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Segregation patterns in rotating cylinders determined by the size difference, density ratio, and cylinder diameter
Authors:
Kurumi Kondo,
Hiroyuki Ebata,
Shio Inagaki
Abstract:
Granular materials often segregate under mechanical agitation, which differs from the expectation of mixing. It is well known that a bidisperse mixture of granular materials in a partially filled rotating cylinder exhibits alternating bands depending on the combination of the two species. The dynamic angle of repose, which is the angle that a steady avalanche makes with the horizontal, has been co…
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Granular materials often segregate under mechanical agitation, which differs from the expectation of mixing. It is well known that a bidisperse mixture of granular materials in a partially filled rotating cylinder exhibits alternating bands depending on the combination of the two species. The dynamic angle of repose, which is the angle that a steady avalanche makes with the horizontal, has been considered the dominant parameter that determines the segregated state. However, the previously known angle of repose condition was not always satisfied in different experimental cases. To clarify the experimental conditions, we conducted an exhaustive parameter search with three dimensionless parameters: the particle size difference normalized by the average particle size, the specific density ratio, and the ratio of the cylinder diameter to the average particle size. Additional experiments were conducted to explore the effect of the rotational speed of the cylinder. This systematic approach enabled us to predict the segregated state. Moreover, we discovered that the band width can be effectively scaled by combining these three parameters.
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Submitted 7 June, 2023; v1 submitted 2 June, 2023;
originally announced June 2023.
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Inter- to Intra-Layer Resistivity Anisotropy of NdFeAs(O,H) with Various Hydrogen Concentrations
Authors:
M. Chen,
K. Iida,
K. Kondo,
J. Hänisch,
T. Hatano,
H. Ikuta
Abstract:
With molecular beam epitaxy and topotactic chemical reaction, we prepared NdFeAs(O,H) epitaxial thin films with various hydrogen concentrations on 5° vicinal cut MgO substrates. By measuring the resistivities along the longitudinal and transversal directions, the ab plane and the c axis resistivities (\{rho}_ab and \{rho}_c) were obtained. The resistivity anisotropy γ_\{rho}=\{rho}_c \ \{rho}_ab o…
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With molecular beam epitaxy and topotactic chemical reaction, we prepared NdFeAs(O,H) epitaxial thin films with various hydrogen concentrations on 5° vicinal cut MgO substrates. By measuring the resistivities along the longitudinal and transversal directions, the ab plane and the c axis resistivities (\{rho}_ab and \{rho}_c) were obtained. The resistivity anisotropy γ_\{rho}=\{rho}_c \ \{rho}_ab of NdFeAs(O,H) with various hydrogen concentrations was compared with that of NdFeAs(O,F). At the H concentrations which led to superconducting transition temperatures Tc over 40 K, γ_\r{ho} recorded ~100-150 at 50 K. On the other hand, a low γ_\{rho} value of 9 was observed with the mostly doped sample. The exponent \{beta} of the ab plane resistivity obtained by fitting a power law expression \{rho}_{ab}(T)=\{rho}_0+AT^\{beta} to the data was close to unity down to low temperature in the vicinity where the second antiferromagnetic phase locates, which may be related to the quantum critical point discussed at the over-doped side of the phase diagram.
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Submitted 4 April, 2022;
originally announced April 2022.
