490 research outputs found
Magnetic and transport properties of iron-platinum arsenide Ca10(Pt4-{\delta}As8)(Fe2-xPtxAs2)5 single crystal
We report superconducting properties of single crystalline
Ca10(Pt4-{\delta}As8)(Fe2-xPtxAs2)5 by X-ray diffraction, magnetization,
resistivity, and magneto-optical imaging measurements. The magnetization
measurements reveal fish-tail hysteresis loop and relatively high critical
current density Jc ~ 0.8\times105 A/cm2 at low temperatures. The exponential
temperature dependence of Jc, which arises from nonlinear effective flux-creep
activation energy, has been observed. Upper critical field determined by
resistive transition shows a relatively large anisotropy. The magneto-optical
images reveal homogenous current flow within the crystal.Comment: 6 pages, 6 figures, Accepted for publication in Phys. Rev.
NMR Study of the New Magnetic Superconductor CaK(Fe$0.951Ni0.049)4As4: Microscopic Coexistence of Hedgehog Spin-vortex Crystal and Superconductivity
Coexistence of a new-type antiferromagnetic (AFM) state, the so-called
hedgehog spin-vortex crystal (SVC), and superconductivity (SC) is evidenced by
As nuclear magnetic resonance study on single-crystalline
CaK(FeNi)As. The hedgehog SVC order is clearly
demonstrated by the direct observation of the internal magnetic induction along
the axis at the As1 site (close to K) and a zero net internal magnetic
induction at the As2 site (close to Ca) below an AFM ordering temperature
52 K. The nuclear spin-lattice relaxation rate 1/ shows
a distinct decrease below 10 K, providing also unambiguous
evidence for the microscopic coexistence. Furthermore, based on the analysis of
the 1/ data, the hedgehog SVC-type spin correlations are found to be
enhanced below 150 K in the paramagnetic state. These results
indicate the hedgehog SVC-type spin correlations play an important role for the
appearance of SC in the new magnetic superconductor.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. B rapid
communicatio
Solving Coupled Differential Equation Groups Using PINO-CDE
As a fundamental mathmatical tool in many engineering disciplines, coupled
differential equation groups are being widely used to model complex structures
containing multiple physical quantities. Engineers constantly adjust structural
parameters at the design stage, which requires a highly efficient solver. The
rise of deep learning technologies has offered new perspectives on this task.
Unfortunately, existing black-box models suffer from poor accuracy and
robustness, while the advanced methodologies of single-output operator
regression cannot deal with multiple quantities simultaneously. To address
these challenges, we propose PINO-CDE, a deep learning framework for solving
coupled differential equation groups (CDEs) along with an equation
normalization algorithm for performance enhancing. Based on the theory of
physics-informed neural operator (PINO), PINO-CDE uses a single network for all
quantities in a CDEs, instead of training dozens, or even hundreds of networks
as in the existing literature. We demonstrate the flexibility and feasibility
of PINO-CDE for one toy example and two engineering applications: vehicle-track
coupled dynamics (VTCD) and reliability assessment for a four-storey building
(uncertainty propagation). The performance of VTCD indicates that PINO-CDE
outperforms existing software and deep learning-based methods in terms of
efficiency and precision, respectively. For the uncertainty propagation task,
PINO-CDE provides higher-resolution results in less than a quarter of the time
incurred when using the probability density evolution method (PDEM). This
framework integrates engineering dynamics and deep learning technologies and
may reveal a new concept for CDEs solving and uncertainty propagation
Suppression of ferromagnetic spin fluctuations in the filled skutterudite superconductor SrOs4 As12 revealed by 75As NMR-NQR measurements
Motivated by the recent observation of ferromagnetic spin correlations in the filled skutterudite SrFe4As12 [Q.-P. Ding et al., Phys. Rev. B 98, 155149 (2018)], we have carried out As-75 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the role of magnetic fluctuations in the newly discovered isostructural superconductor SrOs4As12 with a superconducting transition temperature of T-c similar to 4.8 K. Knight shift K determined by the NQR spectrum under a small magnetic field (\u3c= 0.5 T) is nearly independent of temperature, consistent with the temperature dependence of the magnetic susceptibility. The nuclear spin-lattice relaxation rate divided by temperature, 1/T1T, is nearly independent of temperature above similar to 50 K and increases slightly with decreasing temperature below the temperature. The temperature dependence is reasonably explained by a simple model where a flat band structure with a small ledge near the Fermi energy is assumed. By comparing the present NMR data with those in SrFe4As12, we found that the values of vertical bar K vertical bar and 1/T1T in SrOs4As12 are smaller than those in SrFe4As12, indicating no obvious ferromagnetic spin correlations in SrOs4As12. From the temperature dependence of 1/T-1 in the superconducting state, an s-wave superconductivity is realized
NMR studies of the incommensurate helical antiferromagnet EuCo2P2 : determination of the antiferromagnetic propagation vector
Recently Ding et al. [Phys. Rev. B 95, 184404 (2017)] reported that their
nuclear magnetic resonance (NMR) study on EuCoAs successfully
characterized the antiferromagnetic (AFM) propagation vector of the
incommensurate helix AFM state, showing that NMR is a unique tool for
determination of the spin structures in incommensurate helical AFMs. Motivated
by this work, we have carried out Eu, P and Co NMR
measurements on the helical antiferromagnet EuCoP with an AFM ordering
temperature = 66.5 K. An incommensurate helical AFM structure was
clearly confirmed by Eu and P NMR spectra on single crystalline
EuCoP in zero magnetic field at 1.6 K and its external magnetic field
dependence. Furthermore, based on Co NMR data in both the paramagnetic
and the incommensurate AFM states, we have determined the model-independent
value of the AFM propagation vector k = (0, 0, 0.73 0.09)2/ where
is the -axis lattice parameter. The temperature dependence of k is also
discussed.Comment: 8 pages, 10 figures, accepted for publication in Phys. Rev. B. arXiv
admin note: substantial text overlap with arXiv:1704.0629
Charge disproportionation in the spin-liquid candidate κ − (ET)2Cu2(CN)3 at 6 K revealed by 63Cu NQR measurements
The spin-liquid candidate κ−(ET)2Cu2(CN)3 [ET: bis(ethylenedithio)tetrathiafulvalene] does not exhibit magnetic ordering down to a very low temperature, but shows a mysterious anomaly at 6 K. The origin of the so-called 6-K anomaly is still under debate. We carried out nuclear quadrupole resonance (NQR) measurements on the copper sites of the insulating layers, which are sensitive to the charge dynamics unlike conventional spin-1/2 nuclear magnetic resonance (NMR). The main finding of this Rapid Communication is that the observation of a sharp peak behavior in the nuclear spin-lattice relaxation rate T−11 of 63Cu NQR at 6 K while T−11 of both 13C and 1H NMR show no clear anomaly. This behavior can be understood as a second-order phase transition related to charge disproportionation in the ET layers
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