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Cayao, Jorge
Publications (7 of 7) Show all publications
Tsintzis, A., Black-Schaffer, A. M. & Cayao, J. (2019). Odd-frequency superconducting pairing in Kitaev-based junctions. Physical Review B, 100(11), Article ID 115433.
Open this publication in new window or tab >>Odd-frequency superconducting pairing in Kitaev-based junctions
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 11, article id 115433Article in journal (Refereed) Published
Abstract [en]

We investigate odd-frequency superconducting correlations in normal-superconductor (NS) and short superconductor-normal-superconductor (SNS) junctions with the S region described by the Kitaev model of spinless fermions in one dimension. We demonstrate that, in both the trivial and topological phases, Andreev reflection is responsible for the coexistence of even- and odd-frequency pair amplitudes in N and S close to the interfaces, while normal reflections additionally only contributes to odd-frequency pairing in S. In the S region close to the NS interface we find that the odd-frequency pair amplitude exhibits large, but finite, values in the topological phase at low frequencies due to the emergence of a Majorana zero mode at the interface which also spreads into the N region. We also show that in S both the local density of states and local odd-frequency pairing can be characterized solely by Andreev reflections deep in the topological phase. Moreover, in the topological phase of short SNS junctions, we find that both even- and odd-frequency amplitudes capture the emergence of topological Andreev bound states. For a superconducting phase difference 0 < phi < pi the odd-frequency magnitude exhibits a linear frequency (similar to vertical bar omega vertical bar) dependence at low frequencies, while at phi = pi it develops a resonance peak (similar to 1/vertical bar omega vertical bar) due to the protected Majorana zero modes.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-395838 (URN)10.1103/PhysRevB.100.115433 (DOI)000488255500006 ()
Funder
Swedish Research Council, 621-2014-3721Knut and Alice Wallenberg FoundationEU, European Research Council, ERC-2017-StG-757553Göran Gustafsson Foundation for Research in Natural Sciences and Medicine
Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved
Awoga, O., Cayao, J. & Black-Schaffer, A. M. (2019). Supercurrent Detection of Topologically Trivial Zero-Energy States in Nanowire Junctions. Physical Review Letters, 123(11), Article ID 117001.
Open this publication in new window or tab >>Supercurrent Detection of Topologically Trivial Zero-Energy States in Nanowire Junctions
2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 11, article id 117001Article in journal (Refereed) Published
Abstract [en]

We report the emergence of zero-energy states in the trivial phase of a short nanowire junction with a strong spin-orbit coupling and magnetic field, formed by strong coupling between the nanowire and two superconductors. The zero-energy states appear in the junction when the superconductors induce a large energy shift in the nanowire, such that the junction naturally forms a quantum dot, a process that is highly tunable by the superconductor width. Most importantly, we demonstrate that the zero-energy states produce a re shift in the phase-biased supercurrent, which can be used as a simple tool for their unambiguous detection, ruling out any Majorana-like interpretation.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-395315 (URN)10.1103/PhysRevLett.123.117001 (DOI)000485315000011 ()31573272 (PubMedID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research Knut and Alice Wallenberg Foundation
Available from: 2019-10-18 Created: 2019-10-18 Last updated: 2019-10-18Bibliographically approved
Cayao, J., Black-Schaffer, A. M., Prada, E. & Aguado, R. (2018). Andreev spectrum and supercurrents in nanowire-based SNS junctions containing Majorana bound states. Beilstein Journal of Nanotechnology, 9, 1339-1357
Open this publication in new window or tab >>Andreev spectrum and supercurrents in nanowire-based SNS junctions containing Majorana bound states
2018 (English)In: Beilstein Journal of Nanotechnology, ISSN 2190-4286, Vol. 9, p. 1339-1357Article in journal (Refereed) Published
Abstract [en]

