Tunneling Conductance in Normal Metal/Insulator/Triplet Superconductor Junction

Tunneling conductance in normal metal/insulator/triplet superconductor junctions is studied theoretically as a function of the bias voltage at zero temperature and finite temperature. The results show there are zero-bias conductance peak, zero-bias conductance dip and double-minimum structures in the spectra for p-wave superconductor junctions. The existence of such structures in the conductance spectrum can be taken as evidence that the pairing symmetry of Sr2RuO4 is p-wave symmetry.     

正常金属/自旋三重态p波超导体结隧道谱的奇异性

利用Blonder，Tinkham和Klapwijk理论计算了正常金属/绝缘层/正常金属/自旋三重态的p波超导体结的隧道谱和平均电流.计算结果表明：在自旋三重态p波超导结的隧道谱中存在零偏压电导峰、零偏压电导凹陷和双凹陷结构，并有微分电导随偏压震荡的现象出现，在I-V曲线上出现电流台阶.这些结果在理论上支持Sr₂RuO₄的超导态是自旋三重态p波超导态. 关键词： 自旋三重态超导体 p波超导体 隧道谱     

Tunneling Conductance in Quantum-Wire/Ferromagnetic-Insulator/d-Wave Superconductor Junction

We have studied the quasiparticle transport in quantum-wire /ferromagnetic-insulator/d wave superconductor Junction (q/FI/d) in the framework of the Blonder-Tinkham-Klapwijk model. We calculate the tunneling conductance in q/FI/d as a function of the bias voltage at zero temperature and finite temperature based on Bogoliubov-de Gennes equations. Different from the case in normal-metal/insulator/d wave superconductor Junctions, the zero-bias conductance peaks vanish for the single-mode case. The tunneling conductance spectra depend on the magnitude of the exchange interaction at the ferromagnetic-insulator.     

量子线/绝缘层/p波超导体结的隧道谱

用Bogoliubov-de Gennes方程来研究量子线/绝缘层/p波超导体结(q/I/p)中的准粒子输运过程，利用推广的Blonder，Tinkham和Klapwijk模型计算绝对零度和有限温度下q/I/p的一级谐波隧道谱.和量子线/绝缘层/d波超导体结的一级谐波隧道谱不同的是q/I/p的一级谐波隧道谱中存在零偏压电导峰.随着q/I/p中绝缘层的势垒散射增强，q/I/p的一级谐波隧道谱中零偏压电导峰变高.     

Tunneling Conductance in a Normal Metal/Ferromagnetic Superconductor Nano-Junction at a Finite Temperature

In this study, we investigate the tunneling conductance at a finite temperature in a normal metal/ferromagnetic superconductor nano-junction where the ferromagnetic superconductor (FS) is in three different cooper pairing states: spin singlet s-wave pairing (SWP), spin triplet opposite spin pairing (OSP), and spin triplet equal spin pairing (ESP) while including Fermiwave mismatch (FWM) and effective mass mismatch (EMM) in two sides of the nano-junction. We find that the conductance shows clearly different behaviors all depending on the symmetries of cooper pairing in a mannerthat the conductance spectra shows a gap-like structure, two interior dipsstructure and zero bias peak for SWP, OSP, and ESP, respectively. Also, theeffective FS gap (δ_eff) is a linear and decreasing function of exchange field. The slope of (δ_eff) versus exchange field for OSP is twice the SWP. Thus, we can determine the spin polarization of N/FS nano-junction based on the dependence of (δ_eff) to exchange field.     

dc Josephson Effect in s-Wave Superconductor/Ferromagnet Insulator/p-Wave Superconductor Junctions

The Josephson currents in s-wave superconductor/ferromagnet insulator/p-wave superconductor（s/FI/p） junctions are calculated as a function of temperature and the phase taking into account the roughness scattering effect at interface. The phase dependence of the Josephson current I （φ） between s-wave and px-wave superconductor is predicted to be sin（2φ）. The ferromagnet scattering effect, the barrier strength, and the roughness strength at interface suppress the dc currents in s/FI/p junction.     

