Extraordinary terahertz transmission through subwavelength spindle-like apertures in NbN filmExtraordinary terahertz transmission through subwavelength spindle-like apertures in NbN filmExtraordinary terahertz transmission through subwavelength spindle-like apertures in NbN filmExtraordinary terahertz transmission through subwavelength spindle-like apertures in NbN film

We studied numerically the temperature dependent extraordinary terahertz transmission through niobium nitride （NbN） film perforated with subwavelength spindle-like apertures. Both the resonant frequency and intensity of extraor- dinary terahertz transmission peaks can be greatly modified by the transition of NbN film from the normal state to the superconducting state. An enhancement of the （~1,0） NbN/magnesium oxide （MgO） peak intensity as high as 200% is demonstrated due to the combined contribution of both the superconducting transition and the excitation of localized surface plasmons （LSPs） around the apertures. The extraordinary terahertz transmission through spindle-fike hole arrays patterned on the NbN film can pave the way for us to explore novel active tuning devices.     

浅析电子型掺杂铜氧化物超导体的退火过程

铜氧化物高温超导体的发现, 打破了基于电声子相互作用BCS理论所预言的超导转变温度极限, 掀开了高温超导材料探索和高温超导机理研究的序幕. 根据掺杂类型的不同, 铜氧化物超导材料可以分为空穴型掺杂和电子型掺杂两类. 受限于样品, 对电子型掺杂铜氧化物的研究工作远少于空穴型掺杂体系. 本文简要回顾有关电子型掺杂铜氧化物超导体近期研究成果, 通过对比电子型掺杂和空穴型掺杂铜氧化物的相图来阐明电子型掺杂铜氧化物的研究对探索高温超导机理的必要性, 并特别针对电子型掺杂样品制备中的关键因素“退火过程”展开讨论. 结合课题组最新实验结果和相关实验报道我们发现电子型掺杂铜氧化物超导体在制备过程中除受到温度和氧分压的影响外, 退火效果还受到界面应力的强烈调制. 在综合考虑样品生长过程中温度、气氛及应力等多种因素的基础上, 探讨了“保护退火”方法导致电子型体系化学掺杂相图变化的起因.     

Bi1-xLaxFeO3±δ薄膜的快速制备及铁电性

样品的制备是对影响样品质量的各个工艺参数进行优化的过程. 传统的试错法是对各个参数逐个进行尝试, 需要的周期较长. 与传统的单参数尝试法相比, 高通量样品制备方法可以对参数实现并行筛选, 因而极大地缩短了优化工艺所需的时间. 本工作借助高通量制备方法成功实现系列镧掺杂BiFeO₃薄膜的快速优化, 包括对烧结温度、镧元素含量和高温固态反应气氛等关键工艺参数的快速筛选, 同时分析了不同生长条件下样品的结构并测试了其铁电性. 实验结果表明: 1) 560 ℃ 烧结可得到单相薄膜; 2)测量不同La含量样品的铁电性, 发现当E=75 kV/cm时, La=15%的样品剩余极化值(2Pr)最大, 约为26.7 μC/cm²; 3) 在纯氧气氛下烧结有助于得到结晶性更好的单相Bi_0.75La_0.25FeO_3±δ 薄膜, 并且能够提高薄膜的铁电性.     

Distinction between critical current effects and intrinsic anomalies in the point-contact Andreev reflection spectra of unconventional superconductors

In this work,we discuss the origin of several anomalies present in the point-contact Andreev reflection spectra of(Li_(1-x)Fe_x)OHFeSe,LiTi_2O_4,and La_(2-x)Ce_xCuO_4.While these features are similar to those stemming from intrinsic superconducting properties,such as Andreev reflection,electron-boson coupling,multigap superconductivity,d-wave and p-wave pairing symmetry,they cannot be accounted for by the modified Blonder–Tinkham–Klapwijk(BTK) model,but require to consider critical current effects arising from the junction geometry.Our results point to the importance of tracking the evolution of the dips and peaks in the differential conductance as a function of the bias voltage,in order to correctly deduce the properties of the superconducting state.     

Extraordinary terahertz transmission through subwavelength spindle-like apertures in NbN film

We studied numerically the temperature dependent extraordinary terahertz transmission through niobium nitride(NbN) film perforated with subwavelength spindle-like apertures. Both the resonant frequency and intensity of extraordinary terahertz transmission peaks can be greatly modified by the transition of NbN film from the normal state to the superconducting state. An enhancement of the(±1, 0) NbN/magnesium oxide(MgO) peak intensity as high as 200% is demonstrated due to the combined contribution of both the superconducting transition and the excitation of localized surface plasmons(LSPs) around the apertures. The extraordinary terahertz transmission through spindle-like hole arrays patterned on the NbN film can pave the way for us to explore novel active tuning devices.     

Growth and transport features of electron-doped superconductor Pr1-xLaCexCuO4-δ thin films

<正>T’-phase electron-doped superconductor Pr_1-xLaCe_xCuO_4-δ（PLCCO） thin films are successfully prepared on SrTiO₃（100） substrates by using the dc magnetron sputtering method.It is found that the films each have a highly oriented structure along the c-axis.For optimally doped films with x≈0.10,the superconducting transition temperature T_c is 23.5 K,which is similar to that of a single crystal.The quadratic temperature dependence of the resistivity is observed when T > T_c,which can be attributed to the two-dimensional Fermi liquid behaviour.Besides,the optimal conditions for preparing the T’-phase PLCCO thin films are also discussed in detail.     

高质量FeSe单晶薄膜的制备及相关性能表征

在铁基超导体中,FeSe具有最简单的晶体结构和化学组成,而且其超导转变温度具有较大的调控空间,因此适合作为超导机理研究和应用的载体.高质量样品的研制是物性研究和器件应用的前提,本文系统地研究了利用激光脉冲沉积技术制备FeSe薄膜的工艺条件,在多种衬底上成功地制备出高质量的β-FeSe薄膜,并首次实现了超导临界转变温度从小于2 K到14 K的连续调控,这为FeSe超导机理研究提供了样品支持.为探究FeSe薄膜超导电性变化的起因,从β-FeSe超导电性与晶格常数c正相关出发,基于简单的费米面填充假设,第一性原理计算可以很好地解释晶格常数c的变化规律,但该假设并不能完全符合角分辨光电子能谱实验给出的电子结构演变过程.因此β-FeSe薄膜的超导电性、晶格结构和电子结构三者之间的关系还有待澄清,该问题的解决将为FeSe超导机理研究提供重要的线索,而上述系列高质量的β-FeSe薄膜样品恰好能为该问题的研究提供理想的载体.本文根据实验和已有的相关研究结果,详细介绍了FeSe薄膜的脉冲激光沉积制备及其优化,以期为后续的薄膜研究应用提供参考.