Topological suppression of magnetoconductance oscillations in normal-superconductor junctions

Alomar

Eur. Phys. J. Spec. Top.

2019

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We calculate density and current spatial distributions of a 2D model junction between a normal QAH contact and a superconducting QAH region hosting propagating (chiral) Majorana modes. We use a simplified Hamiltonian describing the spatial coupling of the modes on each side of the junction, as well as the related junction conductance. We study how this coupling is affected by orbital effects caused by an external magnetic field.

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Spatial coupling of quantum-anomalous-Hall and chiral-Majorana modes

Alomar

Eur. Phys. J. Spec. Top.

2019

Self Cite

“…In particular, Takagaki [55] studied the magnetoconductance of a 2D-q1D trivial NS junction. While those works considered a junction between a semiconductor and a true metallic superconductor, we assumed a hybrid topological superconduc-tor [64]. Orbital effects were present only on the normal side of the junction due to the shielding of the metallic superconductor from the magnetic field.…”

Section: Magnetoconductance Oscillations In Ns Junctionsmentioning

confidence: 99%

“…Scheme of experiment proposal to achieve different field orientations in topological NS junctions. From Ref [64]…”

mentioning

confidence: 99%

Complex band-structure analysis and topological physics of Majorana nanowires

2019

Eur. Phys. J. B

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We review applications of complex band structure theory to describe Majorana states in nanowires and nanowire junctions. The dimensionality of the considered wires is gradually increased, from strictly 1D to quasi-1D with one and two transverse dimensions. The complex wave number analysis is applied to two main types of Majorana modes: end states in hybrid semiconductor wires and chiral edge states in hybrid wires of quantum-anomalous Hall insulators. In topological NS and NSN junctions with Majorana modes conductance oscillations and spatial distributions of density and current are described. Finally, the optical absorption in finite systems with both types of Majorana modes is considered.

“…The method is explained in more detail in the Supplemental Material [21] and is based on Refs. [22][23][24][25][26][27][28][29]. In particular, the conductance for a given energy E is determined as…”

Section: the Hamiltonian Readsmentioning

confidence: 99%

Conductance oscillations and speed of chiral Majorana mode in a quantum anomalous Hall two-dimensional strip

2018

Phys. Rev. B

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We predict conductance oscillations in a quantum-anomalous Hall 2d strip having a superconducting region of length Lx with a chiral Majorana mode. These oscillations require a finite transverse extension of the strip Ly of a few microns or less. Measuring the conductance periodicity with Lx and a fixed bias, or with bias and a fixed Lx, yields the speed of the chiral Majorana mode. The physical mechanism behind the oscillations is the interference between backscattered chiral modes from second to first interface of the NSN double junction. The interferometer effect is enhanced by the presence of side barriers.Majorana modes in Condensed Matter systems are object of an intense research due to their peculiar exchange statistics that could allow implementing a robust quantum computer [1]. A breakthrough in the field was the observation of zero-bias anomalies in semiconductor nanowires with proximity-induced superconductivity [2]. Although an intense theoretical debate has followed the experiment, evidence is now accumulating [3,4] that these quasi-1d systems indeed host localized Majorana states on its two ends, for a proper choice of all the system parameters (see Refs. [5,6] for recent reviews).Another breakthrough is the recent observation of a peculiar conductance quantization, 0.5e 2 /h, in a quantumanomalous-Hall 2d (thin) strip, of 2 × 1 mm [7]. A region of L x ≈ 0.8 mm in the central part of the strip is put in proximity of a superconductor bar, whose influence makes the central piece of the strip become a topological system able to host a single chiral Majorana mode. The device can then be seen as a generic NSN double junction with tunable topological properties. The hallmark of transport by a single chiral Majorana mode in the central part is the observed halved quantized conductance, since a Majorana Fermion is half an electron and half a hole [8][9][10][11][12][13].The observed signal of a chiral Majorana mode in the macroscopic device of Ref.[7] naturally leads to the question of how is this result affected when the system dimensions are reduced and quantum properties are enhanced. Can the presence of a Majorana mode still be clearly identified in a smaller strip? Are there additional smoking-gun signals? In this Rapid Communication we provide theoretical evidence predicting a positive answer to these questions. In a smaller strip, with lateral extension L y of a few microns or less, we predict the existence of conductance oscillations as a function of L x (the longitudinal extension of the superconducting piece) and a fixed longitudinal bias. Alternatively, oscillations are also present as a function of bias and a fixed value of L x .We find that the period of the conductance oscillations is related to the speed c of the chiral Majorana mode, as defined from the linear dispersion relation E = c k with k the mode wavenumber. More precisely, the oscillating part of the conductance is ≈ δG cos (2L x E/ c). Therefore, measuring the distance ∆L x between two successive conductance maxima in a fixed bias V (...