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    Magnetoresistivity and filamentary superconductivity in nickel-doped BaFe2As2
    Wei Zhang(张威), Yao-Min Dai(戴耀民), Bing Xu(许兵), Run Yang(杨润), Jin-Yun Liu(刘金云), Qiang-Tao Sui(随强涛), Hui-Qian Luo(罗会仟), Rui Zhang(张睿), Xing-Ye Lu(鲁兴业), Hao Yang(杨浩), Xiang-Gang Qiu(邱祥冈)
    Chin. Phys. B, 2016, 25 (4): 047401.   DOI: 10.1088/1674-1056/25/4/047401
    Abstract690)   HTML    PDF (2352KB)(644)      

    We present magnetotransport studies on a series of BaFe2-xNixAs2 (0.03≤ x ≤ 0.10) single crystals. In the underdoped (x = 0.03) non-superconducting sample, the temperature-dependent resistivity exhibits a peak at 22 K, which is associated with the onset of filamentary superconductivity (FLSC). FLSC is suppressed by an external magnetic field in a manner similar to the suppression of bulk superconductivity in an optimally-doped (x=0.10) compound, suggesting the same possible origin as the bulk superconductivity. Our magnetoresistivity measurements reveal that FLSC persists up to the optimal doping and disappears in the overdoped regime where the long-range antiferromagnetic order is completely suppressed, pointing to a close relation between FLSC and the magnetic order.

    Effect of residual stress on nematic domains in BaFe2-xNixAs2 studied by angular magnetoresistance
    Ding Hu(胡定), Wenliang Zhang(张汶良), Yuan Wei(魏源), Xiaotian Zhang(张笑天), Cong Ren(任聪), Lei Shan(单磊), Yi-feng Yang(杨义峰), Huiqian Luo(罗会仟), Shiliang Li(李世亮)
    Chin. Phys. B, 2016, 25 (5): 057402.   DOI: 10.1088/1674-1056/25/5/057402
    Abstract445)   HTML    PDF (303KB)(423)      

    We have studied the angular magnetoresistance of iron pnictides BaFe2-xNixAs2, which shows clear 180 degree periodicity as fitted by a cosine function. In the x = 0.065 sample, the phase of the two-fold symmetry changes 90 degrees above the tetragonal-to-orthorhombic structural transition temperature Ts. Since the phase at low temperature is associated with the rotation of orthorhombic domains by magnetic field, we show that even vacuum grease can push the presence of orthorhombic domains at temperatures much higher than Ts. Our results suggest that residual stress may have significant effects in studying the nematic orders and its fluctuations in iron pnictides.

    Superconductivity in Sm-doped CaFe2As2 single crystals
    Dong-Yun Chen(陈东云), Bin-Bin Ruan(阮彬彬), Jia Yu(于佳), Qi Guo(郭琦), Xiao-Chuan Wang(王小川), Qing-Ge Mu(穆青隔), Bo-Jin Pan(潘伯津), Tong Liu(刘通), Gen-Fu Chen(陈根富), Zhi-An Ren(任治安)
    Chin. Phys. B, 2016, 25 (6): 067403.   DOI: 10.1088/1674-1056/25/6/067403
    Abstract588)   HTML    PDF (8560KB)(520)      

    In this article, the Sm-doping single crystals Ca1-xSmxFe2As2 (x=0~0.2) were prepared by the CaAs flux method, and followed by a rapid quenching treatment after the high temperature growth. The samples were characterized by structural, resistive, and magnetic measurements. The successful Sm-substitution was revealed by the reduction of the lattice parameter c, due to the smaller ionic radius of Sm3+ than Ca2+. Superconductivity was observed in all samples with onset Tc varying from 27 K to 44 K upon Sm-doping. The coexistence of a collapsed phase transition and the superconducting transition was found for the lower Sm-doping samples. Zero resistivity and substantial superconducting volume fraction only happen in higher Sm-doping crystals with the nominal x >0.10. The doping dependences of the c-axis length and onset Tc were summarized. The high-Tc observed in these quenched crystals may be attributed to simultaneous tuning of electron carriers doping and strain effect caused by lattice reduction of Sm-substitution.

    Raman scattering studies on the collapsed phase of CaCo2As2
    Jianting Ji(籍建葶), Anmin Zhang(张安民), Run Yang(杨润), Yong Tian(田勇), Feng Jin(金峰), Xianggang Qiu(邱祥冈), Qingming Zhang(张清明)
    Chin. Phys. B, 2016, 25 (6): 067803.   DOI: 10.1088/1674-1056/25/6/067803
    Abstract425)   HTML    PDF (648KB)(343)      

    In this work, Raman scattering measurements have been performed on the collapsed phase CaCo2As2 crystals. At least 8 Raman modes were observed at room temperature though CaCo2As2 is structurally similar to other 122 compounds like BaFe2As2. Two Raman modes are assigned to the intrinsic A1g and B1g of this material system respectively. The other ones are considered to originate from the local vibrations relevant to cobalt vacancies. Careful polarized measurements allow us to clearly resolve the four-fold symmetry of the B1g mode, which put strong constraints on possible point group symmetries of the system with Co vacancies. The temperature-dependent measurements demonstrate that the anomalies in both frequency and width of the B1g mode occur around Neel temperature TN. The anomalies are considered to be related to the gap opening near the magnetic transition. The study may shed light on the structural and magnetic changes and their correlations with superconductivity in 122 systems.

