Noncollinear Andreev reflections in semiconductor nanowires

Wu, Binhe; Wu, Yi; Cao, Juncheng; Guo, Guang‐Can

doi:10.1103/physrevb.90.205435

Cited by 17 publications

(17 citation statements)

References 62 publications

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“…In order to isolate the spin symmetry we use the decomposition of Eq. (36). We have, on the retarded side,…”

Section: Green's Function In the Superconductormentioning

confidence: 99%

“…However, the right moving electron can be converted into a right moving hole with the same spin, in the right lead. The latter process, called crossed Andreev reflection (CAR), corresponds to the injection of a Cooper pair in the ↑↑ channel [35,36], and probes directly the exotic pairing induced by the proximity of the FM insulator. We do not expect that charging effects are important in our setup.…”

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confidence: 99%

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Odd-frequency triplet superconductivity at the helical edge of a topological insulator

2015

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Non-local pairing processes at the edge of a two-dimensional topological insulator in proximity to an s-wave superconductor are usually suppressed by helicity. However, additional proximity of a ferromagnetic insulator can substantially influence the helical constraint and therefore open a new conduction channel by allowing for crossed Andreev reflection (CAR) processes. We show a oneto-one correspondence between CAR and the emergence of odd-frequency triplet superconductivity. Hence, non-local transport experiments that identify CAR in helical liquids yield smoking-gun evidence for unconventional superconductivity. Interestingly, we identify a setup -composed of a superconductor flanked by two ferromagnetic insulators -that allows us to favor CAR over electron cotunneling which is known to be a difficult but essential task to be able to measure CAR. PACS numbers: 74.45.+c, 74.78.Na, 71.10.Pm, 74.20.Rp Introduction.-The influence of strong spin-orbit coupling and the constraint of time reversal symmetry are responsible for the appearance of helical electronic channels at the edge of two-dimensional (2D) topological insulators [1][2][3]. Ample evidence for the experimental detection of these edge states has been seen in transport [4][5][6] and scanning SQUID experiments [7]. Proximity of an ordinary s-wave superconductor can induce pairing at the helical edge [8,9]. Interestingly, the interplay of helicity and superconducting order gives rise to unconventional proximity-induced superconductivity (SC) in these systems. However, it is fair to say that it is very difficult to unambiguously probe the emergence of unconventional SC because -often times -conventional and unconventional signatures of SC look alike. Several recent experiments have demonstrated (as a first step towards the detection of unconventional SC) that helical liquids as boundary states of quantum spin Hall systems can indeed be brought in proximity to s-wave superconductors [10] and serve, for instance, as conducting channels of a Josephson junction [11,12]. Importantly, helicity guarantees perfect local Andreev reflection [13] -the conversion of an electron into a hole with opposite spin -at the interface between the normal and the proximity-induced superconducting region called NS junction. Evidently, perfect local Andreev reflection can give rise to sub-gap Andreev states, for instance, in Josephson junction setups. Among these sub-gap states, the one with zero excitation energy is its own chargeconjugate state. It has been coined Majorana (bound) state and has attracted a lot of attention because of potential applications of this anyonic state for topological quantum computing [14]. If a ferromagnet (FM) is placed in vicinity to the NS interface the Majorana (bound) state can be localized in the region between the FM and the SC [9]. This localization allows us to make a formal connection to the physics of a finite-size 1D p-wave topological superconductor [15], and its potential realizations in spin-orbit nanowires [16,17]. In this Letter, ...

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“…In order to isolate the spin symmetry we use the decomposition of Eq. (36). We have, on the retarded side,…”

Section: Green's Function In the Superconductormentioning

confidence: 99%

mentioning

confidence: 99%

Odd-frequency triplet superconductivity at the helical edge of a topological insulator

2015

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“…It was first proposed that the vortex cores of superconducting surface states of topological insulators host Majorana fermions [14]. In a recent experiment, electron tunnelling into the vortex cores using spin polarized scanning tunnelling microscope showed spin dependent conductance [15] which can possibly be caused by spin filtering effects of Majorana fermions [16][17][18][19]. Majorana fermions can also appear as end states of superconducting nanowires which possess Rashba type [20][21][22][23] or Ising type [24][25][26] spin-orbit coupling.…”

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confidence: 99%

Effects of domain walls in quantum anomalous Hall insulator/superconductor heterostructures

Chen

et al. 2017

Phys. Rev. B

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In a recent experiment, half-quantized longitudinal conductance plateaus (HQCPs) of heighthave been observed in quantum anomalous Hall (QAH) insulator/superconductor heterostructure transport measurements. It was predicted that these HQCPs are signatures of chiral Majorana edge states. The HQCPs are supposed to appear in the regimes where the Hall conductance σxy is quantized. However, experimentally, a pair of the HQCPs appear when the Hall conductance σxy is only 80% of the quantized value when dissipative channels appear in the bulk. The dissipative channels in the bulk are expected to induce Andreev reflections and ruin the HQCPs. In this work, we explain how domain walls can cause σxy to deviate from its quantized value and at the same time maintain the quantization of HQCPs. Our work supports the claim that the experimentally observed HQCPs are indeed caused by chiral Majorana modes in the QAH insulator/superconductor heterostructure.

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“…In recent years, the attention of the synthesis of magnetic nanoparticles and magnetic nanostructures has improved rapidly. Not only due to their value in theoretical and experimental research, but also their great potential in technological applications, such as in the fields of sensors, magnetic recording, data storage, optics, catalysis, spintronic, and magnetic particle imaging .…”

Section: Introductionmentioning

confidence: 99%

Low‐temperature properties of a magnetic nanowire

Xianyu

2017

Physica Status Solidi (b)

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The cylindrical core–shell nanowire with an antiferromagnetic core and a ferromagnetic core described by the quantum Heisenberg spin model are studied by using linear spin‐wave theory and Green's function method. Considering the different symmetry of spins, we introduce two different Fourier transforms to spin‐deviate operators. We give the spectrum of the system, analyze the quantum fluctuations of spins at zero temperature, and discuss the low‐temperature behavior of the sublattice magnetization, internal energy and specific heat. It is found that the type of exchange interactions and spin special structure affect the magnetic properties of system very much, changing the magnetic structure of the system making the quantum fluctuation different, but cannot affect the thermal fluctuation dramatically.

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Noncollinear Andreev reflections in semiconductor nanowires

Cited by 17 publications

References 62 publications

Odd-frequency triplet superconductivity at the helical edge of a topological insulator

Odd-frequency triplet superconductivity at the helical edge of a topological insulator

Effects of domain walls in quantum anomalous Hall insulator/superconductor heterostructures

Low‐temperature properties of a magnetic nanowire

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