11 research outputs found
Prediction of a novel type-I antiferromagnetic Weyl semimetal
Topological materials have been a main focus of studies in the past decade
due to their protected properties that can be exploited for the fabrication of
new devices. Among them, Weyl semimetals are a class of topological semimetals
with non-trivial linear band crossing close to the Fermi level. The existence
of such crossings requires the breaking of either time-reversal or inversion
symmetry and is responsible for the exotic physical properties.
In this work we identify the full-Heusler compound InMnTi, as a
promising, easy to synthesize, - and -breaking Weyl semimetal. This
material exhibits several features that are comparatively more intriguing with
respect to other known Weyl semimetals: the distance between two neighboring
nodes is large enough to observe a wide range of linear dispersions in the
bands, and only one kind of such node's pairs is present in the Brillouin zone.
We also show the presence of Fermi arcs stable across a wide range of chemical
potentials. Finally, the lack of contributions from trivial points to the
low-energy properties makes the materials a promising candidate for practical
devices
Pulay forces in density-functional theory with extended Hubbard functionals: From nonorthogonalized to orthogonalized manifolds
We present a derivation of the exact expression for Pulay forces in
density-functional theory calculations augmented with extended Hubbard
functionals, and arising from the use of orthogonalized atomic orbitals as
projectors for the Hubbard manifold. The derivative of the inverse square root
of the orbital overlap matrix is obtained as a closed-form solution of the
associated Lyapunov (Sylvester) equation. The expression for the resulting
contribution to the forces is presented in the framework of ultrasoft
pseudopotentials and the projector-augmented-wave method, and using a plane
wave basis set. We have benchmarked the present implementation with respect to
finite differences of total energies for the case of NiO, finding excellent
agreement. Owing to the accuracy of Hubbard-corrected density-functional theory
calculations - provided the Hubbard parameters are computed for the manifold
under consideration - the present work paves the way for systematic studies of
solid-state and molecular transition-metal and rare-earth compounds.Comment: 16 pages, 1 figur
Born effective charges and vibrational spectra in super and bad conducting metals
Interactions mediated by electron-phonon coupling are responsible for
important cooperative phenomena in metals such as superconductivity and
charge-density waves. The same interaction mechanisms produce strong collision
rates in the normal phase of correlated metals, causing sizeable reductions of
the dc conductivity and reflectivity. As a consequence, low-energy excitations
like phonons, which are crucial for materials characterization, become visible
in optical infrared spectra. A quantitative assessment of vibrational
resonances requires the evaluation of dynamical Born effective charges, which
quantify the coupling between macroscopic electric fields and lattice
deformations. We show that the Born effective charges of metals crucially
depend on the collision regime of conducting electrons. In particular, we
describe, within a first principles framework, the impact of electron
scattering on the infrared vibrational resonances, from the undamped,
collisionless regime to the overdamped, collision-dominated limit. Our approach
enables the interpretation of vibrational reflectance measurements of both
super and bad conducting metals, as we illustrate for the case of strongly
electron-phonon coupled superhydride HS
Rapid Detection of Coherent Tunneling in an InAs Nanowire Quantum Dot through Dispersive Gate Sensing
Dispersive sensing is a powerful technique that enables scalable and
high-fidelity readout of solid-state quantum bits. In particular, gate-based
dispersive sensing has been proposed as the readout mechanism for future
topological qubits, which can be measured by single electrons tunneling through
zero-energy modes. The development of such a readout requires resolving the
coherent charge tunneling amplitude from a quantum dot in a Majorana-zero-mode
host system faithfully on short time scales. Here, we demonstrate rapid
single-shot detection of a coherent single-electron tunneling amplitude between
InAs nanowire quantum dots. We have realized a sensitive dispersive detection
circuit by connecting a sub-GHz, lumped element microwave resonator to a
high-lever arm gate on one of dots. The resulting large dot-resonator coupling
leads to an observed dispersive shift that is of the order of the resonator
linewidth at charge degeneracy. This shift enables us to differentiate between
Coulomb blockade and resonance, corresponding to the scenarios expected for
qubit state readout, with a signal to noise ratio exceeding 2 for an
integration time of 1 microsecond. Our result paves the way for single shot
measurements of fermion parity on microsecond timescales in topological qubits.Comment: 6 pages, 4 figure
Ballistic InSb Nanowires and Networks via Metal-Sown Selective Area Growth
Selective area growth is a promising technique to realize semiconductor-superconductor hybrid nanowire networks, potentially hosting topologically protected Majorana-based qubits. In some cases, however, such as the molecular beam epitaxy of InSb on InP or GaAs substrates, nucleation and selective growth conditions do not necessarily overlap. To overcome this challenge, we propose a metal-sown selective area growth (MS SAG) technique, which allows decoupling selective deposition and nucleation growth conditions by temporarily isolating these stages. It consists of three steps: (i) selective deposition of In droplets only inside the mask openings at relatively high temperatures favoring selectivity, (ii) nucleation of InSb under Sb flux from In droplets, which act as a reservoir of group III adatoms, done at relatively low temperatures, favoring nucleation of InSb, and (iii) homoepitaxy of InSb on top of the formed nucleation layer under a simultaneous supply of In and Sb fluxes at conditions favoring selectivity and high crystal quality. We demonstrate that complex InSb nanowire networks of high crystal and electrical quality can be achieved this way. We extract mobility values of 10※000-25※000 cm V s consistently from field-effect and Hall mobility measurements across single nanowire segments as well as wires with junctions. Moreover, we demonstrate ballistic transport in a 440 nm long channel in a single nanowire under a magnetic field below 1 T. We also extract a phase-coherent length of ∼8 μm at 50 mK in mesoscopic rings
