铁磁-超导隧道结中粗糙界面散射对直流Josephson电流的影响

通过求解Bogoliubov—de Gennes(BdG)方程得到铁磁超导共存态(FS)的自洽方程，在考虑结界面的粗糙情形下，由推广的Furusaki—Tsukada(FT)的电流公式计算了铁磁超导态／绝缘层／s波超导体(FS／I／S)结的直流Josephson电流，讨论了FS/I／S结的直流Josephson临界电流随磁交换能、温度的变化情况．研究表明：铁磁超导态中磁交换能和结界面的粗糙势垒散射均对FS／I／S结的直流Josephson电流有抑制作用．     

Josephson Effect in FS/I/N/I/FS Tunnel Junctions

The Bogoliubov de Gennes equation is applied to the study ofcoherence effects in the ferromagnetic superconductor/insulator/normalmetal/insulator/ferromagnetic/superconductor (FS/I/N/I/FS) junction. We calculated the Josephson current in FS/I/N/I/FS as a function of exchange field in ferromagnetic superconductor, temperature, and normal metal thickness. It is found that the Josephson critical current in FS/I/N/I/FS exhibits oscillations as a function of the length of normal metal. The exchange field always suppresses the Josephson critical current I_p for a parallel configuration of the magnetic moments of two ferromagnetic superconductor (FS) electrodes. In the antiparallel configuration, the Josephson critical current I_Ap at the minimum values of oscillation increases with the exchange field for strong barrier strength and at low temperatures.     

Reentrant superconductivity in Nb/Cu1-xNix bilayers

We report on the first observation of a pronounced reentrant superconductivity phenomenon in a superconductor/ferromagnet layered system. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu(1-x)Ni(x). The superconducting transition temperature T(c) drops sharply with increasing thickness dCuNi) of the ferromagnetic layer, until complete suppression of superconductivity is observed at d(CuNi) approximately equal to 4 nm. Increasing the Cu(1-x)Ni(x) layer thickness further, superconductivity reappears at d(CuNi) > or =13 nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one-dimensional Fulde-Ferrell-Larkin-Ovchinnikov-like state in the ferromagnetic layer.     

正常金属-绝缘层-铁磁/超导结微分电导峰的Zeeman劈裂

通过求解Bogoliubov-de Gennes(BdG)方程，利用推广的Blonder-Tinkham-Klapwijk(BTK)理 论，计算了考虑结界面粗糙散射情况下正常金属-绝缘层-铁磁超导结（N/I/FS）的微分电导 .研究表明，铁磁超导态中的磁交换能E_h能使微分电导峰产生Zeeman劈裂， 劈裂峰的 能量间隔为2E_h，结界面势垒散射和结界面粗糙散射降低了隧道结的微分电导峰 值. 关键词： N/I/FS超导结 铁磁超导共存态 微分电导 Zeeman劈裂     

铁磁超导态/绝缘层/自旋三重态p波超导体结的直流Josephson电流

由Bogoliubov-de Gennes方程得到铁磁超导共存态(FS)的自洽方程，利用推广的Furusaki-Tsukada的电流公式计算了铁磁超导态/绝缘层/自旋三重态p波超导体(FS/I/p)结的直流Josephson电流随结的温度、相位差以及FS中磁交换能、结界面的势垒散射强度的变化关系.研究表明：FS中磁交换能、结界面的势垒散射均抑制FS/I/p结的直流Josephson电流.当自旋三重态超导体具有p_x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. 关键词： 铁磁超导态 自旋三重态超导体 p波超导体 直流Josephson电流     

Josephson current through a ferromagnetic semiconductor/semiconductor/ferromagnetic semiconductor structure

We theoretically calculate the Josephson current for two superconductor/ferromagnetic semiconductor (SC/FS) bilayers separated by a semiconductor (SM) layer. It is found that the critical Josephson current I_C in the junction is strongly determined by not only the relative orientations of the effective exchange field of the two bilayers and scattering potential strengths at the interfaces but also the kinds of holes (the heavy or light) in the two FS layers. Furthermore, a robust approach to measuring the spin polarization P for the heavy and light holes is presented.     

