Spontaneous currents in Josephson junctions between unconventional superconductors and d-wave qubits (Review) (original) (raw)
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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.
Broken time-reversal symmetry in Josephson junction involving two-band superconductors
EPL (Europhysics Letters), 2009
A novel time-reversal symmetry breaking state is found theoretically in the Josephson junction between the two-gap superconductor and the conventional s-wave superconductor. This occurs due to the frustration between the three order parameters analogous to the two antiferromagnetically coupled XY-spins put under a magnetic field. This leads to the interface states with the energies inside the superconducting gap. Possible experimental observations of this state with broken timereversal symmetry are discussed.
European Physical Journal B, 2014
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.
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.
Probing unconventional superconducting symmetries using Josephson interferometry
Physica C: Superconductivity, 2002
We study Josephson junctions formed at grain boundary interfaces in the high-T c cuprate materials. The supercurrents in these junctions depend strongly on the phase anisotropy of the order parameter and on the electronic structure at the interface and can be used to determine the pairing symmetry as well as the physical structure of the grain boundary interface. Andreev reflection at the (1 1 0) surface in d-wave superconductors leads to the formation of zero-energy quasiparticle surface states. It is predicted that these surface states lead to a suppression of the d-wave order parameter, possibly allowing the formation of a subdominant pairing phase with a complex order parameter that is characterized by broken time-reversal symmetry. A similar phenomenon is predicted to occur in the bulk material near magnetic impurities. Calculations demonstrate that the temperature and magnetic field dependence of the critical current of 45-degree asymmetric grain boundary Josephson junctions are extremely sensitive to the onset of a complex order parameter. We have measured the critical current behavior of grain boundary junctions fabricated from pure and magnetically doped cuprate films in an effort to observe the onset of these complex order parameters. Profound departure from the usual sinusoidal current-phase relation have also been predicted for the cuprate materials. We show evidence for a second-order Josephson component in the critical current diffraction patterns of BSCCO junctions.
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
Josephson Effect in Quasi One-dimensional Unconventional Superconductors
Journal of the Physical Society of Japan, 2004
Josephson effect in junctions of quasi one-dimensional triangular lattice superconductors is discussed, where the theoretical model corresponds to organic superconductors (TMTSF)2PF6. We assume the quarter-filling electron band and p, d and f wave like pairing symmetries in organic superconductors. To realize the electronic structures in organic superconductors, we introduce the asymmetric hopping integral, (t ′) among second nearest lattice sites. At t ′ = 0, the Josephson current in the d wave symmetry saturates in low temperatures, whereas those in the p and the f wave symmetries show the low-temperature anomaly due to the zero-energy state at the junction interfaces. The low-temperature anomaly appears even in the d wave symmetry in the presence of t ′ , whereas the anomaly is suppressed in the f wave symmetry. The shape of the Fermi surface is an important factor for the formation of the ZES in the quarter-filling electron systems.
Josephson detection of time-reversal symmetry broken superconductivity in SnTe nanowires
npj Quantum Materials, 2021
A Josephson junction (JJ) couples the supercurrent flowing between two weakly linked superconductors to the phase difference between them via a current-phase relation (CPR). While a sinusoidal CPR is expected for conventional junctions with insulating weak links, devices made from some exotic materials may give rise to unconventional CPRs and unusual Josephson effects. In this work, we present such a case: we investigate the proximity-induced superconductivity in SnTe nanowires by incorporating them as weak links in JJs and observe a deviation from the standard CPR. We report on indications of an unexpected breaking of time-reversal symmetry in these devices, detailing the unconventional characteristics that reveal this behavior. These include an asymmetric critical current in the DC Josephson effect, a prominent second harmonic in the AC Josephson effect, and a magnetic diffraction pattern with a minimum in critical current at zero magnetic field. The analysis examines how multiban...
Superlattices and Microstructures, 1999
We study theoretically the ac Josephson effect in voltage biased planar junctions of d-wave superconductors. For some orientations of the superconductors a current peak is found at finite voltage in the current-voltage characteristics. We pick out the relevant physical processes and write down an analytical formula for the current which clearly shows how the midgap state acts as a resonance and produces the peak. We present a possible explanation for the zero-bias conductance peak, recently found in experiments on grain boundary junctions of high-temperature superconductors, in terms of resonant transmission through midgap state of quasiparticles undergoing multiple Andreev reflections. We note that within our framework the zero-bias conductance peak appears in rather transparent Josephson junctions of d-wave superconductors.