Selectivity Map for Molecular Beam Epitaxy of Advanced III-V Quantum Nanowire Networks
This is an open access article published under an ACS AuthorChoice License. See Standard ACS AuthorChoice/Editors' Choice Usage Agreement - https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlSelective-area growth is a promising technique for enabling of the fabrication of the scalable III-V nanowire networks required to test proposals for Majorana-based quantum computing devices. However, the contours of the growth parameter window resulting in selective growth remain undefined. Herein, we present a set of experimental techniques that unambiguously establish the parameter space window resulting in selective III-V nanowire networks growth by molecular beam epitaxy. Selectivity maps are constructed for both GaAs and InAs compounds based on in situ characterization of growth kinetics on GaAs(001) substrates, where the difference in group III adatom desorption rates between the III-V surface and the amorphous mask area is identified as the primary mechanism governing selectivity. The broad applicability of this method is demonstrated by the successful realization of high-quality InAs and GaAs nanowire networks on GaAs, InP, and InAs substrates of both (001) and (111)B orientations as well as homoepitaxial InSb nanowire networks. Finally, phase coherence in Aharonov-Bohm ring experiments validates the potential of these crystals for nanoelectronics and quantum transport applications. This work should enable faster and better nanoscale crystal engineering over a range of compound semiconductors for improved device performance
Framework for adapting an agile way of working.
This paper aims to propose a multilevel theoretical framework and a set of valuepropositionsto reflect on the adoption of agileworking.We construct a multilevel framework for an agile workingadoptionstrategyby examiningthemost importantinternaland externalvariables.Results find that four components composed of contextual, structural, social andindividual variables are able to influence the adoption of agile working. In addition, a number offactorsthat can facilitateorpreventchangearepresented.This paper aims to provide a valuable contribution to the adoption of agilework, which has increased dramatically during Covid-19 and the lockdown but is still under-explored.Weproposeaframeworkandsetofpropositions,butwedonottestthem.Moreresearchshouldbeconducted aboutthis framework
Ballistic InSb Nanowires and Networks via Metal-Sown Selective Area Growth
Selective area growth is a promising technique to realize semiconductor-superconductor hybrid nanowire networks, potentially hosting topologically protected Majorana-based qubits. In some cases, however, such as the molecular beam epitaxy of InSb on InP or GaAs substrates, nucleation and selective growth conditions do not necessarily overlap. To overcome this challenge, we propose a metal-sown selective area growth (MS SAG) technique, which allows decoupling selective deposition and nucleation growth conditions by temporarily isolating these stages. It consists of three steps: (i) selective deposition of In droplets only inside the mask openings at relatively high temperatures favoring selectivity, (ii) nucleation of InSb under Sb flux from In droplets, which act as a reservoir of group III adatoms, done at relatively low temperatures, favoring nucleation of InSb, and (iii) homoepitaxy of InSb on top of the formed nucleation layer under a simultaneous supply of In and Sb fluxes at conditions favoring selectivity and high crystal quality. We demonstrate that complex InSb nanowire networks of high crystal and electrical quality can be achieved this way. We extract mobility values of 10※000-25※000 cm V s consistently from field-effect and Hall mobility measurements across single nanowire segments as well as wires with junctions. Moreover, we demonstrate ballistic transport in a 440 nm long channel in a single nanowire under a magnetic field below 1 T. We also extract a phase-coherent length of ∼8 μm at 50 mK in mesoscopic rings
Selectivity Map for Molecular Beam Epitaxy of Advanced III-V Quantum Nanowire Networks
This is an open access article published under an ACS AuthorChoice License. See Standard ACS AuthorChoice/Editors' Choice Usage Agreement - https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlSelective-area growth is a promising technique for enabling of the fabrication of the scalable III-V nanowire networks required to test proposals for Majorana-based quantum computing devices. However, the contours of the growth parameter window resulting in selective growth remain undefined. Herein, we present a set of experimental techniques that unambiguously establish the parameter space window resulting in selective III-V nanowire networks growth by molecular beam epitaxy. Selectivity maps are constructed for both GaAs and InAs compounds based on in situ characterization of growth kinetics on GaAs(001) substrates, where the difference in group III adatom desorption rates between the III-V surface and the amorphous mask area is identified as the primary mechanism governing selectivity. The broad applicability of this method is demonstrated by the successful realization of high-quality InAs and GaAs nanowire networks on GaAs, InP, and InAs substrates of both (001) and (111)B orientations as well as homoepitaxial InSb nanowire networks. Finally, phase coherence in Aharonov-Bohm ring experiments validates the potential of these crystals for nanoelectronics and quantum transport applications. This work should enable faster and better nanoscale crystal engineering over a range of compound semiconductors for improved device performance