665 research outputs found
Interface induced high temperature superconductivity in single unit-cell FeSe films on SrTiO3
Searching for superconducting materials with high transition temperature (TC)
is one of the most exciting and challenging fields in physics and materials
science. Although superconductivity has been discovered for more than 100
years, the copper oxides are so far the only materials with TC above 77 K, the
liquid nitrogen boiling point. Here we report an interface engineering method
for dramatically raising the TC of superconducting films. We find that one
unit-cell (UC) thick films of FeSe grown on SrTiO3 (STO) substrates by
molecular beam epitaxy (MBE) show signatures of superconducting transition
above 50 K by transport measurement. A superconducting gap as large as 20 meV
of the 1 UC films observed by scanning tunneling microcopy (STM) suggests that
the superconductivity could occur above 77 K. The occurrence of
superconductivity is further supported by the presence of superconducting
vortices under magnetic field. Our work not only demonstrates a powerful way
for finding new superconductors and for raising TC, but also provides a
well-defined platform for systematic study of the mechanism of unconventional
superconductivity by using different superconducting materials and substrates
KFe_2Se_2 is the parent compound of K-doped iron selenide superconductors
We elucidate the existing controversies in the newly discovered K-doped iron
selenide (KxFe2-ySe2-z) superconductors. The stoichiometric KFe2Se2 with
\surd2\times\surd2 charge ordering was identified as the parent compound of
KxFe2-ySe2-z superconductor using scanning tunneling microscopy and
spectroscopy. The superconductivity is induced in KFe2Se2 by either Se
vacancies or interacting with the anti-ferromagnetic K2Fe4Se5 compound. Totally
four phases were found to exist in KxFe2-ySe2-z: parent compound KFe2Se2,
superconducting KFe2Se2 with \surd2\times\surd5 charge ordering,
superconducting KFe2Se2-z with Se vacancies and insulating K2Fe4Se5 with
\surd5\times\surd5 Fe vacancy order. The phase separation takes place at the
mesoscopic scale under standard molecular beam epitaxy condition
First sodium laser guide star asterism launching platform in China on 1.8m telescope at Gaomeigu Observatory
The application of sodium laser guide star is the key difference between
modern adaptive optics system and traditional adaptive optics system.
Especially in system like multi-conjugate adaptive optics, sodium laser guide
star asterism which is formed by several laser guide stars in certain pattern
is required to probe more atmospheric turbulence in different directions. To
achieve this, a sodium laser guide star asterism launching platform is
required. In this paper, we will introduce the sodium laser guide star asterism
launching platform built and tested on the 1.8m telescope of the Gaomeigu
Observatory. The platform has two functions: one is to compare the performance
of sodium laser guide stars generated by different lasers at the same place;
the other is to generate sodium laser guide star asterism with adjustable
shape. The field test results at the beginning of 2021 verify the important
role of the platform, which is also the first time to realize sodium laser
guide star asterism in China
Geometry and optics calibration of WFCTA prototype telescopes using star light
The Large High Altitude Air Shower Observatory project is proposed to study
high energy gamma ray astronomy ( 40 GeV-1 PeV ) and cosmic ray physics ( 20
TeV-1 EeV ). The wide field of view Cherenkov telescope array, as a component
of the LHAASO project, will be used to study energy spectrum and compositions
of cosmic ray by measuring the total Cherenkov light generated by air showers
and shower maximum depth. Two prototype telescopes have been in operation since
2008. The pointing accuracy of each telescope is crucial to the direction
reconstruction of the primary particles. On the other hand the primary energy
reconstruction relies on the shape of the Cherenkov image on the camera and the
unrecorded photons due to the imperfect connections between photomultiplier
tubes. UV bright stars are used as point-like objects to calibrate the pointing
and to study the optical properties of the camera, the spot size and the
fractions of unrecorded photons in the insensitive areas of the camera.Comment: 5 pages, 6 figures, submitted to Chinese Physics
Depression, anxiety and insomnia in Chinese older adults and their family caregivers during the COVID-19 pandemic: an actor-partner interdependence model approach
AimsThis study aimed to explore the dyadic effects of depression and anxiety on insomnia symptoms in Chinese older adults and their caregivers living in a community setting.MethodsData were collected from 1,507 pairs of older adults and their caregivers who were in the Guangdong Mental Health Survey in China. The 9-item Patient Health Questionnaire (PHQ-9), Generalized Anxiety Disorder module 7 (GAD-7), and Insomnia Severity Index (ISI) were used to measure depression, anxiety, and insomnia symptoms. Actor-Partner Interdependence Models (APIM) were used to determine whether anxiety or depression symptoms predicted individual or dyadic insomnia.ResultsOlder adults' and caregivers' depression and anxiety had significant positive correlations with their own and their caregivers' insomnia symptoms (all P < 0.001). Actor effects were found between depression and insomnia symptoms in both older adults and caregivers (B = 0.695, P < 0.001; B = 0.547, P < 0.001, respectively), with one significant partner effects (B = 0.080, P = 0.007). Actor effects were also found between anxiety and insomnia symptoms in both older adults and caregivers (B = 0.825, P < 0.001; B = 0.751, P < 0.001, respectively), with one significant partner effects (B = 0.097, P = 0.004). However, the caregivers' depression and anxiety were not associated with older adults' insomnia symptoms in the APIM analyses.ConclusionsOlder adults and their caregivers had an interrelationship between psychological distress and insomnia. Consequently, healthcare providers might consider involving dyads when designing programs to reduce insomnia and improve psychological distress for family caregivers
Phase Separation and Magnetic Order in K-doped Iron Selenide Superconductor
Alkali-doped iron selenide is the latest member of high Tc superconductor
family, and its peculiar characters have immediately attracted extensive
attention. We prepared high-quality potassium-doped iron selenide (KxFe2-ySe2)
thin films by molecular beam epitaxy and unambiguously demonstrated the
existence of phase separation, which is currently under debate, in this
material using scanning tunneling microscopy and spectroscopy. The
stoichiometric superconducting phase KFe2Se2 contains no iron vacancies, while
the insulating phase has a \surd5\times\surd5 vacancy order. The iron vacancies
are shown always destructive to superconductivity in KFe2Se2. Our study on the
subgap bound states induced by the iron vacancies further reveals a
magnetically-related bipartite order in the superconducting phase. These
findings not only solve the existing controversies in the atomic and electronic
structures in KxFe2-ySe2, but also provide valuable information on
understanding the superconductivity and its interplay with magnetism in
iron-based superconductors
- …