Diluted magnetic semiconductors (DMSs) that possess both properties of semiconductors and ferromagnetism, have attracted a lot of attentions due to its potential applications for spin-sensitive electronic devices. Rec...Diluted magnetic semiconductors (DMSs) that possess both properties of semiconductors and ferromagnetism, have attracted a lot of attentions due to its potential applications for spin-sensitive electronic devices. Recently, a series of bulk form DMSs isostructural to iron-based superconductors have been reported, which can be readily investigated by microscopic experimental techniques such as nuclear magnetic resonance (NMR) and muon spin rotation (μSR). The measurements have demonstrated that homogeneous ferromagnetism is achieved in these DMSs. In this review article, we summarize experimental evidences from both NMR and μSR measurements. NMR results have shown that carriers facilitate the interactions between distant Mn atoms, while μSR results indicate that these bulk form DMSs and (Ga,Mn)As share a common mechanism for the ferromagnetic exchange interactions.展开更多
Diluted ferromagnetic semiconductors（DMSs） that combine the properties of semiconductors with ferromagnetism have potential application in spin-sensitive electronic（spintronic） devices. The search for DMS material...Diluted ferromagnetic semiconductors（DMSs） that combine the properties of semiconductors with ferromagnetism have potential application in spin-sensitive electronic（spintronic） devices. The search for DMS materials exploded after the observation of ferromagnetic ordering in Ⅲ-Ⅴ（Ga,Mn）As films. Recently, a series of DMS compounds isostructural to iron-based superconductors have been reported. Among them, the highest Curie temperature TCo f 230 K has been achieved in（Ba,K）（Zn,Mn）2As2. However, most DMSs, including（Ga,Mn）As, are p-type, i.e., the carriers that mediate the ferromagnetism are holes. For practical applications, DMSs with n-type carriers are also advantageous. Very recently,a new DMS Ba（Zn,Co）2As2 with n-type carriers has been synthesized. Here we summarize the recent progress on this research stream. We will show that the homogeneous ferromagnetism in these bulk form DMSs has been confirmed by microscopic techniques, i.e., nuclear magnetic resonance（NMR） and muon spin rotation（μSR）.展开更多
The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin fi...The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies(0.5–30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.展开更多
A novel surface muon capture system with a large acceptance was proposed based on the China spallation neutron source(CSNS).This system was designed using a superconducting solenoid where a long graphite target was pu...A novel surface muon capture system with a large acceptance was proposed based on the China spallation neutron source(CSNS).This system was designed using a superconducting solenoid where a long graphite target was put inside it.Firstly,the spin polarization evolution was studied in a constant uniform magnetic field.As the magnetic field can interact with the spin of the surface muon,both the spin polarization and production rate of the surface muons collected by the new capture system were calculated by the G4beamline.Simulation results showed that the surface muons could still keep a high spin polarization([90%)with different magnetic fields(0–10 T),and the larger magnetic field is,the more surface muons can be captured.Finally,the proton phase space,Courant–Snyder parameters,and intensities of surface muons of different beam fractions were given with magnetic fields of 0 and 5T.The solenoid capture system can focus proton and surface muon beams and collect p?and l?particles.It can also provide an intense energetic positron source.展开更多
Non-centrosymmetric superconducting materials represent an exciting class of novel superconductors featuring a variety of unconventional properties,including mixed-parity pairing and very high upper critical fields.He...Non-centrosymmetric superconducting materials represent an exciting class of novel superconductors featuring a variety of unconventional properties,including mixed-parity pairing and very high upper critical fields.Here,we present a comprehensive study of TaIr_(2)B_(2)(with T_(c)=5.1 K),using a set of complementary experimental methods,including bulk-and surface-sensitive techniques.We provide evidence that this system is a two-band,yet it behaves as a single-gap superconductor with a strong coupling.The upper critical field of TaIr_(2)B_(2)significantly exceeds the Pauli limit and exhibits a nearly linear temperature dependence down to the lowest temperatures.This behavior,rarely seen in superconductors,is discussed in terms of anti-symmetric spin-orbit interaction,two-band-,and strong-coupling effects,as well as disorder.展开更多
Muon spin relaxation/rotation(μSR) is a vital technique for probing the superconducting gap structure, pairing symmetry and time reversal symmetry breaking, enabling an understanding of the mechanisms behind the unco...Muon spin relaxation/rotation(μSR) is a vital technique for probing the superconducting gap structure, pairing symmetry and time reversal symmetry breaking, enabling an understanding of the mechanisms behind the unconventional superconductivity of cuprates and Fe-based high-temperature superconductors, which remain a puzzle. Very recently double layered Fe-based superconductors having quasi-2 D crystal structures and Cr-based superconductors with a quasi-1D structure have drawn considerable attention. Here we present a brief review of the characteristics of a few selected Fe-and Cr-based superconducting materials and highlight some of the major outstanding problems, with an emphasis on the superconducting pairing symmetries of these materials. We focus on μSR studies of the newly discovered superconductors ACa_2Fe_4As_4F_2(A = K, Rb, and Cs), ThFeAsN, and A_2Cr_3As_3(A = K, Cs), which were used to determine the superconducting gap structures, the presence of spin fluctuations, and to search for time reversal symmetry breaking in the superconducting states. We also briefly discuss the results of μSR investigations of the superconductivity in hole and electron doped BaFe_2As_2.展开更多
基金supported by MOST (No. 2016YFA0300402)NSF of China (No. 11574265)the Fundamental Research Funds for the Central Universities
文摘Diluted magnetic semiconductors (DMSs) that possess both properties of semiconductors and ferromagnetism, have attracted a lot of attentions due to its potential applications for spin-sensitive electronic devices. Recently, a series of bulk form DMSs isostructural to iron-based superconductors have been reported, which can be readily investigated by microscopic experimental techniques such as nuclear magnetic resonance (NMR) and muon spin rotation (μSR). The measurements have demonstrated that homogeneous ferromagnetism is achieved in these DMSs. In this review article, we summarize experimental evidences from both NMR and μSR measurements. NMR results have shown that carriers facilitate the interactions between distant Mn atoms, while μSR results indicate that these bulk form DMSs and (Ga,Mn)As share a common mechanism for the ferromagnetic exchange interactions.
