Special topic: Superconductivity and magnetism in transition-metal compounds
Credit: ©Science China Press
Transition metals contain d-orbital electrons which quite often exhibit the duality of magnetism and superconductivity in compounds. Up to date, enormous interesting physics has emerged in this field and material class, such as high temperature superconductivity in copper oxides and iron pnictides/chalcogenides, chromium arsenides, etc. The relationship between superconductivity and magnetism is very essential to understand the unconventional superconductivity.
SCIENCE CHINA Physics Mechanics Astronomy recently publishes a topical issue, in which eight articles are collected to touch some of the frontier studies of this field.
First, Bhattacharyya, Adroja, et al.  from ISIS in UK present a brief review on two typical unconventional superconducting systems, namely the Fe- and Cr-based superconductors based on the ?SR measurements. This seems to be a very good review and goes really to some deep insight of the superconducting gap structures and tells the role played by the antiferromagnetic spin fluctuations.
Then two pieces of work concerning the recent progresses in cuprate superconductors are collected. The first piece of them comes from ARPES studies by Hong Ding’s group  of IOP, CAS, China, which reports the determination of the band parameters of cuprate superconductor Bi-2212 with systematic and wide doping level. The second one arises from the scanning tunneling spectroscopy studies in Bi-2212 and Bi-2201 done by the group of Yi Yin  in Zhejiang University, China. They focus on effects of oxygen dopants at different positions on the local electronic properties in two types of Bi-based cuprate families.
For iron based superconductors, three pieces of work are presented. The first one is finished by the group of Guanghan Cao  in Zhejiang University, China, which targets the coexistence of superconductivity and possible ferromagnetism in Eu(Fe0.96Ni0.04)As2. This material provides a complementary playground for the study of the interplay between SC and magnetism. The second piece of work is done by the group of Zhixiang Shi  in Southeast University, China, which attacks the vortex problem of a recently discovered iron based 112-type superconductor. They explores the basic parameters concerning vortex dynamics and the vortex phase diagram of that system. The third piece of work is given by Gang Mu’s group  from SIMIT, CAS, China. They have grown high quality single crystal of CaFeAsF and worked on the high field resistive measurements. An insulator-metal transition is observed upon applying a high magnetic field, and through the scaling analysis, they conclude a quantum phase transition in this material tuned by magnetic field.
Finally, two papers about the exploration of new superconductors or correlated materials are collected. First work is done by the group of Jianlin Luo  in IOP, CAS, China. They report the growth of a new type of FeAs based crystals Ce12Fe57.5As41 and La12Fe57.5As41 and the discovery of multiple magnetic transitions in these correlated materials. The second piece of work comes also from the group of IOP, CAS, China, led by Zhian Ren . They report the discovery of superconductivity in LaPd2Bi2.
All works collected in this topical issue strongly suggest that the d-orbital electrons in related compounds really illustrate rich physics about electron localization and itinerancy, which intimately leads to the emergence of cooperative interactions and phenomena.
 A. Bhattacharyya, D. T. Adroja, M. Smidman, and V. K. Anand, Sci. China-Phys. Mech. Astron. 61, 127402 (2018).
 Y. G. Zhong, Y. M. Chen, J. Y. Guan, J. Zhao, Z. C. Rao, C. Y. Tang, H. J. Liu, Y. J. Sun, H. Ding, Sci. China-Phys. Mech. Astron. 61, 127403 (2018).
 Y. Fei, K. L. Bu, W. H. Zhang, Y. Zheng, X. Sun, Y. Ding, X. J. Zhou, and Y. Yin, Sci. China-Phys. Mech. Astron. 61, 127404 (2018).
 Y.-B. Liu, Y. Liu, W.-H. Jiao, Z. Ren, and G.-H. Cao, Sci. China-Phys. Mech. Astron. 61, 127405 (2018).
 X. Z. Xing, Z. F. Li, X. L. Yi, J. J. Feng, C. Q. Xu, N. Zhou, Y. Meng, Y. F. Zhang, Y. Q. Pan, L. Y. Qin, W. Zhou, H.J. Zhao, and Z. X. Shi, Sci. China-Phys. Mech. Astron. 61, 127406 (2018).
 Y. H. Ma, G. Mu, T. Hu, Z. W. Zhu, Z. J. Li, W. Li, Q. C. Ji, X. Zhang, L. L. Wang, and X. M. Xie, Sci. China-Phys. Mech. Astron. 61, 127408 (2018).
 W. Wu, and J. L. Luo, Sci. China-Phys. Mech. Astron. 61, 127407 (2018).
 Q. G. Mu, B. J. Pan, B. B. Ruan, T. Liu, K. Zhao, L. Shan, G. F. Chen, and Z. A. Ren, Sci. China-Phys. Mech. Astron. 61, 127409 (2018).