Dynamics of the Josephson Multi-Junction Systems with Junctions Characterized by Non-Sinusoidal Current - Phase Relationship (original) (raw)
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Low Temperature Physics, 2004
The modern physics of superconductivity can be called the physics of unconventional superconductivity. The discovery of the d-wave symmetry of the order parameter in hightemperature superconductors and the triplet superconductivity in compound Sr 2 RuO 4 has caused a huge stream of theoretical and experimental investigations of unconventional superconductors. In this review we discuss some novel aspects of the Josephson effect which are related to the symmetry of the order parameter. The most intriguing of them is spontaneous current generation in an unconventional weak link. The example of a Josephson junction in the form of a grain boundary between two disorientated d-wave or f-wave superconductors is considered in detail. Josephson current-phase relations and the phase dependences of the spontaneous current that flows along the interface are analyzed. The spontaneous current and spontaneous phase difference are manifestations of the time-reversal symmetry ͑T ͒ breaking states in the system. We analyzed the region of appearance of T-breaking states as function of temperature and mismatch angle. A review of the basics of superconducting qubits with emphasis on specific properties of d-wave qubits is given. Recent results in the problem of decoherence in d-wave qubits, which is the major concern for any qubit realization, are presented.
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Superconductor Science and Technology, 2014
Two parallel stacks of coupled Josephson junctions are investigated to clarify the physics of transitions between the rotating and oscillating states and their effect on the IV-characteristics of the system. The detailed study of phase dynamics and bias dependence of the superconducting and diffusion currents allows one to explain all features of simulated IV-characteristics and demonstrate the correspondence in their behavior. The coupling between JJ in the stacks leads to the branching of IVcharacteristics and a decrease in the hysteretic region. The crucial role of the diffusion current in the formation of the IV-characteristic of the parallel stacks of coupled Josephson junctions is demonstrated. We discuss the effect of symmetry in a number of junctions in the stacks and show a decrease of the branching in the symmetrical stacks. The observed effects might be useful for development of superconducting electronic devices based on intrinsic Josephson junctions.
Phase dependence of the superconducting current in YBCO Josephson junctions on a bicrystal substrate
Technical Physics Letters, 1999
Dependences of the amplitudes of the harmonic and subharmonic Shapiro steps on an external monochromatic signal were used to study the current-phase dependence of high-temperature superconducting junctions on a bicrystal substrate. It is shown that for a symmetric definition of the transport current across the junction with an edge transparency of the order of barD=10−4\bar D = 10^{ - 4}barD=10−4 and a mirror-symmetric bicrystal interface, the current-phase dependence is close to sinusoidal which differs from the theoretical predictions and is most likely caused by twinning of the high-temperature superconducting films of the electrodes forming the junction. A departure from symmetry in the definition of the transport current across the junction causes the current-phase dependence to deviate from sinusoidal, which increases with increasing degree of asymmetry. This change in the current-phase dependence is accurately described by a model which takes into account the formation of coupled Andreev states in junctions of superconductors with a dx2−y2d_{x^2 - y^2 } dx2−y2 type of superconducting wave function.
Josephson Effect in d-Wave Superconductor Junctions in a Lattice Model
Journal of the Physical Society of Japan, 2003
Josephson current between two d-wave superconductors is calculated by using a lattice model. Here we consider two types of junctions, i.e., the parallel junction and the mirror-type junction. The maximum Josephson current (J c) shows a wide variety of temperature (T) dependence depending on the misorientation angles and the types of junctions. When the misorientation angles are not zero, the Josephson current shows the low-temperature anomaly because of a zero energy state (ZES) at the interfaces. In the case of mirror-type junctions, J c has a non monotonic temperature dependence. These results are consistent with the previous results based on the quasiclassical theory. [Y. Tanaka and S. Kashiwaya: Phys. Rev. B 56 (1997) 892.] On the other hand, we find that the ZES disappears in several junctions because of the Freidel oscillations of the wave function, which is peculiar to the lattice model. In such junctions, the temperature dependence of J c is close to the Ambegaokar-Baratoff relation.
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Stationary Josephson currentIc in symmetric and non-symmetric junctions involving d-wave superconductors with charge density waves (CDWs) was calculated. It was found that, if CDWs are weak or absent, there exists an approximate proportionality betweenIc and the product of superconducting order parameters in the electrodes (the lawof corresponding states) for several factors affecting those quantities, such as the temperature,T, or one of the parameters characterizing the combined CDW superconducting phase (the degree of the Fermi surface dielectric gapping and the ratio between the parent superconducting and CDW order parameters). Otherwise, the dependencesIc(T) were shown to deviate from those in the absence of CDWs, and the relevant corresponding-state dependences from linearity, the deviations being especially strong at certain rotation angles of crystalline electodes with respect to the junction plane. Hence, making use of specially designed experimental setups and analyzing theIc(T) and correspondingstate dependences, the existence of CDWs in cuprates and other non-conventional superconductors can be detected.
Stationary Josephson Effect in Junctions Made of d-Wave Superconductors with Charge Density Waves
Dependences of the stationary Josephson current in symmetric and nonsymmetric tunnel junctions involving d-wave superconductors with charge density waves (CDWs) on the system parameters were calculated. Both the checkerboard and unidirectional CDW patterns were studied. The directionality of tunneling was taken into account. It was shown that CDWs can drastically influence the Josephson current, the changes being more significant in underdoped compositions. Металлофиз. новейшие технол. / Metallofiz. Noveishie Tekhnol. 2013, т. 35, № 4, сс. 1001-1015 Оттиски доступны непосредственно от издателя Фотокопирование разрешено только в соответствии с лицензией 2013 ИМФ (Институт металлофизики им. Г. В. Курдюмова НАН Украины) Напечатано в Украине. 1002 ALEXANDER M. GABOVICH, MAI SUAN LI, HENRYK SZYMCZAK
ac Josephson effect in superconducting d -wave junctions
Physical Review B, 1999
We study theoretically the ac Josephson effect in superconducting planar d-wave junctions. The insulating barrier assumed to be present between the two superconductors may have arbitrary strength. Many properties of this system depend on the orientation of the d-wave superconductor: we calculate the ac components of the Josephson current. In some arrangements there is substantial negative differential conductance due to the presence of mid-gap states. We study how robust these features are to finite temperature and also comment on how the calculated current-voltage curves compare with experiments. For some other configurations (for small barrier strength) we find zero-bias conductance peaks due to multiple Andreev reflections through midgap states. Moreover, the odd ac components are strongly suppressed and even absent in some arrangements. This absence will lead to a doubling of the Josephson frequency. All these features are due to the d-wave order parameter changing sign when rotated 90 • . Recently, there have been several theoretical reports on parallel current in the d-wave case for both the stationary Josephson junction and for the normal metal-superconductor junction. Also in our case there may appear current density parallel to the junction, and we present a few examples when this takes place. Finally, we give a fairly complete account of the method used and also discuss how numerical calculations should be performed in order to produce current-voltage curves.