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首页> 外文期刊>Bulletin of the American Physical Society >APS -APS March Meeting 2017 - Event - Out-of-plane dependence of the CDW and superconducting gap in bulk 2{it H}-NbSe$_2$ revealed by phonon spectroscopy
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APS -APS March Meeting 2017 - Event - Out-of-plane dependence of the CDW and superconducting gap in bulk 2{it H}-NbSe$_2$ revealed by phonon spectroscopy

机译：APS -APS 2017年3月会议-事件-声子光谱显示CDW的面外依赖性和块体2 {it H} -NbSe $ _2 $的超导间隙

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In 2{it H}-NbSe$_2$, the CDW energy gap below $T_{CDW}$=33 K opens only on a small part of the Fermi surface in the ($h,k$) plane, which explains why superconductivity can emerge in this system at lower temperature $T_C$=7.2K. However, the interplay between these competing states and their relative evolution upon intercalation or applied pressure remains puzzling. We will discuss our high-energy-resolution inelastic x-ray scattering investigation of the CDW soft phonon mode upon entering the superconducting state. From the observed changes in the phonon lineshapes, we demonstrate that the superconducting gap exhibits an out-of-plane dependence. Reversely, our data imply that the CDW energy gap is strongly localized along $k_z$, a result that could not be obtained with surface techniques, such as ARPES or STM. This confinement of the CDW gap to a very small momentum region, both within as well as out-of the plane, explains the rather low competition and easy coexistence of CDW order and superconductivity in 2{it H}-NbSe$_2$. Our results further provide a microscopic explanation of the decrease/increase of $T_{C}$/$T_{CDW}$ in single-layer NbSe$_2$ as compared to the bulk system.
机译：在2 {it H} -NbSe $ _2 $中，低于$ T_ {CDW} $ = 33 K的CDW能隙仅在（$ h，k $）平面的费米表面的一小部分打开，这解释了为什么在较低温度$ T_C $ = 7.2K的情况下，系统中会出现超导性。但是，这些竞争状态与其在插层或施加压力时的相对演化之间的相互作用仍然令人费解。进入超导状态后，我们将讨论CDW软声子模式的高能分辨率非弹性X射线散射研究。从声子线形的观察变化中，我们证明了超导间隙表现出平面外依赖性。相反，我们的数据表明CDW的能隙沿$ k_z $强烈定位，这是用ARPES或STM等表面技术无法获得的。将CDW间隙限制在很小的动量范围内，无论是在平面内还是平面外，都说明了2 {it H} -NbSe $ _2 $中CDW有序竞争和低传导性以及超导性容易共存。我们的结果进一步为单层NbSe $ _2 $中的$ T_ {C} $ / $ T_ {CDW} $与批量系统相比的减少/增加提供了微观解释。

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