Anomalous Josephson current through a topological noncoplanar ferromagnetic trilayer

Abstract We present an anomalous Josephson eﬀect in a TI-based Josephson junction with a ferromagnetic insulator (FI) trilayer which has noncoplanar magnetizations. It is shown that there exist equal spin-singlet and -triplet correlations due to the magnetism-tuning chiral Dirac energy band structure combined with the spin precession and selective equal spin Andreev reﬂection by chiral Majorana modes (CMMs). The consequent anomalous Josephson supercurrent is exhibited, in which a 0-π or similar 0 - π state transition through phase shift is induced only by exchange ﬁeld strengths of the ﬁrst FI region, while the ϕ0 supercurrent and the maximum one gradually drop with the increase of exchange ﬁeld strengths of the second and third FI regions without relative state transitions. The much diﬀerent features are found by varying the lengths of trilayer. The Andreev bound states without hybridization for the CMM administrate these features, which could be used to probe and conﬁrm the zero energy CMM. In addition, the corresponding free energies are presented and discussed.

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Josephson effect in junctions of conventional and topological superconductors

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.9.158 ◽

2018 ◽

Vol 9 ◽

pp. 1659-1676 ◽

Cited By ~ 6

Author(s):

Alex Zazunov ◽

Albert Iks ◽

Miguel Alvarado ◽

Alfredo Levy Yeyati ◽

Reinhold Egger

Keyword(s):

Bound States ◽

Josephson Effect ◽

Mean Field ◽

Josephson Current ◽

Field Analysis ◽

Current Phase ◽

Topological Superconductor ◽

Topological Superconductors ◽

Spin Singlet ◽

Hybrid Devices

We present a theoretical analysis of the equilibrium Josephson current-phase relation in hybrid devices made of conventional s-wave spin-singlet superconductors (S) and topological superconductor (TS) wires featuring Majorana end states. Using Green’s function techniques, the topological superconductor is alternatively described by the low-energy continuum limit of a Kitaev chain or by a more microscopic spinful nanowire model. We show that for the simplest S–TS tunnel junction, only the s-wave pairing correlations in a spinful TS nanowire model can generate a Josephson effect. The critical current is much smaller in the topological regime and exhibits a kink-like dependence on the Zeeman field along the wire. When a correlated quantum dot (QD) in the magnetic regime is present in the junction region, however, the Josephson current becomes finite also in the deep topological phase as shown for the cotunneling regime and by a mean-field analysis. Remarkably, we find that the S–QD–TS setup can support φ0-junction behavior, where a finite supercurrent flows at vanishing phase difference. Finally, we also address a multi-terminal S–TS–S geometry, where the TS wire acts as tunable parity switch on the Andreev bound states in a superconducting atomic contact.

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EXCHANGE FIELD EFFECT ON THE ANDREEV BOUND STATE STUDIED BY FERROMAGNET/HIGH Tc SUPERCONDUCTOR INTERFACE

International Journal of Modern Physics B ◽

10.1142/s021797920502889x ◽

2005 ◽

Vol 19 (01n03) ◽

pp. 495-497 ◽

Cited By ~ 1

Author(s):

K.-W. NG ◽

MARIO FREAMAT

Keyword(s):

Bound States ◽

Bound State ◽

Exchange Field ◽

Zero Energy ◽

S Wave ◽

High Tc ◽

Andreev Bound States ◽

High Tc Superconductor ◽

Energy Peak ◽

Andreev Bound State

We have prepared Ag / BSCCO and Fe / Ag / BSCCO planar junctions to study the effect of Fe exchange field on the tunneling spectra. The junctions were constructed so that the tunneling direction is within the ab-plane, either along the maximum or minimum gap direction. Andreev bound states were observed as zero energy peak in the minimum gap direction. The exchange field caused major splitting of the zero energy peak, which did not occur in Ag / BSCCO junctions. We had detected a few percent (6 to 7%) of s-wave subcomponent at the interface in many of these junctions. This s-wave subcomponent had a Tc of about 20K.

