Angle-dependent magnetotransport in GaAs/InAs core/shell nanowires (original) (raw)

Flux periodic magnetoconductance oscillations in GaAs/InAs core/shell nanowires

Physical Review B, 2014

Magnetotransport experiments on epitaxial GaAs/InAs core/shell nanowires are performed in which the InAs shell forms a tube-like conductive channel around the highly resistive GaAs core. The core/shell nanowires are grown by molecular beam epitaxy. It is found that the nanowire conductance oscillates with the magnetic field oriented parallel to its axis, with a period of the magnetic flux quantum φ 0 = h/e. Related to that, it is shown that the electronic transport is mediated by closed loop quantum states encircling the wire axis rather than by electron interference of partial waves. By means of a gate voltage the conductance at zero magnetic field can be changed between an oscillation minimum and maximum. The experimental findings are supported by numerical calculations.

Magnetotransport properties of individual InAs nanowires

Physical Review B, 2009

We probe the magnetotransport properties of individual InAs nanowires in a field effect transistor geometry. In the low magnetic field regime we observe magnetoresistance that is well described by the weak localization (WL) description in diffusive conductors. The weak localization correction is modified to weak anti-localization (WAL) as the gate voltage is increased. We show that the gate voltage can be used to tune the phase coherence length ($l_\phi$) and spin-orbit length ($l_{so}$) by a factor of sim\simsim 2. In the high field and low temperature regime we observe the mobility of devices can be modified significantly as a function of magnetic field. We argue that the role of skipping orbits and the nature of surface scattering is essential in understanding high field magnetotransport in nanowires.

Electron Interference in Hall Effect Measurements on GaAs/InAs Core/Shell Nanowires

Nano Letters, 2017

We present low-temperature magnetotransport measurements on GaAs/InAs core/shell nanowires contacted by regular source−drain leads as well as laterally attached Hall contacts, which only touch parts of the nanowire sidewalls. Low-temperature measurements between source and drain contacts show typical phase coherent effects, such as universal conductance fluctuations in a magnetic field aligned perpendicularly to the nanowire axis as well as Aharonov− Bohm-type oscillations in a parallel aligned magnetic field. However, the signal between the Hall contacts shows a Hall voltage buildup, when the magnetic field is turned perpendicular to the nanowire axis while current is driven through the wire using the source−drain contacts. At low temperatures, the phase coherent effects measured between source and drain leads are superimposed on the Hall voltage, which can be explained by nonlocal probing of large segments of the nanowire. In addition, the Aharonov−Bohm-type oscillations are also observed in the magnetoconductance at magnetic fields aligned parallel to the nanowire axis, using the laterally contacted leads. This measurement geometry hereby directly corresponds to classical Aharonov−Bohm experiments using planar quantum rings. In addition, the Hall voltage is used to characterize the nanowires in terms of charge carrier concentration and mobility, using temperature-and gate-dependent measurements as well as measurements in tilted magnetic fields. The GaAs/InAs core/shell nanowire used in combination with laterally attached contacts is therefore the ideal system to three-dimensionally combine quantum ring experiments using the cross-sectional plane and Hall experiments using the axial nanowire plane.

Landau levels, edge states, and magnetoconductance in GaAs/AlGaAs core-shell nanowires

Physical Review B, 2013

Magnetic states of the electron gas confined in modulation-doped core-shell nanowires are calculated for a transverse field of arbitrary strength and orientation. Magneto-conductance is predicted within the Landauer approach. The modeling takes fully into account the radial material modulation, the prismatic symmetry and the doping profile of realistic GaAs/AlGaAs devices within an envelope-function approach, and electron-electron interaction is included in a mean-field selfconsistent approach. Calculations show that in the low free-carrier density regime, magnetic states can be described in terms of Landau levels and edge states, similar to planar two-dimensional electron gases in a Hall bar. However, at higher carrier density the dominating electron-electron interaction leads to a strongly inhomogeneous localization at the prismatic heterointerface. This gives rise to a complex band dispersion, with local minima at finite values of the longitudinal wave vector, and a region of negative magneto-resistance. The predicted marked anisotropy of the magneto-conductance with field direction is a direct probe of the inhomogeneous electron gas localization of the conductive channel induced by the prismatic geometry.