金属-绝缘层-铁磁/超导结的隧道谱与散粒噪声

通过求解Bogoliubov-de Gennes(BdG)方程,利用推广的Blonder-Tinkham-Klapwijk(BTK)的理论,计算了金属-绝缘层-铁磁／超导态(N／L／FS)结的微分电导、平均电流和散粒噪声功率．研究表明：铁磁超导态中的磁交换能能使微分电导峰产生Zeeman劈裂,劈裂峰的能量问隔为2Eh,结界面势垒散射抑制隧道结的微分电导、平均电流和散粒噪声功率．     

Oscillations of Andreev states in clean ferromagnetic films

We investigate the influence of the exchange field on the Andreev bound states in a ferromagnetic ( F) film backed on one side by a superconductor ( S). Our model accounts for diffusive reflection at the outer surface and possible backscattering at the FS interface. Phase shifting of the Andreev level by the exchange field results in an oscillatory behavior of the density of states of F as a function of the layer thickness. We show that our results agree quantitatively with recent experiments.     

铁磁半导体/d波超导结的自旋极化输运

考虑到铁磁半导体和d波超导体中空穴的有效质量和费米速度错配,运用推广了的B londer-Tinkham-K lapw ijk(BTK)理论模型,研究了铁磁半导体/d波超导隧道结的电导谱。研究表明:(1)铁磁半导体和d波超导体中空穴的有效质量和费米速度错配对系统的微分电导影响显著;(2)铁磁半导体的磁交换能对Andreev反射有抑制作用。     

Shot Noise in Ferromagnetic Superconductor Tunnel Junctions

In this paper, the superconducting order parameter and the energy spectrum of the Bogoliubov excitations are obtained from the Bogoliubov-de Gennes (BdG) equation for a ferromagnetic superconductor (FS). Taking into account the rough interface scattering effect, we calculate the shot noise and the differential conductance of the normal-metal insulator ferromagnetic superconductor junction. It is shown that the exchange energy E_h in FS can lead to splitting of the differential shot noise peaks and the conductance peaks. The energy difference between the two splitting peaks is equal to 2E_h. The rough interface scattering strength results in descent of conductance peaks and the shot noise-to-current ratio but increases the shot noise.     

Reversal of the critical-current sign in SFIFS tunnel contacts

The Josephson current is calculated for an SFIFS tunnel contact where I is an insulator), whose banks are formed by a massive superconductor (S) and a thin layer of a normal ferromagnetic metal (F). Within the microscopic theory of the proximity effect for an SF bilayer, it is shown that, even at mesoscopic dimensions of the ferromagnetic layer in an SFIFS contact, a transition to the state characterized by a π shift of the phase difference between the superconducting wave functions at the banks of the contact can be implemented owing to this effect. The amplitude of the critical current as a function of bilayer parameters is found. It is shown that the exchange-field strength at which the Josephson current in an SFIFS contact is reversed (transition to the π state) can be varied within rather broad limits by changing the parameters of the SF bilayer (resistance of the SF interface and proximity-effect magnitude).     

Josephson current versus potential strength of the interface in ferromagnetic superconductors

Based on the scattering theory, we calculate the Josephson current in a junction between two ferromagnetic superconductors as a function of the interface potential z. We consider the ferromagnetic superconductor(FS) in three different Cooper pairing states: spin singlet s-wave pairing(SWP) state, spin triplet opposite spin pairing(OSP) state, and spin triplet equal spin pairing(ESP) state. We find that the critical Josephson current as a function of z shows clear differences among the SWP, OSP, and ESP states. The obtained results can be used as a useful tool for determining the pair symmetry of the ferromagnetic superconductors.     

Proximity effect in multiterminal hybrid structures

We consider the proximity effect in multiterminal ferromagnet/superconductor (FSF) hybrid structures in which two or three electrodes are connected to a superconductor. We show that two competing effects take place in these systems: (i) pair breaking effects due to the response to the exchange field induced in the superconductor; (ii) a reduction of the superconducting order parameter at the interface that takes place already in NS junctions. We focus on this second effect that dominates if the thickness of the S layer is small enough. We consider several single-channel electrodes connected to the same site. We calculate the superconducting order parameter and the local density of state (LDOS). With two ferromagnetic electrodes connected to a superconductor we find that the superconducting order parameter in the ferromagnetic alignment is larger than the superconducting order parameter in the antiferromagnetic alignment ( > ), in agreement with [Eur. Phys. J. B 25, 373 (2002)]. If a third spin polarized electrode is connected to a superconductor we find that - can change sign as the transparency of the third electrode increases. This can be understood from the fact that the superconducting order parameter is reduced if pair correlations among the ferromagnetic electrodes increase. If the two ferromagnetic electrodes are within a finite distance we find Friedel oscillations in the Gorkov function but we still obtain > .     

