Quantized spin Hall conductance in a magnetically doped two dimensional topological insulator

Shamim, Saquib; Beugeling, Wouter; Shekhar, Pragya; Bendias, Kalle; Lunczer, Lukas; Kleinlein, Johannes; Buhmann, H.; Molenkamp, L. W.

doi:10.1038/s41467-021-23262-1

Cited by 23 publications

(14 citation statements)

References 31 publications

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“…We have observed the quantized spin Hall resistance of h/2e 2 for microscopic devices fabricated using the wetetching process from similar (Hg,Mn)Te quantum wells (see Supplementary Figure 1, Supplementary Note 1 and Ref. [15]). When the chemical potential is tuned in the bulk gap regime (around V * g = 0 V) or the valence band (negative V * g ), the application of a small magnetic field (> 50 mT) results in the formation of emergent quantum Hall plateaus, as evidenced by the quantization of the transverse resistance R xy to −h/e 2 (solid lines in Fig.…”

Section: Resultsmentioning

confidence: 94%

Counterpropagating topological and quantum Hall edge channels

Shamim,

Shekhar,

Beugeling

et al. 2022

Preprint

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The survival of the quantum spin Hall edge channels in presence of an external magnetic field has been a subject of experimental and theoretical research. The inversion of Landau levels that accommodates the quantum spin Hall effect is destroyed at a critical magnetic field, and a trivial insulating gap appears in the spectrum for stronger fields. In this work, we report the absence of this transport gap in disordered two dimensional topological insulators in perpendicular magnetic fields of up to 16 T. Instead, we observe that a topological edge channel (from band inversion) coexists with a counterpropagating quantum Hall edge channel for magnetic fields at which the transition to the insulating regime is expected. For larger fields, we observe only the quantum Hall edge channel with transverse resistance close to h/e 2 . By tuning the disorder using different fabrication processes, we find evidence that this unexpected ν = 1 plateau originates from extended quantum Hall edge channels along a continuous network of charge puddles at the edges of the device.

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Section: Resultsmentioning

confidence: 94%

Counterpropagating topological and quantum Hall edge channels

Shamim,

Shekhar,

Beugeling

et al. 2022

Preprint

Self Cite

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“…Let us now elaborate at the microscopic level how the above explained spin conservation analysis works in the case of the helical edge coupled to an array of the MIs. Such systems regain at present an increased attention since they can provide a platform for the realization of chiral Majorana fermions [55]. The MI can be correlated either via the indirect exchange interaction supported by the itinerant electrons (usually referred to as 'the Kondo array' (KA)) or via the both indirect and direct Heisenberg interaction (usually named 'the Kondo-Heisenberg array' (KHA)).…”

Section: Helical Modes Interacting With a Kondo-heisenberg Array-a Ca...mentioning

confidence: 99%

Protection of edge transport in quantum spin Hall samples: spin-symmetry based general approach and examples

Yevtushenko

Yudson

2022

New J. Phys.

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Understanding possible mechanisms, which can lead to suppression of helical edge transport in Quantum Spin Hall (QSH) systems, attracted huge attention right after the first experiments revealing the fragility of the ballistic conductance. Despite the very intensive research and the abundance of theoretical models, the fully consistent explanation of the experimental results is still lacking. We systematize various theories of helical transport with the help of the spin conservation analysis which allows one to single out setups with the ballistic conductance being robustly protected regardless of the electron backscattering. First, we briefly review different theories of edge transport in the QSH samples with and without the spin axial symmetry of the electrons including those theoretical predictions which are not consistent with the spin conservation analysis and, thus, call for a deeper study. Next, we illustrate the general approach by a detailed study of representative examples. One of them addresses the helical edge coupled to an array of Heisenberg-interacting magnetic impurities (MIs) and demonstrates that the conductance remains ballistic even if the time-reversal symmetry on the edge is (locally) broken but the total spin is conserved. Another example focuses on the effects of the space-fluctuating spin-orbit interaction on the QSH edge. It reveals weakness of the protection in several cases, including, e.g., the presence of either the U(1)-symmetric, though not fully isotropic, MIs or generic electron-electron interactions.

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“…By combining the scattering at the QPC, described in Eqs. (31) and (35), with the generic reflection matrix in Eq. ( 11) of the main text, it is straightforward to compute the coefficients of the resulting scattering matrix on the FIG.…”

Section: Particular Values Of Phase and Energymentioning

confidence: 99%

“…To date, 2DTIs have been proposed and realized in a variety of materials [21][22][23][24][25][26][27][28][29]. One of the most mature platforms is represented by HgTe quantum wells where robust ballistic transport on the edges has been experimentally observed [1,[30][31][32] and superconducting contacts have been successfully fabricated [33]. The latter advancement has allowed for the realization of 2DTI-based Josephson junctions (JJs) and to the subsequent observation of fractional Josephson effect [34][35][36] and superconducting edge transport [33,35].…”

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confidence: 99%

Spin-resolved spectroscopy of helical Andreev bound states

Calzona,

Trauzettel

2021

Preprint

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We propose a versatile setup that allows performing spin-resolved spectroscopy of helical Andreev bound states, proving their existence and therefore the topological nature of the Josephson junction that hosts them. The latter is realized on the helical edge of a 2D topological insulator, proximitized with two superconducting electrodes. The spectroscopic analysis is enabled by a quantum point contact, which couples the junction with another helical edge acting as a spin-sensitive prove. By means of straightforward transport measurements, it is possible to detect the particular spin structure of the helical Andreev bound state and to shine light on the mechanism responsible for their existence, i.e. the presence of protected Andreev reflection within the Josephson junction. We discuss the robustness of this helical Andreev spectrometer with respect to processes that weaken spin to charge conversion.

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Quantized spin Hall conductance in a magnetically doped two dimensional topological insulator

Cited by 23 publications

References 31 publications

Counterpropagating topological and quantum Hall edge channels

Counterpropagating topological and quantum Hall edge channels

Protection of edge transport in quantum spin Hall samples: spin-symmetry based general approach and examples

Spin-resolved spectroscopy of helical Andreev bound states

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