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Reproducing topological properties with quasi-Majorana states

SciPost Physics ◽

10.21468/scipostphys.7.5.061 ◽

2019 ◽

Vol 7 (5) ◽

Cited By ~ 34

Author(s):

Adriaan Vuik ◽

Bas Nijholt ◽

Anton Akhmerov ◽

Michael Wimmer

Keyword(s):

Bound States ◽

Josephson Effect ◽

Tunnel Barrier ◽

Topological Properties ◽

Zero Energy ◽

Tunneling Spectrum ◽

Zero Bias ◽

Andreev Bound States ◽

Zero Bias Conductance ◽

Coupling Strengths

Andreev bound states in hybrid superconductor-semiconductor devices can have near-zero energy in the topologically trivial regime as long as the confinement potential is sufficiently smooth. These quasi-Majorana states show zero-bias conductance features in a topologically trivial phase, mimicking spatially separated topological Majorana states. We show that in addition to the suppressed coupling between the quasi-Majorana states, also the coupling of these states across a tunnel barrier to the outside is exponentially different for increasing magnetic field. As a consequence, quasi-Majorana states mimic most of the proposed Majorana signatures: quantized zero-bias peaks, the 4\pi4π Josephson effect, and the tunneling spectrum in presence of a normal quantum dot. We identify a quantized conductance dip instead of a peak in the open regime as a distinguishing feature of true Majorana states in addition to having a bulk topological transition. Because braiding schemes rely only on the ability to couple to individual Majorana states, the exponential control over coupling strengths allows to also use quasi-Majorana states for braiding. Therefore, while the appearance of quasi-Majorana states complicates the observation of topological Majorana states, it opens an alternative route towards braiding of non-Abelian anyons and protected quantum computation.

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Spectral singularities and zero energy bound states

The European Physical Journal D ◽

10.1140/epjd/e2011-20174-4 ◽

2011 ◽

Vol 63 (3) ◽

pp. 369-373 ◽

Cited By ~ 5

Author(s):

W. D. Heiss ◽

R. G. Nazmitdinov

Keyword(s):

Bound States ◽

Zero Energy ◽

Spectral Singularities ◽

Energy Bound

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Zero-energy scattering and bound states in theHe4trimer and tetramer

Physical Review A ◽

10.1103/physreva.28.692 ◽

1983 ◽

Vol 28 (2) ◽

pp. 692-696 ◽

Cited By ~ 44

Author(s):

S. Nakaichi-Maeda ◽

T. K. Lim

Keyword(s):

Bound States ◽

Zero Energy ◽

Energy Scattering

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Zero-Energy Bound States of Two Dirac Particles

Progress of Theoretical Physics ◽

10.1143/ptp.43.1035 ◽

1970 ◽

Vol 43 (4) ◽

pp. 1035-1049 ◽

Cited By ~ 5

Author(s):

Hitoshi Ito

Keyword(s):

Bound States ◽

Zero Energy ◽

Dirac Particles ◽

Energy Bound

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ANDREEV SPECTRUM AND SUPERCURRENT IN A DOUBLE FERROMAGNET CLEAN JOSEPHSON JUNCTION

Modern Physics Letters B ◽

10.1142/s021798490701292x ◽

2007 ◽

Vol 21 (09) ◽

pp. 505-529 ◽

Cited By ~ 1

Author(s):

V. PALTOGLOU ◽

I. MARGARIS ◽

N. FLYTZANIS

Keyword(s):

Energy Spectrum ◽

Bound States ◽

Reasonable Agreement ◽

Double Resonance ◽

Exchange Field ◽

Extensive Investigation ◽

Andreev Bound States ◽

Weak Exchange ◽

Interface Potential ◽

Analytical Formulas

We consider a superconductor/double-ferromagnet/superconductor (S/I1/F/IC/F'/I2/S) ballistic junction with thin insulating layers in the interfaces. An extensive investigation is carried out for the possibility of 0- or π-junction and the important phaseshift. The average exchange field for the two ferromagnets has limited use, only for weak exchange fields. Several analytical formulas are obtained for the energy spectrum in simple cases with interface potential (a) absent, (b) between ferromagnets only, (c) double resonance barrier between S and F layers. They give reasonable agreement even outside their range of validity. For the case of strong S/F barriers we find a strong interplay of Andreev bound states and interbarrier resonances.

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