碱性铁硒化物$A$ Fe $_{1.6+x}$ Se $_2$（$A=$ K，Rb，Cs）超导体的发现在凝聚态物理学界引起了相当大的兴奋，因为这些材料中的超导性可能与符号反转的s波电子配对机制有不同的起源，这是所有其他铁基超导体的主要候选者。虽然$A$ Fe $_{1.6+x}$ Se $_2$与金属反铁磁（AF）铁磷属元素化物（如（Ba，Ca，Sr）Fe $_2$ As $_2$）是同构的，但它们是$x=0$附近的绝缘体，并形成与铁磷属元素化物完全不同的$\sqrt{5}\times\sqrt{5}$阻断AF结构（图1a）。如果磁性是所有铁基材料的超导性的原因，那么确定它们共同的磁性特征就很重要。在这里，我们使用中子散射映射出AF绝缘Rb $_{0.89}$ Fe $_{1.58}$ Se $_2$中的自旋波。我们发现，虽然Rb $_{0.89}$ Fe $_{1.58}$ Se $_2$的N $\rm \acute{e}$ el温度（$T_N=475$ K）远高于铁磷属元素化物（$T_N\leq 220$ K），这两类材料的自旋波具有相似的区域边界能。比较Rb $_{0.89}$ Fe $_{1.58}$ Se $_2$、（Ba，Ca，Sr）Fe $_2$ As $_2$和铁硫属化物Fe $_{1.05}$ Te中使用局部矩海森堡哈密顿量拟合的有效交换耦合，揭示它们的次近邻（NNN）交换耦合是相似的。因此，所有铁基材料中的超导性可能具有与NNN磁交换相互作用密切相关的共同磁起源，即使它们具有金属或绝缘基态，不同的AF阶和电子能带结构。
英文摘要：
The discovery of alkaline iron selenide $A$Fe$_{1.6+x}$Se$_2$ ($A=$ K, Rb, Cs) superconductors has generated considerable excitement in the condensed matter physics community because superconductivity in these materials may have a different origin from the sign reversed s-wave electron pairing mechanism, a leading candidate proposed for all other Fe-based superconductors. Although $A$Fe$_{1.6+x}$Se$_2$ are isostructural with the metallic antiferromagnetic (AF) iron pnictides such as (Ba,Ca,Sr)Fe$_2$As$_2$, they are insulators near $x=0$ and form a $\sqrt{5}\times\sqrt{5}$ blocked AF structure (Fig. 1a) completely different from the iron pnictides. If magnetism is responsible for superconductivity of all iron-based materials, it is important to determine their common magnetic features. Here we use neutron scattering to map out spin waves in the AF insulating Rb$_{0.89}$Fe$_{1.58}$Se$_2$. We find that although Rb$_{0.89}$Fe$_{1.58}$Se$_2$ has a N$\rm \acute{e}$el temperature ($T_N=475$ K) much higher than that of the iron pnictides ($T_N\leq 220$ K), spin waves for both classes of materials have similar zone boundary energies. A comparison of the fitted effective exchange couplings using a local moment Heisenberg Hamiltonian in Rb$_{0.89}$Fe$_{1.58}$Se$_2$, (Ba,Ca,Sr)Fe$_2$As$_2$, and iron chalcogenide Fe$_{1.05}$Te reveals that their next nearest neighbor (NNN) exchange couplings are similar. Therefore, superconductivity in all Fe-based materials may have a common magnetic origin that is intimately associated with the NNN magnetic exchange interactions, even though they have metallic or insulating ground states, different AF orders and electronic band structures.
Magnetic Field Tuned Quantum Phase Transition in the Insulating Regime of Ultrathin Amorphous Bi Films
在经历厚度调谐的超导体-绝缘体转变的一系列非晶Bi的均匀、猝灭凝聚膜的绝缘膜中发现了电阻随垂直磁场的惊人的强变化，以及电阻对场的峰值R（B）。发现磁电阻而不是电阻与磁场的等温线在一个明确定义的磁场处相交，该磁场高于对应于R（B）峰值的磁场。对于B的所有值，R（T）被发现服从阿耳修斯形式。在交叉磁场中，前因子等于电子对的量子电阻h/4 e ^2，激活能回到零场值。这些观察结果表明，交叉是两个不同的绝缘基态之间的量子相变的标志，由磁场调谐。
The 0 and the pi phase Josephson coupling through an insulating barrier with magnetic impurities
本文研究了由顺磁绝缘层形成隧穿势垒的Nb-Fe $_{0.1}$ Si $_{0.9}$ -Nb约瑟夫森结中临界电流$I_{C}$与温度和电场的关系。我们表明，在这些结中的0和$π$状态的共存在一个隧道结内发生，这导致出现一个尖锐的尖点的温度依赖性$I_{C}(T)$类似的$I_{C}(T)$尖点发现的$0-π$过渡金属$π$结。这个尖点与$0-π$温度诱导跃迁本身无关，而是由穿过势垒的相反的0和$π$超电流的不同温度依赖性引起的。
