铁磁-绝缘层-d波超导结中的Andreev反射特性

考虑到铁磁层中的磁交换作用和界面散射效应,利用推广的Blonder-Tinkham-Klapwijk散射理论,计算铁磁-绝缘层-d波超导结中的准粒子输运系数与隧道谱.研究表明：铁磁层中的交换场能抑制Andreev反射,使得依赖于准粒子入射角的Andreev反射表现出瞬息波的行为,呈现一些新的隧道谱特征. 关键词： Andreev反射 d波超导 隧道谱     

正常金属/超导/正常金属双垒隧道结中的量子相干输运

考虑到量子相干效应和界面散射效应 ,利用 L ambert理论模型 ,计算正常金属 /绝缘层 /超导 /绝缘层 /正常金属双垒隧道结中的准粒子输运系数和隧道谱。研究表明 :( 1)所有的准粒子输运系数和电导谱在超导能隙之上都随能量作周期性振荡 ,其振荡周期依赖于超导层的厚度 ;( 2 )在超导能隙之上 Andreev反射系数随能量呈现周期性消失现象 ;( 3)在绝缘层势垒强度取很大的隧道极限下 ,超导层中会形成一系列的准粒子束缚态 ,其位置由量子化条件决定 ;( 4)界面散射效应不仅能压低各子能隙电导峰 ,还能使子能隙电导峰劈裂为两个峰。     

d波超导体NIS结中的时间反演对称态的破缺与准粒子寿命效应

考虑到d波超导表面时间反演对称态的破缺与准粒子的有限寿命效应,在BlonderTinkhamKlapwijk(BTK)理论框架下,通过求解BogoliubovdeGennes(BdG)方程,计算正常金属d波超导隧道结中的准粒子输运系数与隧道谱.研究表明:1)d波超导表面时间反演对称态的破缺会导致零偏压电导峰位移,位移的程度取决于分解d波超导表面时间反演对称态中s波分量的强度;2)准粒子的寿命效应与粗糙界面散射效应都能压低零偏压电导峰,其中粗糙界面散射还会阻碍零偏压电导峰的位移.这些结果能较好地解释Tc氧化 关键词：     

正常金属-铁磁绝缘层-d波超导结中的磁散射对量子输运的影响

在正常金属-铁磁绝缘层-d波超导隧道结中,考虑到铁磁绝缘层的粗糙界面散射和磁散射效应,运用Bogoliubov-de Gennes(BdG)方程和Blonder-Tinkham-klapwijk(BTk)理论模型,计算隧道结中的准粒子传输系数和微分电导.计算表明：1)粗糙界面散射和磁散射都能压低零偏压电导峰,其中磁散射能使零偏压峰滑移,而粗糙界面却能阻止零偏压峰的滑移,且随着两种散射强度的逐渐增大,又能使零偏压电导峰渐渐变为凹陷;(2)当铁磁层离开超导表面有若干相干长度时,隧道谱中将呈现一些子能隙谐振峰. 关键词：     

铁磁-d波超导结中的自旋极化隧道谱

考虑到铁磁层中准粒子输运的自旋极化效应以及 d波超导表面时间反演对称态的破缺效应 ,在 Blonder-Tinkham-Klapwijk散射理论框架下 ,研究铁磁 -d波超导隧道结中的隧道谱 ,所得结果能展示一些新奇特征 ,并能解释一些实验现象     

0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3压电薄膜的摩擦、磨损性能

具有准同型相界组分的0.5Ba(Ti_0.8Zr_0.2)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (BZT-0.5BCT)陶瓷, 表现出优异的铁电、压电性能, 作为一种具有潜在应用前景的无铅压电材料得到广泛关注. 本文采用溶胶-凝胶方法在Si(100)基底上制备了BZT-0.5BCT压电薄膜. 使用原子力显微镜和扫描电子显微镜测量得到样品的形貌图, 形貌图表明该方法制备的无铅压电薄膜表面光滑, 晶粒大小均匀、呈半球形, 直径为80–100 nm, 厚度为1.7 μm, 膜的内部有气孔.摩擦力实验表明, 压电薄膜样品与硅针尖之间存在静电力的作用, 导致其摩擦力远大于硅针尖与SiO₂之间的摩擦力, 但是两者的摩擦系数基本相同.划痕实验表明, BZT-0.5BC薄膜具有很强的法向承载能力, 但是切向抗磨损能力差, 样品的平均弹性模量为23.64 GPa± 5 GPa, 其硬度为2.7–4 GPa, 两者均略低于压电陶瓷Pb(Zr, Ti)O₃材料的体态值. 关键词： BZT-BCT薄膜 纳米摩擦力 纳米压痕 纳米划痕     

