794 research outputs found
Absence of signatures of Weyl orbits in the thickness dependence of quantum transport in cadmium arsenide
In a Weyl orbit, the Fermi arc surface states on opposite surfaces of the
topological semimetal are connected through the bulk Weyl or Dirac nodes.
Having a real-space component, these orbits accumulate a sample-size-dependent
phase. Following recent work on the three-dimensional Dirac semimetal cadmium
arsenide (Cd3As2), we have sought evidence for this thickness-dependent effect
in quantum oscillations and quantum Hall plateaus in (112)-oriented Cd3As2 thin
films grown by molecular beam epitaxy. We compare quantum transport in films of
varying thickness at apparently identical gate-tuned carrier concentrations and
find no clear dependence of the relative phase of the quantum oscillations on
the sample thickness. We show that small variations in carrier densities,
difficult to detect in low-field Hall measurements, lead to shifts in quantum
oscillations that are commensurate with previously reported phase shifts.
Future claims of Weyl orbits based on the thickness dependence of quantum
transport data require additional studies that demonstrate that these competing
effects have been disentangled
Observation of the quantum Hall effect in confined films of the three-dimensional Dirac semimetal Cd3As2
The magnetotransport properties of epitaxial films of Cd3As2, a paradigm
three-dimensional Dirac semimetal, are investigated. We show that an energy gap
opens in the bulk electronic states of sufficiently thin films and, at low
temperatures, carriers residing in surface states dominate the electrical
transport. The carriers in these states are sufficiently mobile to give rise to
a quantized Hall effect. The sharp quantization demonstrates surface transport
that is virtually free of parasitic bulk conduction and paves the way for novel
quantum transport studies in this class of topological materials. Our results
also demonstrate that heterostructuring approaches can be used to study and
engineer quantum states in topological semimetals.Comment: Accepted, Phys. Rev. Let
Basal-plane growth of cadmium arsenide by molecular beam epitaxy
(001)-oriented thin films of the three-dimensional Dirac semimetal cadmium
arsenide can realize a quantum spin Hall insulator and other kinds of
topological physics, all within the flexible architecture of epitaxial
heterostructures. Here, we report a method for growing (001) cadmium arsenide
films using molecular beam epitaxy. The introduction of a thin indium arsenide
wetting layer improves surface morphology and structural characteristics, as
measured by x-ray diffraction and reflectivity, atomic force microscopy, and
scanning transmission electron microscopy. The electron mobility of 50-nm-thick
films is found to be 9300 cm2/Vs at 2 K, comparable to the highest-quality
films grown in the conventional (112) orientation. This work demonstrates a
simple experimental framework for exploring topological phases that are
predicted to exist in proximity to the three-dimensional Dirac semimetal phase
Identification of novel pathogen-derived agonists for human and mouse formyl peptide receptors
Possible signatures of mixed-parity superconductivity in doped polar SrTiO3 films
Superconductors that possess both broken spatial inversion symmetry and
spin-orbit interactions exhibit a mix of spin singlet and triplet pairing.
Here, we report on measurements of the superconducting properties of
electron-doped, strained SrTiO3 films. These films have an enhanced
superconducting transition temperature and were previously shown to undergo a
transition to a polar phase prior to becoming superconducting. We show that
some films show signatures of an unusual superconducting state, such as an
in-plane critical field that is higher than both the paramagnetic and orbital
pair breaking limits. Moreover, nonreciprocal transport, which reflects the
ratio of odd versus even pairing interactions, is observed. Together, these
characteristics indicate that these films provide a tunable platform for
investigations of unconventional superconductivity
Point group symmetry of cadmium arsenide thin films determined by convergent beam electron diffraction
Cadmium arsenide (Cd3As2) is one of the first materials to be discovered to
belong to the class of three-dimensional topological semimetals. Reported room
temperature crystal structures of Cd3As2 reported differ subtly in the way the
Cd vacancies are arranged within its antifluorite-derived structure, which
determines if an inversion center is present and if Cd3As2 is a Dirac or Weyl
semimetal. Here, we apply convergent beam electron diffraction (CBED) to
determine the point group of Cd3As2 thin films grown by molecular beam epitaxy.
Using CBED patterns from multiple zone axes, high-angle annular dark-field
images acquired in scanning transmission electron microscopy, and Bloch wave
simulations, we show that Cd3As2 belongs to the tetragonal 4/mmm point group,
which is centrosymmetric. The results show that CBED can distinguish very
subtle differences in the crystal structure of a topological semimetal, a
capability that will be useful for designing materials and thin film
heterostructures with topological states that depend on the presence of certain
crystal symmetries.Comment: Accepted for publication in Physical Review Material
Negative magnetoresistance due to conductivity fluctuations in films of the topological semimetal Cd3As2
Recently discovered Dirac and Weyl semimetals display unusual
magnetoresistance phenomena, including a large, non-saturating, linear
transverse magnetoresistance and a negative longitudinal magnetoresistance. The
latter is often considered as evidence of fermions having a defined chirality.
Classical mechanisms, due to disorder or non-uniform current injection, can
however, also produce negative longitudinal magnetoresistance. Here, we report
on magnetotransport measurements performed on epitaxial thin films of Cd3As2, a
three-dimensional Dirac semimetal. Quasi-linear positive transverse
magnetoresistance and negative longitudinal magnetoresistance are observed. By
evaluating films of different thickness and by correlating the temperature
dependence of the carrier density and mobility with the magnetoresistance
characteristics, we demonstrate that both the quasi-linear positive and the
negative magnetoresistance are caused by conductivity fluctuations. Chiral
anomaly is not needed to explain the observed features.Comment: Accepted for publication as Rapid Communication in Physical Review
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