High quality PdTe_2 thin films grown by molecular beam epitaxy

PdTe_2,a member of layered transition metal dichalcogenides(TMDs),has aroused significant research interest due to the coexistence of superconductivity and type-II Dirac fermions.It provides a promising platform to explore the interplay between superconducting quasiparticles and Dirac fermions.Moreover,PdTe_2 has also been used as a substrate for monolayer antimonene growth.Here in this paper,we report the epitaxial growth of high quality PdTe_2 films on bilayer graphene/SiC(0001)by molecular beam epitaxy(MBE).Atomically thin films are characterized by scanning tunneling microscopy(STM),X-ray photoemission spectroscopy(XPS),low-energy electron diffraction(LEED),and Raman spectroscopy.The band structure of 6-layer PdTe_2 film is measured by angle-resolved photoemission spectroscopy(ARPES).Moreover,our air exposure experiments show excellent chemical stability of epitaxial PdTe_2 film.High-quality PdTe_2 films provide opportunities to build antimonene/PdTe_2 heterostructure in ultrahigh vacuum for future applications in electronic and optoelectronic nanodevices.     

新型铁基超导体角分辨光电子能谱研究

最近发现的新型122结构的铁基超导体掀起了铁基高温超导研究的又一轮热潮.文章利用角分辨光电子能谱实验手段,研究了这类新型铁基材料的电子结构、费米面拓扑和超导能隙.实验结果表明,其在布里渊区中心的能带结构及费米面与其他铁基超导体存在明显差异,并导致嵌套在粒子-空穴通道的费米面消失.另外,在布里渊区边缘的电子型费米面发现了较强的并且有各向同性的超导能隙.这些结果对可能的超导配对机制提出了严格的限制.     

Coexistence of Polaronic States and Superconductivity in Iron-Pnictide Compound Ba_2Ti_2Fe_2As_4O

The electronic structure of iron-pnictide compound superconductor Ba_2Ti_2Fe_2As_4O, which has metallic intermediate Ti_2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a‘peak-dip-hump' line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below T_c(~21 K). Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.     

Bi0:9-xGdxLa0:1FeO3的磁性

详细地研究了Bi0:9-xGdxLa0:1FeO3 (x=0.3,0.5,0.6和0.7)的磁化强度(M)和矫顽场随温度(T)的变化． 实验发现， 在一定温度范围内，M-T曲线上出现异常的负磁矩； 矫顽场与温度的关系不是单调变化的， 而是在温度补偿点到最大值． 这些结果表明Bi0:9-xGdxLa0:1FeO3体系中Gd和Fe磁晶格呈反铁磁耦合．但由于Gd离子和Fe离子的磁矩不相等，导致该体系中存在亚铁磁性．     

Al和Sn离子掺杂对La1.2Ca1.8Mn2O7输运性质的影响

研究了Al和Sn离子掺杂对层状钙钛矿结构锰氧化物La1.2Ca1.8Mn2O7输运性质的影响.发现Al,Sn掺杂后样品电阻率增加,并且半导体导电区域电阻值与可变程跃迁导电模型符合得较好;同时掺杂样品金属-绝缘转变温度逐步降低,最大磁电阻值比未掺杂样品增大.     

La0.9Na0.1MnO3的反常超声特性

系统地测量了La0.9Na0.1MnO3单相陶瓷样品的电阻、磁化率、超声声 速和衰减随温度的变化关系，发现在245K附近体系发生顺磁绝缘体－铁磁金属相变，同时超声声速出现剧烈的软化现象，其相对变化超过2％。超声衰减也出现一个尖锐的衰减峰。经分析认为这些发生在Curie温度附近的反常超声现象，可能是由自旋－声子和电－声子相互作用共同引起的。     

RUSr2EU1.4Ce0.6Cu2O10-δ超导体的磁特性研究

RuSr2Eu1.4Ce0.6Cu2O10-δ超导样品的交流磁化率曲线在TM2～125 K和Tp～75 K处出现峰值.我们通过测量不同频率下的交流磁化率和电子自旋共振谱,对这两个峰的起源进行了详细的研究.通过对铁磁共振线的强度、线宽和共振场与温度依赖关系的讨论,我们得出TM2附近的峰对应着体系的反铁磁转变.Tp处的峰随着测量频率的增加向高温移动,且峰的强度逐渐减小,这一结果证实了体系中存在自旋玻璃态.     

过渡金属离子掺杂对La1.2Ca1.8Mn2O7输运性质的影响

研究了过渡金属元素掺杂对层状钙钛矿结构锰氧化物La1.2Ca1.8Mn2O7体系输运性质的影响.实验结果表明不同过渡金属离子掺杂均导致体系的金属-绝缘转变温度降低,电阻率与最大磁电阻值(Cr除外)增加.当掺杂量较高时,磁性Cr、Fe、Co、Ni离子对体系性质的影响与其磁性相互作用密切相关.     

Fe1+yTexSe1-x:A Delicate and Tunable Majorana Material

We report the observation for the pz electron band and the band inversion in Fe_1+yTe_xSe_1-x with angleresolved photoemission spectroscopy. Furthermore, we found that excess Fe(y>0) inhibits the topological band inversion in Fe_1+yTe_xSe_1-x,which explains the absence of Majorana zero modes in previous reports for Fe_1+yTe_xSe_1-x with excess Fe. Based on our analysis of different amounts of Te doping a...     

Electronic Structure of the Weak Topological Insulator Candidate Zintl Ba3Cd2Sb4

One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology.The existence of topological protected dissipationless surface state makes topological insulators great potential for applications and hotly studied.However,compared with the prosperity of strong topological insulators,theoretical predicted candidate materials and experimental confirmation of weak topological insulators(WTIs) are both extremely rare.By com...