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Nanoscale Texture and Microstructure in NdFeAs(O,F)/IBAD-MgO Superconducting Thin Film with Superior Critical Current Properties
Authors:
Zimeng Guo,
Hongye Gao,
Keisuke Kondo,
Takafumi Hatano,
Kazumasa Iida,
Jens Hänisch,
Hiroshi Ikuta,
Satoshi Hata
Abstract:
This paper reports the nanoscale texture and microstructure of a high-performance NdFeAs(O,F) superconducting thin film grown by molecular beam epitaxy on a textured MgO/Y$_2$O$_3$/Hastelloy substrate. The NdFeAs(O,F) film forms a highly textured columnar grain structure by epitaxial growth on the MgO template. Although the film contains stacking faults along the $ab$-plane as well as grain bounda…
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This paper reports the nanoscale texture and microstructure of a high-performance NdFeAs(O,F) superconducting thin film grown by molecular beam epitaxy on a textured MgO/Y$_2$O$_3$/Hastelloy substrate. The NdFeAs(O,F) film forms a highly textured columnar grain structure by epitaxial growth on the MgO template. Although the film contains stacking faults along the $ab$-plane as well as grain boundaries perpendicular to the $ab$-plane, good superconducting properties are measured: a critical temperature, $T _{\rm c}$, of 46 K and a self-field critical current density, $J_{\rm c}$, of $2 \times 10^6 \,{\rm A/cm^2}$ at 4.2 K. Automated crystal orientation mapping by scanning precession electron diffraction in transmission electron microscopy is employed to analyze the misorientation angles between adjacent grains in a large ensemble (247 grains). 99% of the grain boundaries show in-plane misorientation angles ($Δγ$) less than the critical angle $θ_{\rm c}$, which satisfies one of the necessary conditions for the high $J_{\rm c}$. Comparing the columnar grain size distribution with the mean distance of the flux line lattice, the triple junctions of low-angle grain boundaries are found to be effective pinning centers, even at high temperatures ($\ge$35 K) and/or low magnetic fields.
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Submitted 19 November, 2021;
originally announced November 2021.
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High $J_{\rm c}$ and low anisotropy of hydrogen doped NdFeAsO superconducting thin film
Authors:
Kazumasa Iida,
Jens Hänisch,
Keisuke Kondo,
Mingyu Chen,
Takafumi Hatano,
Chao Wang,
Hikaru Saito,
Satoshi Hata,
Hiroshi Ikuta
Abstract:
The recent realisations of hydrogen doped $Ln$FeAsO ($Ln$=Nd and Sm) superconducting epitaxial thin films call for further investigation of their structural and electrical transport properties. Here, we report on the microstructure of a NdFeAs(O,H) epitaxial thin film and its temperature, field, and orientation dependencies of the resistivity and the critical current density $J_{\rm c}$. The super…
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The recent realisations of hydrogen doped $Ln$FeAsO ($Ln$=Nd and Sm) superconducting epitaxial thin films call for further investigation of their structural and electrical transport properties. Here, we report on the microstructure of a NdFeAs(O,H) epitaxial thin film and its temperature, field, and orientation dependencies of the resistivity and the critical current density $J_{\rm c}$. The superconducting transition temperature $T_{\rm c}$ is comparable to NdFeAs(O,F). Transmission electron microscopy investigation supported that hydrogen is homogenously substituted for oxygen. A high self-field $J_{\rm c}$ of over 10 MA/cm$^2$ was recorded at 5 K, which is likely to be caused by a short London penetration depth. The anisotropic Ginzburg-Landau scaling for the angle dependence of $J_{\rm c}$ yielded temperature-dependent scaling parameters $γ_{\rm J}$ that decreased from 1.6 at 30 K to 1.3 at 5 K. This is opposite to the behaviour of NdFeAs(O,F). Additionally, $γ_{\rm J}$ of NdFeAs(O,H) is smaller than that of NdFeAs(O,F). Our results indicate that heavily electron doping by means of hydrogen substitution for oxygen in $Ln$FeAsO is highly beneficial for achieving high $J_{\rm c}$ with low anisotropy without compromising $T_{\rm c}$, which is favourable for high-field magnet applications.
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Submitted 26 February, 2021;
originally announced February 2021.
