Absence of BCS–BEC crossover in FeSe_(0.45)Te_(0.55) superconductor

In iron-based superconductor Fe(Se,Te), a flat band-like feature near the Fermi level was observed around the Brillouin zone center in the superconducting state. It is under debate whether this is the evidence on the presence of the BCS–BEC[Bardeen–Cooper–Schrieffer(BCS), Bose–Einstein condensation(BEC)] crossover in the superconductor. High-resolution laser-based angle-resolved photoemission measurements are carried out on high quality single crystals of FeSe_(0.45)Te_(0.55) superconductor to address the issue. By employing different polarization geometries, we have resolved and isolated the dyz band and the topological surface band, making it possible to study their superconducting behaviors separately. The dyz band alone does not form a flat band-like feature in the superconducting state and the measured dispersion can be well described by the BCS picture. We find that the flat band-like feature is formed from the combination of the dyz band and the topological surface state band in the superconducting state. These results reveal the origin of the flat band-like feature and rule out the presence of BCS-BEC crossover in Fe(Se,Te) superconductor.

Negligible normal fluid in superconducting state of heavily overdoped Bi_(2)Sr_(2)CaCu_(2)O_(8+δ) detected by ultra-low temperature angle-resolved photoemission spectroscopy

In high temperature cuprate superconductors,it was found that the superfluid density decreases with the increase of hole doping.One natural question is whether there exists normal fluid in the superconducting state in the overdoped region.In this paper,we have carried out high-resolution ultra-low temperature laser-based angle-resolved photoemission measurements on a heavily overdoped Bi2212 sample with a T_(c) of 48 K.We find that this heavily overdoped Bi2212 remains in the strong coupling regime with 2Δ_(0)/(k_(B)T_(c))=5.8.The single-particle scattering rate is very small along the nodal direction(~5 meV) and increases as the momentum moves from the nodal to the antinodal regions.A hard superconducting gap opening is observed near the antinodal region with the spectral weight at the Fermi level fully suppressed to zero.The normal fluid is found to be negligibly small in the superconducting state of this heavily overdoped Bi2212.These results provide key information to understand the high T_(c) mechanism in the cuprate superconductors.

非等温DSC法研究TSPZ-EP环氧树脂的固化动力学

采用一锅两步法合成了一种含硅和二氮杂萘酮结构的环氧树脂(TSPZ-EP),并通过非等温差示扫描量热分析(DSC)研究了树脂在不同升温速率下的固化行为。采用n级模型和自催化(m,n)模型确定了固化反应动力学方程;选用商用双酚A环氧树脂(DGEBA)与其进行共混改性,通过外推法确定固化工艺,测试其力学性能。结果表明,n级反应模型与实验值相差较大,自催化(m,n)模型计算得到的曲线能够很好地与实验值吻合;固化工艺为100℃2h+130℃2h+160℃2h+180℃2h,并通过红外光谱测试证实了环氧固化物均已固化完全;冲击性能表明,添加TSPZ-EP后改善了环氧固化物的韧性。

高强高韧环氧树脂的制备与性能

以4-(4-羟基苯基)-2,3-二氮杂萘-1-酮(DHPZ)和环氧氯丙烷(ECH)为原料,苄基三乙基氯化铵为催化剂,设计合成了一种含有二氮杂萘酮结构的新型环氧树脂,并通过红外光谱和核磁共振氢谱证实其结构,测定其环氧值为0.30(记为ER30)。ER30在150~200℃范围内黏度为0.5 Pa·s,具有较好的加工流动性。将其与双酚A型环氧树脂(DGEBA)按照不同比例进行共混,以4-4′-二氨基二苯甲烷(DDM)为固化剂,固化后材料的力学性能较DGEBA有显著提升,当ER30与DGEBA树脂的质量比为3∶7时,冲击强度为61.24 kJ/m^2,弯曲强度为156.43 MPa,分别提升了67%和46%,实现了本征增韧与增强。

含碳硼烷耐高温环氧树脂的合成与性能

以1,2-双(4-羟基苯基)-邻碳硼烷(BHCB)为原料,一锅法合成了碳硼烷环氧树脂(DECB),选用市售环氧树脂AG80与DECB和本课题组的含杂萘联苯酮结构的四官能度环氧(TEPZ)进行复配,以DDS为固化剂制备固化产品。利用差示扫描量热分析探究了复配体系的固化反应动力学,并由此确定了固化条件;借助红外测试证实了该固化过后环氧基团反应完全。流变测试表明,少量DECB的加入能够使复配体系的加工窗口进一步拓宽,在150℃恒温条件下,复配体系黏度低于10Pa·s的时间可以维持2h,便于加工成型;动态力学热分析(DMA)表明,少量低环氧值DECB的加入对玻璃化转变变温T_(g)影响不大,保持在278℃以上;热失重分析(TGA)表明,少量DECB的加入即可明显提升800℃的残碳率;力学性能测试结果显示,大体积碳硼烷结构的加入可以增加固化交联网络结构的刚性,复配体系的弯曲强度最高至142.3MPa。