基金Project supported by the Chinese Ministry of Science and Technology(Grant No.2016YFA0300402)the National Natural Science Foundation of China(Grant No.11574265)+1 种基金the Natural Science Foundation of Zhejiang Province,China(Grant Nos.LR15A040001 and LY14A040007)the Fundamental Research Funds for the Central Universities,China
文摘Diluted ferromagnetic semiconductors（DMSs） that combine the properties of semiconductors with ferromagnetism have potential application in spin-sensitive electronic（spintronic） devices. The search for DMS materials exploded after the observation of ferromagnetic ordering in Ⅲ-Ⅴ（Ga,Mn）As films. Recently, a series of DMS compounds isostructural to iron-based superconductors have been reported. Among them, the highest Curie temperature TCo f 230 K has been achieved in（Ba,K）（Zn,Mn）2As2. However, most DMSs, including（Ga,Mn）As, are p-type, i.e., the carriers that mediate the ferromagnetism are holes. For practical applications, DMSs with n-type carriers are also advantageous. Very recently,a new DMS Ba（Zn,Co）2As2 with n-type carriers has been synthesized. Here we summarize the recent progress on this research stream. We will show that the homogeneous ferromagnetism in these bulk form DMSs has been confirmed by microscopic techniques, i.e., nuclear magnetic resonance（NMR） and muon spin rotation（μSR）.
基金a scholarship from the China Scholarship Council (CSC)financial support from PSI for her stay at PSI
文摘The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies(0.5–30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.
基金supported by the National Natural Science Foundation of China(No.11527811)
文摘A novel surface muon capture system with a large acceptance was proposed based on the China spallation neutron source(CSNS).This system was designed using a superconducting solenoid where a long graphite target was put inside it.Firstly,the spin polarization evolution was studied in a constant uniform magnetic field.As the magnetic field can interact with the spin of the surface muon,both the spin polarization and production rate of the surface muons collected by the new capture system were calculated by the G4beamline.Simulation results showed that the surface muons could still keep a high spin polarization([90%)with different magnetic fields(0–10 T),and the larger magnetic field is,the more surface muons can be captured.Finally,the proton phase space,Courant–Snyder parameters,and intensities of surface muons of different beam fractions were given with magnetic fields of 0 and 5T.The solenoid capture system can focus proton and surface muon beams and collect p?and l?particles.It can also provide an intense energetic positron source.
基金supported by the National Science Center(Poland),Grant No.2022/45/B/ST5/03916The work at Slovak Academy of Sciences was supported by Projects APVV-23-0624,VEGA 2/0073/24,COST Action No.CA21144(SUPERQUMAP),Slovak Academy of Sciences Project IMPULZ IM-2021-42.
文摘Non-centrosymmetric superconducting materials represent an exciting class of novel superconductors featuring a variety of unconventional properties,including mixed-parity pairing and very high upper critical fields.Here,we present a comprehensive study of TaIr_(2)B_(2)(with T_(c)=5.1 K),using a set of complementary experimental methods,including bulk-and surface-sensitive techniques.We provide evidence that this system is a two-band,yet it behaves as a single-gap superconductor with a strong coupling.The upper critical field of TaIr_(2)B_(2)significantly exceeds the Pauli limit and exhibits a nearly linear temperature dependence down to the lowest temperatures.This behavior,rarely seen in superconductors,is discussed in terms of anti-symmetric spin-orbit interaction,two-band-,and strong-coupling effects,as well as disorder.
基金supported by the National Natural Science Foundation of China(Grant No.11874320)the National Key Research and Development Program of China(Grant No.2017YFA0303100)+2 种基金the Royal Society of London for the UK-China Newton funding and CMPC-STFC(Grant No.CMPC-09108)the DST India,for Inspire Faculty Research(Grant No.DST/INSPIRE/04/2015/000169)and UK-India Newton funding
文摘Muon spin relaxation/rotation(μSR) is a vital technique for probing the superconducting gap structure, pairing symmetry and time reversal symmetry breaking, enabling an understanding of the mechanisms behind the unconventional superconductivity of cuprates and Fe-based high-temperature superconductors, which remain a puzzle. Very recently double layered Fe-based superconductors having quasi-2 D crystal structures and Cr-based superconductors with a quasi-1D structure have drawn considerable attention. Here we present a brief review of the characteristics of a few selected Fe-and Cr-based superconducting materials and highlight some of the major outstanding problems, with an emphasis on the superconducting pairing symmetries of these materials. We focus on μSR studies of the newly discovered superconductors ACa_2Fe_4As_4F_2(A = K, Rb, and Cs), ThFeAsN, and A_2Cr_3As_3(A = K, Cs), which were used to determine the superconducting gap structures, the presence of spin fluctuations, and to search for time reversal symmetry breaking in the superconducting states. We also briefly discuss the results of μSR investigations of the superconductivity in hole and electron doped BaFe_2As_2.