Magneto-optics of electronic transport in nanowires

Physical Review B, 1998

Effects of irradiation on the electronic conductance in nanowires, for field-free conditions and under the influence of applied longitudinal magnetic fields, were investigated. The nanowires were modeled within the free-electron framework with a parabolic ͑transverse͒ confining potential. Our results for the dependence of the photoconductance of irradiated nanowires on the photon energy and/or the strength of the applied magnetic field show that such measurements may be used as a magneto-optic spectroscopy for determination of ͑i͒ the electron Fermi energy, ͑ii͒ the electron effective mass, and ͑iii͒ the number of quantized modes in the nanowire. Such measurements may also be used to assess to what degree the electron transport through the nanowire is adiabatic. Furthermore, our results suggest a method for controlling and tuning electronic transport in nanowires via external electromagnetic fields. ͓S0163-1829͑98͒07348-2͔

Magnetotransport Subband Spectroscopy in InAs Nanowires

Physical Review Letters, 2014

We report on magneto-transport measurements in InAs nanowires under large magnetic field (up to 55T), providing a direct spectroscopy of the 1D electronic band structure. Large modulations of the magneto-conductance mediated by an accurate control of the Fermi energy reveal the Landau fragmentation, carrying the fingerprints of the confined InAs material. Our numerical simulations of the magnetic band structure consistently support the experimental results and reveal key parameters of the electronic confinement.

Vectorial control of the spin-orbit interaction in suspended InAs nanowires

Nano Letters

Semiconductor nanowires featuring strong spin-orbit interactions (SOI), represent a promising platform for a broad range of novel technologies, such as spintronic applications or topological quantum computation. However, experimental studies into the nature and the orientation of the SOI vector in these wires remain limited despite being of upmost importance. Typical devices feature the nanowires placed on top of a substrate which modifies the SOI vector and spoils the intrinsic symmetries of the system. In this work, we report experimental results on suspended InAs nanowires, in which the wire symmetries are fully preserved and clearly visible in transport measurements. Using a vectorial magnet, the non-trivial evolution of weak anti-localization (WAL) is tracked through all 3D space, and both the spin-orbit length l SO and coherence length l ϕ are determined as a function of the magnetic field magnitude and direction. Studying the angular maps of the WAL signal, we demonstrate that the average SOI within the nanowire is isotropic and that our findings are consistent with a semiclassical quasi-1D model of WAL adapted to include the geometrical constraints of the nanostructure. Moreover, by acting on properly designed side gates, we apply an external electric field introducing an additional vectorial Rashba spin-orbit component whose strength can be controlled by external means. These results give important hints on the intrinsic nature of suspended nanowire and can be interesting for the field of spintronics as well as for the manipulation of Majorana bound states in devices based on hybrid semiconductors.

Crystal orientation dependence of the spin-orbit coupling in InAs nanowires

Physical Review B

We compare the spin-orbit interaction (SOI) in InAs nanowires grown in the conventional 0001 crystal direction and the perpendicular 0110 direction. It is theoretically shown that, for individual transverse modes, the intrinsic contribution due to the bulk inversion asymmetry of the crystal vanishes for wires in the 0001 direction but remains finite for 0110. Experimental spin-orbit scattering lengths extracted from low-temperature magnetoresistance measurements of individual nanowires yields, however, comparable values in the two cases, suggesting that the intrinsic intramode spin-orbit term is not the dominant source of the SOI. We discuss the implications for the manipulation of SOI in nanowire devices.

Anomalous ambipolar transport in depleted GaAs nanowires

Physical review, 2022

We have used a polarized microluminescence technique to investigate photocarrier charge and spin transport in n-type depleted GaAs nanowires (≈ 10 17 cm −3 doping level). At 6K, a longdistance tail appears in the luminescence spatial profile, indicative of charge and spin transport, only limited by the length of the NW. This tail is independent on excitation power and temperature. Using a self-consistent calculation based on the drift-diffusion and Poisson equations as well as on photocarrier statistics (Van Roosbroeck model), it is found that this tail is due to photocarrier drift in an internal electric field nearly two orders of magnitude larger than electric fields predicted by the usual ambipolar model. This large electric field appears because of two effects. Firstly, for transport in the spatial fluctuations of the conduction band minimum and valence band maximum, the electron mobility is activated by the internal electric field. This implies, in a counter intuitive way, that the spatial fluctuations favor long distance transport. Secondly, the range of carrier transport is further increased because of the finite NW length, an effect which plays a key role in one-dimensional systems.

Evidence for Spontaneous Spin-Polarized Transport in Magnetic Nanowires

Physical Review Letters, 2003

The exploitation of the spin in charge-based systems is opening revolutionary opportunities for device architecture. Surprisingly, room temperature electrical transport through magnetic nanowires is still an unresolved issue. Here, we show that ferromagnetic (Co) suspended atom chains spontaneously display an electron transport of half a conductance quantum, as expected for a fully polarized conduction channel. Similar behavior has been observed for Pd (a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal). These results suggest that the nanowire low dimensionality reinforces or induces magnetic behavior, lifting off spin degeneracy even at room temperature and zero external magnetic field.