Spin entropy as the likely source of enhanced thermopower in NaxCo2O4
Spin entropy as the likely source of enhanced thermopower in NaxCo2O4
复制标题
DOI：
10.1038/nature01639
复制
发表时间：
2003-05-22
期刊：
影响因子：
64.8
通讯作者：
Ong, NP
中科院分区：
文献类型：
--
作者：
Wang, YY;Rogado, NS;Ong, NP
在电场中，固体中的电子流动除了产生我们所熟悉的电荷电流外，还产生熵电流。这就是珀尔帖效应，它是所有热电冰箱的基础。对热电冷却应用的兴趣增加导致了对更有效的珀尔帖材料的研究，并对电子-电子相互作用如何增强过渡金属氧化物等材料的热能进行了新的理论研究（1-4）。这种增强的一个重要因素是电子自旋熵，它被预测（4-6）将主导熵流。然而，自旋熵项的关键证据，即其在纵向磁场中的完全抑制，至今尚未报道。在这里，我们从纵向和横向磁场的热功率和磁化测量中报告了层状氧化物NaxCo2O4中这种抑制的证据。热功率对磁场的强烈依赖提供了一个罕见的、明确的例子，说明强电子-电子相互作用效应如何定性地改变固体中的电子行为。我们讨论了我们的发现——自旋熵在过渡金属氧化物的热能增强中占主导地位——对寻找更好的珀尔帖材料的意义。
In an electric field, the flow of electrons in a solid produces an entropy current in addition to the familiar charge current. This is the Peltier effect, and it underlies all thermoelectric refrigerators. The increased interest in thermoelectric cooling applications has led to a search for more efficient Peltier materials and to renewed theoretical investigation into how electron-electron interaction may enhance the thermopower of materials such as the transition-metal oxides(1-4). An important factor in this enhancement is the electronic spin entropy, which is predicted(4-6) to dominate the entropy current. However, the crucial evidence for the spin-entropy term, namely its complete suppression in a longitudinal magnetic field, has not been reported until now. Here we report evidence for such suppression in the layered oxide NaxCo2O4, from thermopower and magnetization measurements in both longitudinal and transverse magnetic fields. The strong dependence of thermopower on magnetic field provides a rare, unambiguous example of how strong electron-electron interaction effects can qualitatively alter electronic behaviour in a solid. We discuss the implications of our finding-that spin-entropy dominates the enhancement of thermopower in transition-metal oxides-for the search for better Peltier materials.