder compounds with weak intraladder exchange. It has a monoclinic structure ͑space group P2 1 / c͒ with the ladders running along the a axis. The rung exchange J Ќ Ӎ 13 K is about four times larger than the leg exchange J ʈ Ӎ 3.6 K. [8][9][10][11][12][13][14] The zero-field spin excitation gap ⌬ Ӎ 9.5 K decreases in an external magnetic field, so that between B c1 Ӎ 7.1 T and the full saturation field B c2 Ӎ 14.5 T ͓for B ʈ a, where g = 2.06 ͑Ref. 7͔͒ the spin excitations are gapless and the system is in the Luttinger-liquid ͑LL͒ state. The LL state extends down to the temperature of a 3D magnetic ordering transition at T N Յ 110 mK, suggesting an interladder coupling JЈ ϳ 27 mKӶ J Ќ , J ʈ . 10,12,13 In this Rapid Communication, we present measurements of the thermal conductivity of ͑C 5 H 12 N͒ 2 CuBr 4 between 0.3 and 10 K in magnetic fields up to 17 T. Surprisingly, no sign of spin-me...

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Evidence for spinon localization in the heat transport of the spin-12ladder compound(C5<

et al. 2009

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“…Second, around half-filling (B = B0) there is a positive spinonic contribution to transport observed as a maximum at B = B0 . The double dip feature resembles results obtained for spin-chains 15,16 where the minimum in the magnetothermal conductivity corresponds to moving the chemical potential away from half filling, to a scale of order T .…”

Section: Introduction and Principal Resultssupporting

confidence: 77%

“…These features can be compared with the effects seen in chains 16 (by interchanging B ef f and B) where the single minimum is at a field B ∼ T and the maximum at B = 0. Our results for the thermal conductivity isotherms (Fig.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Two primary effects are expected to dominate the B-dependance in the coupled phonon-spinon system: one arises from the positive contribution of spinons as heat carriers, and the other from the negative contribution of spinons acting as scatterers of the phonons. The former contribution is governed by the interplay of two scattering mechanisms, umklapp and disorder, and consequently depends on the deviation of the spinon chemical potential from a commensurate value 16 . At the same time, the scattering due to phonon-spinon interaction is also dependant on the filling of the spinon band, which dictates the available phase-space for scattering.…”

Section: Thermal Transport Of the Spin-ladder Systemmentioning

confidence: 99%

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Magnetothermal transport in spin-ladder systems

Shlagman

Shimshoni

2012

Phys. Rev. B

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We study a theoretical model for the magnetothermal conductivity of a spin-1 2 ladder with low exchange coupling (J ΘD) subject to a strong magnetic field B. Our theory for the thermal transport accounts for the contribution of spinons coupled to lattice phonon modes in the onedimensional lattice. We employ a mapping of the ladder Hamiltonian onto an XXZ spin-chain in a weaker effective field B ef f = B − B0, where B0 = B c1 +B c2 2 corresponds to half-filling of the spinon band. This provides a low-energy theory for the spinon excitations and their coupling to the phonons. The coupling of acoustic longitudinal phonons to spinons gives rise to hybridization of spinons and phonons, and provides an enhanced B-dependant scattering of phonons on spinons. Using a memory matrix approach, we show that the interplay between several scattering mechanisms, namely: umklapp, disorder and phonon-spinon collisions, dominates the relaxation of heat current. This yields magnetothermal effects that are qualitatively consistent with the thermal conductivity measurements in the spin-1 2 ladder compound Br4(C5H12N)2 (BPCB).

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“…Cu(pyz)(NO 3 ) 2 has been chosen because it provides a good experimental realisation of the S = 1/2 1D antiferromagnetic Heisenberg model [14,15]. As a result, its magnetic [11,[14][15][16][17][18], spin-dynamic [19][20][21][22][23][24], thermal [25,26], and vibrational [27,28] properties have been the subject of experimental and theoretical investigation. Cu(pyz)(NO 3 ) 2 in a coordination polymer consisting of a crystalline arrangement of chains of Cu 2+ ions linked by pyrazine (pyz) ligands parallel to the a axis of its unit cell, where each Cu 2+ ion is also bonded to a pair of nitrate ions, illustrated in Fig.…”

Section: Introductionmentioning

confidence: 99%

Exchange constants in molecule-based magnets derived from density functional methods

2017

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Cu(pyz)(NO3)2 is a quasi one-dimensional molecular antiferromagnet that exhibits three dimensional long-range magnetic order below TN = 110 mK due to the presence of weak inter-chain exchange couplings. Here we compare calculations of the three largest exchange coupling constants in this system using two techniques based on plane-wave basis-set density functional theory: (i) a dimer fragment approach and (ii) an approach using periodic boundary conditions. The calculated values of the large intrachain coupling constant are found to be consistent with experiment, showing the expected level of variation between different techniques and implementations. However, the interchain coupling constants are found to be smaller than the current limits on the resolution of the calculations. This is due to the computational limitations on convergence of absolute energy differences with respect to basis set, which are larger than the inter-chain couplings themselves. Our results imply that errors resulting from such limitations are inherent in the evaluation of small exchange constants in systems of this sort, and that many previously reported results should therefore be treated with caution.

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Large thermomagnetic effects in weakly disordered Heisenberg chains

Cited by 8 publications

References 26 publications

Evidence for spinon localization in the heat transport of the spin-12ladder compound(C5<

Evidence for spinon localization in the heat transport of the spin-12ladder compound(C5<

Magnetothermal transport in spin-ladder systems

Exchange constants in molecule-based magnets derived from density functional methods

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