Transformative Research Project on Iron Pnictides TRIP

Tokyo, Japan

Transformative Research Project on Iron Pnictides TRIP

Tokyo, Japan

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Allan M.P.,Cornell University | Allan M.P.,Brookhaven National Laboratory | Lee K.,Cornell University | Rost A.W.,Cornell University | And 18 more authors.
Nature Physics | Year: 2015

Cooper pairing in the iron-based high-T c superconductors is often conjectured to involve bosonic fluctuations. Among the candidates are antiferromagnetic spin fluctuations and d-orbital fluctuations amplified by phonons. Any such electron-boson interaction should alter the electron's 'self-energy', and then become detectable through consequent modifications in the energy dependence of the electron's momentum and lifetime. Here we introduce a novel theoretical/experimental approach aimed at uniquely identifying the relevant fluctuations of iron-based superconductors by measuring effects of their self-energy. We use innovative quasiparticle interference (QPI) imaging techniques in LiFeAs to reveal strongly momentum-space anisotropic self-energy signatures that are focused along the Fe-Fe (interband scattering) direction, where the spin fluctuations of LiFeAs are concentrated. These effects coincide in energy with perturbations to the density of states N(ω) usually associated with the Cooper pairing interaction. We show that all the measured phenomena comprise the predicted QPI 'fingerprint'of a self-energy due to antiferromagnetic spin fluctuations, thereby distinguishing them as the predominant electron-boson interaction. © 2015 Macmillan Publishers Limited.


Okabe H.,Aoyama Gakuin University | Takeshita N.,Japan National Institute of Advanced Industrial Science and Technology | Takeshita N.,Transformative Research Project on Iron Pnictides TRIP | Horigane K.,Tohoku University | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

In this study, we performed high-pressure electrical resistivity measurements of polycrystalline FeSe in the pressure range of 1-16.0 GPa at temperatures of 4-300 K. A precise evaluation of Tc from zero-resistivity temperatures revealed that Tc shows a slightly distorted dome-shaped curve with maximum Tc offset (30 K) at 6 GPa. With the application of pressure, the temperature dependence of resistivity above Tc changes dramatically to a linear dependence, that the high- Tc phase appears above 3 GPa. We found a striking correlation between Tc and the Se height: the lower the Se height, the more enhanced is Tc. Moreover, this relation is broadly applicable to other iron pnictides, strongly indicating that high-temperature superconductivity can appear only around the optimum anion height (∼1.38Å). On the basis of these results, we suggest that the anion height should be considered as a key determining factor of Tc of iron-based superconductors containing various anions. © 2010 The American Physical Society.


Awana V.P.S.,National Physical Laboratory India | Nowik I.,Hebrew University of Jerusalem | Pal A.,National Physical Laboratory India | Yamaura K.,Transformative Research Project on Iron Pnictides TRIP | And 5 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Magnetization, x-ray diffraction, and specific-heat measurements reveal that SmCoAsO undergoes three magnetic phase transitions. A ferromagnetic transition attributed to the Co ions, emerges at TC =57 K with a small saturation moment of ∼0.15 μB/Co. Reorientation of the Co moment to an antiferromagnetic state is obtained at TN2 =45 K. The relative high paramagnetic effective moment Peff =1.57 μB/Co indicates an itinerant ferromagnetic state of the Co sublattice. The third magnetic transition at TN1=5 K is observed clearly in the specific-heat study only. Both magnetic and F 57 e Mossbauer studies show that substitution of small quantities of Fe for Co was unsuccessful. © 2010 The American Physical Society.


Takahashi H.,University of Tokyo | Takahashi H.,Transformative Research Project on Iron Pnictides TRIP | Imai Y.,University of Tokyo | Imai Y.,Transformative Research Project on Iron Pnictides TRIP | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We report microwave surface impedances of FeSe0.4Te 0.6 single crystals measured at 12, 19, and 44 GHz. The penetration depth exhibits a power-law behavior, δλL= λL(T)-λL(0) CTn with an exponent n2, which is considered to result from impurity scattering. The temperature dependence of the superfluid density largely deviates from the behavior expected in the BCS theory. We believe that this deviation is caused by the crossover from the dirty regime near Tc to the clean regime at low temperatures, which is supported by the rapid increase of the quasiparticle scattering time obtained from the microwave conductivity. We also believe that the previously published data of the superfluid density can be interpreted in this scenario. © 2011 American Physical Society.


Li J.,Japan National Institute of Materials Science | Li J.,Hokkaido University | Guo Y.,Japan International Center for Materials Nanoarchitectonics | Zhang S.,Japan International Center for Materials Nanoarchitectonics | And 9 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The nonmagnetic impurity effect is studied on the Fe-based BaFe 1.89-2xCo0.11As2 superconductor (Tc = 25 K) with Zn substitution for Fe up to 8 at. %, which is achieved by means of high-pressure and high-temperature heating. Tc decreases almost linearly with increasing Zn content and disappears at ∼8 at. %. It is different in the shared phenomenology of the early Zn doping studies, where Tc decreased little. The decreasing Tc rate, however, remains much lower (3.63 K/%) than what is expected for the s ±-wave model, implying the model is inaccurate. Another symmetry model such as the non-sign-reversal s-wave model may better account for the result. © 2011 American Physical Society.


