300 research outputs found
Evidence of a subenergy gap in the overdoped regime of Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7-\delta} thin films from THz Spectroscopy
We measured the terahertz (THz) complex conductivity of Ca doped
YBa_{2}Cu_{3}O_{7-\delta} thin films in the frequency range of 0.1 to 3 THz (3
to 100 cm^{-1}) and at a temperature range of 20 to 300 K. The films were
measured using both time domain and frequency domain THz methods. We showed
evidence for the existence of a sub-gap in overdoped
Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7-\delta} samples doped with 5% and 10% Ca.
Evidence for the opening of this sub-gap appears as a sharp decrease in the
spectrum of the real part of conductivity at frequencies equivalent to a gap
energy of 1 meV and is more prominent with increased doping. This decrease in
conductivity can be explained by using d-wave pairing symmetry with an
imaginary part of is or id_{xy} which suggests node removal.Comment: 7 pages, 7 figure
Mott transition and collective charge pinning in electron doped Sr2IrO4
We studied the in-plane dynamic and static charge conductivity of electron
doped Sr2IrO4 using optical spectroscopy and DC transport measurements. The
optical conductivity indicates that the pristine material is an indirect
semiconductor with a direct Mott-gap of 0.55 eV. Upon substitution of 2% La per
formula unit the Mott-gap is suppressed except in a small fraction of the
material (15%) where the gap survives, and overall the material remains
insulating. Instead of a zero energy mode (or Drude peak) we observe a soft
collective mode (SCM) with a broad maximum at 40 meV. Doping to 10% increases
the strength of the SCM, and a zero-energy mode occurs together with metallic
DC conductivity. Further increase of the La substitution doesn't change the
spectral weight integral up to 3 eV. It does however result in a transfer of
the SCM spectral weight to the zero-energy mode, with a corresponding reduction
of the DC resistivity for all temperatures from 4 to 300 K. The presence of a
zero-energy mode signals that at least part of the Fermi surface remains
ungapped at low temperatures, whereas the SCM appears to be caused by pinning a
collective frozen state involving part of the doped electrons
Synthesis of benzimidazole-cyclohexanone derivatives
This work reports the synthesis and characterization of new benzimidazole-cyclohexanone derivatives 3a-d, 4a-d and 5a-d under different reaction conditions. The intermediates and final compounds were purified and their chemical structures were elucidated using 1H-NMR, 13C-NMR and mass spectral data.Keywords: Benzimidazole, Cyclohexanone, NMR, Reaction intermediate
Mott transition and collective charge pinning in electron doped Sr_2IrO_4
We studied the in-plane dynamic and static charge conductivity of electron doped Sr_2IrO_4 using optical spectroscopy and DC transport measurements. The optical conductivity indicates that the pristine material is an indirect semiconductor with a direct Mott gap of 0.55 eV. Upon substitution of 2% La per formula unit the Mott gap is suppressed except in a small fraction of the material (15%) where the gap survives, and overall the material remains insulating. Instead of a zero energy mode (or Drude peak) we observe a soft collective mode (SCM) with a broad maximum at 40 meV. Doping to 10%
increases the strength of the SCM, and a zero-energy mode occurs together with metallic DC conductivity. Further increase of the La substitution doesn't change the spectral weight integral up to 3 eV. It does however result in a transfer of the SCM spectral weight to the zero-energy mode, with a corresponding reduction of the DC resistivity for all temperatures from 4 to 300 K. The presence of a zero-energy mode signals that at least part of the Fermi surface remains ungapped at low temperatures, whereas the SCM appears to be caused by pinning a collective frozen state involving part of the doped electrons
Optical properties of LaNiO3 films tuned from compressive to tensile strain
Materials with strong electronic correlations host remarkable -- and
technologically relevant -- phenomena such as magnetism, superconductivity and
metal-insulator transitions. Harnessing and controlling these effects is a
major challenge, on which key advances are being made through lattice and
strain engineering in thin films and heterostructures, leveraging the complex
interplay between electronic and structural degrees of freedom. Here we show
that the electronic structure of LaNiO3 can be tuned by means of lattice