Hybrid superconductor-semiconductor nanowires with Rashba spin-orbit coupling are arguably becoming the leading platform for the search of Majorana bound states (MBSs) in engineered topological superconductors. We perform a systematic numerical study of the low-energy Andreev spectrum and supercurrents in short and long superconductor-normal-superconductor junctions made of nanowires with strong Rashba spin-orbit coupling, where an external Zeeman field is applied perpendicular to the spin-orbit axis. In particular, we investigate the detailed evolution of the Andreev bound states from the trivial into the topological phase and their relation with the emergence of MBSs. Due to the finite length, the system hosts four MBSs, two at the inner part of the junction and two at the outer one. They hybridize and give rise to a finite energy splitting at a superconducting phase difference of p, a wellvisible effect that can be traced back to the evolution of the energy spectrum with the Zeeman field: from the trivial phase with Andreev bound states into the topological phase with MBSs. Similarly, we carry out a detailed study of supercurrents for short and long junctions from the trivial to the topological phases. The supercurrent, calculated from the Andreev spectrum, is 2 pi-periodic in the trivial and topological phases. In the latter it exhibits a clear sawtooth profile at a phase difference of pi when the energy splitting is negligible, signalling a strong dependence of current-phase curves on the length of the superconducting regions. Effects of temperature, scalar disorder and reduction of normal transmission on supercurrents are also discussed. Further, we identify the individual contribution of MBSs. In short junctions the MBSs determine the current-phase curves, while in long junctions the spectrum above the gap (quasi-continuum) introduces an important contribution.

Place, publisher, year, edition, pages
BEILSTEIN-INSTITUT, 2018
Keywords
hybrid superconductor-semiconductor nanowire-superconductor junctions, Josephson effect, Majorana bound states, nanowires, spin-orbit coupling, Zeeman interaction
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-356396 (URN)10.3762/bjnano.9.127 (DOI)000431383200001 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research Knut and Alice Wallenberg Foundation
Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2018-07-25Bibliographically approved
Cayao, J. & Black-Schaffer, A. M. (2018). Finite length effect on supercurrents between trivial and topological superconductors. The European Physical Journal Special Topics, 227(12), 1387-1396
Open this publication in new window or tab >>Finite length effect on supercurrents between trivial and topological superconductors
2018 (English)In: The European Physical Journal Special Topics, ISSN 1951-6355, E-ISSN 1951-6401, Vol. 227, no 12, p. 1387-1396Article in journal (Refereed) Published
Abstract [en]

We numerically analyze the effect of finite length of the superconducting regions on the low-energy spectrum, current-phase curves, and critical currents in junctions between trivial and topological superconductors. Such junctions are assumed to arise in nanowires with strong spin-orbit coupling under external magnetic fields and proximity-induced superconductivity. We show that all these quantities exhibit a strong dependence on the length of the topological sector in the topological phase and serve as indicators of the topological phase and thus the emergence of Majorana bound states at the end of the topological superconductor.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-375853 (URN)10.1140/epjst/e2018-800101-0 (DOI)000455553900008 ()
Funder
Swedish Research Council, 621-2014-3721Swedish Foundation for Strategic Research Knut and Alice Wallenberg FoundationGöran Gustafsson Foundation for Research in Natural Sciences and Medicine
Available from: 2019-02-01 Created: 2019-02-01 Last updated: 2019-02-01Bibliographically approved
Cayao, J. & Black-Schaffer, A. M. (2018). Odd-frequency superconducting pairing in junctions with Rashba spin-orbit coupling. Physical Review B, 98(7), Article ID 075425.
Open this publication in new window or tab >>Odd-frequency superconducting pairing in junctions with Rashba spin-orbit coupling
2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 7, article id 075425Article in journal (Refereed) Published
Abstract [en]

