Spin-1/2 Kondo effect in a InAs nanowire quantum dot: the Unitary limit, conductance scaling and Zeeman splitting (original) (raw)
Related papers
Physical Review B - Condensed Matter and Materials Physics, 2011
We report on a comprehensive study of spin-1 2 Kondo effect in a strongly coupled quantum dot realized in a high-quality InAs nanowire. The nanowire quantum dot is relatively symmetrically coupled to its two leads, so the Kondo effect reaches the unitary limit. The measured Kondo conductance demonstrates scaling with temperature, Zeeman magnetic field, and out-of-equilibrium bias. The suppression of the Kondo conductance with magnetic field is much stronger than would be expected based on a g-factor extracted from Zeeman splitting of the Kondo peak. This may be related to strong spin-orbit coupling in InAs.
Kondo-Enhanced Andreev Tunneling in InAs Nanowire Quantum Dots
Physical Review Letters, 2007
We report measurements of the nonlinear conductance of InAs nanowire quantum dots coupled to superconducting leads. We observe a clear alternation between odd and even occupation of the dot, with sub-gap-peaks at |V sd | = ∆/e markedly stronger(weaker) than the quasiparticle tunneling peaks at |V sd | = 2∆/e for odd(even) occupation. We attribute the enhanced ∆-peak to an interplay between Kondo-correlations and Andreev tunneling in dots with an odd number of spins, and substantiate this interpretation by a poor man's scaling analysis.
Conductance of a spin-1 quantum dot: The two-stage Kondo effect
Physical Review B, 2007
We discuss the physics of a of a spin-1 quantum dot, coupled to two metallic leads and develop a simple model for the temperature dependence of its conductance. Such quantum dots are described by a two-channel Kondo model with asymmetric coupling constants and the spin screening of the dot by the leads is expected to proceed via a two-stage process. When the Kondo temperatures of each channel are widely separated, on cooling, the dot passes through a broad cross-over regime dominated by underscreened Kondo physics. A singular, or non-fermi liquid correction to the conductance develops in this regime. At the lowest temperatures, destructive interference between resonant scattering in both channels leads to the eventual suppression of the conductance of the dot. We develop a model to describe the growth, and ultimate suppression of the conductance in the two channel Kondo model as it is screened successively by its two channels. Our model is based upon large-N approximation in which the localized spin degrees of freedom are described using the Schwinger boson formalism.
Direct measurement of the spin-orbit interaction in a two-electron InAs nanowire quantum dot
Physical Review Letters, 2007
We demonstrate control of the electron number down to the last electron in tunable few-electron quantum dots defined in catalytically grown InAs nanowires. Using low temperature transport spectroscopy in the Coulomb blockade regime we propose a simple method to directly determine the magnitude of the spin-orbit interaction in a two-electron artificial atom with strong spin-orbit coupling. Due to a large effective g-factor |g * | = 8 ± 1 the transition from singlet S to triplet T + groundstate with increasing magnetic field is dominated by the Zeeman energy rather than by orbital effects. We find that the spin-orbit coupling mixes the T + and S states and thus induces an avoided crossing with magnitude ∆ SO = 0.25±0.05 meV. This allows us to calculate the spin-orbit length λ SO ≈ 127 nm in such systems using a simple model.
Kondo effect in quantum dots coupled to ferromagnetic leads
2002
We study the Kondo effect in a quantum dot which is coupled to ferromagnetic leads and analyse its properties as a function of the spin polarization of the leads. Based on a scaling approach we predict that for parallel alignment of the magnetizations in the leads the strong-coupling limit of the Kondo effect is reached at a finite value of the magnetic field. Using an equation-of-motion technique we study nonlinear transport through the dot. For parallel alignment the zero-bias anomaly may be split even in the absence of an external magnetic field. For antiparallel spin alignment and symmetric coupling, the peak is split only in the presence of a magnetic field, but shows a characteristic asymmetry in amplitude and position.
Kondo physics in tunable semiconductor nanowire quantum dots
Physical Review B, 2006
We have observed the Kondo effect in strongly coupled semiconducting nanowire quantum dots. The devices are made from indium arsenide nanowires, grown by molecular beam epitaxy, and contacted by titanium leads. The device transparency can be tuned by changing the potential on a gate electrode, and for increasing transparencies the effects dominating the transport changes from Coulomb Blockade to Universal Conductance Fluctuations with Kondo physics appearing in the intermediate region.
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.
Kondo effect in quantum dots coupled to ferromagnetic leads with noncollinear magnetizations
Physica B: Condensed Matter, 2006
We study the Kondo effect in a quantum dot which is coupled to ferromagnetic leads and analyse its properties as a function of the spin polarization of the leads. Based on a scaling approach we predict that for parallel alignment of the magnetizations in the leads the strong-coupling limit of the Kondo effect is reached at a finite value of the magnetic field. Using an equation-of-motion technique we study nonlinear transport through the dot. For parallel alignment the zero-bias anomaly may be split even in the absence of an external magnetic field. For antiparallel spin alignment and symmetric coupling, the peak is split only in the presence of a magnetic field, but shows a characteristic asymmetry in amplitude and position.
Spintronic transport and Kondo effect in quantum dots
2005
We investigate the spin-dependent transport properties of quantum-dot based structures where Kondo correlations dominate the electronic dynamics. The coupling to ferromagnetic leads with parallel magnetizations is known to give rise to nontrivial effects in the local density of states of a single quantum dot. We show that this influence strongly depends on whether charge fluctuations are present or absent in the dot. This result is confirmed with numerical renormalization group calculations and perturbation theory in the on-site interaction. In the Fermi-liquid fixed point, we determine the correlations of the electric current at zero temperature (shot noise) and demonstrate that the Fano factor is suppressed below the Poissonian limit for the symmetric point of the Anderson Hamiltonian even for nonzero lead magnetizations. We discuss possible avenues of future research in this field: coupling to the low energy excitations of the ferromagnets (magnons), extension to double quantum dot systems with interdot antiferromagnetic interaction and effect of spin-polarized currents on higher symmetry Kondo states such as SU(4).
Spin dynamics in InAs nanowire quantum dots coupled to a transmission line
Physical Review B, 2008
We study theoretically electron spins in nanowire quantum dots placed inside a transmission line resonator. Because of the spin-orbit interaction, the spins couple to the electric component of the resonator electromagnetic field and enable coherent manipulation, storage, and read-out of quantum information in an all-electrical fashion. Coupling between distant quantum-dot spins, in one and the same or different nanowires, can be efficiently performed via the resonator mode either in real time or through virtual processes. For the latter case we derive an effective spin-entangling interaction and suggest means to turn it on and off. We consider both transverse and longitudinal types of nanowire quantum-dots and compare their manipulation timescales against the spin relaxation times. For this, we evaluate the rates for spin relaxation induced by the nanowire vibrations (phonons) and show that, as a result of phonon confinement in the nanowire, this rate is a strongly varying function of the spin operation frequency and thus can be drastically reduced compared to lateral quantum dots in GaAs. Our scheme is a step forward to the formation of hybrid structures where qubits of different nature can be integrated in a single device.