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1.
We report a direct microwave synthesis method for the preparation of 11-type high quality Fe(Te,Se) polycrystalline superconductors. The bulk samples are rapidly synthesized under the microwave irradiation during several minutes, with a subsequent annealing process at 400℃. The samples exhibit a nearly single phase of the tetragonal PbO-type crystal structure with minor impurities. Morphology characterization shows high density, tight grain connectivity and large grain sizes around 100 μm with small cavities inside the sample. Resistivity and magnetization measurements both show similar superconducting transitions above 14 K. The magnetic hysteresis measurements display broad and symmetric loops without magnetic background, and a high critical current density J_c about 1.2 × 10~4 A/cm~2 at 2 K and 7 T is estimated by the Bean model. Compared with the solidstate reaction synthesized samples, these superconducting bulks from microwave-assisted synthesis are possibly free of the interstitial Fe due to smaller c-axis, higher T_c in magnetic transitions, better M–H loops without magnetic background and greatly enhanced J_c, and are promising as raw materials for the non-toxic Fe-based superconducting wires for large currents and high field applications.  相似文献   
2.
本文通过对不同晶体结构Re_3W样品的点接触测量和对比研究,证实具有中心对称结构和非中心对称结构的Re_3W都是弱耦合Bardeen-Cooper-Schrieffer超导体,同时发现在两个相表面都可以形成很理想的点接触结,即电子通过界面时受到的非弹性散射很弱.将Re_3W样品置于大气环境近六个月后重新进行测量,仍然能够得到类似的结果,表明Re_3W具有很好的稳定性. Re_3W的这种优良特性,不仅可通过点接触实验得到的参数推算出Re_3W两个相的费米速度,而且提供了一种简单的方法,可以在点接触实验中利用Re_3W来印证针尖材料的费米速度和测量其自旋极化率等.作为尝试,本文用Re_3W/Ni点接触结测量了铁磁性金属Ni的自旋极化率,得到了与前人报道一致的结果.  相似文献   
3.
We report the magnetoresistance(MR), de Haas-van Alphen(dHvA) effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field, a metal-to-insulator-like transition in ρ(T) and a nonsaturating MR are observed at low temperatures. The dHvA oscillations reveal a small Fermi-surface pocket with a nontrivial Berry phase. The analysis of the nonlinear Hall resistivity shows that TiSi is a multiband system with low carrier densities and high mobilities. All these results unambiguously prove the existence of Dirac fermions in TiSi.  相似文献   
4.
<正>在一根金属线两端加上电压,电子就会在电场的驱动下做定向移动,从而产生电流。由于电子在移动过程中受到晶格原子的不断散射因而改变运动方向,这会对其流动产生阻碍,这就是电阻,它被定义为所施加电压和电流的比值。早在19世纪人们就发现一个规律,金属的电阻会随着温度的不断下降而减小。那么当温度趋近于绝对零度时,电阻会呈现什么状态?在1911年,荷兰物理学家昂内斯  相似文献   
5.
We report the synthesis, crystal structure, and superconductivity of Ti4Ir2O. The title compound crystallizes in an η-carbide type structure of the space group Fd3m(No. 227), with lattice parameters a=b=c=11.6194(1) ?. The superconducting temperature Tc is found to be 5.1–5.7 K. Most surprisingly, Ti4Ir2O hosts an upper critical field of 16.45 T, which is far beyond the Pauli paramagnetic limit. Strong coupled superconductivity with evidence...  相似文献   
6.
The newly discovered superconductor MgB2 has a transition temperature Tc of about 40 K, which is touching the upper line of that predicted by the phonon-mediated Bardeen--Cooper--Schrieffer (BCS) theory. It is interesting to investigate the flux creep in MgB2 and compare it with other superconductors. We have measured the magnetization relaxation of MgB2 sintered at high temperature and high pressure. It is found that the quantum tunnelling and the thermally activated flux creep are very weak, implying a strong pinning in this material.  相似文献   
7.
通过对系列(La1-xSmx)0.185Sr0.15CuO4(x=0,0.05,0.10,0.15)的多晶样品在4.2K-300K的电阻率和液氮温区内的热电势的测量,发现(La1-xSmx)0.185Sr0.15CuO4的电阻率在高温区呈现出线性关系,其斜率也随着x的增大而增大,在x=0.10时达到最大,而在Tc到100K的温区,随着Sm含量的增加,则呈现出由金属行为到类半导体行为的转变,同时超导温度Tc也随着降低,液氮温区内的温差热电势反映了随着Sm含量的增加,体系的载流子浓度也随之降低。  相似文献   
8.
We report a systematic study on magnetotransport properties of the single crystal of cadmium(Cd). When the applied magnetic field B is perpendicular to the current I, the resistivities for both directions(I ‖ a, I ‖ c) show field induced metal-to-insulator-like transitions. The isothermal magnetoresistance(MR) at low temperatures increases approximately as the square of the magnetic field without any sign of saturation, and reaches up to 1140000% and 58000% at T = 2 K and B = 9 T for I ‖ a and I ‖ c, respectively. As the magnetic field rotates to parallel to the current, no sign of negative MR is observed for I ‖ a, while an obvious negative MR appears up to-70% at 2 K and 9 T for the current flowing along the c-axis, and the negative longitudinal MR shows a strong dependence of the electrode position on the single crystal. These results suggest that the negative longitudinal MR is caused by the dislocations formed in the process of crystal growing along the c-axis. Further studies are needed to clarify this point.  相似文献   
9.
Hao OuYang 《中国物理 B》2021,30(12):127101-127101
We report the transport properties of a topological insulator candidate, LiMgBi. The electric resistivity of the title compound exhibits a metal-to-semiconductor-like transition at around 160 K and tends to saturation below 50 K. At low temperatures, the magnetoresistance is up to ~260% at 9 T and a clear weak antilocalization effect is observed in the low magnetic-field region. The Hall measurement reveals that LiMgBi is a multiband system, where hole-type carriers (nh~1018 cm-3) play a major role in the transport process. Remarkably, LiMgBi possess a large Seebeck coefficient (~440 μV/K) and a moderate thermal conductivity at room temperature, which indicate that LiMgBi is a promising candidate in thermoelectric applications.  相似文献   
10.
于佳  刘通  赵康  潘伯津  穆青隔  阮彬彬  任治安 《物理学报》2018,67(20):207403-207403
铁基超导体中含有一类特殊的112型结构化合物,其层状结构中含有一层锯齿形的As链构型.本文报道了用CsCl助熔剂法生长新型铁基112型EuFeAs2母体单晶的具体方法,以及对该单晶的结构和物性的详细表征.通过能量色散X射线能谱扫描对单晶样品进行的化学成分分析,以及单晶X射线衍射的结构解析,确定该单晶样品属于EuFeAs2相,结构精修得到EuFeAs2具有空间群为Imm2(No.44)的正交晶体结构,晶格常数分别是a=21.285(9)Å,b=3.9082(10)Å,c=3.9752(9)Å.通过低温电阻测量,发现在110 K附近和46 K附近存在两个异常电阻跳变.进一步分析表明,110 K附近存在两个邻近的相变,这两个相变与铁基母体材料中常见的结构相变和Fe2+的反铁磁相变相符合.结合磁化率测量分析,可知46 K附近的相变属于Eu2+的反铁磁相变.  相似文献   
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