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′^\prime-MoTe2_2

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$^\prime$-MoTe$_2$. The two orders are spatially modulated unidirectionally at the same wavevector, but have a marked spatial phase difference of about 2$\pi$/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$^\prime$-MoTe$_2$ 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$^{3}$) −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

Fig. 1 in The Morphology and Temperature-dependent Development of Mylabris phalerata Pallas (Coleoptera: Meloidae)

Fig. 1. Developmental stages of Mylabris phalerata. A: Egg (2.4 mm); B: L1 (2.6 mm); C: L2 (5.1 mm); D: L3 (13.7 mm); E: L4 (22.4 mm); F: L5 (29.2 mm); G: Pupa (30.1 mm); H: Adult (31.2 mm).Published as part of <i>Zhu, Fen, Lei, Chao-Liang & Xue, Fangsen, 2005, The Morphology and Temperature-dependent Development of Mylabris phalerata Pallas (Coleoptera: Meloidae), pp. 521-527 in The Coleopterists Bulletin 59 (4)</i> on page 523, DOI: 10.1649/838.1, <a href="http://zenodo.org/record/10105854">http://zenodo.org/record/10105854</a&gt

Fig. 2. Soil temperature changes from July 2003 in The Morphology and Temperature-dependent Development of Mylabris phalerata Pallas (Coleoptera: Meloidae)

Fig. 2. Soil temperature changes from July 2003 to June 2004 at Wuhan, P. R. China.Published as part of <i>Zhu, Fen, Lei, Chao-Liang & Xue, Fangsen, 2005, The Morphology and Temperature-dependent Development of Mylabris phalerata Pallas (Coleoptera: Meloidae), pp. 521-527 in The Coleopterists Bulletin 59 (4)</i> on page 526, DOI: 10.1649/838.1, <a href="http://zenodo.org/record/10105854">http://zenodo.org/record/10105854</a&gt