engineering. We use different substrates to induce compressive and tensile
biaxial epitaxial strain in LaNiO3 thin films. Our measurements reveal
systematic changes of the optical spectrum as a function of strain and,
notably, an increase of the low-frequency free carrier weight as tensile strain
is applied. Using density functional theory (DFT) calculations, we show that
this apparently counter-intuitive effect is due to a change of orientation of
the oxygen octahedra.The calculations also reveal drastic changes of the
electronic structure under strain, associated with a Fermi surface Lifshitz
transition. We provide an online applet to explore these effects. The
experimental value of integrated spectral weight below 2 eV is significantly
(up to a factor of 3) smaller than the DFT results, indicating a transfer of
spectral weight from the infrared to energies above 2 eV. The suppression of
the free carrier weight and the transfer of spectral weight to high energies
together indicate a correlation-induced band narrowing and free carrier mass
enhancement due to electronic correlations. Our findings provide a promising
avenue for the tuning and control of quantum materials employing lattice
engineering.Comment: 12 pages, 11 figure
Midgut microbiota of the malaria mosquito vector Anopheles gambiae and Interactions with plasmodium falciparum Infection
The susceptibility of Anopheles mosquitoes to Plasmodium infections relies on complex interactions between the insect vector and the malaria parasite. A number of studies have shown that the mosquito innate immune responses play an important role in controlling the malaria infection and that the strength of parasite clearance is under genetic control, but little is known about the influence of environmental factors on the transmission success. We present here evidence that the composition of the vector gut microbiota is one of the major components that determine the outcome of mosquito infections. A. gambiae mosquitoes collected in natural breeding sites from Cameroon were experimentally challenged with a wild P. falciparum isolate, and their gut bacterial content was submitted for pyrosequencing analysis. The meta-taxogenomic approach revealed a broader richness of the midgut bacterial flora than previously described. Unexpectedly, the majority of bacterial species were found in only a small proportion of mosquitoes, and only 20 genera were shared by 80% of individuals. We show that observed differences in gut bacterial flora of adult mosquitoes is a result of breeding in distinct sites, suggesting that the native aquatic source where larvae were grown determines the composition of the midgut microbiota. Importantly, the abundance of Enterobacteriaceae in the mosquito midgut correlates significantly with the Plasmodium infection status. This striking relationship highlights the role of natural gut environment in parasite transmission. Deciphering microbe-pathogen interactions offers new perspectives to control disease transmission.Institut de Recherche pour le Developpement (IRD); French Agence Nationale pour la Recherche [ANR-11-BSV7-009-01]; European Community [242095, 223601]info:eu-repo/semantics/publishedVersio
Mott transition and collective charge pinning in electron doped Sr_2IrO_4
We studied the in-plane dynamic and static charge conductivity of electron doped Sr_2IrO_4 using optical spectroscopy and DC transport measurements. The optical conductivity indicates that the pristine material is an indirect semiconductor with a direct Mott gap of 0.55 eV. Upon substitution of 2% La per formula unit the Mott gap is suppressed except in a small fraction of the material (15%) where the gap survives, and overall the material remains insulating. Instead of a zero energy mode (or Drude peak) we observe a soft collective mode (SCM) with a broad maximum at 40 meV. Doping to 10%
increases the strength of the SCM, and a zero-energy mode occurs together with metallic DC conductivity. Further increase of the La substitution doesn't change the spectral weight integral up to 3 eV. It does however result in a transfer of the SCM spectral weight to the zero-energy mode, with a corresponding reduction of the DC resistivity for all temperatures from 4 to 300 K. The presence of a zero-energy mode signals that at least part of the Fermi surface remains ungapped at low temperatures, whereas the SCM appears to be caused by pinning a collective frozen state involving part of the doped electrons
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