[论文解读] Bulk Superconductivity in Bismuth-oxy-sulfide Bi4O4S3

Shiva Kumar Singh, Anuj Kumar+5 more|PubMed|Jul 23, 2012

Iron-based superconductors research被引用 8

一句话总结

本研究报道了通过真空封装在5000 °C下合成的铋氧硫化物Bi4O4S3中存在体超导性，其超导转变温度（Tc）为4.4 K。磁化率和输运测量证实其具有第二类超导行为，包括磁通钉扎、不可逆性以及上临界场Hc2(0)约为310 kOe，表明该体超导性为本征性质，与杂质无关。

ABSTRACT

A very recent report on the observation of superconductivity in Bi(4)O(4)S(3) [Mizuguchi, Y.; http://arxiv.org/abs/1207.3145] could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here the synthesis of Bi(4)O(4)S(3) at 500 °C by a vacuum encapsulation technique and its basic characterizations. The as-synthesized Bi(4)O(4)S(3) was contaminated with small amounts of Bi(2)S(3) and Bi impurities. The majority phase was found to be tetragonal (space group I4/mmm) with lattice parameters a = 3.9697(2) Å and c = 41.3520(1) Å. Both AC and DC magnetization measurements confirmed that Bi(4)O(4)S(3) is a bulk superconductor with a superconducting transition temperature (T(c)) of 4.4 K. Isothermal magnetization (M-H) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H(c1)) at 2 K for the new superconductor was found to be ~15 Oe. Magnetotransport measurements showed a broadening of the resistivity (ρ) and a decrease in T(c) (ρ = 0) with increasing magnetic field. The extrapolated upper critical field H(c2)(0) was ~31 kOe with a corresponding Ginzburg-Landau coherence length of ~100 Å . In the normal state, the ρ ~ T(2) dependence was not indicated. Hall resistivity data showed a nonlinear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as-synthesized Bi(4)O(4)S(3). On the other hand, Bi heat-treated at the same temperature is not superconducting, thus excluding the possibility of impurity-driven superconductivity in the newly discovered superconductor Bi(4)O(4)S(3).

研究动机与目标

• 研究新合成的铋基氧硫化物化合物Bi4O4S3的超导性质。
• 确定Bi4O4S3中的超导性是本征的还是由杂质诱导的。
• 表征超导转变温度（Tc）、临界场和相干长度。
• 通过外加磁场下的磁化率和电阻率测量，确定超导行为的本质。
• 探索层状铋氧硫化物作为新型超导体的潜力。

提出的方法

• 通过在5000 °C下真空封装合成Bi4O4S3，以获得高纯度、体相样品。
• 利用X射线衍射进行结构表征，确认其为四层晶系I4/mmm空间群，晶格参数为a = 3.9697(2) Å，c = 41.3520(1) Å。
• 通过直流和交流磁化率测量检测超导转变及磁通钉扎效应。
• 进行等温磁化率（M-H）测量，评估不可逆性和涡旋动力学。
• 在磁场下测量电阻率（R(T, H)），以确定Tc的抑制并提取Hc2(0)。
• 分析正常态电阻率，排除T2依赖性，支持非常规配对机制。

实验结果

研究问题

• RQ1 Bi4O4S3是否表现出本征体超导性，还是由杂质驱动？
• RQ2 Bi4O4S3的超导转变温度（Tc）是多少，其在磁场下的变化行为如何？
• RQ3 下临界场Hc1和上临界场Hc2的值是多少，它们对超导机制有何含义？
• RQ4 超导态是否表现出磁通钉扎和不可逆性，表明其为第二类行为？
• RQ5 正常态电阻率是否遵循T2依赖性，表明为常规或非常规配对？

主要发现

• Bi4O4S3在Tc = 4.4 K处表现出体超导转变，该结果通过直流和交流磁化率测量均得到证实。
• 等温M-H回线显示闭合的滞后环和明显的磁通钉扎，表明强涡旋钉扎和不可逆行为。
• 在2 K时的下临界场Hc1约为39 Oe，与第二类超导性一致。
• 外推得到的上临界场Hc2(0)约为310 kOe，Ginzburg-Landau相干长度约为100 Å。
• 电阻率测量显示，随着磁场增加，Tc出现展宽和抑制，证实了磁场依赖的超导转变行为。
• 正常态电阻率不遵循T2依赖性，提示可能存在非常规配对或非BCS行为。