Insights into atomic structure of next-generation superconductors

Insights into atomic structure of next-generation superconductors

Neutron diffraction at the Australian Centre for Neutron Scattering has clarified the absence of magnetic order and classified the superconductivity of a new next-generation of superconductors in a paper published in Europhysics Letters.

The iron-based nitride, ThFeAsN, which contains Th2N2 and FeAs2 layers, has been of considerable interest because unconventional superconductivity occurring at a temperature of 30 K. This material was of particular interest as the superconductivity was seen to arise without oxygen doping.

A large group of predominantly Chinese researchers, led by Prof Huiqian Luo from the Beijing National Laboratory for Condensed Matter Physics gathered diffraction measurements on the high intensity diffractometer WOMBAT, assisted by instrument scientists Dr Helen Maynard-Casely and Dr Guochu Deng based at the Australian Centre for Neutron Scattering. This enabled them to determine the crystal structure of the compound over a large temperature range.

In similar types of materials, the onset of a superconducting state is thought to be associated with magnetic ordering within the crystal structure. Earlier measurements had shown no magnetic ordering in the ThFeAsN material, and hence this neutron study was an opportunity to confirm this and search for other structural insights into the material’s properties.

The lack of magnetic order was confirmed because no difference was found between the data sets at 6 K and 40 K. All of the observed reflections could be could be identified as having arisen from the atomic structure from 6K up to 300K – no magnetic reflections were identified.

Diffraction patterns over the temperature range from 300 K to 6 K also indicated there was no structural phase transition from tetragonal to orthorhombic in the crystal lattice.

The investigators reported that the lattice parameters continuously increased with temperature due to thermal expansion and a weak distortion in the tetrahedron possibly took place at 160 K. Details from the structure point to this distortion coming from the FeAs2 layers.

The close relationship between local structure of the FeAs4 tetrahedron and the superconducting temperature, suggested TheFeAsN is in a nearly optimised superconducting state.

This is different to many other discovered superconducting materials, which require tweaks in their chemistry to produce the highest critical temperature.

The authors also surmised that the close distance of Fe-As would favour electron hopping, reducing electron correlations and orbital order, thereby providing a reasonable explanation for the absence of magnetic order, structural transition and resistivity anomaly.

Carrier density measurements indicated that ThFeAsN could already be doped by electrons, which are probably introduced by the N deficiency or O occupancy or the reduced valence of nitrogen. The self-doping effect could be responsible for the superconductivity and suppression of magnetic order.

 

[“Source-phys”]

Woman Forces Minor Daughter Into Flesh Trade For Money

SHILLONG: A woman forced her minor daughter into prostitution to earn money citing poverty prompting her relatives to file a complaint on Tuesday.
The girl, who is pregnant and admitted in a city hospital, was sexually abused by two men facilitated by the mother.
This was reflected in the FIR lodged at Madanrting police station by the girl’s brother, Lapynkupbor Umsong, and her uncle Korishon Umsong.
The girl hailing from a village under Mawkynrew Block in East Khasi Hills District passed Class VI from a school in the city.
The 16-year-old victim stayed with a relative here and attended school in the morning and helped the relatives during the day along with her elder sister.
Last December after the examinations, the victim, third of the nine siblings, was taken away by her mother, Aitimon Umsong, from Shillong to her village.
She stayed there for two days and the mother took her away to the house of a distant relative in another village about an hour from her native village in Mawkynrew.
According to the relatives, at night she was taken to the house of a youth identified as Shngain Nongrum (22) and the mother compelled her to sleep with him.
When the victim confronted her mother, she was told to keep quiet and her objections went in vain.
The next day, they came back to her village and Lapynkupbor, a daily wage earner working in the Assam-Meghalaya border area, came to know about the incident.
The brother and his uncle filed the FIR on January 12. Police went in search of the accused but since they could not find him, his father was brought to the police station.
On January 16, the accused, the girl and her mother came to the police station. She told the police that her daughter was above 18 years. She had even threatened the girl to tell them she went willingly to the residence of the accused.
However, the brother of the victim produced the Baptismal Certificate that showed her date of birth as December 15, 2001.
No one was arrested in connection with the crime and from the police station, the mother took her to the village of the accused who again sexually exploited her and the next day she was brought back.
The agony continued as the accused came to stay in the girl’s house and though her aged father objected by saying his daughter was a minor, the youth ignored the plea. The father was also chided by his wife.
The relatives said no action was taken against Nongrum and Aitimon though the FIR was lodged on January 12. This prompted the brother and the uncle to file another FIR on Tuesday.
The relatives said following the sexual abuse, the girl became pregnant and after a few months, she was brought to another village in East Khasi Hills by her mother who rented a house.
It was when the girl was assisting her mother in selling betel nuts in Shillong that she collapsed following which she was admitted in Ganesh Das Hospital.
In the hospital, she mentioned her daughter’s age as 22.
The relatives said she was hospitalised for five days and after she was discharged, Aitimon brought another man identified as Hep on August 31.
According to the relatives, Hep entered the bathroom in her rented house and tried to molest her. When she protested and called for help, her mother told her to accept him.
After Hep left, the girl was beaten up for refusal.
The relatives said once the mother locked Hep and the victim in one room but the neighbours tried to rescue her after she cried for help.
The relatives of the victim said it was for money that the mother was forcing her into flesh trade.

