69 research outputs found
High temperature superconducting FeSe films on SrTiO3 substrates
Interface enhanced superconductivity at two dimensional limit has become one
of most intriguing research directions in condensed matter physics. Here, we
report the superconducting properties of ultra-thin FeSe films with the
thickness of one unit cell (1-UC) grown on conductive and insulating SrTiO3
(STO) substrates. For the 1-UC FeSe on conductive STO substrate (Nb-STO), the
magnetization versus temperature (M-T) measurement shows a diamagnetic signal
at 85 K, suggesting the possibility of superconductivity appears at this high
temperature. For the FeSe films on insulating STO substrate, systematic
transport measurements were carried out and the sheet resistance of FeSe films
exhibits Arrhenius TAFF behavior with a crossover from a single-vortex pinning
region to a collective creep region. More intriguing, sign reversal of Hall
resistance with temperature is observed, demonstrating a crossover from hole
conduction to electron conduction above Tc in 1-UC FeSe films
Discovery of smectic charge and pair-density-wave orders in topological monolayer 1T-MoTe
Electronic liquid-crystal phases are observed in numerous strongly-correlated
systems including high-temperature superconductors. However, identifying these
exotic phases and understanding their interplay with superconductivity in
topological materials remain challenging. Here we employ a cryogenic scanning
tunneling microscopy to discover a smectic (stripe) charge order (CO) and a
primary pair-density-wave (PDW) in topological monolayer 1T-MoTe.
The two orders are spatially modulated unidirectionally at the same wavevector,
but have a marked spatial phase difference of about 2/5. Importantly, the
primary PDW state features a two-gap superconductivity below the transition
temperature of 6.0 K and induces another unique particle-hole-symmetric CO at
twice the PDW wavevector. Combining these results and our density functional
calculations, we reveal that the two smectic orders are primarily driven by
nesting behaviors between electron and hole pockets. Our findings establish
monolayer 1T-MoTe as a topological paradigm for exploring
electronic smecticity, which intertwines with multiple preexisting
symmetry-breaking states.Comment: 16 pages, 4 figures, Supplementary material
Direct transformation of-alkane into all-conjugated polyene via cascade dehydrogenation
Selective C(sp) −H activation is of fundamental importance in processing alkane feedstocks to produce high-value-added chemical products. By virtue of an on-surface synthesis strategy, we report selective cascade dehydrogenation of n-alkane molecules under surface constraints, which yields monodispersed all-trans conjugated polyenes with unprecedented length controllability. We are also able to demonstrate the generality of this concept for alkyl-substituted molecules with programmable lengths and diverse functionalities, and more importantly its promising potential in molecular wiring
Direct observation of high temperature superconductivity in one-unit-cell FeSe films
Heterostructure based interface engineering has been proved an effective
method for finding new superconducting systems and raising superconductivity
transition temperature (TC). In previous work on one unit-cell (UC) thick FeSe
films on SrTiO3 (STO) substrate, a superconducting-like energy gap as large as
20 meV, was revealed by in situ scanning tunneling microscopy/spectroscopy
(STM/STS). Angle resolved photoemission spectroscopy (ARPES) further revealed a
nearly isotropic gap of above 15 meV, which closes at a temperature of ~ 65 K.
If this transition is indeed the superconducting transition, then the 1-UC FeSe
represents the thinnest high TC superconductor discovered so far. However, up
to date direct transport measurement of the 1-UC FeSe films has not been
reported, mainly because growth of large scale 1-UC FeSe films is challenging
and the 1-UC FeSe films are too thin to survive in atmosphere. In this work, we
successfully prepared 1-UC FeSe films on insulating STO substrates with
non-superconducting FeTe protection layers. By direct transport and magnetic
measurements, we provide definitive evidence for high temperature
superconductivity in the 1-UC FeSe films with an onset TC above 40 K and a
extremely large critical current density JC ~ 1.7*106 A/cm2 at 2 K. Our work
may pave the way to enhancing and tailoring superconductivity by interface
engineering
The Morphology and Temperature-dependent Development of Mylabris phalerata Pallas (Coleoptera: Meloidae)
Zhu, Fen, Lei, Chao-Liang, Xue, Fangsen (2005): The Morphology and Temperature-dependent Development of Mylabris phalerata Pallas (Coleoptera: Meloidae). The Coleopterists Bulletin 59 (4): 521-527, DOI: 10.1649/838.1, URL: http://dx.doi.org/10.1649/838.
Evidence for inbreeding depression and pre-copulatory, but not post copulatory inbreeding avoidance in the cabbage beetle Colaphellus bowringi.
Inbreeding is known to have adverse effects on fitness-related traits in a range of insect species. A series of theoretical and experimental studies have suggested that polyandrous insects could avoid the cost of inbreeding via pre-copulatory mate choice and/or post-copulatory mechanisms. We looked for evidence of pre-copulatory inbreeding avoidance using female mate preference trials, in which females were given the choice of mating with either of two males, a sibling and a non-sibling. We also tested for evidence of post-copulatory inbreeding avoidance by conducting double mating experiments, in which four sibling females were mated with two males sequentially, either two siblings, two non-siblings or a sibling and a non-sibling in either order. We identified substantial inbreeding depression: offspring of females mated to full siblings had lower hatching success, slower development time from egg to adult, lower survival of larval and pupal stages, and lower adult body mass than the offspring of females mated to non-sibling males. We also found evidence of pre-copulatory inbreeding avoidance, as females preferred to mate with non-sibling males. However, we did not find any evidence of post-copulatory inbreeding avoidance: egg hatching success of females mating to both sibling and non-sibling males were consistent with sperm being used without bias in relation to mate relatedness. Our results suggest that this cabbage beetle has evolved a pre-copulatory mechanism to avoid matings between close relative, but that polyandry is apparently not an inbreeding avoidance mechanism in C. bowringi
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