Coupling of Two Superconductors through a Ferromagnet: Evidence for a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>π</mml:mi></mml:math>Junction

Ryazanov, V. V.; Oboznov, V.V.; Rusanov, A. Yu.; Veretennikov, A. V.; Golubov, Alexandre Avraamovitch; Aarts, J.

doi:10.1103/physrevlett.86.2427

Cited by 1,191 publications

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“…A negative sign of the real part of the order parameter may occur when the thickness of the F layer is larger than the coherence length of the F layer. The occurrence of the π-phase shift makes it possible to realize the SFS π -junctions 1 , as was confirmed experimentally 4,5,6,7,8 . The order parameter oscillations also lead to nonmonotonous dependence of T c in SF bilayers on the F-layer thickness 9,10,11,12,13 .…”

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confidence: 63%

Resonant peak in the density of states in normal-metal/diffusive-ferromagnet/superconductor junctions

2005

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The conditions for the formation of zero-energy peak in the density of states (DOS) in the normal metal / insulator / diffusive ferromagnet / insulator / s-wave superconductor (N/I/DF/I/S) junctions are studied by solving the Usadel equations. The DOS of the DF is calculated in various regimes for different magnitudes of the resistance, Thouless energy and the exchange field of the DF, as well as for various resistances of the insulating barriers. The conditions for the DOS peak are formulated for the cases of weak proximity effect (large resistance of the DF/S interface) and strong proximity effect (small resistance of the DF/S interface).In ferromagnet/superconductor (F/S) junctions Cooper pairs penetrating into the F layer from the S layer have a nonzero momentum due to the influence of exchange field 1,2,3 . This results in oscillating behavior of the pair amplitude or a π-phase shift of the order parameter in the ferromagnet. A negative sign of the real part of the order parameter may occur when the thickness of the F layer is larger than the coherence length of the F layer. The occurrence of the π-phase shift makes it possible to realize the SFS π -junctions 1 , as was confirmed experimentally 4,5,6,7,8 . The order parameter oscillations also lead to nonmonotonous dependence of T c in SF bilayers on the F-layer thickness 9,10,11,12,13 . Effects of resonant transmission in conductivity of SF structures were discussed in Ref 14,15,16 .Another interesting consequence of the oscillations of the pair amplitude is the spatially damped oscillating behavior of the density of states (DOS) in a ferromagnet predicted theoretically 17,18,19,20 in various regimes. The energy dependent DOS calculated in the clean 18 and the dirty 21 limits exhibits rich structures. Experimentally DOS in F/S bilayers was measured by Kontos et al. who found a broad DOS peak around zero energy when the π-phase shift occurs 22 . In diffusive ferromagnet/superconductor (DF/S) junctions the zeroenergy DOS may have a sharp peak 21 . However the conditions for the appearance of such anomaly have not been studied systematically so far.The purpose of the present paper is to calculate DOS in N/DF/S junctions and to formulate the conditions for the zero-energy DOS peak in two regimes corresponding to the weak proximity effect (large DF/S interface resistance) and strong proximity effect (small DF/S interface resistance). We will show that in the former case the condition is equivalent to the one of Ref. 21 , while in the latter case the new condition is found. The calculation will be performed in the zero-temperature regime by varying the interface resistances as well as the resistance, the exchange field and the Thouless energy of the DF layer.We consider a junction consisting of normal and superconducting reservoirs connected by a quasi-onedimensional diffusive ferromagnet conductor (DF) with a resistance R d and a length L much larger than the mean free path. The DF/N interface located at x = 0 has the resistance R ′ b , while the DF/S interface...

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confidence: 63%

Resonant peak in the density of states in normal-metal/diffusive-ferromagnet/superconductor junctions

2005

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“…In the upper state, for all q not close to 0 mod(2e) and not very large values of the ratio E J /E c the dependence has a phase shift of π, which is typical of the Josephson junctions with ferromagnetic interlayer [21]. This behavior of the supercurrent results in the strong dependence of the Josephson inductance (see Eq.…”

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Cooper-pair qubit and Cooper-pair electrometer in one device