量子线/铁基超导隧道结中隧道谱的研究

考虑铁基超导中能带间的相互作用和界面对每一个能带的散射作用, 利用推广的Blonder-Tinkham-Klapwijk模型, 并通过求解Bogoliubov-de Gennes 方程研究了具有不同类型双能隙系统的量子线/铁基超导隧道结中准粒子的输运系数和隧道谱. 研究表明: 1)在弹道极限时, 随着带间相互作用的增大, s_± 波隧道谱中零偏压附近的平台演变成电导峰; s₊₊ 波的平台演变成凹陷; p波的零偏压电导峰被压低. 2)界面对两个能带的散射作用不为零时, 随着带间相互作用的增大, s_± 波和s₊₊ 波两能隙处的峰值将降低, 而两峰间的凹陷值将变大; p波的零偏压电导峰被压低, 非零偏压电导增大. 3)界面对每个能带的散射, 可使其产生的电导峰变得更加尖锐, 但可压低和抹平另一个带产生的电导峰值. 这些结果对于澄清铁基超导体的能隙结构和区别不同类型铁基超导体有所帮助.     

d(x2-y2)+idxy混合波正常金属/绝缘层/超导体结中的隧道谱

考虑界面粗糙散射,在Blonder-Tinkham-Klapwijk(BTK)理论框架下,通过求解Bogoliubov-de-Gennes(BdG)方程,分别计算T=0K和有限温度下,d_(x²-y²)+id_xy混合波正常金属绝缘层超导体结中的准粒子输运系数和隧道谱.研究表明:隧道谱中的电导峰的劈裂程度强烈地依赖于d_xy波分量的强度、超导体的晶轴方位和界面粗糙强度,而温度的升高能压低电导峰. 关键词： NIS结 (x²-y²)+id_xy混合波超导体')" href="#">d_(x²-y²)+id_xy混合波超导体 隧道谱     

YBa2Cu3O7-δ外延膜中的非线性光响应

实验结果表明，在连续波He-Ne激光(λ=0.63μm)照射下，YBa₂Cu₃O_7-δ(YBCO)外延膜在超导转变温度T_c以下附近温区的光响应行为，表现为辐射热效应和非辐射热效应同时存在，尤其当样品的R-T变化率dR/dT→0温区明显地表现为一种非平衡光响应行为，且随电流的变化呈非线性关系.基于上述实验事实，在光致准粒子激发假设下，对T_c附近YBCO薄膜中的非线性光响应机制进行了讨论；给出了光辐射 关键词：     

正常金属-铁磁绝缘层-dx2-y2+idxy混合波超导结中的磁散射对隧道谱的影响

在正常金属铁磁绝缘层dx2-y2 idxy混合波超导隧道结中,考虑到铁磁绝缘层的磁散射和界面的粗糙散射效应,运用BogoliubovdeGennes(BdG)方程和BlonderTinkhamKlapwijk(BTK)理论,计算了隧道结中的准粒子传输系数和微分电导.研究表明:(1)磁散射和界面粗糙散射均可以压低电导峰,其中磁散射能使电导峰滑移,而粗糙界面散射却能阻止这种滑移,且两散射的共同作用可抑制由混合波两序参数的幅值比不同所导致的电导峰滑移;(2)随铁磁层离超导表面距离的增加,隧道谱在零偏压处由凹陷变成了零偏压电导峰,继而又演化为凹陷中的中心峰;(3)当铁磁层离开超导表面有若干相干长度时,隧道谱中将呈现一些子能级谐振峰.     

Superconductivity of M3C60 Within Eliashberg Theory

The important feature of the alkali-metal-doped C₆₀ is that the intramolecular high, frequency vibration modes arising from the covalent interaction and the intermolecular lowfrequency vibration modes arising from the weak Van der Wads interaction both play important roles in the properties of superconductivity. We propose a two-peak form for the phonon density of states. By solving the Eliashberg equations we get the formula for the reduced gap 2Δ₀/k_BT_c and the transition temperature T_c whidh are all in accordance with the experimental values.     

