Akihiro Koda - Academia.edu (original) (raw)

Papers by Akihiro Koda

Research paper thumbnail of Oxidation Annealing Effects on the Spin-Glass-Like Magnetism and Appearance of Superconductivity in T*-type La1−x/2Eu1−x/2SrxCuO4 (0.14 ≤ x ≤ 0.28)

Journal of the Physical Society of Japan, 2019

Research paper thumbnail of Possible unconventional superconductivity and weak magnetism in Na x CoO 2� yH 2O probed by �SR

Physica B, 2006

The superconducting property of sodium cobalt oxyhydrate, Na 0.35CoO 2·1.3H 2O, has been studied ... more The superconducting property of sodium cobalt oxyhydrate, Na 0.35CoO 2·1.3H 2O, has been studied by means of muon spin relaxation (μSR) down to 2 K. It was found that the zero-field muon spin relaxation rate is independent of temperature, indicating that no static magnetism appears in this compound above 2 K. The result also provides evidence against the breakdown of time-reversal symmetry for the superconducting order parameter. In water excess sample Na 0.334CoO 2·1.32H 2O, which shows no superconductivity, the weak magnetism was observed below 6 K. This fact suggests that the magnetic interaction plays an important role for the appearance of the unconventional superconductivity.

Research paper thumbnail of Knight shift measurements in the superconducting state of Pr1-xLaxOs4Sb12Pr1-xLaxOs4Sb12 (x=0.4)(x=0.4) probed by μSRμSR

Research paper thumbnail of Magnetic response in the superconducting state of 1H-Ca(Al0.5Si0.5)2Ca(Al0.5Si0.5)2studied by ��SR

Research paper thumbnail of Low-temperature magnetic order and spin dynamics in YbRh 2 Si 2

Physical Review B, 2003

Muon spin rotation and relaxation experiments have been carried out in single crystals of YbRh 2 ... more Muon spin rotation and relaxation experiments have been carried out in single crystals of YbRh 2 Si 2 , a compound that exhibits non-Fermi-liquid (NFL) behavior associated with a quantum critical point (QCP) at T=0. The zero-field muon relaxation rate is found to be independent ...

Research paper thumbnail of Magnetic Phase Diagram of Hole-Doped Ca_ Na_xCuO_2Cl_2 Cuprate Superconductor(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

Journal of the Physical Society of Japan, Sep 15, 2005

Research paper thumbnail of Investigation of Spontaneous Magnetic Field in Spin-Triplet Superconductor Sr 2 RuO 4

Proceedings of the International Symposium on Science Explored by Ultra Slow Muon (USM2013), 2014

Research paper thumbnail of Field-induced magnetism in the high-$T_c$ superconductor Ca$_{2-x}$Na$_x$CuO$_2$Cl$_2$ with flat CuO$_2$ planes

The internal magnetic field distribution in a mixed state of a cuprate superconductor, Ca$_{2-x}$... more The internal magnetic field distribution in a mixed state of a cuprate superconductor, Ca$_{2-x}$Na$_x$CuO$_2$Cl$_2$ ($T_{\rm c}\simeq28.5$ K, near the optimal doping), was measured by muon spin rotation ($\mu$SR) technique up to 60 kOe. The mu\mumuSR linewidth Lambda(B)\Lambda(B)Lambda(B) which exhibits excess broadening at higher fields ($B>5$ kOe) due to field-induced magnetism (FIM), is described by a relation, Lambda(B)proptosqrtB\Lambda(B)\propto\sqrt{B}Lambda(B)proptosqrtB. This suggests that

Research paper thumbnail of Possible nodal vortex state in CeRu 2

Physical Review B, 2001

The microscopic property of magnetic vortices in the mixed state of a high-quality CeRu2 crystal ... more The microscopic property of magnetic vortices in the mixed state of a high-quality CeRu2 crystal has been studied by muon spin rotation. We have found that the spatial distribution of magnetic induction B(r) probed by muons is perfectly described by the London model for the triangular vortex lattice with appropriate modifications to incorporate the high-field cutoff around the vortex core

Research paper thumbnail of Performance of a superconducting magnet system operated in the Super Omega Muon beam line at J-PARC

