交替键自旋链系统Pb2V3O9中三重子玻色-爱因斯坦凝聚态的热导率
Thermal Conductivity in the Bose-Einstein Condensed State of Triplons in the Bond-Alternating Spin-Chain System Pb2V3O9
摘要：
为了阐明场致三重子玻色-爱因斯坦凝聚态（BEC）热导率增强的原因，我们测量了S=1/2交替键自旋链系统Pb_2 V_3 O_9在磁场下沿[101]方向平行于自旋链$kappa_{\|[101]}$和垂直于自旋链$kappa_{\perp[101]}$的热导率.随着磁场的增加，在3 K，已经发现，$kappa_{\|[101]}$和$kappa_{\perp[101]}$都被抑制在带隙的正常状态在低场。另一方面，在高场的场致三重子的BEC态中，$kappa_{\|[101]}$随着场的增加而增强，而$kappa_{\perp[101]}$被抑制。也就是说，沿着磁相互作用强的方向的热导率在BEC状态下显著增强。因此，我们的研究结果表明，在BEC状态下的$kappa_{\|[101]}$的增强是由于在双流体模型的基础上，在液体4 He的超流态的情况下，由于三重子的热导率的增强引起的。
英文摘要：
In order to clarify the origin of the enhancement of the thermal conductivity in the Bose-Einstein Condensed (BEC) state of field-induced triplons, we have measured the thermal conductivity along the [101] direction parallel to spin-chains, $kappa_{\|[101]}$, and perpendicular to spin-chains, $kappa_{\perp[101]}$, of the S=1/2 bond-alternating spin-chain system Pb2V3O9 in magnetic fields up to 14 T. With increasing field at 3 K, it has been found that both $kappa_{\|[101]}$ and $kappa_{\perp[101]}$ are suppressed in the gapped normal state in low fields. In the BEC state of field-induced triplons in high fields, on the other hand, $kappa_{\|[101]}$ is enhanced with increasing field, while $kappa_{\perp[101]}$ is suppressed. That is, the thermal conductivity along the direction, where the magnetic interaction is strong, is markedly enhanced in the BEC state. Accordingly, our results suggest that the enhancement of $kappa_{\|[101]}$ in the BEC state is caused by the enhancement of the thermal conductivity due to triplons on the basis of the two-fluid model, as in the case of the superfluid state of liquid 4He.
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