Ab initio lattice dynamics and electron-phonon coupling in LixZrNCl -: art. no. 134527
Ab initio lattice dynamics and electron-phonon coupling in LixZrNCl -: art. no. 134527
复制标题
DOI：
10.1103/physrevb.72.134527
复制
发表时间：
2005-10-01
影响因子：
3.7
通讯作者：
Bohnen, KP
中科院分区：
文献类型：
--
作者：
Heid, R;Bohnen, KP
过渡金属氯氮化物代表一类层状化合物，其在嵌入之后成为超导体，其T-c高达25.5K。我们提出了一个理论研究的声子色散和电子-声子耦合的未掺杂和锂掺杂的ZrNCl，这是这类材料的一个突出的代表。计算是基于密度泛函微扰理论的框架下的混合基赝势方法。对于未掺杂的母体化合物β-ZrNCl，我们能够确定所有的结构，在测量的声子态密度。对于掺杂的系统，通过人工掺杂的方法处理Li位点的部分占据。掺杂部分填充了准二维导带，并在带边界K点周围产生了几乎圆柱形的费米面。掺杂诱导的电子-声子耦合也是非常二维的，并表现出很强的动量相关的重整化，涉及Zr和N的面内振动的选择性声子模式。虽然存在与较高频率N振动的较大耦合，但平均耦合常数仅近似于0.5。在肮脏极限的标准Eliashberg分析中，计算出的电子-声子耦合太弱，无法解释观察到的T-c。我们的研究结果指出，需要一个更准确的治疗库仑屏蔽效应在这些高度各向异性的层状超导体。
Transition metal chloronitrides represent a class of layered compounds, which after intercalation, become superconductors with T-c's up to 25.5 K. We present a theoretical investigation of the phonon dispersions and electron-phonon coupling for the undoped and Li-doped ZrNCl, which is one prominent representative of this class of materials. The calculations are based on density functional perturbation theory in the framework of the mixed-basis pseudopotential method. For the undoped parent compound beta-ZrNCl, we are able to identify all structures in the measured phonon-density of states. For the doped system, the partial occupation of the Li site is treated by an artificial doping approach. Doping partially fills a quasi-2D conduction band and gives rise to almost cylindrical Fermi surfaces around the zone boundary K point. The doping induced electron-phonon coupling is also very 2D-like and exhibits a strong momentum-dependent renormalization involving selective phonon modes of in-plane vibrations of Zr and N. Although there is a larger coupling to the higher-frequency N vibrations, the average coupling constant is only approximate to 0.5. Within the standard Eliashberg analysis in the dirty limit, the calculated electron-phonon coupling is too weak to explain the observed T-c. Our results point to the need for a more accurate treatment of the Coulomb screening effects in these highly anisotropic layered superconductors.