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Anisotropy of the transport properties of NdFeAs(O,F) thin films grown on vicinal substrates
Authors:
Kazumasa Iida,
Takuya Matsumoto,
Keisuke Kondo,
Takafumi Hatano,
Hiroshi Ikuta
Abstract:
NdFeAs(O,F) thin films having different fluorine contents were grown on 5 deg. or 10 deg. vicinal cut MgO and CaF2 single crystalline substrates by molecular beam epitaxy. Structural characterisations by reflection high-energy electron diffraction and x-ray diffraction confirmed the epitaxial growth of NdFeAs(O,F). The resistivities of the ab-plane and along the c-axis were derived from the resist…
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NdFeAs(O,F) thin films having different fluorine contents were grown on 5 deg. or 10 deg. vicinal cut MgO and CaF2 single crystalline substrates by molecular beam epitaxy. Structural characterisations by reflection high-energy electron diffraction and x-ray diffraction confirmed the epitaxial growth of NdFeAs(O,F). The resistivities of the ab-plane and along the c-axis were derived from the resistivity measurements in the longitudinal and transversal directions. The c-axis resistivity was always higher than the ab-plane resistivity, resulting from the anisotropic electronic structure. The resistivity anisotropy at 300 K was almost constant in the range of 50-90 irrespective of the F content. On the other hand, the resistivity anisotropy at 56 K showed a strong fluorine dependence: the resistivity anisotropy was over 200 for the films with optimum F contents (superconducting transition temperature Tc around 50 K), whereas the resistivity anisotropy was around 70 for the films in the under-doped regime (Tc between 35 and 45 K). The mass anisotropy are the effective masses along the c-axis and on the ab-plane) close to Tc derived from the anisotropic Ginzburg-Landau approach using the angular-dependency of the ab-plane resistivity was in the range from 2 to 5. On the assumption that the square of the mass anisotropy is equal to the resistivity anisotropy, those values are small compared to the normal state anisotropy.
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Submitted 20 March, 2020;
originally announced March 2020.
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Superconductivity of Electron-Doped NdOBiS2 by Substitution of Mixed-Valence Ce ions
Authors:
Naoki Kase,
Masaya Matsumoto,
Katsuo Kondo,
Jun Gouchi,
Yoshiya Uwatoko,
Toshiro Sakakibara,
Nobuaki Miyakawa
Abstract:
Superconductivity is achieved in Nd1-xCexOBiS2 via electron doping using mixed-valence Ce ions. Single crystals with x = 0.2, 0.3, 0.4, and 0.5 are generated using a CsCl flux method. Plate-like single crystals with dimensions of 0.8 0.8 0.2 mm3 were obtained. The magnetic susceptibility chi(T) indicates large diamagnetism, and the electrical resistivity rho(T) indicates zero resistivity. The maxi…
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Superconductivity is achieved in Nd1-xCexOBiS2 via electron doping using mixed-valence Ce ions. Single crystals with x = 0.2, 0.3, 0.4, and 0.5 are generated using a CsCl flux method. Plate-like single crystals with dimensions of 0.8 0.8 0.2 mm3 were obtained. The magnetic susceptibility chi(T) indicates large diamagnetism, and the electrical resistivity rho(T) indicates zero resistivity. The maximum value of Tc is observed at 4.7 K in Nd0.8Ce0.2OBiS2 from chi(T). From the rho(T) measurements taken in several magnetic fields, the upper critical field mu0Hc2(0) is estimated to be about 12 and 0.34 T for the ab- and c-planes, respectively. We redetermined mu0Hc2(0) of NdO0.7F0.3BiS2, as about 35 and 0.78 T for the ab- and c-planes, respectively. The anisotropic parameter is estimated to be about 35 for Nd0.7Ce0.3OBiS2 and 45 for NdO0.7F0.3BiS2. The mu0Hc2(0) of Nd0.7Ce0.3OBiS2 is approximately two times smaller than that of NdO0.7F0.3BiS2, although the difference of Gamma is approximately 10.
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Submitted 4 September, 2019;
originally announced September 2019.
