| 1. |
- Maiani, A., et al.
(författare)
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Topological superconductivity in semiconductor-superconductor-magnetic-insulator heterostructures
- 2021
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Ingår i: Physical Review B. - 2469-9950. ; 103:10
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid superconductor-semiconductor heterostructures are promising platforms for realizing topological superconductors and exploring Majorana bound state physics. Motivated by recent experimental progress, we theoretically study how magnetic insulators offer an alternative to the use of external magnetic fields for reaching the topological regime. We consider different setups, where (1) the magnetic insulator induces an exchange field in the superconductor, which leads to a splitting in the semiconductor by proximity effect, and (2) the magnetic insulator acts as a spin-filter tunnel barrier between the superconductor and the semiconductor. We show that the spin splitting in the superconductor alone cannot induce a topological transition in the semiconductor. To overcome this limitation, we propose to use a spin-filter barrier that enhances the magnetic exchange and provides a mechanism for a topological phase transition. Moreover, the spin-dependent tunneling introduces a strong dependence on the band alignment, which can be crucial in quantum-confined systems. This mechanism opens up a route towards networks of topological wires with fewer constraints on device geometry compared to previous devices that require external magnetic fields.
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| 2. |
- Razmadze, D., et al.
(författare)
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Supercurrent reversal in ferromagnetic hybrid nanowire Josephson junctions
- 2023
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Ingår i: Physical Review B. - 2469-9950. ; 107:8
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Tidskriftsartikel (refereegranskat)abstract
- We report supercurrent transport measurements in hybrid Josephson junctions comprising semiconducting InAs nanowires with epitaxial ferromagnetic insulator EuS and superconducting Al coatings. The wires display a hysteretic superconducting window close to the coercivity, away from zero external magnetic field. Using a multi-interferometer setup, we measure the current-phase relation of multiple magnetic junctions and find an abrupt switch between π and 0 phases within the superconducting window. We attribute the 0-π transition to the discrete flipping of the EuS domains and provide a qualitative theory showing that a sizable exchange field can polarize the junction and lead to the supercurrent reversal. Both 0 and π phases can be realized at zero external field by demagnetizing the wire.
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| 3. |
- Razmadze, D., et al.
(författare)
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Supercurrent transport through 1e -periodic full-shell Coulomb islands
- 2024
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Ingår i: Physical Review B. - 2469-9950. ; 109:4
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally investigate supercurrent through Coulomb islands, where island and leads are fabricated from semiconducting nanowires with fully surrounding superconducting shells. Applying flux along the wire yields a series of destructive Little-Parks lobes with reentrant supercurrent. We find Coulomb blockade with 2e peak spacing in the zeroth lobe and 1e average spacing, with regions of significant even-odd modulation, in the first lobe. Evolution of Coulomb-peak amplitude through the first lobe is consistent with a theoretical model of supercurrent carried predominantly by zero-energy states in the leads and the island.
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| 4. |
- Seoane Souto, R., et al.
(författare)
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Transient dynamics of a magnetic impurity coupled to superconducting electrodes : Exact numerics versus perturbation theory
- 2021
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Ingår i: Physical Review B. - 2469-9950. ; 104:21
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Tidskriftsartikel (refereegranskat)abstract
- Impurities coupled to superconductors offer a controlled platform to understand the interplay between superconductivity, many-body interactions, and nonequilibrium physics. In the equilibrium situation, local interactions at the impurity induce a transition from the spin-singlet to the spin-doublet ground state, resulting in a supercurrent sign reversal (0-π transition). In this work, we apply the exact time-dependent density matrix renormalization group method to simulate the transient dynamics of such superconducting systems. We also use a perturbative approximation to analyze their properties at longer times. These two methods agree for a wide range of parameters. In a phase-biased situation, the system gets trapped in a metastable state characterized by a lower supercurrent compared to the equilibrium case. We show that local Coulomb interactions do not provide an effective relaxation mechanism for the initially trapped quasiparticles. In contrast, other relaxation mechanisms, such as coupling to a third normal lead, make the impurity spin relax for parameter values corresponding to the equilibrium 0 phase. For parameters corresponding to the equilibrium π phase the impurity converges to a spin-polarized stationary state. Similar qualitative behavior is found for a voltage-biased junction, which provides an effective relaxation mechanism for the trapped quasiparticles in the junction.
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