ABSTRACT A superconducting magnet system, which is composed of an 8 m long solenoid for transport... more ABSTRACT A superconducting magnet system, which is composed of an 8 m long solenoid for transportation and 12 short solenoids for focusing, has been developed for Muon Science Establishment facility of J-PARC. The transport solenoid is composed of a 6 m straight section connected to a 45 degree curved section at each end. Muons of various momenta and of both electric charges are transported through the solenoid inner bore with an effective diameter of 0.3 m, where 2 T magnetic field is induced. There are 12 focusing solenoids with an effective bore diameter of 0.6 m and a length of 0.35 m arranged on a straight line at suitable intervals. The maximum central field of each focusing solenoid is 0.66 T. All solenoid coils are cooled by GM cryocoolers through their own conductions. The magnet system has been installed into the beam line in the summer of 2012, and its performance has been checked. Beam commissioning has been carried out since October 2012. During beam operation, temperature rise over 6 K in the transport solenoid due to a nuclear heating from the muon production target is observed at beam intensity of about 300 kW.

Research paper thumbnail of Field-Induced Quasiparticle Excitation in Ca(Al0.5Si0.5)2: Evidence for Unconventional Superconductivity

The temperature (T) and magnetic field (H) dependence of the magnetic penetration depth, �(T,H), ... more The temperature (T) and magnetic field (H) dependence of the magnetic penetration depth, �(T,H), in Ca(Al0.5Si0.5)2 exhibits significant deviation from that expected for conventional BCS superconductors. In particular, it is inferred from a field dependence of �(H) (/ H) at 2.0 K that the quasiparticle excitation is strongly enhanced by the Doppler shift. This suggests that the superconducting order parameter

Research paper thumbnail of Magnetism of Ca_2-xNa_xCuO_2Cl2 Probed by Muon Spin Relaxation

Insight into the pairing mechanism of high-Tc superconductors is being sought by studying the par... more Insight into the pairing mechanism of high-Tc superconductors is being sought by studying the parent compounds which are generally undoped antiferromagnetic insulators. La_2CuO4 is one of such superconducting parent compounds which have CuO2 planes consisting of CuO6 octahedra. La_2CuO4 is orthorhombic below ˜ 530 K, and the distortion associated with it brings about weak ferromagnetism of the Dzyalochinsky-Moriya type. Neither

Research paper thumbnail of Muonium in stishovite: implications for the possible existence of neutral atomic hydrogen in the earth's deep mantle

Scientific reports, 2015

Hydrogen in the Earth's deep interior has been thought to exist as a hydroxyl group in high-p... more Hydrogen in the Earth's deep interior has been thought to exist as a hydroxyl group in high-pressure minerals. We present Muon Spin Rotation experiments on SiO2 stishovite, which is an archetypal high-pressure mineral. Positive muon (which can be considered as a light isotope of proton) implanted in stishovite was found to capture electron to form muonium (corresponding to neutral hydrogen). The hyperfine-coupling parameter and the relaxation rate of spin polarization of muonium in stishovite were measured to be very large, suggesting that muonium is squeezed in small and anisotropic interstitial voids without binding to silicon or oxygen. These results imply that hydrogen may also exist in the form of neutral atomic hydrogen in the deep mantle.

Research paper thumbnail of Magnetism of anomalous A-phase in Ce1+xCu2+ySi2: a μSR study

Research paper thumbnail of Muon science in J-PARC

Research paper thumbnail of U-Line at MLF/J-PARC for Ultra Slow Muon Microscopy

Proceedings of the International Symposium on Science Explored by Ultra Slow Muon (USM2013), 2014

ABSTRACT The second muon beamline in the Materials and Life Science Experimental Facility (MLF) o... more ABSTRACT The second muon beamline in the Materials and Life Science Experimental Facility (MLF) of the Japan Accelerator Research Complex (J-PARC) is under construction. Our beam commissioning for U-line revealed that the U-line was the highest pulsed muon source in the world. After the commissioning, we plan to upgrade and to modify the some components of U-line. Here, we report mainly on the plan for upgrade and modification of the U-line components.

