Department of Physics, Princeton University, Princeton, NJ 08544, USA.
Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.
Science. 2015 Apr 3;348(6230):106-9. doi: 10.1126/science.1257340.
In frustrated quantum magnets, long-range magnetic order fails to develop despite a large exchange coupling between the spins. In contrast to the magnons in conventional magnets, their spin excitations are poorly understood. Here, we show that the thermal Hall conductivity κ(xy) provides a powerful probe of spin excitations in the "quantum spin ice" pyrochlore Tb2Ti2O7. The thermal Hall response is large, even though the material is transparent. The Hall response arises from spin excitations with specific characteristics that distinguish them from magnons. At low temperature (<1 kelvin), the thermal conductivity resembles that of a dirty metal. Using the Hall angle, we construct a phase diagram showing how the excitations are suppressed by a magnetic field.
在受挫的量子磁体中，尽管自旋之间存在很大的交换耦合，但长程磁序仍未能发展。与传统磁体中的磁振子不同，它们的自旋激发还没有被很好地理解。在这里，我们表明热霍尔电导率 κ(xy) 为“量子自旋冰”烧绿石 Tb2Ti2O7 中的自旋激发提供了一个强大的探针。尽管材料是透明的，但热霍尔响应仍然很大。霍尔响应来自具有特定特征的自旋激发，这些特征将它们与磁振子区分开来。在低温（<1 开尔文）下，热导率类似于污浊金属的热导率。通过霍尔角，我们构建了一个相图，展示了磁场如何抑制激发。
