Enhancement of superconductivity by pressure-induced critical ferromagnetic fluctuations in UCoGe
Enhancement of superconductivity by pressure-induced critical ferromagnetic fluctuations in UCoGe
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DOI：
10.1103/physrevb.99.020506
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发表时间：
2019-01
影响因子：
3.7
通讯作者：
M. Manago;S. Kitagawa;K. Ishida;K. Deguchi;N. Sato;T. Yamamura
中科院分区：
文献类型：
--
作者：
M. Manago;S. Kitagawa;K. Ishida;K. Deguchi;N. Sato;T. Yamamura
在压力下对单晶铁磁超导体UCoGe进行了$^{59}$Co核四极共振（NQR）。在临界压力$P_c$下，调频相消失；在居里温度$T_{\textrm{Curie}}$下，NQR谱显示调频相与顺磁相分离，提示一阶调频量子相变（QPT）。我们发现$P_c$以上没有内场，但超导性几乎没有变化。这一结果表明在$P_c$附近存在非酉到酉的超导跃迁。核自旋-晶格弛豫率$1/T_1$在$P_c$附近出现FM临界波动，在$P_c$以上持续存在，与PM相的超导性明显相关。该FM QPT被理解为具有临界波动的弱一阶。单组分超导态$1/T_1$在$P_c$以上急剧下降，而双组分超导态$1/T_1$则相反，说明非均匀超导态是UCoGe中FM SC态的一个特征。
A $^{59}$Co nuclear quadrupole resonance (NQR) was performed on a single-crystalline ferromagnetic (FM) superconductor UCoGe under pressure. The FM phase vanished at a critical pressure $P_c$, and the NQR spectrum just below $P_c$ showed phase separation of the FM and paramagnetic (PM) phases below Curie temperature $T_{\textrm{Curie}}$, suggesting first-order FM quantum phase transition (QPT). We found that the internal field was absent above $P_c$, but the superconductivity is almost unchanged. This result suggests the existence of the nonunitary to unitary transition of the superconductivity around $P_c$. Nuclear spin-lattice relaxation rate $1/T_1$ showed the FM critical fluctuations around $P_c$, which persist above $P_c$ and are clearly related to superconductivity in the PM phase. This FM QPT is understood to be a weak first order with critical fluctuations. $1/T_1$ sharply decreased in the superconducting (SC) state above $P_c$ with a single component, in contrast to the two-component $1/T_1$ in the FM SC state, indicating that the inhomogeneous SC state is a characteristic feature of the FM SC state in UCoGe.