Research paper thumbnail of Suppression of time reversal symmetry breaking superconcutivity in Pr(Os,Ru)4Sb12 and (Pr,La)Os4Sb12

Zero-field muon spin relaxation (muSR) experiments have been carried out in the Pr(Os1-xRux)4Sb12... more Zero-field muon spin relaxation (muSR) experiments have been carried out in the Pr(Os1-xRux)4Sb12 and Pr1-yLayOs4Sb12 alloy systems to investigate broken time-reversal symmetry (TRS) in the superconducting state, signaled by the onset of a spontaneous static local magnetic field Bs. In both alloy series Bs initially decreases linearly with solute concentration. Ru doping is considerably more efficient than La doping ,with

Research paper thumbnail of SR studies on in comparison with the time-reversal-symmetry-broken superconductor

Physica B-condensed Matter, 2005

We have studied the zero-field muon spin relaxation (ZF-μSR) on a filled-skutterudite superconduc... more We have studied the zero-field muon spin relaxation (ZF-μSR) on a filled-skutterudite superconductor LaOs4Sb12 (Tc=0.74K) to compare with the time-reversal-symmetry (TRS)-broken superconductor PrOs4Sb12. The relaxation rate is independent of temperature down to 20mK, suggesting that the absence of TRS breaking in LaOs4Sb12. This finding provides convincing evidence for the Pr 4f-electrons playing an essential role for the realization of the

Research paper thumbnail of Status of Decay/Surface Muon Channel for the Muon Science in J-PARC

AIP Conference Proceedings, 2008

ABSTRACT Muon Science laboratory at Material Life Science Facility is now under construction in J... more ABSTRACT Muon Science laboratory at Material Life Science Facility is now under construction in J‐PARC, where, four types of muon channels are planed to install. Present status of the superconducting and surface muon channel is briefly reported.

Research paper thumbnail of Design of the Large Acceptance Muon Beamline at J-PARC

AIP Conference Proceedings, 2008

The Materials and Life Science Facility (MLF) is currently under construction at J-PARC in Tokai,... more The Materials and Life Science Facility (MLF) is currently under construction at J-PARC in Tokai, Japan. The muon section of the facility will house the muon production target and four secondary beamlines used to transport the muons into two experimental halls. One of the beamlines is a large acceptance beamline (the so called Super Omega Muon beamline) which, when completed,

Research paper thumbnail of Oxidation Annealing Effects on the Spin-Glass-Like Magnetism and Appearance of Superconductivity in T*-type La1−x/2Eu1−x/2SrxCuO4 (0.14 ≤ x ≤ 0.28)

Journal of the Physical Society of Japan, 2019

Research paper thumbnail of Possible unconventional superconductivity and weak magnetism in Na x CoO 2� yH 2O probed by �SR

Physica B, 2006

The superconducting property of sodium cobalt oxyhydrate, Na 0.35CoO 2·1.3H 2O, has been studied ... more The superconducting property of sodium cobalt oxyhydrate, Na 0.35CoO 2·1.3H 2O, has been studied by means of muon spin relaxation (μSR) down to 2 K. It was found that the zero-field muon spin relaxation rate is independent of temperature, indicating that no static magnetism appears in this compound above 2 K. The result also provides evidence against the breakdown of time-reversal symmetry for the superconducting order parameter. In water excess sample Na 0.334CoO 2·1.32H 2O, which shows no superconductivity, the weak magnetism was observed below 6 K. This fact suggests that the magnetic interaction plays an important role for the appearance of the unconventional superconductivity.

Research paper thumbnail of Knight shift measurements in the superconducting state of Pr1-xLaxOs4Sb12Pr1-xLaxOs4Sb12 (x=0.4)(x=0.4) probed by μSRμSR

Research paper thumbnail of Magnetic response in the superconducting state of 1H-Ca(Al0.5Si0.5)2Ca(Al0.5Si0.5)2studied by ��SR

Research paper thumbnail of Low-temperature magnetic order and spin dynamics in YbRh 2 Si 2

Physical Review B, 2003

Muon spin rotation and relaxation experiments have been carried out in single crystals of YbRh 2 ... more Muon spin rotation and relaxation experiments have been carried out in single crystals of YbRh 2 Si 2 , a compound that exhibits non-Fermi-liquid (NFL) behavior associated with a quantum critical point (QCP) at T=0. The zero-field muon relaxation rate is found to be independent ...