大环化合物的合成及对环氧树脂的增韧改性

以4,4’-二氟-二苯砜、双酚芴和双酚A为原料,碳酸钾为催化剂,通过"假高稀"条件设计合成了大环化合物MCO-1和MCO-2。通过高分辨质谱、核磁共振氢谱和红外光谱证实其结构。MCO-1和MCO-2在多种有机溶剂中具有良好的溶解性能。将2种大环化合物与E44型环氧树脂以4,4’-二氨基-二苯砜(DDS)为固化剂进行共混固化。改性后的环氧树脂体系耐热性和力学性能提升,2种改性树脂的5%热失重温度为405℃,比E44提升4%;E44/MCO-1体系的冲击强度和弯曲强度分别提升了62.6%和18.8%;E44/MCO-2体系的冲击强度和弯曲强度则提升了22.8%和6.7%。提供了利用大环化合物增韧环氧树脂的思路。

Application Progress of Headspace Gas Chromatography in Analytical Chemistry

This paper briefly expounds the basic principle and classification of headspace gas chromatography,summarizes its application in food analysis,environmental analysis and medical analysis,and forecasts the application prospect of headspace gas chromatography in analytical chemistry in the future.

Conservation of the particle–hole symmetry in the pseudogap state in optimally-doped Bi_(2)Sr_(2)CuO_(6+δ) superconductor

The pseudogap state is one of the most enigmatic characteristics in the anomalous normal state properties of the high temperature cuprate superconductors. A central issue is to reveal whether there is a symmetry breaking and which symmetries are broken across the pseudogap transition. By performing high resolution laser-based angle-resolved photoemission measurements on the optimally-doped Bi_(2)Sr_(1.6)La_(0.4)CuO_(6+δ) superconductor, we report the observations of the particle-hole symmetry conservation in both the superconducting state and the pseudogap state along the entire Fermi surface. These results provide key insights in understanding the nature of the pseudogap and its relation with high temperature superconductivity.

Evidence for bosonic mode coupling in electron dynamics of LiFeAs superconductor

Super-high resolution laser-based angle-resolved photoemission measurements are carried out on LiFeAs superconductor to investigate its electron dynamics. Three energy scales at ~ 20 meV, ~ 34 meV, and ~ 55 meV are revealed for the first time in the electron self-energy both in the superconducting state and normal state. The ~ 20 meV and ~ 34 meV scales can be attributed to the coupling of electrons with sharp bosonic modes which are most likely phonons. These observations provide definitive evidence on the existence of mode coupling in iron-based superconductors.

Determination of Copper and Lead Contents in Soil of the Yellow River Wetland in Shaanxi Province by Flame Atomic Absorption Spectrometry

[Objectives] The contents of copper and lead in the soil of the Yellow River Wetland were determined by flame atomic absorption spectrometry, which provides a theoretical basis for the treatment of soil pollution. [Methods] The soil was digested with a concentrated nitric acid-hydrofluoric acid-perchloric acid system, and the contents of heavy metals such as copper and lead in the Yellow River Wetland of Shaanxi Province were determined by flame atomic absorption spectrometry. [Results] The correlation coefficients reached 0.999 5 in the range of 0.00-1.00 mg/L, indicating good linearity. [Conclusions] The method is simple in operation, good in reproducibility, high in sensitivity to most elements, and can be widely used.

Storage Stability of Imidacloprid Residues in Different Matrixes of Lycium barbarum

The storage stability and degradation trends of imidacloprid residues in different matrix of Lycium barbarum were investigated by directly adding 0.1 mg/kg imidacloprid, frozen storage and phase detection. The results showed that under frozen condition, the storage stability of imidacloprid residues remained good for half a year in dry fruit, and a year in fresh fruit of L. barbarum . There was no significant change of imidacloprid residues between different processing of dry fruit and fresh fruit, and sample processing methods （crushing or homogenizing） had no significant effect on the degradation trends of imidacloprid. Therefore, the samples could be processed into crushed samples or homogenized samples for storage as soon as possible according to the needs, and the dry fruit should be detected within half a year, while the fresh fruit should be detected within a year.