Tunneling Conductance in dx2-y2+idxy Mixed Wave Superconductor Graphene Junctions

Using the extended Blonder-Tinkham-Klapwijk formalism, we investigate the conductance spectra of normal metal/d_x²-y²+id_xy mixed wave superconductor graphene junctions. It is found that the conductance spectra vary strongly with the orientation of the gap and the amplitude ratio (Δ₁/Δ₀) of two components for d_x²-y²+id_xy mixed wave. The zero bias conductance isnearly 2 and the conductance peak vanishes in doped graphene forα=0 and Δ₁/Δ₀=1. The conductance increases with increasing the amplitude ratio of two components for α=π/4 and Δ₁/Δ₀=1. The ZBCP becomesobservable wide with 1F/Δ₀<100 for α=π/4 and Δ₁/Δ₀=1. This property is different from that in normal metal/d_x²-y² wave superconductor graphenejunctions.     

Spin-polarized quasiparticle transport in ferromagnet/insulator/p-wave superconductor junction

We have studied the tunneling conductance in ferromagnet/insulator/p-wave superconductor junctions, taking into account the rough interface scattering effect. We find that there exist zero-bias conductance peaks and single-minimum structure in tunneling spectroscopy. As the exchange energy increases, the Andreev reflection is always suppressed and the differential conductance decreases. The differential conductance depends on the barrier strength and the roughness at the interface. Supported by the Natural Science Foundation of Jiangsu Higher Education Institutions, China (Grant No. 06KJB140009)     

正常金属/铁磁绝缘层/p波超导体结的隧道谱

利用Blonder-Tinkham-Klapwijk理论,计算了正常金属/铁磁绝缘层/p波超导体结的隧道谱.结果表明:(1)在正常金属/铁磁绝缘层/p波超导体结的隧道谱中存在零偏压电导峰、零偏压电导凹陷;(2)在Px波结的隧道谱中,磁散射能导致零偏压电导峰的劈裂,而界面的粗糙散射却可以阻止其劈裂;(3)界面的势垒散射,磁散射及其与粗糙散射的共同作用对px、py波结零偏压电导的影响是不同的.     

Conductance Fluctuation of the Normal Metal in an SNS Structure

The conductance of a clean normal metal spanning between two superconductors (SNS structure) has been investigated. It is found that the conductance fluctuates periodically with the phase difference of two superconductors. When the pairing symmetry in one side of the superconductors is d_x²-y², the fluctuation period tends to be π instead of 2π, and the phase dependence of its conductance depends strongly on the orientation of the junction in contradistinction to the s-wave case. It can be used as a new method to determine the pairing symmetry of the high-Tc superconductors.     

Andreev Tunneling Through a Ferromagnet/Quantum-Dot/Superconductor System

We study Andreev tunneling through a ferromagnet/quantum-dot (QD)/superconductor system. By usingnonequilibrum Green function method, the averaged occupation of electrons in QD and the Andreev tunneling currentare studied. Comparing to the norma-metal/quantum-dot/superconductor, the system shows significant changes: (i)The averaged occupations of spin-up and spin-down electrons are not equal. (ii) With the increase of the polarizationof ferromagnetic lead, the Andreev reflection current decreases. (iii) However, even the ferromagnetic lead reaches fullpolarization, the averaged occupation of spin-down electrons is not zero. The physics of these changes is discussed.     

Tunneling Conductance and Magnetoresistance in Ferromagnet/Ferromagnet/d-Wave Superconductor Double Tunnel Junctions

The tunneling conductance and tunneling magnetoresistance (TMR) are investigated in ferromagnet/insulator/ferromagnet/insulator/d-wave superconductor (FM/I/FM/I/d-wave SC) structures by applying an extended Blonder-Tinkham-Klapwijk (BTK) approach. We study the effects of the exchange splitting in the FM, the magnetic impurity scattering in the thin insulator interface of FM/I/FM, and noncollinear magnetizations in adjacent magnetic layers on the TMR. It is shown (1) that the tunneling conductance and TMR exhibit amplitude-varying oscillating behavior with exchange splitting, (2) that with the presence of spin-flip scattering in insulator interface of FM/I/FM, the TMR can be dramatically enhanced, and (3) that the TMR depends strongly on the angle between the magnetization of two FMs.     

