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Mn-doping induced ferromagnetism and enhanced superconductivity in Bi4−xMnxO4S3 (0.075 ≤ x ≤ 0.15) [Zhenjie Feng et al., Phys. Rev. B 94, 064522 (2016)]

The physical mechanism for high-temperature superconductivity remains one of the most challenging issues in modern condensed matter physics. Interestingly, one of the commonalities among high-temperature superconducting cuprates and iron-based compounds is their layered structures. Even among conventional superconductors, the highest superconducting transition temperature (Tc) has been found in layered magnesium diboride MgB2. Recently, superconductivity with Tc = 4.5 K was discovered in a new superconductor Bi4O4S3. This compound has a layered structure composed of two superconducting BiS2 layers and spacer layers of Bi4O4(SO4)1x, where x indicates the deficiency of (SO4)2 ions at the interlayer sites. Since the discovery of Bi4O4S3, several other BiS2-based superconductors LnO1xF xBiS2 (Ln = La, Ce, Pr, Nd) with the highest Tc ~ 10.6 K have been reported. Both experimental and theoretical studies to date have indicated that the BiS2 layers play the role of the superconducting planes in these sulfide superconductors, similar to the CuO2 planes in the cuprate superconductors and the Fe2An2 (An = P, As, Se, Te) layers in the iron-based superconductors. A major challenge facing this new class of layered superconductors is to optimize Tc by exploring different spacer layers. Additionally, the effects of doping by either nonmagnetic or magnetic elements are important issues for investigation.

In collaboration with Professor Zhenjie Feng’s group at the Shanghai University in China, we demonstrate in this latest publication that Mn-doping in the layered sulfides Bi4O4S3 leads to stable Bi4xMnxO4S3 compounds that exhibit both long-range ferromagnetism and enhanced superconductivity for 0.075  x  0.15, with a record Tc ~ 15 K amongst all BiS2-based superconductors. Based on our experimental investigations of Bi4xMnxO4S3 and comparative studies of related compounds Bi4xCoxO4S3 and Bi4xNixO4S3, we suggest that that the coexistence of superconductivity and ferromagnetism may be attributed to Mn-doping in the spacer Bi2O2 layers away from the superconducting BiS2 layers, whereas the enhancement of Tc may be due to excess electron transfer to BiS2 from the Mn4+/Mn3+-substitutions in Bi2O2. These findings therefore shed new light on feasible pathways to enhance the Tc values of BiS2-based superconductors.
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Mn-doping induced ferromagnetism and enhanced superconductivity in Bi4−xMnxO4S3 (0.075 ≤ x ≤ 0.15)

Mn-doping induced ferromagnetism and enhanced superconductivity in Bi4−xMnxO4S3 (0.075 ≤ x ≤ 0.15) Zhenjie Feng, Xunqing Yin, Yiming Cao, Xianglian Peng, Tian Gao, Chuan Yu, Jingzhe Chen, Baojuan Kang, Bo Lu, Juan Guo, Qing Li, Wei-Shiuan Tseng, Zhongquan Ma, Chao Jing, Shixun Cao, Jincang Zhang, and N.-C. Yeh Phys. Rev. B 94, 064522 (2016). arXiv:1608.04410
http://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.064522

Professor Yeh interviewed by Voice of SCIENCE!

Professor Nai-Chang Yeh, Co-Director of the Kavli Nanoscience Institute (KNI), was recently interviewed by Silver Rose Entertainment and Voice of Science for their series: BADASS WOMEN in SCIENCE for her research efforts on graphene. SRE Studios and Voice of Science are creating a video series to celebrate women working and succeeding in Science Technology Engineering and Math (STEM) fields. The interview was filmed in several of Professor Yeh’s labs with primary emphasis on our room temperature graphene growth process and also on our current research and technological applications of graphene. The interview and video was produced by Micah Haughey and can be found at the following youtube link:
https://www.youtube.com/watch?v=DRlzGJznTiI

Horizons series “Abundant World”

Professor Nai-Chang Yeh, Co-Director of the Kavli Nanoscience Institute (KNI), was featured in a recent episode of the Horizons series “Abundant World” by the BBC World News for her research on graphene. The episode was filmed in one of Professor Yeh’s labs and also at the KNI, with primary emphasis on our room temperature graphene growth process (described by Staff Scientist Dr. David Boyd) and also on our current research and technological applications of graphene (described by Professor Yeh). The “Abundant World” episode was broadcasted on May 13, 14, 15 and 17 of 2016 worldwide by the BBC World News, which can also be found at the following BBC link:

http://www.bbc.com/specialfeatures/horizonsbusiness/seriessix/abundant-world/?vid=p03vmfg1

Nanoscale strain engineering of graphene and graphene-based devices

Our recent paper “Nanoscale strain engineering of graphene and graphene-based devices”, published in Acta Mechanic Sinica 32 (3), 497 – 509 (2016), was identified as a Key Scientific Article contributing to excellence in scientific and engineering research and was featured in the May 28, 2016 edition of Advances in Engineering Series under the category of Nanotechnology Engineering. For more information, see the websites:
N.-C. Yeh et al., Acta Mechanica Sinica 32 (3), 497 (2016).
https://advanceseng.com/ and https://advanceseng.com/nanotechnology-engineering/nanoscale-strain-engineering-graphene-graphene-based-devices/

Observation of Fermi-energy dependent unitary impurity resonances in a strong topological insulator Bi2Se3 with scanning tunneling spectroscopy

“Observation of Fermi-energy dependent unitary impurity resonances in a strong topological insulator Bi2Se3 with scanning tunneling spectroscopy” M. L. Teague, F.-X. Xiu, L. He, K.-L. Wang and N.-C. Yeh, fast-track communication in Solid State Communications 152, 747 – 751 (2012). [arXiv:1201.5618]
http://www.sciencedirect.com/science/article/pii/S0038109812000749