Strain induced effects on the transport properties of metamorphic InAlAs/InGaAs quantum wells

“…25 As barriers. Details on the growth parameters can be found elsewhere 20 . A two dimensional electron gas (2DEG), confined in a narrow asymmetric In 0.75 Ga 0.…”

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confidence: 99%

Andreev reflection at the edge of a two-dimensional electron system with strong spin-orbit coupling

et al. 2013

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We experimentally investigate transport properties of a single planar junction between the niobium superconductor and the edge of a two-dimensional electron system in a narrow In0.75Ga0.25As quantum well with strong Rashba-type spin-orbit coupling. We experimentally demonstrate suppression of Andreev reflection at low biases at ultra low temperatures. From the analysis of temperature and magnetic field behavior, we interpret the observed suppression as a result of a spin-orbit coupling. There is also an experimental sign of the topological superconductivity realization in the present structure. Recent interest to transport investigations of hybrid superconductor-normal structures is mostly stimulated by the search for Majorana fermions, which are their own anti-particles 1 . The key feature of hybrid structures 2 is the allowed regime of topological superconductivity 3-5 . The regime of topological superconductivity is connected 3-5 with spectrum modification in normal metal, induced by cooperation of strong spin-orbit (SO) splitting ∆ SO , Zeeman splitting E Z and the gap ∆ ind induced due to a proximity with s-wave superconductor.For moderate values of magnetic fields (∆ SO > E Z ), topological superconductivity appears 3-5 in the regimeIt is clear, that experimental realization of this regime requires a normal conductor with strong SO coupling. Different types of normal conductors have been proposed: topological insulator 3 ; two-dimensional (2D) electron systems 6-8 ; one-dimensional (1D) semiconductor wires 9-11 . The experimental signatures of Majorana fermions have been only obtained in the case of 1D wires 12-14 . On the other hand, the edge of a 2D electron system is well-known to exhibit 1D behavior both in quantizing 15,16 and in zero 17,18 magnetic fields. Thus, it is quite reasonable 8 to study charge transport in a hybrid planar device, where the normal side is a 2D structure edge. Even disregarding Majorana problem, the physics is expected 19 to be quite sophisticated in the case of strong SO coupling in 2D system.Here, we experimentally investigate transport properties of a single planar junction between the niobium superconductor and the edge of a two-dimensional electron system in a narrow In 0.75 Ga 0.25 As quantum well with strong Rashba-type spin-orbit coupling. We experimentally demonstrate suppression of Andreev reflection at low biases at ultra low temperatures. From the analysis of temperature and magnetic field behavior, we interpret the observed suppression as a result of a spin-orbit coupling. There is also an experimental sign of the topological superconductivity realization in the present structure.Our samples are grown by solid source molecular beam epitaxy on semi-insulating GaAs substrates. The active layer is composed of a 20-nm thick In 0.75 Ga 0.25 As quantum well sandwiched between a lower 50-nm thick and an upper 120-nm thick In 0.75 Al 0.25 As barriers. Details on the growth parameters can be found elsewhere 20 . A two dimensional electron gas (2DEG), confined in a narrow a...

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“…We employ two dimensional electron gases (2DEGs) confined in metamorphic In .75 Ga .25 As/ In .75 Al .25 As heterostructures grown on undoped (001) GaAs substrates by solid-source molecular beam epitaxy 18,19 . A ≈1 µm-thick In x Al 1−x As "virtual crystal" with stepwise increasing indium concentration (x = 0.15 to 0.75) is grown between the GaAs substrate and the active region in order to match the GaAs lattice constant to that of In .75 Ga .25 As and In .75 Al .25 As.…”

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Singlet-triplet transition in a few-electron lateral In0.75Ga0.25As/In0.75Al0.25As quantum dot

Deon

Pellegrini

Carillo

et al. 2010

Applied Physics Letters

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The magnetic-field evolution of Coulomb blockade peaks in lateral In.75Ga.25As/ In.75Al.25As quantum dots in the few-electron regime is reported. Quantum dots are defined by gates evaporated onto a 60 nm-thick hydrogen silsesquioxane insulating film. A gyromagnetic factor g * ≈ 4.4 is measured via zero-bias spin spectroscopy and a transition from singlet to triplet spin configuration is found at an in-plane magnetic field B = 0.7 T. This observation opens the way to the manipulation of singlet and triplet states at moderate fields and its relevance for quantum information applications will be discussed.Renewed interest in quantum dots (QDs) defined by lateral electrostatic gates stems from the relevance of these systems in the field of quantum information processing. Indeed QDs containing few electron spins can be operated as qubits 1,2 . State initialization, measurement and quantum-gate operation were experimentally demonstrated 3,4 . Manipulation of the electron spin was obtained through magnetic fields or electrically by exploiting spin-orbit interaction 5 . Much of the experimental work performed so far is based on GaAs-based heterostructures, for which a well-established technology is available. On the other hand, InGaAs QDs with high In concentration are attractive systems for spin manipulation thanks to their high effective g-factor 6 and strong spin-orbit coupling 7,8 . Their exploitation was hindered, however, by the absence of a sufficiently large Schottky barrier. Indeed, the latter is virtually absent in In .75 Ga .25 As-metal contacts, a fact that stimulated the use of these alloys for the investigation of proximity effects 9 in hybrid semiconductor/superconductor devices 10,11 . Moreover, few-electron QDs were realized in InAs-based nanowires 12,13 . Recently, the realization of In .75 Ga .25 As lateral QDs was reported by Sun et al. 14 using atomic layer deposition-grown hafnium oxide and by Larsson et al., with an approach that combines wet chemical etching and metal gating 15,16 , following insulation by a 500 nm-thick dielectric layer.In this letter we report magnetotransport measurements on lateral In .75 Ga .25 As QDs defined on an In .75 Ga .25 As/In .75 Al .25 As heterostructure, with gate insulation obtained with a 60 nm-thick layer of hydrogen silsesquioxane (HSQ) 17 . We report a crossover from a singlet to a triplet spin state that occurs with an inplane magnetic field of 0.7 T. The observation that singlet and triplet spin states can be realized and manipulated in these lateral QDs at moderate fields offers promising venues for their exploitation in studies of spin physics and for quantum information processing.We employ two dimensional electron gases (2DEGs) confined in metamorphic In .75 Ga .25 As/ In .75 Al .25 As heterostructures grown on undoped (001) GaAs substrates by solid-source molecular beam epitaxy 18,19 . A ≈1 µm-thick In x Al 1−x As "virtual crystal" with stepwise increasing indium concentration (x = 0.15 to 0.75) is grown between the GaAs substrate and the active region...

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Strain induced effects on the transport properties of metamorphic InAlAs/InGaAs quantum wells

Cited by 77 publications

References 35 publications

Fast broad-band photon detector based on quantum well devices and charge-integrating electronics for non-invasive FEL monitoring

Fast broad-band photon detector based on quantum well devices and charge-integrating electronics for non-invasive FEL monitoring

Andreev reflection at the edge of a two-dimensional electron system with strong spin-orbit coupling

Singlet-triplet transition in a few-electron lateral In0.75Ga0.25As/In0.75Al0.25As quantum dot

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