塞曼效应对正常金属/d波超导结中微分电导的影响

通过外加塞曼磁场在d波超导中,研究磁场对d波超导及其正常金属/d波超导结中隧道谱的影响。研究表明(1)塞曼磁场能使能隙变小,且随着磁场变大,超导态会变为正常态,产生一级相变;(2)塞曼磁场可导致零偏压电导峰劈裂,劈裂宽度为2h0(h0为塞曼能)。     

Superconductivity of the Pb/Ag superlattice

Layered Pb/Ag thin films were produced by vacuum evaporation on cooled glass substrates. Measured x-ray diffraction spectra showed peaks characteristic of a superlattice. The superconducting energy gap and the transition temperature of the Pb/Ag superlattice were measured by tunneling experiments. BCS-reduced tunneling conductance revealed the dependence the phonon structure on the superlattice period value. It was also observed that the order of the crystal structure has an influence on the superconducting parameters.     

Differential conductance of normal metal-insulator-d-wave superconductor junctions with interface roughness

Within the framework of Blonder-Tinkham-Klapwijk (BTK) model and taking into account the interface roughness, we calculate the differential conductance of normal metal-insulator-d-wave superconductor junctions. We find that the tunneling spectrum depends strongly on both the incident angle of electrons and the crystalline axis orientation of the superconductor, and exhibits the zero-bias anomaly under suitable arrangements. Interestingly, even in the absence of the insulating layer, the tunneling spectrum of normal metal-d-wave superconductor junctions differs significantly from that for normal metal-s-wave superconductor due to the interface roughness. Moreover, both the tunnel conductance peak at the energy gap and the zero-bias conductance peak are suppressed by the interface roughness. Our results can explain many experimental measurements on the tunneling spectra of high-T_c superconductors.     

A POSSIBLE SOLITON-LIKE POLARON MODEL FOR SUPERCONDUCTORS Y1-xCaxBa2Cu3-xMxO7-δ(M=Fe,Ni)

Using 1+1 soliton-like polaron model of a deformable continuum, the critical temperature and the energy gap in high-temperature superconductors Y_1-xCa_xBa₂Cu_3-xM_xO_7-δ(M=Fe,Ni) are studied in the framework of finite temperature Green's function theory. The ratio 2Δ/k_BT_c=3.9 is obtained. Theoretical results are found in good agreement with the experimental data.     

Scanning tunneling spectroscopy on the novel superconductor CaC6

We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC6. The tunneling conductance spectra, measured between 3 and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with Delta0=1.6+/-0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows us to deduce a coherence length in the ab plane xiab approximately 33 nm.     

Modeling study of peak-dip-hump structure in tunneling spectra of high-temperature superconducting cuprates

We propose new specific model for quasiparticle (QP) tunneling across thesuperconductor-insulator-normal metal (SIN) junction based on two mechanisms. Origin ofthe many features of the tunneling spectra, such as peak-dip-hump (PDH) structure, U- andV-shapes, temperature dependence of differential tunneling conductance, asymmetricconductance peaks, zero-bias conductance, subgap feature and gap inhomogeneity have beenexplained by the proposed model. We show that the energy scales of the binding energies oflarge polarons and polaronic Cooper pairs are identified by pseudogap (PG) crossovertemperature on the cuprate phase diagram.     

Zeeman effects on d-wave superconductor and tunneling spectrum in normal-metal/d-wave superconductor tunnel junction

We study the Zeeman effect on the d-wave superconductor and tunneling spectrum in normal-metal(N)/d-wave superconductor(S) junction by applying a Zeeman magnetic field to the S. It is shown that: (1) the Zeeman magnetic field can lead to the S gap decreasing, and with the increase in Zeeman energy, the superconducting state is changed to the normal state, exhibiting a first-order phase transition; (2) the Zeeman magnetic field may make the zero-bias conductance peak split into two peaks, and the energy difference between the two splitting peaks in the conductance spectrum is equal to 2h ₀ (h ₀ is the Zeeman energy); (3) both the barrier strength of interface scattering and the temperature can lower the magnitudes of splitting peaks, of which the barrier strength can lead to the splitting peaks becoming sharp and the temperature can smear out the peaks, however, neither of them can influence the Zeeman effect.     

Tunneling studies on NdBa2Cu3O7−y

Tunneling measurements were performed at 4.2 K on well-characterized NdBa₂Cu₃O_7−y samples using a sandwich configuration with an artificially grown barrier layer (sputtered indium oxide) and Pb_0.5In_0.5 counter electrode. The conductance spectra exhibited well-defined structures characteristic of gap opening. Fitting the data to a life-time broadened BCS density of states function yielded the following values: 20 meV for the energy gap Δ, 1.5 meV for the line width Γ and 5.3 for 2Δ/k_BT_c.