586 research outputs found
Microscopic Origin of the Valley Hall Effect in Transition Metal Dichalcogenides Revealed by Wavelength Dependent Mapping
The band structure of many semiconducting monolayer transition metal
dichalcogenides (TMDs) possesses two degenerate valleys, with equal and
opposite Berry curvature. It has been predicted that, when illuminated with
circularly polarized light, interband transitions generate an unbalanced
non-equilibrium population of electrons and holes in these valleys, resulting
in a finite Hall voltage at zero magnetic field when a current flows through
the system. This is the so-called valley Hall effect that has recently been
observed experimentally. Here, we show that this effect is mediated by
photo-generated neutral excitons and charged trions, and not by inter-band
transitions generating independent electrons and holes. We further demonstrate
an experimental strategy, based on wavelength dependent spatial mapping of the
Hall voltage, which allows the exciton and trion contributions to the valley
Hall effect to be discriminated in the measurement. These results represent a
significant step forward in our understanding of the microscopic origin of
photo-induced valley Hall effect in semiconducting transition metal
dichalcogenides, and demonstrate experimentally that composite quasi-particles,
such as trions, can also possess a finite Berry curvature.Comment: accepted for publication in Nano Letter
Eritrichium parvulum Macloskie, hom. illeg.
CalderaAriza Espinar, Luis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, FÃsicas y Naturales; Consejo Nacional de Investigaciones CientÃficas y Técnicas. Instituto Multidisciplinario de BiologÃa Vegetal; Argentin
Lithium-ion conducting glass ceramics for electrostatic gating
We explore solid electrolytes for electrostatic gating using field-effect
transistors (FETs) in which thin WSe crystals are exfoliated and
transferred onto a lithium-ion conducting glass ceramic substrate. For negative
gate voltages () the devices work equally well as ionic liquid gated
FETs while offering specific advantages, whereas no transistor action is seen
for . For the devices can nevertheless be driven into the
ambipolar injection regime by applying a large source-drain bias, and strong
electroluminescence is observed when direct band-gap WSe monolayers are
used. Detecting and imaging the emitted light is much simpler in these FETs as
compared to ionic liquid gated transistors, because the semiconductor surface
is exposed (i.e., not covered by another material). Our results show that solid
electrolytes are complementary to existing liquid gates, as they enable
experiments not possible when the semiconductor is buried under the liquid
itself
Effect of the cation structure on the properties of homobaric imidazolium ionic liquids
In this work we investigate the structure–property relationships in a series of alkylimidazolium ionic liquids with almost identical molecular weight. Using a combination of theoretical calculations and experimental measurements, we have shown that re-arranging the alkyl side chain or adding functional groups results in quite distinct features in the resultant ILs. The synthesised ILs, although structurally very similar, cover a wide spectrum of properties ranging from highly fluid, glass forming liquids to high melting point crystalline salts. Theoretical ab initio calculations provide insight on minimum energy orientations for the cations, which then are compared to experimental X-ray crystallography measurements to extract information on hydrogen bonding and to verify our understanding of the studied structures. Molecular dynamics simulations of the simplest (core) ionic liquids are used in order to help us interpret our experimental results and understand better why methylation of C2 position of the imidazolium ring results in ILs with such different properties compared to their non-methylated analogues
Cryptantha dimorpha (Phil.) Greene
Cordillera de SantiagoUniversidad Nacional de Córdoba. Facultad de Ciencias Exactas, FÃsicas y Naturales; Consejo Nacional de Investigaciones CientÃficas y Técnicas. Instituto Multidisciplinario de BiologÃa Vegetal; Argentin
Cryptantha diffusa (Phil.) I.M. Johnst.
Paroma, in des. AtacamaUniversidad Nacional de Córdoba. Facultad de Ciencias Exactas, FÃsicas y Naturales; Consejo Nacional de Investigaciones CientÃficas y Técnicas. Instituto Multidisciplinario de BiologÃa Vegetal; Argentin
Parent based language intervention for 2-year-old children with specific expressive language delay: a randomised controlled trial
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