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

Abstract

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...

EffectiveS=12description of theS=1chain with strong easy-plane anisotropy

“…Moreover, the characteristic double peak of C v as a function of magnetic field presented in Fig. 4 has been found experimentally [22,23]. Note that the S = 1/2 ladder compounds are considered to be good candidates to explore effects that occur in 1D quantum systems, with the interladder coupling being 2 orders of magnitude smaller than the intraladder couplings.…”

Anisotropy of magnetic interactions in the spin-ladder compound(C5H12N)2CuBrČižmár1, Ozerov2, Wosnitza3 et al. 2010Phys. Rev. BSelf Cite355420View full textAdd to dashboardCite

“…The gap closes at B c1 ≈ 6.8 T. At B c2 ≈ 13.8 T, a fully spinpolarized phase is induced. The field-induced transition from the quantum-disordered phase into the LuttingerLiquid (LL) phase 20 has been observed between B c1 and B c2 [8][9][10][11] , for the first time giving the comprehensive insight into the Luttinger-Liquid paradigm in spin ladders. The transition into the field-induced magneticallyordered phase at lower temperatures 8,9 can effectively be described by employing the Bose-Einstein condensation (BEC) formalism 21 .…”

Magnetothermal transport in spin-ladder systems

“…[17] are a consequence of the interplay between different scattering mechanisms which result in the change of the thermal conductivity as a function of magnetic field [κ(B)]. 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.…”