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LASORセミナー:Multiprobe characterization of AF/SC phase boundary of Ba(Fe,Ni)2As2
標題: LASORセミナー:Multiprobe characterization of AF/SC phase boundary of Ba(Fe,Ni)2As2
日時: 2014年3月12日(水)  午後2:00~
場所: 物性研究所本館6階 第1会議室(A636)  
講師: Dr.Yasutomo Uemura
所属: Physics Department, Columbia University, New York, USA
要旨: To elucidate coexistance of antiferromagnetic (AF) and superconducting (SC)
phases in Ba(Fe,Ni)2As2, MuSR (Uemura, Luke), Moessbauer (Saitovitch), neutron (Dai),
Specific Heat (Ronning), optical conductivity (Tajima/Uchida) and STM (Pasupathy)
measurements have been performed using the same single crystal specimens (Dai).
For the (Fe1.915Ni0.085) sample at near AF/SC boundary, MuSR found
static magnetic order in the entire volume fraction with half/half volumes
of strong/weak magnetism, and Moessbauer detected the half volume of the
strong magnetic region alone.
These local probes found static magnetism much more robust than does the
neutron Bragg peak, indicating highly random spatial spin correlations.
Specific heat, optical and STM revealed superconducting gap in nearly full
volume fraction developing below superconducting Tc in the same specimen.
These results provide decisive evidence for nearly full overlap of the AF and
SC orders in real space, which is consistent with the s+- pairing but putting
constraints in possible role of quantum criticality.
In systems with higher dopings, the static magnetic order disappears as
the results of dimishing volume fraction of the magnetically ordered
region, suggesting phase separation and first-order quantum evolution.
This observation further gives caution to the popular view of stressing
2-nd order quantum criticality in unconventional superconductors.

Collaborative work performed by the groups shown in () above.
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