Research paper thumbnail of Magnetic Phase Diagram of Hole-Doped Ca_ Na_xCuO_2Cl_2 Cuprate Superconductor(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

Journal of the Physical Society of Japan, Sep 15, 2005

Research paper thumbnail of Investigation of Spontaneous Magnetic Field in Spin-Triplet Superconductor Sr 2 RuO 4

Proceedings of the International Symposium on Science Explored by Ultra Slow Muon (USM2013), 2014

Research paper thumbnail of Field-induced magnetism in the high-$T_c$ superconductor Ca$_{2-x}$Na$_x$CuO$_2$Cl$_2$ with flat CuO$_2$ planes

The internal magnetic field distribution in a mixed state of a cuprate superconductor, Ca$_{2-x}$... more The internal magnetic field distribution in a mixed state of a cuprate superconductor, Ca$_{2-x}$Na$_x$CuO$_2$Cl$_2$ ($T_{\rm c}\simeq28.5$ K, near the optimal doping), was measured by muon spin rotation ($\mu$SR) technique up to 60 kOe. The mu\mumuSR linewidth Lambda(B)\Lambda(B)Lambda(B) which exhibits excess broadening at higher fields ($B>5$ kOe) due to field-induced magnetism (FIM), is described by a relation, Lambda(B)proptosqrtB\Lambda(B)\propto\sqrt{B}Lambda(B)proptosqrtB. This suggests that

Research paper thumbnail of Possible nodal vortex state in CeRu 2

Physical Review B, 2001

The microscopic property of magnetic vortices in the mixed state of a high-quality CeRu2 crystal ... more The microscopic property of magnetic vortices in the mixed state of a high-quality CeRu2 crystal has been studied by muon spin rotation. We have found that the spatial distribution of magnetic induction B(r) probed by muons is perfectly described by the London model for the triangular vortex lattice with appropriate modifications to incorporate the high-field cutoff around the vortex core

Research paper thumbnail of Performance of a superconducting magnet system operated in the Super Omega Muon beam line at J-PARC

ABSTRACT A superconducting magnet system, which is composed of an 8 m long solenoid for transport... more ABSTRACT A superconducting magnet system, which is composed of an 8 m long solenoid for transportation and 12 short solenoids for focusing, has been developed for Muon Science Establishment facility of J-PARC. The transport solenoid is composed of a 6 m straight section connected to a 45 degree curved section at each end. Muons of various momenta and of both electric charges are transported through the solenoid inner bore with an effective diameter of 0.3 m, where 2 T magnetic field is induced. There are 12 focusing solenoids with an effective bore diameter of 0.6 m and a length of 0.35 m arranged on a straight line at suitable intervals. The maximum central field of each focusing solenoid is 0.66 T. All solenoid coils are cooled by GM cryocoolers through their own conductions. The magnet system has been installed into the beam line in the summer of 2012, and its performance has been checked. Beam commissioning has been carried out since October 2012. During beam operation, temperature rise over 6 K in the transport solenoid due to a nuclear heating from the muon production target is observed at beam intensity of about 300 kW.

Research paper thumbnail of Field-Induced Quasiparticle Excitation in Ca(Al0.5Si0.5)2: Evidence for Unconventional Superconductivity

The temperature (T) and magnetic field (H) dependence of the magnetic penetration depth, �(T,H), ... more The temperature (T) and magnetic field (H) dependence of the magnetic penetration depth, �(T,H), in Ca(Al0.5Si0.5)2 exhibits significant deviation from that expected for conventional BCS superconductors. In particular, it is inferred from a field dependence of �(H) (/ H) at 2.0 K that the quasiparticle excitation is strongly enhanced by the Doppler shift. This suggests that the superconducting order parameter

Research paper thumbnail of Magnetism of Ca_2-xNa_xCuO_2Cl2 Probed by Muon Spin Relaxation

Insight into the pairing mechanism of high-Tc superconductors is being sought by studying the par... more Insight into the pairing mechanism of high-Tc superconductors is being sought by studying the parent compounds which are generally undoped antiferromagnetic insulators. La_2CuO4 is one of such superconducting parent compounds which have CuO2 planes consisting of CuO6 octahedra. La_2CuO4 is orthorhombic below ˜ 530 K, and the distortion associated with it brings about weak ferromagnetism of the Dzyalochinsky-Moriya type. Neither