Zorin

2002

Physica C: Superconductivity

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An all-superconductor charge qubit enabling a radio-frequency readout of its quantum state is described. The core element of the setup is a superconducting loop which includes the single-Cooperpair (Bloch) transistor. This circuit has two functions: First, it operates as a charge qubit with magnetic control of Josephson coupling and electrostatic control of the charge on the transistor island. Secondly, it acts as the transducer of the rf electrometer, which probes the qubit state by measuring the Josephson inductance of the transistor. The evaluation of the basic parameters of this device shows its superiority over the rf-SET-based qubit setup.PACS numbers: 74.50.+r, 85.25.Na, 03.67.Lx Superconducting structures with small Josephson tunnel junctions serve as a basis for electronic devices operating on single Cooper pairs and possessing remarkable characteristics. The paper Ref.[1] has demonstrated the potential of the single-Cooper-pair box circuit [2] as a charge qubit and thus has attracted renewed attention to this field. The practical realization of the Cooper pair qubit is not, however, simple and the main problems here are the achievement of a reliable readout of the quantum state and an elongation of the decoherence time. For the most part, these two issues are interrelated because a charge detector coupled to the qubit presents the principal source of quantum decoherence.The qubit setup consisting of a Cooper pair box and a capacitively coupled single electron transistor (SET, including the rf-SET [3]) has been extensively explored [4,5,6]. Although a preliminary analysis shows that qubit states can, in principle, be measured in the snapshot regime [6], the 'mismatch' of the charge carriers in the setup components (namely, the incoherent nature of charges in the SET) might lead to an unaccounted enhancement of decoherence in the system. Alternatively, the generic type of Cooper-pair (Bloch-transistor [7]) electrometers made from superconductors [8,9] seems to be quite promising as regards matching with the Cooper pair box. Furthermore, similar to dc-SQUIDs [10] and in contrast to SETs, the resistively shunted Cooper-pair electrometer belongs to the category of perfect (quantumlimited) linear detectors [11,12] and, therefore, can perform continuous measurements of a quantum object [13].Recently, we have proposed an rf-driven single-Cooperpair electrometer [14] whose energy-resolution figure ǫ can approach the standard quantum limit of /2. The transducer of this electrometer is a Bloch transistor inserted into a superconducting loop. The magnitude of the supercurrent circulating in the loop depends on the polarization charge (quasicharge) on the transistor island induced via a coupling capacitance by the charge source, e.g., the qubit.In this paper we present a circuit in which the electrometer's transducer takes over the function of the Cooper pair box (qubit) as well. The device's core el- ement is a superconducting loop including a mesoscopic double Josephson junction with a capacitive gate (transis...

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“…Thus, the current density j through the barrier is determined by the first two terms on the rhs of Eq. (2.9): 3 . The Green's functionsǦ l,r correspond to the case of the magnetization vector oriented parallel to the z axis.…”

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confidence: 99%

“…On the one hand, this interest is due to the progress in technology that allows a controllable fabrication of nanohybrid systems using a wide range of superconducting and magnetic materials. On the other hand, this interest is due to the discovery of new and interesting fundamental phenomena, as for example the so-called π state in S/F /S Josephson junctions [1][2][3][4][5][6][7][8][9] and more recently the long-range proximity effect mediated by odd-frequency triplet superconducting correlations in S/F structures [10][11][12][13][14][15][16][17] (for an overview, see Refs. [18][19][20][21][22].…”

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confidence: 99%

Electronic transport through ferromagnetic and superconducting junctions with spin-filter tunneling barriers

2012

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We present a theoretical study of the quasiparticle and subgap conductance of generic X/I sf /S M junctions with a spin-filter barrier I sf , where X is either a normal N or a ferromagnetic metal F and S M is a superconductor with a built-in exchange field. Our study is based on the tunneling Hamiltonian and the Green's-function technique. First, we focus on the quasiparticle transport, both above and below the superconducting critical temperature. We obtain a general expression for the tunneling conductance which is valid for arbitrary values of the exchange field and arbitrary magnetization directions in the electrodes and in the spin-filter barrier. In the second part, we consider the subgap conductance of a N/I sf /S junction, where S is a conventional superconductor. In order to account for the spin-filter effect at interfaces, we heuristically derive boundary conditions for the quasiclassical Green's functions. With the help of these boundary conditions, we show that the proximity effect and the subgap conductance are suppressed by spin filtering in a N/I sf /S junction. Our work provides useful tools for the study of spin-polarized transport in hybrid structures both in the normal and in the superconducting state.

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Coupling of Two Superconductors through a Ferromagnet: Evidence for aπJunction

Cited by 1,191 publications

References 13 publications

Resonant peak in the density of states in normal-metal/diffusive-ferromagnet/superconductor junctions

Resonant peak in the density of states in normal-metal/diffusive-ferromagnet/superconductor junctions

Cooper-pair qubit and Cooper-pair electrometer in one device

Electronic transport through ferromagnetic and superconducting junctions with spin-filter tunneling barriers

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