准粒子注入下超导膜能隙变化的一些计算

利用 Schn-Tremblay 理论计算了 Pb、Sn 超导薄膜在注入准粒子且注入电压很小(ev<2△(?))时的能隙微小增加的效应.同时,把此理论扩展到 ev>>2△_i 的大电压情况,计算出能隙明显减小及超导-正常混合态的结果.     

常压和高压合成MgB2的低温比热及两个超导能隙研究

测量了常压和高压合成MgB2超导样品6K—80K的比热,并在数据拟合中考虑了爱因斯坦振动模的贡献,得到其电子比热数据.解释了超声测量得到的德拜温度和低温比热拟合结果之间的巨大差异.并且在12K附近观察到了异常的电子比热,此异常来源于MgB2的第二个能隙.此外,对高压和常压合成对样品的影响做了初步分析. 关键词： 低温比热 MgB2 能隙     

MgB2超导体中的双能隙

MgB2的超导机制不同于传统的金属超导体.最近,来自美国加州大学(Berkeley)的Choi等采用从头计算的理论方法,研究了MgB2的超导能隙,即电荷载流子配对的形成能.研究结果表明,MgB2是一个双能隙超导体.在此基础上,一些可测量物理参数的理论结果被给出,从而解释了MgB2反常的超导特性,这包括:高的超导转变温度Tc,比热对温度的依赖关系,以及角分辨光发射谱和隧穿实验所给出的多能隙证据(小能隙Δ≈1.5-3.5meV,大能隙Δ≈5.5-8meV).MgB2晶体由B原子层和Mg原子层交替堆叠而成,具有六方对称性.B层的结构类似于石墨片,呈峰窝状;从M…     

双能隙超导体MgB2的热导

测量了多晶MgB2的热导，实验温区为5—300K.在双能隙模型下，用基于BCS超导理论的BRT热导理论对实验结果进行了分析，给出MgB2中两个能隙大小分别为16和51meV.对电子热导的分析结果表明σ能带准粒子受到的杂质散射远小于π能带准粒子受到的杂质散射.与单晶MgB2的热导实验结果相比，多晶MgB2的声子热导结果表明在c方向上热传导声子受到来自σ能带准粒子的散射，显示了MgB2在能量输运上的各向异性. 关键词： MgB2 热导率 能隙     

电子型超导体Sm1.85Ce0.15CuO4单晶的赝能隙行为研究

测量了在O2中退火不同时间的Sm1.85Ce0.15CuO4单晶样品的热电势S与电阻率ρ的温度依赖关系.所有的样品电阻率高温下呈现线性温度依赖行为.未退火的样品在148K发生超导转变,而退火后的样品在低温下发生金属半导体相变,其超导电性消失,表明退火引起了载流子浓度下降,体系进入欠掺杂态.随着温度降低,所有的样品ST和ρT曲线在200K附近(T)都发生斜率的改变,可以用赝能隙现象解释.热电势S在低温下出现一个正的曳引峰,意味着载流子符号发生改变,由电子型转变为空穴型 关键词： 电子型超导体 热电势 赝能隙     

新型超导体MgB2和MgCNi3热、电输运性质研究

报道了两种新型超导体MgB₂,MgCNi₃和氧化物高温超导体Bi_{2< /sub>Sr2Ca0.9Ce0.1Cu2O8+y 的热导率-温度关系和电阻率-温度关系.实验发现氧化物高温超导 体在进入超导态后热导有所上升，出现极大值后再下降，而MgB2和MgCNi3 则单调下降. 由Wiedemann-Fra 关键词： 热导率 超导体 2}')" href="#">MgB₂ 3')" href="#">MgCNi₃     

利用三阶微商吸收光谱确定C60分子能隙

利用三阶微商吸收光谱观测到可见区C₆₀分子电子光谱中丰富的振动光谱结构.通过对此类电子-振动跃迁的指认分析，给出了C₆₀分子部分振动模频率，确定了C₆₀分子能隙. 关键词：     

拉伸形变下BC3纳米管的能带结构

运用紧束缚能带理论,研究拉伸形变下BC₃纳米管的能带结构. 研究表明:随着拉伸和压缩强度的不断增加,BC₃纳米管的导带能级和价带能级逐渐靠近,最终发生能带交叠. 压缩形变下能带的交叠程度可达05 eV,而拉伸形变下只有02 eV. 对于扶手椅型BC₃纳米管,随着拉伸和压缩的不断增加,BC₃纳米管首先由直接半导体转化为间接半导体,进而发生能带的交叠,表现出金属性. 在无形变时,扶手椅型BC₃纳米 关键词： 3纳米管')" href="#">BC₃纳米管 能隙 拉伸形变 半导体     

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.     

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.     

