Mechanism of the Anomalous Superconductivity in Black Phosphorus

在P-T相图中沿着五条不同的路径测量了黑磷的压力诱导超导性。压力对超导转变温度（Tc）的影响很大程度上取决于相图中的路径。在高压下，黑磷沿路径(D)的Tc高达10.7 K，转变起始温度超过13k。以红磷为起始材料，沿路径(D)加压4.2 K时，Tc随压力的增加急剧增加；升温至13k，在30gpa下转变起始温度达到18k。这是元素中的最高温度。在液氮温度下，用x射线同步辐射研究了压力诱导相变。在77 K时的转变压强高于室温时的转变压强。在77 K、6 ~ 14 GPa的宽压力范围内存在两相或三相共存。这些结果表明，在液氦温度下，简单立方相必然存在非均匀态，而非均匀性与异常超导性密切相关。

The pressure-induced superconductivity in black phosphorus was measured along five different paths in a P-T phase diagram. The effect of pressure on the superconductivity transition temperature(Tc) strongly depends on the path in the phase diagram. The Tc of black phosphorus along the path(D) went up to 10.7 K and onset temperature of transition was beyond 13 K at very high pressures. When the red phosphorus as a starting material was pressurized at 4.2 K along the path(D), the Tc steeply increased with increasing pressure; it raised up to 13 K and onset temperature of transition reached 18 K at 30 GPa. This is the highest temperature in elements.Pressure-induced phase transitions have also studied by X-ray study with synchrotron radiation at liquid nitrogen temperature. The pressure of the transition at 77 K was higher than that at room temperature. Two or three phases coexisted in wide pressure range 6-14 GPa at 77 K. These results suggest that there must be inhomogeneous state in simple cubic phase at liquid helium temperature and the inhomogeneity is closely related to the anomalous superconductivity.