Thermal aging effects on surface of 2.5 Me V Fe ion-irradiated Fe–0.6%Cu alloy were investigated using positron annihilation techniques. The samples were irradiated at 573 K to a dose of 0.1 dpa. Their thermal aging ...Thermal aging effects on surface of 2.5 Me V Fe ion-irradiated Fe–0.6%Cu alloy were investigated using positron annihilation techniques. The samples were irradiated at 573 K to a dose of 0.1 dpa. Their thermal aging was performed at 573 K for 5, 50 and 100 h. From the results of Doppler broadening measurement, an obvious trough could be seen in near-surface region from the S parameters and inflection point form at S–W curves. This indicates changes in the annihilation mechanism of positrons in surface region after thermal aging. Coincident Doppler broadening indicates that the density of Cu precipitates in the thermal aged samples decreased, due to recovery of the vacancies.展开更多
Ising superconductivity,observed in NbSe2 and similar materials,has generated tremendous interest.Recently,attention was called to the possible role that spin fluctuations(SF)play in this phenomenon,in addition to the...Ising superconductivity,observed in NbSe2 and similar materials,has generated tremendous interest.Recently,attention was called to the possible role that spin fluctuations(SF)play in this phenomenon,in addition to the dominant electron–phonon coupling(EPC);the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet Leggett oscillations.However,these hypotheses have not been put to a quantitative test.In this paper,we report first principle calculations of the EPC and also estimate coupling with SF,including full momentum dependence.We find that:(1)EPC is strongly anisotropic,largely coming from the K-K0 scattering,and therefore excludes triplet symmetry even as an excited state;(2)superconductivity is substantially weakened by SF,but anisotropy remains as above;and,(3)we do find the possibility of a Leggett mode,not in a singlet–triplet but in an s_(++)–s_(±)channel.展开更多
We investigate the magnetism of a previously unexplored distorted spin-1/2 kagome model consisting of three symmetry-inequivalent nearest-neighbor antiferromagnetic Heisenberg couplings J_(■),J,and J′,and uncover a ...We investigate the magnetism of a previously unexplored distorted spin-1/2 kagome model consisting of three symmetry-inequivalent nearest-neighbor antiferromagnetic Heisenberg couplings J_(■),J,and J′,and uncover a rich ground state phase diagram even at the classical level.Using analytical arguments and numerical techniques we identify a collinear Q^(→)=0 magnetic phase,two unusual non-collinear coplanar Q^(→)=(1/3,1/3)phases and a classical spin liquid phase with a degenerate manifold of non-coplanar ground states,resembling the jammed spin liquid phase found in the context of a bond-disordered kagome antiferromagnet.We further show with density functional theory calculations that the recently synthesized Y-kapellasite Y_(3)Cu_(9)(OH)_(19)C_(l8) is a realization of this model and predict its ground state to lie in the region of Q^(→)=(1/3,1/3)order,which remains stable even after the inclusion of quantum fluctuation effects within variational Monte Carlo and pseudofermion functional renormalization group.The presented model opens a new direction in the study of kagome antiferromagnets.展开更多
基金supported by the National Natural Science Foundation of China(Nos.91026006,91226103,11475193,11475197,11575205and 11505192)Beijing Natural Science Foundation(No.1164017)
文摘Thermal aging effects on surface of 2.5 Me V Fe ion-irradiated Fe–0.6%Cu alloy were investigated using positron annihilation techniques. The samples were irradiated at 573 K to a dose of 0.1 dpa. Their thermal aging was performed at 573 K for 5, 50 and 100 h. From the results of Doppler broadening measurement, an obvious trough could be seen in near-surface region from the S parameters and inflection point form at S–W curves. This indicates changes in the annihilation mechanism of positrons in surface region after thermal aging. Coincident Doppler broadening indicates that the density of Cu precipitates in the thermal aged samples decreased, due to recovery of the vacancies.
基金The work at GMU(S.D.and I.I.M.)was supported by Office of Naval Research through grant N00014-20-1-2345H.P.and E.R.M.acknowledge support from the National Science Foundation(NSF)under Grant No.DMR-2035518 and Grant No.OAC-2103991 for method development,superconductivity analysis,and code develop-ment.D.F.A+2 种基金was supported by the U.S.Department of Energy,Office of Basic Energy Sciences,Division of Materials Sciences and Engineering,under Award No.DE-SC0021971This work used the Extreme Science and Engineering Discovery Environment(XSEDE)70 which is supported by NSF Award No.ACI-1548562Specifically,this work used Comet at the San Diego Supercomputer Center through allocation TG-DMR180071.
文摘Ising superconductivity,observed in NbSe2 and similar materials,has generated tremendous interest.Recently,attention was called to the possible role that spin fluctuations(SF)play in this phenomenon,in addition to the dominant electron–phonon coupling(EPC);the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet Leggett oscillations.However,these hypotheses have not been put to a quantitative test.In this paper,we report first principle calculations of the EPC and also estimate coupling with SF,including full momentum dependence.We find that:(1)EPC is strongly anisotropic,largely coming from the K-K0 scattering,and therefore excludes triplet symmetry even as an excited state;(2)superconductivity is substantially weakened by SF,but anisotropy remains as above;and,(3)we do find the possibility of a Leggett mode,not in a singlet–triplet but in an s_(++)–s_(±)channel.
基金F.F.acknowledges support from the Alexander von Humboldt Foundation through a postdoctoral Humboldt fellowship.A.R.,R.V.,and J.R.acknowledge support by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)for funding through TRR 288-422213477(projects A05,B05)(A.R.and R.V.)CRC 183(project A04)(J.R.).I.I.M.acknowledges support from the U.S.Department of Energy through Grant no.DE-SC0021089 and from the Wilhelm and Else Heraeus Foundation.
文摘We investigate the magnetism of a previously unexplored distorted spin-1/2 kagome model consisting of three symmetry-inequivalent nearest-neighbor antiferromagnetic Heisenberg couplings J_(■),J,and J′,and uncover a rich ground state phase diagram even at the classical level.Using analytical arguments and numerical techniques we identify a collinear Q^(→)=0 magnetic phase,two unusual non-collinear coplanar Q^(→)=(1/3,1/3)phases and a classical spin liquid phase with a degenerate manifold of non-coplanar ground states,resembling the jammed spin liquid phase found in the context of a bond-disordered kagome antiferromagnet.We further show with density functional theory calculations that the recently synthesized Y-kapellasite Y_(3)Cu_(9)(OH)_(19)C_(l8) is a realization of this model and predict its ground state to lie in the region of Q^(→)=(1/3,1/3)order,which remains stable even after the inclusion of quantum fluctuation effects within variational Monte Carlo and pseudofermion functional renormalization group.The presented model opens a new direction in the study of kagome antiferromagnets.