[“Source-theshillongtimes”]

Brazil artists turn former government building into creative centre

Image result for Brazil artists turn former government building into creative centre

Creativity is blooming in one of the least likely of places in Brazil.

The 13-storey Ouvidor building in the heart of Sao Paulo used to be a local government building before it fell out of use.

Empty and derelict, the site was wasted until 300 painters, sculptors, circus performers and musicians moved in, transforming it into an artistic hub.

Now, they want the house officially declared a creative centre.

Al Jazeera’s Daniel Schweimler reports from Sao Paulo.

[“Source-aljazeera”]

Doctoral Student in Religion Delves into Printmaking for Insights on Suffering

Stephanie Gehring Ladd and one of her prints

Stephanie Gehring Ladd, a doctoral student in Religion at Duke’s Graduate School, received a grant to take a printmaking course at the University of North Carolina in Chapel Hill and to spend time in a Durham printmaking studio. Her aim was to gain insight into the process of intaglio printmaking in order to enhance her observational powers in writing about prints and inform her dissertation on attention to suffering in the work of Simone Weil and Käthe Kollwitz.

Ladd was among 19 graduate students from five schools at Duke who received Graduate Student Training Enhancement Grants in 2016 for training beyond their core disciplines. Her faculty mentor was Paul J. Griffiths. She shared this update.

I took a printmaking course at UNC this fall, and Professor Brian Garner was fantastic to work with. He let me custom-tailor a course within his Introduction to Intaglio, so that I was able to focus on the intaglio printmaking techniques most used by the artist I am studying, Käthe Kollwitz. She mainly did copper etching, with a shading technique called aquatint, and I produced one small print (it’s a long process!) using copperplate etching and aquatint.

I learned an enormous amount about how her work was done—the main striking thing about etching is that it is a process that goes backwards, compared to drawing. In a drawing, you put down your lightest lines first, and then darken as you want to in the places where you’d prefer it to be darker. But in intaglio, once a piece of the plate is “open” (i.e., the protective ground is removed so that it can be etched, either by scratching or scraping or by washing off the ground), it is difficult to cover it back up in a precise way. This means that the first lines one puts in end up being the ones that get etched over and over in each round; therefore, they are the darkest. So instead of the first lines ending up being the lightest lines, the first ones are the darkest.

While intaglio prints can look a great deal like pen and ink drawings, they require enormously more planning in order to execute. The “fresh from the artist’s pen” look that they can have is, therefore, quite deceptive. It’s been a great gift having the GSTEG grant.

This internal funding mechanism from the Office of the Vice Provost for Interdisciplinary Studies encourages graduate students to step away from their core research and training to acquire additional skills, knowledge or co-curricular experiences that will give them new perspectives on their research agendas. Graduate Student Training Enhancement Grants are intended to deepen preparation for academic positions and other career trajectories.

Read about other 2016-2017 recipients’ experiences:

  • Nanotechnology at Los Alamos
  • Christian Engagement with Architecture
  • Singapore’s Urbanization
  • Brazilian Governance
  • Capitalism, Slavery and Freedom

Image: Copper intaglio print by Stephanie Gehring Ladd; Stephanie with her baby

[“Source-ndtv”]