    Hybrid crystals of cuprates and iron-based superconductors
    Xia Dai(代霞), Cong-Cong Le(勒聪聪), Xian-Xin Wu(吴贤新), Jiang-Ping Hu(胡江平)
    Chin. Phys. B, 2016, 25 (7): 077402.   DOI: 10.1088/1674-1056/25/7/077402
    Abstract452)   HTML    PDF (2074KB)(502)      

    We propose two possible new compounds, Ba2CuO2Fe2As2 and K2CuO2Fe2Se2, which hybridize the building blocks of two high temperature superconductors, cuprates and iron-based superconductors. These compounds consist of square CuO2 layers and antifluorite-type Fe2X2 (X=As, Se) layers separated by Ba/K. The calculations of binding energies and phonon spectra indicate that they are dynamically stable, which ensures that they may be experimentally synthesized. The Fermi surfaces and electronic structures of the two compounds inherit the characteristics of both cuprates and iron-based superconductors. These compounds can be superconductors with intriguing physical properties to help to determine the pairing mechanisms of high Tc superconductivity.

    Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe3-xSex
    Shan Cui(崔珊), Lan-Po He(何兰坡), Xiao-Chen Hong(洪晓晨), Xiang-De Zhu(朱相德), Cedomir Petrovic, Shi-Yan Li(李世燕)
    Chin. Phys. B, 2016, 25 (7): 077403.   DOI: 10.1088/1674-1056/25/7/077403
    Abstract469)   HTML    PDF (663KB)(708)      

    It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk superconductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe3-xSex near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe3-xSex single crystals (x = 0.044 and 0.051) down to 80 mK. For both samples, the residual linear term κ0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe3-xSex, which indicates conventional superconductivity despite of the existence of a CDW QCP.

    Synthesis of large FeSe superconductor crystals via ion release/introduction and property characterization
    Dongna Yuan(苑冬娜), Yulong Huang(黄裕龙), Shunli Ni(倪顺利), Huaxue Zhou(周花雪), Yiyuan Mao(毛义元), Wei Hu(胡卫), Jie Yuan(袁洁), Kui Jin(金魁), Guangming Zhang(张广铭), Xiaoli Dong(董晓莉), Fang Zhou(周放)
    Chin. Phys. B, 2016, 25 (7): 077404.   DOI: 10.1088/1674-1056/25/7/077404
    Abstract670)   HTML    PDF (1421KB)(512)      

    Large superconducting FeSe crystals of (001) orientation have been prepared via a hydrothermal ion release/introduction route for the first time. The hydrothermally derived FeSe crystals are up to 10 mm×5 mm×0.3 mm in dimension. The pure tetragonal FeSe phase has been confirmed by x-ray diffraction (XRD) and the composition determined by both inductively coupled plasma atomic emission spectroscopy (ICP-AES) and energy dispersive x-ray spectroscopy (EDX). The superconducting transition of the FeSe samples has been characterized by magnetic and transport measurements. The zero-temperature upper critical field Hc2 is calculated to be 13.2-16.7 T from a two-band model. The normal-state cooperative paramagnetism is found to be predominated by strong spin frustrations below the characteristic temperature Tsn, where the Ising spin nematicity has been discerned in the FeSe superconductor crystals as reported elsewhere.

    Doping Mn into (Li1-xFex)OHFe1-ySe superconducting crystals via ion-exchange and ion-release/introduction syntheses
    Huaxue Zhou(周花雪), Shunli Ni(倪顺利), Jie Yuan(袁洁), Jun Li(李军), Zhongpei Feng(冯中沛), Xingyu Jiang(江星宇), Yulong Huang(黄裕龙), Shaobo Liu(刘少博), Yiyuan Mao(毛义元), Fang Zhou(周放), Kui Jin(金魁), Xiaoli Dong(董晓莉), Zhongxian Zhao(赵忠贤)
    Chin. Phys. B, 2017, 26 (5): 057402.   DOI: 10.1088/1674-1056/26/5/057402
    Abstract699)   HTML    PDF (1050KB)(592)      

    We report the success in introducing Mn into (Li1-xFex)OHFe1-ySe superconducting crystals by applying two different hydrothermal routes, ion exchange (1-step) and ion release/introduction (2-step). The micro-region x-ray diffraction and energy dispersive x-ray spectroscopy analyses indicate that Mn has been doped into the lattice, and its content in the 1-step fabricated sample is higher than that in the 2-step one. Magnetic susceptibility and electric transport properties reveal that Mn doping influences little on the superconducting transition, regardless of 1-step or 2-step routes. By contrast, the characteristic temperature T*, at which the negative Hall coefficient reaches its minimum, is significantly reduced by Mn doping. This implies that the hole carriers contribution is obviously modified, and hence the hole band might have no direct relationship with the superconductivity in (Li1-xFex)OHFe1-ySe superconductors. Our present hydrothermal methods of ion exchange and ion release/introduction provide an efficient way for elements substitution/doping into (Li1-xFex)OHFe1-ySe superconductors, which will promote the in-depth investigations on the role of multiple electron and hole bands and their interplay with the high-temperature superconductivity in the FeSe-based superconductors.