Hybridization gap-open in CeIn3

Reflectivity spectra of CeIn₃ are measured at 7, 30, 50, 100, 150, 200 and 300 K in wild energy regions from 6 meV to 30 eV. Optical conductivity spectra are obtained from a Kramers–Kronig’ relation. A hump in the optical conductivity σ₁ is observed at about 500 cm⁻¹ below 100 K, resulting from strong hybridization between conduction electrons and Ce 4f electronic states. The low frequency plasmon indicating the existence of heavy particles is also observed below coherence temperature T^*  100 K.     

Transport in the heavy-fermion superconductor UPt3

We report new theoretical results and analysis for the transport properties of superconducting UPt₃ based on the leading models for the pairing symmetry. We use Fermi surface data and the measured inelastic scattering rate to show that the low-temperature thermal conductivity and transverse sound attenuation in the A- and B-phase of UPt₃ are in excellent agreement with pairing states belonging to the two-dimensional orbital E_2u representation.     

Nonlinear conductivity of quasi-one-dimensional layered compound TiS3

The crystal structure and transport properties of TiS₃ whiskers in the plane of layers (ab) have been studied. Maxima of the logarithmic derivative of resistance, dln R/d(1/T), are observed at 17, 60 and 120 K both along and across the chains. Strong nonlinearity of the current–voltage characteristics has been revealed in both directions. Nonlinear conductivity along the chains is observed up to T=60 K, while in the transverse direction it is observed up to T=130 K. The results indicate possible phase transitions of electrons to collective states, probably, charge density waves.     

Superconducting energy gap in MgCNi3 single crystals

Even though MgCNi₃ contains large molar volume of magnetic Ni atoms it clearly shows superconductivity. The origin of superconductivity in this material has not yet been clarified. There is a lot of discrepancy in experimental results and physical interpretation where even unconventional pairing or a two-band model have been proposed for the system. All that is based on results obtained on polycrystalline samples. Here we present the first point-contact spectroscopy and ac-calorimetry measurements on the MgCNi₃ single crystals of very good quality. Measurements have been performed in the temperature range from 1.5 to 10 K and in magnetic fields up to 8 T. The temperature dependence of the energy gap of the system is presented and compared to the BCS model.     

Electronic properties of Th3As4U3As4 solid solutions

(Th_xU_1?x)₃As₄ solid solutions were obtained in the range 1 ≥ x ≥ 0.85 by the modified Van Arkel method. Their resistivity, thermopower and Hall constant were determined in temperatures 4.2—700 K. The condition of impurity band formation, its merging with conduction band, as well as location of the 5?-electron states have been discussed.     

Ca0.5Sr0.5TiO3弹性和热学性质的第一性原理研究

利用能量最小原理, 确定了Ca_0.5Sr_0.5TiO₃晶体中4c位置的Ca/Sr原子对称分布, 建立了Ca_0.5Sr_0.5TiO₃稳定的晶体结构, 在此基础上利用基于密度泛函理论第一性原理的平面波超软赝势方法, 采用局域密度近似和广义梯度近似函数, 计算了Ca_0.5Sr_0.5TiO₃的晶格参数、弹性常数、体弹模量、剪切模量、杨氏模量、泊松比, 并基于Christoffel方程的本征值研究了平面声波的特征, 基于Cahill和Cahill-Pohl模型研究了最小热导率的特征. 计算结果表明: Ca_0.5Sr_0.5TiO₃晶格参数和实验值很接近, 体弹模量大于剪切模量, [100], [010], [001]晶向的杨氏模量、泊松比、普适弹性常数(A^U)以及杨氏模量三维图均显示了弹性各向异性; 平面声波在(010), (001)平面呈现各向异性, 在(100)平面呈现各向同性, 平面声波大小与平均横波和平均纵波的数值很接近. Cahill模型最小热导率在各平面呈现各向同性, Cahill-Pohl模型最小热导率在高温时趋于恒定. 准谐德拜模型下Ca_0.5Sr_0.5TiO₃ 晶体的摩尔热容和热膨胀系数与CaTiO₃晶体的接近, 并且高温下具有稳定的热膨胀性能. 计算所得禁带宽度为2.19 eV, 导带底主要是Ti-3d与O-2p态电子贡献; 由电荷布居和电荷密度图理论证实Ca_0.5Sr_0.5TiO₃具有稳定的Ti-O八面体结构.     

Optical band-gap of Zn3As2

Absorption measurements of single Zn₃As₂ crystals were made at temperatures 5, 80 and 300 K. Free-carrier absorption is interpreted in the simple classical model. Interband absorption shows contributions from Urbach-like excitations. The direct optical gap has been estimated as 0.99 eV at 300 K, 1.09 eV at 80 K and 1.11 eV at 5 K. The linear dependence of band-gap on temperature was found in the range 80–300 K with dE_g/dT = ? 4.55 × 10^?4eVK^?1.     

Thermoreflectance spectra of Cd3As2

The near normal incidence thermoreflectance spectra of Cd₃As₂ have been investigated at room temperature and liquid nitrogen temperature in the spectral range 2.5–6.2 eV.