Time-domain classification of charge-density-wave insulators
Time-domain classification of charge-density-wave insulators
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DOI：
10.1038/ncomms2078
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发表时间：
2012-09-01
影响因子：
16.6
通讯作者：
Rossnagel, K.
中科院分区：
文献类型：
--
作者：
Hellmann, S.;Rohwer, T.;Rossnagel, K.
根据主要的相互作用类型区分绝缘体是凝聚态物理中的一个中心问题。基本模型包括由电子-晶格相互作用引起的Bloch-Wilson绝缘体和Peierls绝缘体，由电子-电子相互作用引起的Mott和激子绝缘体，以及由电子-杂质相互作用引起的Anderson绝缘体。然而，在真实的材料中，所有的相互作用都是同时存在的，因此分类往往并不简单。在这里，我们证明了时间和角度分辨光电子能谱可以直接测量电子有序参数的熔化时间，从而通过对基本电子和结构过程的系统的时间分辨来识别主导相互作用。具体地，我们解决了关于过渡金属二盐系化合物家族中两个特殊的电荷密度波态性质的争论，并表明Rb嵌入1T-TaS_2是一种Peierls绝缘体，而1T-TiSe_2的超快响应是一种激子绝缘体。
Distinguishing insulators by the dominant type of interaction is a central problem in condensed matter physics. Basic models include the Bloch-Wilson and the Peierls insulator due to electron-lattice interactions, the Mott and the excitonic insulator caused by electron-electron interactions, and the Anderson insulator arising from electron-impurity interactions. In real materials, however, all the interactions are simultaneously present so that classification is often not straightforward. Here, we show that time- and angle-resolved photoemission spectroscopy can directly measure the melting times of electronic order parameters and thus identify-via systematic temporal discrimination of elementary electronic and structural processes-the dominant interaction. Specifically, we resolve the debates about the nature of two peculiar charge-density-wave states in the family of transition-metal dichalcogenides, and show that Rb intercalated 1T-TaS2 is a Peierls insulator and that the ultrafast response of 1T-TiSe2 is highly suggestive of an excitonic insulator.