We consider normal-superconductor (NS) and superconductor-normal-superconductor (SNS) junctions based on one-dimensional nanowires with Rashba spin-orbit coupling and proximity-induced s-wave spin-singlet superconductivity and analytically demonstrate how both even- and odd-frequency and spin-singlet and -triplet superconducting pair correlations are always present. In particular, by using a fully quantum mechanical scattering approach, we show that Andreev reflection induces mixing of spatial parities at interfaces, thus being the unique process which generates odd-frequency pairing; on the other hand, both Andreev and normal reflections contribute to even-frequency pairing. We further find that locally neither odd-frequency nor spin-triplet correlations are induced, but only even-frequency spin-singlet pairing. In the superconducting regions of NS junctions, the interface-induced amplitudes decay into the bulk, with the odd-frequency components being generally much larger than the even-frequency components at low frequencies. The odd-frequency pairing also develops short- and long-period oscillations due to the chemical potential and spin-orbit coupling, respectively, leading to a visible beating feature in their magnitudes. Moreover, we find that in short SNS junctions at pi-phase difference and strong spin-orbit coupling, the odd-frequency spin-singlet and -triplet correlations strongly dominate with an alternating spatial pattern for a large range of subgap frequencies.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-362496 (URN)10.1103/PhysRevB.98.075425 (DOI)000442544300004 ()
Funder
Swedish Research Council, 621-2014-3721Knut and Alice Wallenberg FoundationEU, Horizon 2020, ERC-2017-StG-757553Göran Gustafsson Foundation for Research in Natural Sciences and Medicine
Available from: 2018-10-05 Created: 2018-10-05 Last updated: 2018-10-05Bibliographically approved
Cayao, J., San-Jose, P., Black-Schaffer, A. M., Aguado, R. & Prada, E. (2017). Majorana splitting from critical currents in Josephson junctions. Physical Review B, 96(20), Article ID 205425.
Open this publication in new window or tab >>Majorana splitting from critical currents in Josephson junctions
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 20, article id 205425Article in journal (Refereed) Published
Abstract [en]

A semiconducting nanowire with strong Rashba spin-orbit coupling and coupled to a superconductor can be tuned by an external Zeeman field into a topological phase with Majorana zero modes. Here we theoretically investigate how this exotic topological superconductor phase manifests in Josephson junctions based on such proximitized nanowires. In particular, we focus on critical currents in the short junction limit (L-N << xi, where L-N is the junction length and xi is the superconducting coherence length) and show that they contain important information about nontrivial topology and Majoranas. This includes signatures of the gap inversion at the topological transition and a unique oscillatory pattern that originates from Majorana interference. Interestingly, this pattern can be modified by tuning the transmission across the junction, thus providing complementary evidence of Majoranas and their energy splittings beyond standard tunnel spectroscopy experiments, while offering further tunability by virtue of the Josephson effect.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-342376 (URN)10.1103/PhysRevB.96.205425 (DOI)000415678400007 ()
Funder
Swedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologySwedish Foundation for Strategic Research Knut and Alice Wallenberg Foundation
Available from: 2018-02-22 Created: 2018-02-22 Last updated: 2018-02-22Bibliographically approved
Cayao, J. & Black-Schaffer, A. M. (2017). Odd-frequency superconducting pairing and subgap density of states at the edge of a two-dimensional topological insulator without magnetism. Physical Review B, 96(15), Article ID 155426.
Open this publication in new window or tab >>Odd-frequency superconducting pairing and subgap density of states at the edge of a two-dimensional topological insulator without magnetism
2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 15, article id 155426Article in journal (Refereed) Published
Abstract [en]

We investigate the emergence and consequences of odd-frequency spin-triplet s-wave pairing in superconducting hybrid junctions at the edge of a two-dimensional topological insulator without any magnetism. More specifically, we consider several different normal-superconductor hybrid systems at the topological insulator edge, where spin-singlet s-wave superconducting pairing is proximity induced from an external conventional superconductor. We perform fully analytical calculations and show that odd-frequency mixed spin-triplet s-wave pairing arises due to the unique spin-momentum locking in the topological insulator edge state and the naturally nonconstant pairing potential profile in hybrid systems. Importantly, we establish a one-to-one correspondence between the local density of states (LDOS) at low energies and the odd-frequency spin-triplet pairing in NS, NSN, and SNS junctions along the topological insulator edge; at interfaces the enhancement in the LDOS can directly be attributed to the contribution of odd-frequency pairing. Furthermore, in SNS junctions we show that the emergence of the zero-energy LDOS peak at the superconducting phase phi = pi is associated purely with odd-frequency pairing in the middle of the junction.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-338519 (URN)10.1103/PhysRevB.96.155426 (DOI)000412699800006 ()
Funder
Swedish Research CouncilGöran Gustafsson Foundation for Research in Natural Sciences and MedicineSwedish Foundation for Strategic Research Knut and Alice Wallenberg Foundation
Available from: 2018-01-15 Created: 2018-01-15 Last updated: 2018-01-15Bibliographically approved
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