Computational Science and E-Systems Research

11-2 J-PARC and Supercomputer, a Collaborative Challenge to
Solve the Mechanism of Superconductivity:=A Quest for Electron Pairing through Computer Simulation of Neutron Scattering in Iron-Based Superconductors=NN
NeutronSS

Table 11 - 1 Comparison between the intensities ofexperiments and theoretical values for BaFe2(As, P)2
Two electrons form a pair in superconductors because of
attractive forces; different attractive forces result in different typesof electron pair. We have shown that the pair in case III isconsistent with experimental results.

Property

Intensity

Experiment atJ-PARC

Relatively lower intensity thanthat in other iron-based
superconductors.

㨪1.7

Case I (S±-wave)

Pairs originated from magneticforces㨪2.1

Case II (dxy-wave)

Magnetic pairs in non-iron-based
superconductors<1

Case III (S±-wavewith horizontal nodes)

Pairs originated from relatively
weaker magnetic forces

㨪1.6

NIron-based
S Superconductor
Fig.11-4 Schematic figure of a neutron scatteringexperiment
Neutrons can detect magnetic fields originating fromelectrons.

Superconductivity is a phenomenon that typically involves
sudden disappearance of electric resistance below thesuperconducting transition temperature. In the nuclear R&D
field, a superconducting coil is indispensable for nuclear
fusion reactors and accelerators.
A new superconducting material, an iron - based
superconductor, was discovered in 2008. This type ofmaterial exhibits a very high transition temperature and arichly varied chemical composition. Neutron scatteringexperiments for the iron-based superconductor BaFe2(As, P)2
have been conducted at the Japan Proton Accelerator
Research Complex (J-PARC) in JAEA (Fig.11-4). The resultsof these experiments indicate that the magnetism of ironatoms is important in the mechanism of superconductivity.
Further evidence is required to clarify this mechanism
because it has proven difficult to ascertain from previous
experiments how the pairing of electrons results insuperconductivity.
To address this, we attempted to identify the relevant
electron pairs in a superconductor in order to simulate
neutron scattering using a supercomputer. Previous studies
have been unable to offer a reasonable explanation owing to

insufficient accuracy; to overcome this problem, wedeveloped a method on the basis of the random phaseapproximation and constructed a model using first-principle
calculations in order to consider the electron correlations. To
reduce the computational cost, we changed the algorithm anddeveloped the hybrid parallel codes with OpenMP+MPI.
Some candidates exist for possible electron pairs, withdifferent magnetic origin, in iron-based superconductors. We
simulated neutron scattering using what we considered to begood candidates for neutron scattering experiments andcompared our results with those of previous experiments(Table 11-1). We have shown that the pairing in case III canreproduce the experimental results and that the magnetism ofthe iron atom is important for the mechanism ofsuperconductivity. Our results can help clarify the mechanism
involved because this magnetism is also important in otheriron-based superconductor compounds.
This work is supported by the CREST Framework
Development for Multiscale and Multiphysics Simulations
toward Novel Application of Superconductivity from theJapan Science and Technology Agency (JST).

Reference
Nagai, Y. et al., Theoretical Analysis for Inelastic Neutron Scattering on BaFe2(As1-x ,Px)2 using Realistic Three-Dimensional 10-Orbital Tight-Binding
Model, Journal of the Physical Society of Japan, vol.80, Supplement B, 2011, p.SB021-1-SB021-4.
JAEA R&D Review 2012103