Spin-Polarized Tunneling Spectroscopy and Shot Noise in Ferromagnet/f-Wave Superconductor Junctions

The tunneling spectroscopy and shot noise in ferromagnet/insulator/triplet-superconductor (FM/I/triplet-SC) structures are studied by taking into account the roughness interfacial barrier and exchange splitting in the FM. For the triplet-SC of Sr₂RuO₄, we consider two-dimensional f-wave order parameter symmetries having nodes within the RuO₂ plane, which reasonably describe both thermodynamic and thermal conductivity data. It is shown that the ferromagnetic exchange splitting gives rise to a decrease in the differential conductance, the average current, and the shot noise power, while the noise power-to-current ratio is increased; the interface roughness is found to lead to a decrease in the differential conductance and the average current, and an increase in the noise power-to-current ratio.     

正常金属d_(x~2-y~2)+id_(xy)混合波超导结中的隧道谱

在Blonder-Tinkham-Klapwijk散射理论框架下,通过求解Bogoliubov-deGennes方程,计算正常金属dx2-y2+idxy混合波超导结中的准粒子输运系数和隧道谱。研究表明:隧道谱中的电导峰位置强烈地依赖电子的入射角、超导的晶轴方位和dxy波分量的强度。     

Analytical Result on the Supercurrent Through a Superconductor/Quantum-Dot/Superconductor Junction

We present an analytical result for the supercurrent across a superconductor/quantum-dot/superconductor junction. By converting the current integration into a special contour integral, we can express the current as a sum of the residues of poles. These poles are real and give a natural definition of the Andreev bound states. We also use the exact result to explain some features of the supercurrent transport behavior.     

Analytical Result on the Supercurrent Through a Superconductor/Quantum-Dot/Superconductor Junction

We present an analytical result for the supercurrent across a superconductor/quantum-dot/superconductor junction. By converting the current integration into a special contour integral, we can express the current as a sum of the residues of poles. These poles are real and give a natural definition of the Andreev bound states. We also use the exact result to explain some features of the supercurrent transport behavior.     

Josephson Current in Superconductor-Ferromagnet/Insulator/d-Wave Superconductor Junctions

Solving the Bogoliubov-de Gennes equation, the energy levels of bound states are obtained in the ferromagnetic superconductor. The Josephson currents in a ferromagnetic superconductor/Insulator/d-wave superconductor junction are calculated as a function of the exchange field, temperature, and insulating barrier strength. It is found that the Josephson critical current is always suppressed by the presence of exchange field h and depends on crystalline axis orientation of d-wave superconductor.     

自旋三重态超导体结的直流Josephson电流

在s波超导体/绝缘层/自旋三重态超导体结中,计算了直流Josephson电流随结的温度、相位差以及绝缘层势垒强度的变化关系.当自旋三重态超导体具有px波配对势时,自旋三重态超导体结的直流Josephson电流随结两侧相位差的振荡周期是π,与结的相位差的关系为sin(2).结界面的绝缘层势垒散射均抑制结的直流Josephson电流.     

Topological Aspects of Triplet Superconductors

In this paper, using the Φ-mapping theory, it is shown that two kinds of topological defects, i.e., the vortex lines and the monopoles exist in the helical configuration of magnetic field in triplet superconductors. And the inner topological structure of these defects is studied. Because the knot solitons in the triplet superconductors are characterized by the Hopf invariant, we also establish a relationship between the Hopf invariant and the linking number of knots family, and reveal the inner topological structure of the Hopf invariant.     

正常金属-f波超导结中的隧道谱与散粒噪声

很多实验证实 Sr2 Ru O4 超导体具有自旋三重态 ,其序参数存有结点的 f波对称结构。我们考虑到粗糙的界面势垒散射 ,利用 f波超导模型 ,研究正常金属 - Sr2 Ru O4 超导结中的隧道谱与散粒噪声。所得结果既不同于传统的 s波超导 ,亦不同于具有 d波对称结构的高 Tc铜氧化物超导体。