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Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films
Authors:
A. Kirihara,
K. Kondo,
M. Ishida,
K. Ihara,
Y. Iwasaki,
H. Someya,
A. Matsuba,
K. Uchida,
E. Saitoh,
N. Yamamoto,
S. Kohmoto,
T. Murakami
Abstract:
We demonstrated a flexible thermoelectric (TE) sheet based on the longitudinal spin Seebeck effect (LSSE) that is especially suitable for heat-flow sensing applications. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as ferrite plating. The experimental results suggest that the ferrite-plated film, which has a column…
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We demonstrated a flexible thermoelectric (TE) sheet based on the longitudinal spin Seebeck effect (LSSE) that is especially suitable for heat-flow sensing applications. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as ferrite plating. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors.
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Submitted 22 February, 2016;
originally announced February 2016.
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Field-induced long-range magnetic order in the spin-singlet ground state system YbAl3C3: Neutron diffraction study
Authors:
D. D. Khalyavin,
D. T. Adroja,
P. Manuel,
A. Daoud-Aladine,
M. Kosaka,
K. Kondo,
K. A. McEwen,
J. H. Pixley,
Qimiao Si
Abstract:
The $4f$-electron system YbAl$_3$C$_3$ with a non-magnetic spin-dimer ground state has been studied by neutron diffraction in an applied magnetic field. A long-range magnetic order involving both ferromagnetic and antiferromagnetic components has been revealed above the critical field H$_C\sim $ 6T at temperature T=0.05K. The magnetic structure indicates that the geometrical frustration of the pro…
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The $4f$-electron system YbAl$_3$C$_3$ with a non-magnetic spin-dimer ground state has been studied by neutron diffraction in an applied magnetic field. A long-range magnetic order involving both ferromagnetic and antiferromagnetic components has been revealed above the critical field H$_C\sim $ 6T at temperature T=0.05K. The magnetic structure indicates that the geometrical frustration of the prototype hexagonal lattice is not fully relieved in the low-temperature orthorhombic phase. The suppression of magnetic ordering by the remanent frustration is the key factor stabilizing the non-magnetic singlet ground state in zero field. Temperature dependent measurements in the applied field H=12T revealed that the long-range ordering persists up to temperatures significantly higher than the spin gap indicating that this phase is not directly related to the singlet-triplet excitation. Combining our neutron diffraction results with the previously published phase diagram, we support the existence of an intermediate disordered phase as the first excitation from the non-magnetic singlet ground state. Based on our results, we propose YbAl$_3$C$_3$ as a new material for studying the quantum phase transitions of heavy-fermion metals under the influence of geometrical frustration.
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Submitted 9 February, 2013;
originally announced February 2013.
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Half-Quantum Vortices in Thin Film of Superfluid $^3$He
Authors:
Kenji Kondo,
Tetsuo Ohmi,
Mikio Nakahara,
Takuto Kawakami,
Yasumasa Tsutsumi,
Kazushige Machida
Abstract:
Stability of a half-quantum vortex (HQV) in superfluid $^3$He has been discussed recently by Kawakami, Tsutsumi and Machida in Phys. Rev. B {\bf 79}, 092506 (2009). We further extend this work here and consider the A$_2$ phase of superfluid $^3$He confined in thin slab geometry and analyze the HQV realized in this setting. Solutions of HQV and singly quantized singular vortex are evaluated numeric…
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Stability of a half-quantum vortex (HQV) in superfluid $^3$He has been discussed recently by Kawakami, Tsutsumi and Machida in Phys. Rev. B {\bf 79}, 092506 (2009). We further extend this work here and consider the A$_2$ phase of superfluid $^3$He confined in thin slab geometry and analyze the HQV realized in this setting. Solutions of HQV and singly quantized singular vortex are evaluated numerically by solving the Ginzburg-Landau (GL) equation and respective first critical angular velocities are obtained by employing these solutions. We show that the HQV in the A$_2$ phase is stable near the boundary between the A$_2$ and A$_1$ phases. It is found that temperature and magnetic field must be fixed first in the stable region and subsequently the angular velocity of the system should be increased from zero to a sufficiently large value to create a HQV with sufficiently large probability. A HQV does not form if the system starts with a fixed angular velocity and subsequently the temperature is lowered down to the A$_2$ phase. It is estimated that the external magnetic field with strength on the order of 1 T is required to have a sufficiently large domain in the temperature-magnetic field phase diagram to have a stable HQV.
