Andreev spectroscopy of doped HgTe quantum wells

Guigou, M.; Cayssol, Jérôme

doi:10.1103/physrevb.82.115312

Cited by 16 publications

(17 citation statements)

References 45 publications

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“…Since the QSH state exists under zero magnetic field, in contrast to the integer and fractional quantum Hall states, it can also be probed by the powerful methods of superconducting proximity effect [9]. Along these lines, Andreev spectroscopy has been recently suggested to characterize the quasi-relativistic dynamics of 2D bulk carriers in doped HgTe/CdTe quantum wells [10]. Furthermore helical liquids might also be useful to analyze the entanglement of electrons injected from a singlet s−wave superconductor [11,12].…”

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confidence: 99%

Probing the helical edge states of a topological insulator by Cooper-pair injection

et al. 2010

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We consider the proximity effect between a singlet s-wave superconductor and the edge of a Quantum Spin Hall (QSH) topological insulator. We establish that Andreev reflection at a QSH edge state/superconductor interface is perfect while nonlocal Andreev processes through the superconductor are totally suppressed. We compute the corresponding conductance and noise.The prediction [1] and the observation [2,3] of the Quantum Spin Hall (QSH) state in mercury telluride (HgTe/CdTe) heterostructures have triggered a great deal of excitation in the condensed matter community [4][5][6] since the QSH state realizes a two dimensional (2D) topologically ordered phase in the absence of magnetic field. The QSH state is distinguished from ordinary band insulators by the presence of a one-dimensional metal along its edge [7]. Owing to the dominant role of the spin-orbit interaction, this edge state provides a unique strictly one-dimensional metal where the spin is tied to the direction of motion of the carriers [8]. This so-called helical property and the associated time-reversal symmetry imply the absence of backscattering on non magnetic impurities.So far the existence of the helical liquid has been confirmed by multiterminal transport measurements performed with normal leads [2,3]. Since the QSH state exists under zero magnetic field, in contrast to the integer and fractional quantum Hall states, it can also be probed by the powerful methods of superconducting proximity effect [9]. Along these lines, Andreev spectroscopy has been recently suggested to characterize the quasi-relativistic dynamics of 2D bulk carriers in doped HgTe/CdTe quantum wells [10]. Furthermore helical liquids might also be useful to analyze the entanglement of electrons injected from a singlet s−wave superconductor [11,12].In this Rapid Communication, we theoretically investigate the edge transport of a Quantum Spin Hall insulator in presence of a single superconducting probe. As a result of helicity conservation and absence of backscattering channel, we find that an electron can be either Andreev reflected as a hole, or transmitted as an electron. In a standard metal or in a carbon nanotube, there would be two additional possibilities whereby the electron can be reflected as an electron, or transmitted as a hole [13][14][15][16][17][18][19]. We compute the conductance and the noise associated to this partitioning in two outgoing channels, instead of four channels in standard 1D metals. The related experiments could be implemented readily using a side superconductor contacted to current HgTe/CdTe

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Probing the helical edge states of a topological insulator by Cooper-pair injection

et al. 2010

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“…Following the procedure given in Refs. [16,37] we solve the scattering problem based on the Bogoliubov-de Gennes equation…”

Section: Modelmentioning

confidence: 99%

“…[16,17]). As a consequence, the periodic boundary conditions applied in y-direction yield the quantized transverse momentum k n y = 2πn/W with the index n = 0, ±1, ±2, .... Then, the wave function of the n-mode writes as Ψ n (x, y) = e ik n y y ψ n (x).…”

Section: Scattering Problemmentioning

confidence: 99%

Bulk transport through superconducting hybrid structures in HgTe quantum wells

2014

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We investigate the subgap bulk transport through short and wide superconducting hybrid structures based on HgTe quantum wells (QWs). We show that the differential conductance of a normal metal−insulator−superconductor (NIS) proximity structure behaves in a qualitatively different way with respect to the topological phase of the HgTe QW. We compare the differential conductance for the NIS structure within the wave-matching method based on the Bogoliubov-de Gennes equation and the matrix method based on the normal-state scattering matrix and find that the two models agree for highly-doped N and S contacts. We also show that the effect of a possible Rashba spin-orbit interaction on the differential conductance can be significant for weakly doped N and S contacts. Our findings should be important in samples with a large aspect ratio where bulk contributions in transport are dominant.

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“…Although a magnetic field also induces an orbital effect not taken into account here, we note that the vector potential of a perpendicular magnetic field induces an additional Zeeman splitting between the Kramer spins with an effective giant g-factor of g * ∼ 55.5 [28] so that only small external magnetic fields below 1 T would be needed. The resulting QW system is described in terms of the BHZ model [20], complemented with extra terms accounting for BIA [22], Rashba-SOC [21], Zeeman field [22,29] and the proximity to an s-wave superconductor [30]. The Hamiltonian can be written in the basis…”

Section: The Modelmentioning

confidence: 99%

Chiral Majorana edge states in HgTe quantum wells

Weithofer

Recher

2013

New J. Phys.

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HgTe-based quantum wells (QWs) recently attracted a lot of attention for the realization of a two-dimensional topological insulator with protected helical edge states. Another class of topological systems is topological superconductors (TSCs) with Majorana edge states. In this paper, we show how proximity induced s-wave superconductivity in the bulk of HgTe-QWs and in the presence of a Zeeman field can exhibit a TSC with chiral Majorana edge states. We calculate the topological invariants and the corresponding Majorana edge states explicitly within a four-band model accounting for inversion symmetry breaking terms due to the Rashba spin-orbit coupling and bulk inversion asymmetry present in these QWs.

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Andreev spectroscopy of doped HgTe quantum wells

Cited by 16 publications

References 45 publications

Probing the helical edge states of a topological insulator by Cooper-pair injection

Probing the helical edge states of a topological insulator by Cooper-pair injection

Bulk transport through superconducting hybrid structures in HgTe quantum wells

Chiral Majorana edge states in HgTe quantum wells

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