CrAs中超导电性半球附近磁双阻和量子临界的演化
Evolution of Magnetic Double Helix and Quantum Criticality near a Dome of Superconductivity in CrAs
摘要：
在环境压力下，CrAs在TN = 265 K时经历了一级转变，进入双螺旋磁态，并伴随着结构转变。最近发现的压力诱导的CrAs超导电性，使其重要的是澄清量子相变的性质，其耦合的结构/helmagnetic顺序。在这里，我们通过在静水压力（P）下的单晶CrAs的中子衍射表明，在Pc ~ 10 kbar的组合顺序被抑制，在此附近的体超导性发展的最大转变温度Tc ~ 2 K。我们进一步表明，在临界xc ~ 0.05时，CrAs 1-xPx中的磷掺杂也完全抑制了耦合序，在临界xc ~ 0.05以上，非弹性中子散射证明了持续的反铁磁相关性，提供了磁性和超导性之间的可能联系。与Pc（xc）附近反铁磁涨落的存在一致，电阻率的二次温度依赖性的A系数随着P（x）接近Pc（xc）而呈现出显著的增强，在Pc（xc）附近Res（T）具有非费米液体形式。因此，CrAs 1-xPx的电子比热系数在xc附近达到峰值。这些性质提供了明确的证据，量子临界性，我们解释为起源于一个近二阶helmagnetic量子相变，这是伴随着一阶结构转变。我们在CrAs中的发现突出了坏金属中量子临界性的独特特征，从而为非常规超导性的物理学带来了新的见解，例如发生在高Tc铁磷属元素化物中的超导性。
英文摘要：
At ambient pressure CrAs undergoes a first-order transition into a double-helical magnetic state at TN = 265 K, which is accompanied by a structural transition. The recent discovery of pressure-induced superconductivity in CrAs makes it important to clarify the nature of quantum phase transitions out of its coupled structural/helimagnetic order. Here we show, via neutron diffraction on the single-crystal CrAs under hydrostatic pressure (P), that the combined order is suppressed at Pc ~ 10 kbar, near which bulk superconductivity develops with a maximal transition temperature Tc ~ 2 K. We further show that the coupled order is also completely suppressed by phosphorus doping in CrAs1-xPx at a critical xc ~ 0.05, above which inelastic neutron scattering evidenced persistent antiferromagnetic correlations, providing a possible link between magnetism and superconductivity. In line with the presence of antiferromagnetic fluctuations near Pc (xc), the A coefficient of the quadratic temperature dependence of resistivity exhibits a dramatic enhancement as P (x) approaches Pc (xc), around which Res(T) has a non-Fermi-liquid form. Accordingly, the electronic specific-heat coefficient of CrAs1-xPx peaks out around xc. These properties provide clear evidences for quantum criticality, which we interpret as originating from a nearly second-order helimagnetic quantum phase transition that is concomitant with a first-order structural transition. Our findings in CrAs highlight the distinct characteristics of quantum criticality in bad metals, thereby bringing out new insights into the physics of unconventional superconductivity such as occurring in the high-Tc iron pnictides.
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