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Submitted 13 June, 2012;
originally announced June 2012.
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Longitudinal and transverse exciton spin relaxation times in single InP/InAsP/InP nanowire quantum dots
Authors:
H. Sasakura,
C. Hermannstädter,
S. N. Dorenbos,
N. Akopian,
M. P. van Kouwen,
J. Motohisa,
Y. Kobayashi,
H. Kumano,
K. Kondo,
K. Tomioka,
T. Fukui,
I. Suemune,
V. Zwiller
Abstract:
We have investigated the optical properties of a single InAsP quantum dot embedded in a standing InP nanowire. A regular array of nanowires was fabricated by epitaxial growth and electron-beam patterning. The elongation of transverse exciton spin relaxation time of the exciton state with decreasing excitation power was observed by first-order photon correlation measurements. This behavior is well…
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We have investigated the optical properties of a single InAsP quantum dot embedded in a standing InP nanowire. A regular array of nanowires was fabricated by epitaxial growth and electron-beam patterning. The elongation of transverse exciton spin relaxation time of the exciton state with decreasing excitation power was observed by first-order photon correlation measurements. This behavior is well explained by the motional narrowing mechanism induced by Gaussian fluctuations of environmental charges in the InP nanowire. The longitudinal exciton spin relaxation time was evaluated by the degree of the random polarization of emission originating from exciton state confined in a single nanowire quantum dots by using Mueller Calculus based on Stokes parameters representation.
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Submitted 29 September, 2011;
originally announced September 2011.
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Possible Multiple Gap Superconductivity with Line Nodes in Heavily Hole-Doped Superconductor KFe2As2 Studied by 75As-NQR and Specific Heat
Authors:
H. Fukazawa,
Y. Yamada,
K. Kondo,
T. Saito,
Y. Kohori,
K. Kuga,
Y. Matsumoto,
S. Nakatsuji,
H. Kito,
P. M. Shirage,
K. Kihou,
N. Takeshita,
C. -H. Lee,
A. Iyo,
H. Eisaki
Abstract:
We report the 75As nuclear quadrupole resonance (NQR) and specific heat measurements of the heavily hole-doped superconductor KFe2As2 (Tc = 3.5 K). The spin-lattice relaxation rate 1/T1 in the superconducting state exhibits quite gradual temperature dependence with no coherence peak below Tc. The quasi-particle specific heat C_QP/T shows small specific heat jump which is about 30% of electronic…
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We report the 75As nuclear quadrupole resonance (NQR) and specific heat measurements of the heavily hole-doped superconductor KFe2As2 (Tc = 3.5 K). The spin-lattice relaxation rate 1/T1 in the superconducting state exhibits quite gradual temperature dependence with no coherence peak below Tc. The quasi-particle specific heat C_QP/T shows small specific heat jump which is about 30% of electronic specific heat coefficient just below Tc. In addition, it suggests the existence of low-energy quasi-particle excitation at the lowest measurement temperature T = 0.4 K \simeq Tc/10. These temperature dependence of 1/T1 and C_QP/T can be explained by multiple nodal superconducting gap scenario rather than multiple fully-gapped s_\pm-wave one within simple gap analysis.
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Submitted 25 June, 2009;
originally announced June 2009.
