轨道选择性导致$2H$ - TaS $_2$电荷密度波隙的各向异性和粒子-空穴不对称性
Orbital selectivity causing anisotropy and particle-hole asymmetry in the charge density wave gap of $2H$-TaS$_2$
摘要：
本文报道了对$2H$ -TaS $_2$（一个正则无公度电荷密度波）体系的角分辨光电子能谱（ARPES）的深入研究。研究表明，正如在相关的非公度CDW系统，$2H$ -TaSe $_2$和$2H$ -NbSe $_2$中一样，$2H$ -TaS $_2$的能隙（$Δ_{\text{cdw}}\,$）沿着K中心费米表面桶定位并且是粒子-空穴不对称的。即使在高于$2H$ -TaS $_2$中的CDW转变温度$\it{T}_{\text{cdw}}\,$的温度下，$Δ_{\text{cdw}}\,$的持久性反映了先前在$2H$ -TaSe $_2$和$2H$ -NbSe $_2$中观察到的类似的赝能隙（PG）行为。然而，与$2H$ -NbSe $_2$形成鲜明对比的是，其中$Δ_{\text{cdw}}\,$仅在内部K中心费米表面桶上的几个“热点”附近为非零，而$2H$ -TaS中的$Δ_{\text{cdw}}\,$沿着两个K中心费米表面桶的整体都为非零。$_2$。基于一个紧束缚模型，我们属性这种二分法的动量依赖性和费米面特异性的$Δ_{\text{cdw}}\,$之间，否则类似的CDW化合物的不同轨道取向的电子状态，参与CDW配对。我们的研究结果表明，轨道选择性起着至关重要的作用，在无公度CDW材料的描述。
英文摘要：
We report an in-depth Angle Resolved Photoemission Spectroscopy (ARPES) study on $2H$-TaS$_2$, a canonical incommensurate Charge Density Wave (CDW) system. This study demonstrates that just as in related incommensurate CDW systems, $2H$-TaSe$_2$ and $2H$-NbSe$_2$, the energy gap ($Δ_{\text{cdw}}\,$) of $2H$-TaS$_2$ is localized along the K-centered Fermi surface barrels and is particle-hole asymmetric. The persistence of $Δ_{\text{cdw}}\,$ even at temperatures higher than the CDW transition temperature $\it{T}_{\text{cdw}}\,$ in $2H$-TaS$_2$, reflects the similar pseudogap (PG) behavior observed previously in $2H$-TaSe$_2$ and $2H$-NbSe$_2$. However, in sharp contrast to $2H$-NbSe$_2$, where $Δ_{\text{cdw}}\,$ is non-zero only in the vicinity of a few "hot spots" on the inner K-centered Fermi surface barrels, $Δ_{\text{cdw}}\,$ in $2H$-TaS$_2$ is non-zero along the entirety of both K-centered Fermi surface barrels. Based on a tight-binding model, we attribute this dichotomy in the momentum dependence and the Fermi surface specificity of $Δ_{\text{cdw}}\,$ between otherwise similar CDW compounds to the different orbital orientations of their electronic states that are involved in CDW pairing. Our results suggest that the orbital selectivity plays a critical role in the description of incommensurate CDW materials.
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