Research paper thumbnail of Muonium in stishovite: implications for the possible existence of neutral atomic hydrogen in the earth's deep mantle

Scientific reports, 2015

Hydrogen in the Earth's deep interior has been thought to exist as a hydroxyl group in high-p... more Hydrogen in the Earth's deep interior has been thought to exist as a hydroxyl group in high-pressure minerals. We present Muon Spin Rotation experiments on SiO2 stishovite, which is an archetypal high-pressure mineral. Positive muon (which can be considered as a light isotope of proton) implanted in stishovite was found to capture electron to form muonium (corresponding to neutral hydrogen). The hyperfine-coupling parameter and the relaxation rate of spin polarization of muonium in stishovite were measured to be very large, suggesting that muonium is squeezed in small and anisotropic interstitial voids without binding to silicon or oxygen. These results imply that hydrogen may also exist in the form of neutral atomic hydrogen in the deep mantle.

Research paper thumbnail of Magnetism of anomalous A-phase in Ce1+xCu2+ySi2: a μSR study

Research paper thumbnail of Muon science in J-PARC

Research paper thumbnail of U-Line at MLF/J-PARC for Ultra Slow Muon Microscopy

Proceedings of the International Symposium on Science Explored by Ultra Slow Muon (USM2013), 2014

ABSTRACT The second muon beamline in the Materials and Life Science Experimental Facility (MLF) o... more ABSTRACT The second muon beamline in the Materials and Life Science Experimental Facility (MLF) of the Japan Accelerator Research Complex (J-PARC) is under construction. Our beam commissioning for U-line revealed that the U-line was the highest pulsed muon source in the world. After the commissioning, we plan to upgrade and to modify the some components of U-line. Here, we report mainly on the plan for upgrade and modification of the U-line components.

Research paper thumbnail of Suppression of time reversal symmetry breaking superconcutivity in Pr(Os,Ru)4Sb12 and (Pr,La)Os4Sb12

Zero-field muon spin relaxation (muSR) experiments have been carried out in the Pr(Os1-xRux)4Sb12... more Zero-field muon spin relaxation (muSR) experiments have been carried out in the Pr(Os1-xRux)4Sb12 and Pr1-yLayOs4Sb12 alloy systems to investigate broken time-reversal symmetry (TRS) in the superconducting state, signaled by the onset of a spontaneous static local magnetic field Bs. In both alloy series Bs initially decreases linearly with solute concentration. Ru doping is considerably more efficient than La doping ,with

Research paper thumbnail of SR studies on in comparison with the time-reversal-symmetry-broken superconductor

Physica B-condensed Matter, 2005

We have studied the zero-field muon spin relaxation (ZF-μSR) on a filled-skutterudite superconduc... more We have studied the zero-field muon spin relaxation (ZF-μSR) on a filled-skutterudite superconductor LaOs4Sb12 (Tc=0.74K) to compare with the time-reversal-symmetry (TRS)-broken superconductor PrOs4Sb12. The relaxation rate is independent of temperature down to 20mK, suggesting that the absence of TRS breaking in LaOs4Sb12. This finding provides convincing evidence for the Pr 4f-electrons playing an essential role for the realization of the

Research paper thumbnail of Status of Decay/Surface Muon Channel for the Muon Science in J-PARC

AIP Conference Proceedings, 2008

ABSTRACT Muon Science laboratory at Material Life Science Facility is now under construction in J... more ABSTRACT Muon Science laboratory at Material Life Science Facility is now under construction in J‐PARC, where, four types of muon channels are planed to install. Present status of the superconducting and surface muon channel is briefly reported.

Research paper thumbnail of Design of the Large Acceptance Muon Beamline at J-PARC

AIP Conference Proceedings, 2008

The Materials and Life Science Facility (MLF) is currently under construction at J-PARC in Tokai,... more The Materials and Life Science Facility (MLF) is currently under construction at J-PARC in Tokai, Japan. The muon section of the facility will house the muon production target and four secondary beamlines used to transport the muons into two experimental halls. One of the beamlines is a large acceptance beamline (the so called Super Omega Muon beamline) which, when completed,