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75As NMR Study of Hole-Doped Superconductor Ba1-xKxFe2As2 (Tc = 38K)
Authors:
H. Fukazawa,
T. Yamazaki,
K. Kondo,
Y. Kohori,
N. Takeshita,
P. M. Shirage,
K Kihou,
K. Miyazawa,
H. Kito,
H. Eisaki,
A. Iyo
Abstract:
We report the 75As nuclear magnetic resonance (NMR) measurement of the hole-doped superconductor Ba1-xKxFe2As2 with different lattice parameters and different superconducting volume fractions (Tc = 38K). 75As-NMR spectra revealed that the magnetically ordered and superconducting phases are microscopically separated. The spin-lattice relaxation rate 1/T1 in the normal state reflects the existence…
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We report the 75As nuclear magnetic resonance (NMR) measurement of the hole-doped superconductor Ba1-xKxFe2As2 with different lattice parameters and different superconducting volume fractions (Tc = 38K). 75As-NMR spectra revealed that the magnetically ordered and superconducting phases are microscopically separated. The spin-lattice relaxation rate 1/T1 in the normal state reflects the existence of a large two-dimensional antiferromagnetic spin fluctuation. The 1/T1 in the superconducting state down to the lowest measurement temperature T varies close to T^3. In addition, it exhibits no coherence peak just below Tc. This shows a T dependence similar to those of other iron pnictides.
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Submitted 2 February, 2009; v1 submitted 1 January, 2009;
originally announced January 2009.
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Suppression of Magnetic Order by Pressure in BaFe2As2
Authors:
H. Fukazawa,
N. Takeshita,
T. Yamazaki,
K. Kondo,
K. Hirayama,
Y. Kohori,
K. Miyazawa,
H. Kito,
H. Eisaki,
A. Iyo
Abstract:
We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2 under high pressure. The T-P phase diagram of BaFe2As2 determined from resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly is quite robust against P.
We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2 under high pressure. The T-P phase diagram of BaFe2As2 determined from resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly is quite robust against P.
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Submitted 5 August, 2008;
originally announced August 2008.
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75As NMR study of the ternary iron arsenide BaFe2As2
Authors:
H. Fukazawa,
K. Hirayama,
K. Kondo,
T. Yamazaki,
Y. Kohori,
N. Takeshita,
K. Miyazawa,
H. Kito,
H. Eisaki,
A. Iyo
Abstract:
We report 75As-NMR measurements of the ternary iron arsenide BaFe2As2. 75As-NMR spectra clearly revealed that magnetic transition occurs at around 131 K in our samples, which corresponds to the emergence of spin density wave. Temperature dependence of the internal magnetic field suggests that the transition is likely of the first order. The critical-slowing-down phenomenon in the spin-lattice re…
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We report 75As-NMR measurements of the ternary iron arsenide BaFe2As2. 75As-NMR spectra clearly revealed that magnetic transition occurs at around 131 K in our samples, which corresponds to the emergence of spin density wave. Temperature dependence of the internal magnetic field suggests that the transition is likely of the first order. The critical-slowing-down phenomenon in the spin-lattice relaxation rate 1/T1 is not pronounced in this material.
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Submitted 14 July, 2008; v1 submitted 27 June, 2008;
originally announced June 2008.
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First-order Phase Transition in Three-dimensional QED with Chern--Simons Term
Authors:
Kei-Ichi Kondo,
Pieter Maris
Abstract:
We have studied the chiral phase transition in three-dimensional QED in the presence of a Chern--Simons term for the gauge field. There exists a phase where the chiral symmetry is broken dynamically and we have determined the critical line for this symmetry breaking as a function of the effective coupling and the strength of the additional Chern--Simons term. In the presence of a Chern--Simons t…
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We have studied the chiral phase transition in three-dimensional QED in the presence of a Chern--Simons term for the gauge field. There exists a phase where the chiral symmetry is broken dynamically and we have determined the critical line for this symmetry breaking as a function of the effective coupling and the strength of the additional Chern--Simons term. In the presence of a Chern--Simons term, the chiral phase transition turns out to be first order, in sharp contrast to the phase transition in pure three-dimensional QED.
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Submitted 16 March, 1995; v1 submitted 2 August, 1994;
originally announced August 1994.