Spin-Nano

Institutions
  • FB Physik
Publications
    Pearce, Alexander J.; Burkard, Guido(2017): Electron spin relaxation in a transition-metal dichalcogenide quantum dot 2D Materials ; 4 (2017), 2. - 025114. - eISSN 2053-1583

Electron spin relaxation in a transition-metal dichalcogenide quantum dot

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We study the relaxation of a single electron spin in a circular quantum dot in a transition-metal dichalcogenide monolayer defined by electrostatic gating. Transition-metal dichalcogenides provide an interesting and promising arena for quantum dot nano-structures due to the combination of a band gap, spin-valley physics and strong spin–orbit coupling. First we will discuss which bound state solutions in different B-field regimes can be used as the basis for qubits states. We find that at low B-fields combined spin-valley Kramers qubits to be suitable, while at large magnetic fields pure spin or valley qubits can be envisioned. Then we present a discussion of the relaxation of a single electron spin mediated by electron–phonon interaction via various different relaxation channels. In the low B-field regime we consider the spin-valley Kramers qubits and include impurity mediated valley mixing which will arise in disordered quantum dots. Rashba spin–orbit admixture mechanisms allow for relaxation by in-plane phonons either via the deformation potential or by piezoelectric coupling, additionally direct spin-phonon mechanisms involving out-of-plane phonons give rise to relaxation. We find that the relaxation rates scale as α B<sup>6</sup> for both in-plane phonons coupling via deformation potential and the piezoelectric effect, while relaxation due to the direct spin-phonon coupling scales independant to B-field to lowest order but depends strongly on device mechanical tension. We will also discuss the relaxation mechanisms for pure spin or valley qubits formed in the large B-field regime.

Origin (projects)

  Rancic, Marko J.; Burkard, Guido(2017): Ultracoherent operation of spin qubits with superexchange coupling Physical Review B ; 96 (2017), 20. - 201304. - ISSN 2469-9950. - eISSN 2469-9969

Ultracoherent operation of spin qubits with superexchange coupling

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With the use of nuclear-spin-free materials such as silicon and germanium, spin-based quantum bits (qubits) have evolved to become among the most coherent systems for quantum information processing. The new frontier for spin qubits has therefore shifted to the ubiquitous charge noise and spin-orbit interaction, which are limiting the coherence times and gate fidelities of solid-state qubits. In this paper we investigate superexchange, as a means of indirect exchange interaction between two single electron spin qubits, each embedded in a single semiconductor quantum dot (QD), mediated by an intermediate, empty QD. Our results suggest the existence of “supersweet spots”, in which the qubit operations implemented by superexchange interaction are simultaneously first-order-insensitive to charge noise and to errors due to spin-orbit interaction. The proposed spin-qubit architecture is scalable and within the manufacturing capabilities of semiconductor industry.

Origin (projects)

  Brooks, Matthew; Burkard, Guido(2017): Spin-degenerate regimes for single quantum dots in transition metal dichalcogenide monolayers Physical Review B ; 95 (2017), 24. - 245411. - ISSN 2469-9950. - eISSN 2469-9969

Spin-degenerate regimes for single quantum dots in transition metal dichalcogenide monolayers

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Brooks, Matthew; Burkard, Guido

Origin (projects)

  Pearce, Alexander J.; Mariani, Eros; Burkard, Guido(2016): Tight-Binding Approach to Strain and Curvature in Monolayer Transition-Metal Dichalcogenides Physical Review B ; 94 (2016), 15. - 155416. - ISSN 2469-9950. - eISSN 2469-9969

Tight-Binding Approach to Strain and Curvature in Monolayer Transition-Metal Dichalcogenides

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We present a model of the electronic properties of monolayer transition-metal dichalcogenides based on a tight binding approach which includes the effects of strain and curvature of the crystal lattice. Mechanical deformations of the lattice offer a powerful route for tuning the electronic structure of the transition-metal dichalcogenides, as changes to bond lengths lead directly to corrections in the electronic Hamiltonian while curvature of the crystal lattice mixes the orbital structure of the electronic Bloch bands. We first present an effective low energy Hamiltonian describing the electronic properties near the K point in the Brillouin zone, then present the corrections to this Hamiltonian due to arbitrary mechanical deformations and curvature in a way which treats both effects on an equal footing. This analysis finds that local area variations of the lattice allow for tuning of the band gap and effective masses, while the application of uniaxial strain decreases the magnitude of the direct band gap at the K point. Additionally, strain induced bond length modifications create a fictitious gauge field with a coupling strength that is smaller than that seen in related materials like graphene. We also find that curvature of the lattice leads to the appearance of both an effective in-plane magnetic field which couples to spin degrees of freedom and a Rashba-like spin-orbit coupling due to broken mirror inversion symmetry.

Origin (projects)

Funding sources
NameProject no.DescriptionPeriod
Europäische Union435/16no information
Further information
Period: 01.01.2016 – 31.12.2017