论文标题
通过相关的准二维磁波动来抑制超导参数
Suppression of superconducting parameters by correlated quasi-two-dimensional magnetic fluctuations
论文作者
论文摘要
我们考虑了一个干净的分层磁性超导体，其中在超导状态内发生连续的磁过渡，而超导和磁性子系统之间的交换相互作用很弱，因此在磁过渡时不会破坏超导性。此类材料的一个例子是rbeufe $ _ {4} $ as $ _ {4} $。我们通过磁性转变附近的相关磁波动来研究超导间隙和超流体密度的抑制。非均匀交换场对超导参数的影响对磁相关长度，$ξ_{h} $和超导相干长度$ $ξ_{s} $之间的关系敏感政权。由于一个小均匀的交换场不会影响零温度下的超导间隙和超流体密度，因此交换场的空间变化平稳会降低其对这些参数的影响。对于准二维磁波动的情况，我们开发了对这种“散射到平滑的”交叉的定量描述。由于磁散射的概率在能量尺度上与间隙相当，因此准经典近似不适用于交叉区域，需要微观处理。我们发现，对间隙和超流体密度的校正都与$ξ_{h} $成比例地生长，直到它保持远小于$ξ_{s} $。当$ξ_{h} $超过$ξ_{s} $时，两个参数对$ξ_{h} $的依赖性较弱。此外，在磁过渡附近，差距校正可能会随着$ξ_{h} $的增加而减小。我们还发现，交叉意外是宽阔的：仅当$ξ_{h} $大大小于$ξ_{s} $时，标准散射近似才变得足够。
We consider a clean layered magnetic superconductor in which a continuous magnetic transition takes place inside superconducting state and the exchange interaction between superconducting and magnetic subsystems is weak so that superconductivity is not destroyed at the magnetic transition. An example of such material is RbEuFe$_{4}$As$_{4}$. We investigate the suppression of the superconducting gap and superfluid density by correlated magnetic fluctuations in the vicinity of the magnetic transition. The influence of nonuniform exchange field on superconducting parameters is sensitive to the relation between the magnetic correlation length, $ξ_{h}$, and superconducting coherence length $ξ_{s}$ defining the 'scattering' ($ξ_{h}<ξ_{s}$) and 'smooth' ($ξ_{h}>ξ_{s}$) regimes. As a small uniform exchange field does not affect the superconducting gap and superfluid density at zero temperature, smoothening of the spatial variations of the exchange field reduces its effects on these parameters. We develop a quantitative description of this 'scattering-to-smooth' crossover for the case of quasi-two-dimensional magnetic fluctuations. Since the magnetic-scattering probability varies at the energy scale comparable with the gap, the quasiclassical approximation is not applicable in the crossover region and microscopic treatment is required. We find that the corrections to both the gap and superfluid density grow proportionally to $ξ_{h}$ until it remains much smaller than $ξ_{s}$. When $ξ_{h}$ exceeds $ξ_{s}$, both parameters have much weaker dependence on $ξ_{h}$. Moreover, the gap correction may decrease with increasing of $ξ_{h}$ in the vicinity of the magnetic transition. We also find that the crossover is unexpectedly broad: the standard scattering approximation becomes sufficient only when $ξ_{h}$ is substantially smaller than $ξ_{s}$.