Emergence of superconductivity from fully incoherent normal state in an iron-based superconductor (Ba_(0.6)K_(0.4))Fe_2As_2

In unconventional superconductors, it is generally believed that understanding the physical properties of the normal state is a pre-requisite for understanding the superconductivity mechanism. In conventional superconductors like niobium or lead, the normal state is a Fermi liquid with a well-defined Fermi surface and well-defined quasipartcles along the Fermi surface. Superconductivity is realized in this case by the Fermi surface instability in the superconducting state and the formation and condensation of the electron pairs(Cooper pairing). The high temperature cuprate superconductors, on the other hand, represent another extreme case that superconductivity can be realized in the underdoped region where there is neither well-defined Fermi surface due to the pseudogap formation nor quasiparticles near the antinodal regions in the normal state. Here we report a novel scenario that superconductivity is realized in a system with well-defined Fermi surface but without quasiparticles along the Fermi surface in the normal state.High resolution laser-based angle-resolved photoemission measurements have been performed on an optimally-doped iron-based superconductor(Ba_(0.6)K_(0.4))Fe_2As_2. We find that, while sharp superconducting coherence peaks emerge in the superconducting state on the hole-like Fermi surface sheets, no quasiparticle peak is present in the normal state. Its electronic behaviours deviate strongly from a Fermi liquid system. The superconducting gap of such a system exhibits an unusual temperature dependence that it is nearly a constant in the superconducting state and abruptly closes at Tc. These observations have provided a new platform to study unconventional superconductivity in a non-Fermi liquid system.

Temperature-induced Lifshitz transition in topological insulator candidate HfTe_5

The ongoing discoveries and studies of novel topological quantum materials have become an emergent and important field of condensed matter physics. Recently, Hfres ignited renewed interest as a candidate of a novel topological material. The single-layer Hffes is predicted to be a tWOldimensional large band gap topological insulator and can be stacked into a bulk that may host a temperatureldriven topological phase transition. Historically, Hfres attracted considerable interest for its anomalous transport properties characterized by a peculiar resistivity peak accompanied by a sign reversal carrier type. The origin of the transport anomaly remains under a hot debate. Here we report the first high-resolution laserlbased anglelresolved photoemission measurements on the temperature-dependent electronic structure in Hffes. Our results indicated that a temperature-induced Lifshitz transition occurs in Hffes, which provides a natural understanding on the origin of the transport anomaly in Hffe~. In addition, our observa- tions suggest that Hffes is a weak topological insulator that is located at the phase boundary between weak and strong topological insulators at very low temperature.

The effect of oxygen on the epitaxial growth of diamond

We studied the effect of oxygen on the growth quality of diamond epitaxial layers. After oxygen is added during the growth of the diamond epitaxial layer, as the thickness of the epitaxial layer increases, the full width at half maximum of the rocking curve of the(004) plane of diamond epitaxial layer increases continuously, and, in addition, the intensities of both the Raman peaks and the free exciton emission peaks of the diamond epitaxial layer decrease continuously. These experimental results demonstrate that as the thickness of the diamond epitaxial layer increases, the quality of the diamond epitaxial layer degrades. The strong etching effect of the OH radical groups in the plasma on the diamond epilayers leads to the degradation of their crystallinity.

Methyl Group in Isocopalane Derivative Showed an Unusual Negative 1H NMR Chemical Shift

An unusual negative 1H NMR chemical shift of methyl group was discovered in condensation product of isoco-palane diterpenoid with p-toluenesulfonyl hydrazide.2D NMR,computational studies and single-crystal X-ray dif-fraction analysis showed that the C-20 methyl group was shielded.

Genuine electronic structure and superconducting gap structure in (Ba_(0.6)K_(0.4)Fe_(2)As_(2)FeAs superconductor

The electronic structure and superconducting gap structure are prerequisites to establish microscopic theories in understanding the superconductivity mechanism of iron-based superconductors.However,even for the most extensively studied optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2),there remain outstanding controversies on its electronic structure and superconducting gap structure.Here we resolve these issues by carrying out high-resolution angle-resolved photoemission spectroscopy(ARPES)measurements on the optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2)superconductor using both Helium lamp and laser light sources.Our results indicate the‘‘flat band"feature observed around the Brillouin zone center in the superconducting state originates from the combined effect of the superconductivity-induced band back-bending and the folding of a band from the zone corner to the center.We found direct evidence of the band folding between the zone corner and the center in both the normal and superconducting state.Our resolution of the origin of the flat band makes it possible to assign the three hole-like bands around the zone center and determine their superconducting gap correctly.Around the zone corner,we observe a tiny electronlike band and an M-shaped band simultaneously in both the normal and superconducting states.The obtained gap size for the bands around the zone corner(~5.5 meV)is significantly smaller than all the previous ARPES measurements.Our results establish a new superconducting gap structure around the zone corner and resolve a number of prominent controversies concerning the electronic structure and superconducting gap structure in the optimally-doped Ba_(0.6)K_(0.4)Fe_(2)As_(2).They provide new insights in examining and establishing theories in understanding superconductivity mechanism in iron-based superconductors.