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arXiv 1608.08902cond-mat.supr-con
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YB $_6$的晶格不稳定性和超导电性的增强

Lattice instability and enhancement of superconductivity in YB$_6$

N. Sluchanko, V. Glushkov, S. Demishev, A. Azarevich, M. Anisimov, A. Bogach, S. Gavrilkin, K. Mitsen, A. Kuznetsov, I. Sannikov, N. Shitsevalova, V. Filippov, … 展开作者

N. Sluchanko, V. Glushkov, S. Demishev, A. Azarevich, M. Anisimov, A. Bogach, S. Gavrilkin, K. Mitsen, A. Kuznetsov, I. Sannikov, N. Shitsevalova, V. Filippov, M. Kondrin, K. Flachbart

摘要:

本文研究了六硼化钇(YBPDMATHABMM)的超导和正常态特性,其转变温度$T_c$在6 ~ 7.6 K之间。所提取的微观参数组[相干长度$ξ$(0)$\sim$ 320 $÷$ 340 $Å$,穿透深度$λ$(0)$\sim$ 1100 $÷$ 1600 $Å$和载流子的平均自由程$l$ = 31 $÷$ 58 $Å$,Ginzburg-Landau-Maki参数$κ$ $_{1,2}$(0)$\sim$ 3.3 $÷$ 4.8和超导能隙$Δ$(0)$\sim$ 10.3 $÷$ 14.8 K]证实了“脏限”中的II型超导性($ξ$ $\gg$ $l$)具有中等至强的电子-声子相互作用(电子-声子相互作用常数$λ_{e-ph}$ = 0.93 $÷$ 0.96)和该化合物中的电荷载流子的$s$型配对[2 $Δ$(0)$/k_BT_c$ $\approx$ 4]。的电荷传输(电阻率,霍尔和塞贝克系数)和热力学(热容量,磁化强度)性能的比较分析,在正常状态下的Yb $_6$允许检测到的笼玻璃态的过渡在$T^*$ $\sim$ 50 K的静态无序的Y $^{3+}$离子的安排。我们认为,YBPDMATHABMM单晶中的显著的$T_c$变化是由两个主要因素决定的:(1)超导性的增强与钇和硼位置上孤立空位数目的增加有关,这导致六硼化物晶格的不稳定性的发展;(ii)$T_c$抑制还受到在YBPDMATHABMM基质中缺陷复合物附近出现并被磁场增强的传导电子的自旋极化的刺激。

英文摘要:

The superconducting and normal state characteristics of yttrium hexaboride (YB$_6$) have been investigated for the single crystals with a transition temperatures $T_c$ ranging between 6 K and 7.6 K. The extracted set of microscopic parameters [the coherence length $ξ$(0) $\sim$ 320$÷$340 $Å$, the penetration depth $λ$(0) $\sim$ 1100$÷$1600 $Å$ and the mean free path of charge carriers $l$ = 31$÷$58 $Å$, the Ginzburg-Landau-Maki parameters $κ$$_{1,2}$(0) $\sim$ 3.3$÷$4.8 and the superconducting gap $Δ$(0) $\sim$ 10.3$÷$14.8 K] confirms the type II superconductivity in "dirty limit" ($ξ$$\gg$ $l$) with a medium to strong electron-phonon interaction (the electron-phonon interaction constant $λ_{e-ph}$ = 0.93$÷$0.96) and $s$-type pairing of charge carriers in this compound [2$Δ$(0)$/k_BT_c$ $\approx$ 4]. The comparative analysis of charge transport (resistivity, Hall and Seebeck coefficients) and thermodynamic (heat capacity, magnetization) properties in the normal state in YB$_6$ allowed to detect a transition into the cage-glass state at $T^*$ $\sim$ 50 K with a static disorder in the arrangement of the Y$^{3+}$ ions. We argue that the significant $T_c$ variations in the YB$_6$ single crystals are determined by two main factors: (i) the superconductivity enhancement is related with the increase of the number of isolated vacancies, both at yttrium and boron sites, which leads to the development of an instability in the hexaboride lattice; (ii) the $T_c$ depression is additionally stimulated by the spin polarization of conduction electrons emerged and enhanced by the magnetic field in the vicinity of defect complexes in the YB$_6$ matrix.

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