双层结构铁磁-超导隧道结的直流Josephson电流

通过求解Bogoliubov_de Gennes(BdG)方程得到铁磁超导共存态(FS)的自洽方程，在考虑结 界面的粗糙情形下，由推广的Furusaki_Tsukada(FT)的电流公式计算了铁磁超导态/ 绝缘层 / 铁磁超导态(FS/I/FS)结的直流Josephson电流，讨论了FS/I/FS结的直流Josephson临界 电流随磁交换能、温度的变化情况.研究表明：当结界面势垒散射强度和粗糙势垒散射强度 比较弱时磁交换能总是抑制FS/I/FS结的直流Josephson临界电流，而当结左右两边FS中铁 关键词： FS/I/FS超导隧道结 铁磁超导共存态 直流Josephson电流 粗糙势垒散射     

Ferromagnetic 0–<Emphasis Type="BoldItalic">π</Emphasis> Josephson junctions

We present a study on low-T_c superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson junctions. SIFS junctions have gained considerable interest in recent years because they show a number of interesting properties for future classical and quantum computing devices. We optimized the fabrication process of these junctions to achieve a homogeneous current transport, ending up with high-quality samples. Depending on the thickness of the ferromagnetic layer and on temperature, the SIFS junctions are in the ground state with a phase drop of either 0 or π. By using a ferromagnetic layer with variable step-like thickness along the junction, we obtained a so-called 0–π Josephson junction, in which 0 and π ground states compete with each other. At a certain temperature the 0 and π parts of the junction are perfectly symmetric, i.e. the absolute critical current densities are equal. In this case the degenerate ground state corresponds to a vortex of supercurrent circulating clock- or counterclockwise and creating a magnetic flux which carries a fraction of the magnetic flux quantum Φ₀. PACS  74.50.+r; 74.78.Fk; 74.81.-g; 85.25.Cp     

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.     

超导体/铁磁体绝缘层-超导体隧道结的直流Josephson效应

在超导体铁磁体绝缘层超导体结(SFIS)中,运用BogoliubovdeGennes(BdG)方程和FurusakiTsukada(FT)电流公式,计算铁磁超导共存态的自洽方程和SFIS结中的直流Josephson电流.研究表明,铁磁超导态的磁交换能h对准粒子的Andreev反射有抑制作用,使得SFIS结中的直流Josephson电流随铁磁超导共存态的磁交换能h增大而减弱 关键词： S/F-I-S结 铁磁超导态 直流Josephson电流     

绝缘层方势垒影响下N/I/自旋三重态p波超导体结的隧道谱

以方势垒描述正常金属/绝缘层/自旋三重态p波超导结中绝缘层对准粒子输运的影响,通过求解Bogoliubov-de Gennes(BdG)方程,利用Blonder-Tinkham-Klapwijk(BTK)理论,计算了p波超导结的隧道谱.研究表明:(1)绝缘层厚度的增加,可导致自旋三重态p波超导结隧道谱中出现亚能隙共振峰...     

Proximity-driven source of highly spin-polarized ac current on the basis of superconductor/weak ferromagnet/superconductor voltage-biased Josephson junction

We theoretically investigate an opportunity to implement a source of highly spin-polarized ac current on the basis of superconductor/weak ferromagnet/superconductor (SFS) voltage-biased junction in the regime of essential proximity effect and calculate the current flowing through the probe electrode tunnel coupled to the ferromagnetic interlayer region. It is shown that while the polarization of the dc current component is generally small in case of weak exchange field of the ferromagnet, there is an ac component of the current in the system. This ac current is highly spin-polarized and entirely originated from the non-equilibrium proximity effect in the interlayer. The frequency of the current is controlled by the voltage applied to SFS junction. We discuss a possibility to obtain a source of coherent ac currents with a certain phase shift between them by tunnel coupling two probe electrodes at different locations of the interlayer region. The article is published in the original.     

Ferromagnetic superconductivity driven by changing Fermi surface topology

We introduce a simple but powerful zero temperature Stoner model to explain the unusual phase dia-gram of the ferromagnetic superconductor, UGe2. Triplet superconductivity is driven in the ferromagnetic phase by tuning the majority spin Fermi level through one of two peaks in the paramagnetic density of states (DOS). Each peak is associated with a metamagnetic jump in magnetization. The twin-peak DOS may be derived from a tight-binding, quasi-one-dimensional band structure, inspired by previous band-structure calculations.