Study of giant thermal conductivity due to magnons in low-dimensional quantum spin system copper oxides

我们研究了几种被认为是低维量子自旋系统的铜氧化物的热导率和其他物理性质，以阐明磁子引起的巨大热导率的机制，并阐明热导率测量是否对相变的检测具有强大的作用。我们发现在四臂自旋梯形系统La_2Cu2O_5和二维自旋系统Cu3B_2O_6中，由于磁子的存在而产生了较大的热导率。在一维自旋系统Sr2CuO3和SrCuO2中，通过对杂质效应的研究，证明了磁子的导热系数很大，理论上认为磁子的导热是弹道的。从这些结果可以看出，自旋之间的大反铁磁相互作用和磁子的大弥散都导致了磁子的大的导热系数。此外，在随后的相变中观察到了热导率的显著变化；Ca2Y2Cu5O&lt；10&gt；和Cu3B2O6的反铁磁有序的自旋-翻转相变，低温强磁场下TlCuCl3中磁子的玻色-爱因斯坦凝聚相变，以及La&lt；2-x&gt；SrxCuO4和La&lt；2-x&gt；BaxCuO4的场致磁序。因此，热导率测量是探测和研究相变的有力探针。

We have studied the thermal conductivity and other physical properties of several copper oxides regarded as low-dimensional quantum spin systems, in order to clarify the mechanism of the giant thermal conductivity due to magnons and also to clarify whether the thermal conductivity measurement is powerful for the detection of a phase transition or not.We have discovered large thermal conductivity due to magnons in the four-leg spin-ladder system La_2Cu_2O_5 and the two-dimensional spin system Cu_3B_2O_6.In one-dimensional spin systems Sr_2CuO_3 and SrCuO_2, we have proved from the study of the impurity effects that the thermal conductivity due to magnons is very large and that the thermal conduction is ballistic as theoretically expected.From these results, it has been concluded that both the large antiferromagnetic interaction between spins and the large dispersion of magnons give rise to the large thermal conductivity due to magnons.Moreover, marked changes of the thermal conductivity have been observed at the following phase transitions; the spin-flop transition in the antiferromagnetically ordered state of Ca_2Y_2Cu_5O_<10> and Cu_3B_2O_6, the Bose-Einstein condensation transition off magnons in TlCuCl_3 under high magnetic fields at low temperatures, and the field-induced magnetic order in La_<2-x>Sr_xCUO_4 and La_<2-x>Ba_xCuO_4. Accordingly, we have concluded that the thermal conductivity measurement is a powerful probe to detect and study a phase transition.