Tateiwa N.,Japan Atomic Energy Agency | Haga Y.,Japan Atomic Energy Agency | Haga Y.,Transformative Research Project on Iron Pnictides TRIP | Matsuda T.D.,Japan Atomic Energy Agency | And 2 more authors.
Review of Scientific Instruments | Year: 2012

A miniature ceramic anvil high pressure cell (mCAC) was earlier designed by us for magnetic measurements at pressures up to 7.6 GPa in a commercial superconducting quantum interference magnetometer [N. Tateiwa, Rev. Sci. Instrum. 82, 053906 (2011)]10.1063/1.3590745. Here, we describe methods to generate pressures above 10 GPa in the mCAC. The efficiency of the pressure generation is sharply improved when the Cu-Be gasket is sufficiently preindented. The maximum pressure for the 0.6 mm culet anvils is 12.6 GPa when the Cu-Be gasket is preindented from the initial thickness of 300-60 μm. The 0.5 mm culet anvils were also tested with a rhenium gasket. The maximum pressure attainable in the mCAC is about 13 GPa. The present cell was used to study YbCu 2Si 2 which shows a pressure induced transition from the non-magnetic to magnetic phases at 8 GPa. We confirm a ferromagnetic transition from the dc magnetization measurement at high pressure. The mCAC can detect the ferromagnetic ordered state whose spontaneous magnetic moment is smaller than 1 μ B per unit cell. The high sensitivity for magnetic measurements in the mCAC may result from the simplicity of cell structure. The present study shows the availability of the mCAC for precise magnetic measurements at pressures above 10 GPa. © 2012 American Institute of Physics.


Taen T.,University of Tokyo | Nakajima Y.,University of Tokyo | Nakajima Y.,Transformative Research Project on Iron Pnictides TRIP | Tamegai T.,University of Tokyo | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The effect of proton irradiation in Ba(Fe 0.93Co 0.07)2As 2 single crystals is reported. We analyze temperature dependence of the current density and normalized flux relaxation rate in the framework of the collective-creep model. The glassy exponent and barrier height for flux creep are directly determined by Maley's method. Our model functions for barrier height and critical current density in the absence of flux creep are explained by the superposition of δT c and δl pinnings. We also approach true critical current density by means of the generalized inversion scheme, and the obtained result is in reasonable agreement with our model function. The proton-irradiation effect on temperature dependence of the current density and normalized relaxation rate can be summarized as doubling of the barrier height at the beginning of flux creep. © 2012 American Physical Society.


Nakajima Y.,University of Tokyo | Nakajima Y.,Transformative Research Project on Iron Pnictides TRIP | Taen T.,University of Tokyo | Tsuchiya Y.,University of Tokyo | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We report the effect of 3 MeV proton irradiation on the suppression of the critical temperature Tc in Ba (Fe1-x Cox) 2 As2 single crystals at underdoping, optimal-doping, and overdoping levels. We find that Tc decreases and residual resistivity increases monotonically with increasing dose. We also find no upturn in low-temperature resistivity in contrast with the α -particle-irradiated NdFeAs(O,F), which suggests that defects induced by the proton irradiation behave as nonmagnetic scattering centers. The critical scattering rate for all samples estimated by three different ways is much higher than that expected in s± -pairing scenario based on interband scattering due to antiferromagnetic spin fluctuation. ©2010 The American Physical Society.


Kobayashi T.,Osaka University | Miyasaka S.,Osaka University | Miyasaka S.,Transformative Research Project on Iron Pnictides TRIP | Tajima S.,Osaka University | Tajima S.,Transformative Research Project on Iron Pnictides TRIP
Journal of the Physical Society of Japan | Year: 2012

We report a crystal growth and physical properties of SrFe 2(As1-xPx)2. The single crystals for various xs were grown by a self flux method. For x = 0.35, Tc reaches the maximum value of 30K and the electrical resistivity ρ(T) shows T-linear dependence. As x increases, Tc decreases and ρ (T) changes to T2-behavior, indicating a standard Fermi liquid. These results suggest that a magnetic quantum critical point exists around x = 0.35. © 2012 The Physical Society of Japan.


Mohan S.,University of Tokyo | Tsuchiya Y.,University of Tokyo | Nakajima Y.,University of Tokyo | Nakajima Y.,Transformative Research Project on Iron Pnictides TRIP | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We explore the flux-front patterns during virgin penetration and after remagnetization in the iron-based superconductor Ba(Fe1-xCo x)2As2. After remagnetization, we observe an instability characterized by turbulent dynamics at the vortex-antivortex boundary. Associated with the turbulent flux boundary, a band of excess current density is observed. The turbulence is contrasted with the instability observed in the cuprate superconductors. Our results suggest turbulent instability at the vortex-antivortex interface may be a common feature in all remagnetized type-II superconductors. © 2011 American Physical Society.

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