100 research outputs found
Strong interplay between electron-phonon interaction and disorder in low doped systems
The effects of doping on the spectral properties of low doped systems are
investigated by means of Coherent Potential Approximation to describe the
distributed disorder induced by the impurities and Phonon-Phonon Non-Crossing
Approximation to characterize a wide class of electron-phonon interactions
which dominate the low-energy spectral features. When disorder and
electron-phonon interaction work on comparable energy scales, a strong
interplay between them arises, the effect of disorder can no more be described
as a mere broadening of the spectral features and the phonon signatures are
still visible despite the presence of strong disorder. As a consequence, the
disorder-induced metal-insulator transition, is strongly affected by a weak or
moderate electron-phonon coupling which is found to stabilize the insulating
phase.Comment: New version with improved bibliography and discussio
Unconventional superconductivity in a doped quantum spin Hall insulator
A monolayer of jacutingaite (PtHgSe) has recently been identified as
a novel quantum spin Hall insulator. By first-principles calculations, we study
its Fermiology in the doped regime and unveil a type-I and type-II van Hove
singularity for hole and electron doping, respectively. We find that the common
link between the propensity for a topological band gap at pristine filling and
unconventional superconductivity at finite doping roots in the longer ranged
hybridization integrals on the honeycomb lattice. In a combined effort of
random phase approximation and functional renormalization group, we find chiral
-wave order for the type-I and odd-parity -wave order for the type-II
regime.Comment: 5 pages, 4 figures, Supplemental Materia
Substrate-supported triplet superconductivity in Dirac semimetals
Stimulated by the success of graphene and its emerging Dirac physics, the
quest for versatile and tunable electronic properties in atomically thin
systems has led to the discovery of various chemical classes of 2D compounds.
In particular, honeycomb lattices of group-IV elements, such as silicene and
germanene, have been found experimentally. Whether it is a necessity of
synthesis or a desired feature for application purposes, most 2D materials
demand a supporting substrate. In this work, we highlight the constructive
impact of substrates to enable the realization of exotic electronic quantum
states of matter, where the buckling emerges as the decisive material parameter
adjustable by the substrate. At the example of germanene deposited on MoS,
we find that the coupling between the monolayer and the substrate, together
with the buckled hexagonal geometry, conspire to provide a highly suited
scenario for unconventional triplet superconductivity upon adatom-assisted
doping.Comment: 11 pages, 8 figure
Emergence of ferroelectricity and spin-valley properties in two-dimensional honeycomb binary compounds
By means of density functional theory calculations, we predict that several
two dimensional AB binary monolayers, where A and B atoms belong to group IV or
III-V, are ferroelectric. Dipoles arise from the buckled structure, where the A
and B ions are located on the sites of a bipartite corrugated honeycomb lattice
with trigonal symmetry. We discuss the emerging valley-dependent properties and
the coupling of spin and valley physics, which arise from the loss of inversion
symmetry, and explore the interplay between ferroelectricity and Rashba
spin-spitting phenomena. We show that valley-related properties originate
mainly from the binary nature of AB monolayers, while the Rashba spin-texture
developing around valleys is fully controllable and switchable by reversing the
ferroelectric polarization
Custodial glide symmetry of quantum spin Hall edge modes in WTe monolayer
A monolayer of WTe has been shown to display quantum spin Hall (QSH) edge
modes persisting up to 100~K in transport experiments. Based on
density-functional theory calculations and symmetry-based model building
including the role of correlations and substrate support, we develop an
effective electronic model for WTe which fundamentally differs from other
prototypical QSH settings: we find that the extraordinary robustness of quantum
spin Hall edge modes in WTe roots in a glide symmetry due to which the
topological gap opens away from high-symmetry points in momentum space. While
the indirect bulk gap is much smaller, the glide symmetry implies a large
direct gap of up to 1~eV in the Brillouin zone region of the dispersing edge
modes, and hence enables sharply boundary-localized QSH edge states depending
on the specific boundary orientation.Comment: 4+ page
Fe/GeTe(111) heterostructures as an avenue towards 'ferroelectric Rashba semiconductors'-based spintronics
By performing density functional theory (DFT) and Green's functions
calculations, complemented by X-ray Photoemission Spectroscopy, we investigate
the electronic structure of Fe/GeTe(111), a prototypical
ferromagnetic/Rashba-ferroelectric interface. We reveal that such system
exhibits several intriguing properties resulting from the complex interplay of
exchange interaction, electric polarization and spin-orbit coupling. Despite a
rather strong interfacial hybridization between Fe and GeTe bands, resulting in
a complete suppression of the surface states of the latter, the bulk Rashba
bands are hardly altered by the ferromagnetic overlayer. This could have a deep
impact on spin dependent phenomena observed at this interface, such as
spin-to-charge interconversion, which are likely to involve bulk rather than
surface Rashba states.Comment: 8 pages, 4 figure
Strongly correlated double Dirac fermions
Double Dirac fermions have recently been identified as possible
quasiparticles hosted by three-dimensional crystals with particular
non-symmorphic point group symmetries. Applying a combined approach of
ab-initio methods and dynamical mean field theory, we investigate how
interactions and double Dirac band topology conspire to form the electronic
quantum state of BiCuO. We derive a downfolded eight-band model of the
pristine material at low energies around the Fermi level. By tuning the model
parameters from the free band structure to the realistic strongly correlated
regime, we find a persistence of the double Dirac dispersion until its
constituting time reveral symmetry is broken due to the onset of magnetic
ordering at the Mott transition. We analyze pressure as a promising route to
realize a double-Dirac metal in BiCuO
Intertwined Rashba, Dirac and Weyl Fermions in Hexagonal Hyperferroelectrics
By means of density functional theory based calculations, we study the role
of spin-orbit coupling in the new family of ABC hyperferroelectrics [Phys. Rev.
Lett. 112, 127601 (2014)]. We unveil an extremely rich physics strongly linked
to ferroelectric properties, ranging from the electric control of bulk Rashba
effect to the existence of a three dimensional topological insulator phase,
with concomitant topological surface states even in the ultrathin film limit.
Moreover, we predict that the topological transition, as induced by alloying,
is followed by a Weyl semi-metal phase of finite concentration extension, which
is robust against disorder, putting forward hyperferroelectrics as promising
candidates for spin-orbitronic applications.Comment: 5 pages, 3 figure
The origin of Mooij correlations in disordered metals
Sufficiently disordered metals display systematic deviations from the
behavior predicted by semi-classical Boltzmann transport theory. Here the
scattering events from impurities or thermal excitations can no longer be
considered as additive independent processes, as asserted by Matthiessen's rule
following from this picture. In the intermediate region between the regime of
good conduction and that of insulation, one typically finds a change of sign of
the temperature coefficient of resistivity (TCR), even at elevated temperature
spanning ambient conditions, a phenomenology that was first identified by Mooij
in 1973. Traditional weak coupling approaches to identify relevant corrections
to the Boltzmann picture focused on long distance interference effects such as
"weak localization", which are especially important in low dimensions (1D, 2D)
and close to the zero temperature limit. Here we formulate a strong-coupling
approach to tackle the interplay of strong disorder and lattice deformations
(phonons) in bulk three-dimensional metals at high temperatures. We identify a
polaronic mechanism of strong disorder renormalization, which describes how a
lattice locally responds to the relevant impurity potential. This mechanism,
which quantitatively captures the Mooij regime, is physically distinct and
unrelated to Anderson localization, but realizes early seminal ideas of
Anderson himself, concerning the interplay of disorder and lattice
deformations
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