    Transition from tunneling regime to local point contact realized on Ba0.6K0.4Fe2As2 surface
    Xingyuan Hou(侯兴元), Yunyin Jie(揭云印), Jing Gong(巩靖), Bing Shen(沈冰), Hai Zi(子海), Chunhong Li(李春红), Cong Ren(任聪), Lei Shan(单磊)
    Chin. Phys. B, 2017, 26 (6): 067402.   DOI: 10.1088/1674-1056/26/6/067402
    Abstract527)   HTML    PDF (3072KB)(375)      

    Using scanning tunneling spectroscopy, we studied the transition from tunneling regime to local point contact on the iron-based superconductor Ba0.6K0.4Fe2As2. By gradually reducing the junction resistance, a series of spectra were obtained with the characteristics evolving from single-particle tunneling into Andreev reflection. The spectra can be well fitted to the modified Blonder-Tinkham-Klapwijk (BTK) model and exhibit significant changes of both spectral broadening and orbital selection due to the formation of point contact. The spatial resolution of the point contact was estimated to be several nanometers, providing a unique way to study the inhomogeneity of unconventional superconductors on such a scale.

    Electronic structure of heavy fermion system CePt2In7 from angle-resolved photoemission spectroscopy
    Bing Shen(沈兵), Li Yu(俞理), Kai Liu(刘凯), Shou-Peng Lyu(吕守鹏), Xiao-Wen Jia(贾小文), E D Bauer, J D Thompson, Yan Zhang(张艳), Chen-Lu Wang(王晨露), Cheng Hu(胡成), Ying Ding(丁颖), Xuan Sun(孙璇), Yong Hu(胡勇), Jing Liu(刘静), Qiang Gao(高强), Lin Zhao(赵林), Guo-Dong Liu(刘国东), Zu-Yan Xu(许祖彦), Chuang-Tian Chen(陈创天), Zhong-Yi Lu(卢仲毅), X J Zhou(周兴江)
    Chin. Phys. B, 2017, 26 (7): 077401.   DOI: 10.1088/1674-1056/26/7/077401
    Abstract399)   HTML    PDF (7247KB)(345)      

    We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7 that exhibits stronger two-dimensional character than the prototypical heavy fermion system CeCoIn5. Multiple Fermi surface sheets and a complex band structure are clearly resolved. We have also performed detailed band structure calculations on CePt2In7. The good agreement found between our measurements and the calculations suggests that the band renormalization effect is rather weak in CePt2In7. A comparison of the common features of the electronic structure of CePt2In7 and CeCoIn5 indicates that CeCoIn5 shows a much stronger band renormalization effect than CePt2In7. These results provide new information for understanding the heavy fermion behaviors and unconventional superconductivity in Ce-based heavy fermion systems.

    Electronic structure and nematic phase transition in superconducting multiple-layer FeSe films grown by pulsed laser deposition method
    Bing Shen(沈兵), Zhong-Pei Feng(冯中沛), Jian-Wei Huang(黄建伟), Yong Hu(胡勇), Qiang Gao(高强), Cong Li(李聪), Yu Xu(徐煜), Guo-Dong Liu(刘国东), Li Yu(俞理), Lin Zhao(赵林), Kui Jin(金魁), X J Zhou(周兴江)
    Chin. Phys. B, 2017, 26 (7): 077402.   DOI: 10.1088/1674-1056/26/7/077402
    Abstract498)   HTML    PDF (3502KB)(479)      

    We report comprehensive angle-resolved photoemission investigations on the electronic structure of single crystal multiple-layer FeSe films grown on CaF2 substrate by pulsed laser deposition (PLD) method. Measurements on FeSe/CaF2 samples with different superconducting transition temperatures Tc of 4 K, 9 K, and 14 K reveal electronic difference in their Fermi surface and band structure. Indication of the nematic phase transition is observed from temperature-dependent measurements of these samples; the nematic transition temperature is 140–160 K, much higher than~90 K for the bulk FeSe. Potassium deposition is applied onto the surface of these samples; the nematic phase is suppressed by potassium deposition which introduces electrons to these FeSe films and causes a pronounced electronic structure change. We compared and discussed the electronic structure and superconductivity of the FeSe/CaF2 films by PLD method with the FeSe/SrTiO3 films by molecular beam epitaxy (MBE) method and bulk FeSe. The PLD-grown multilayer FeSe/CaF2 is more hole-doped than that in MBE-grown multiple-layer FeSe films. Our results on FeSe/CaF2 films by PLD method establish a link between bulk FeSe single crystal and FeSe/SrTiO3 films by MBE method, and provide important information to understand superconductivity in FeSe-related systems.