The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band- like ones, yielding heavy quasiparticles with an effective mass about 100 times （or more） of the ba...The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band- like ones, yielding heavy quasiparticles with an effective mass about 100 times （or more） of the bare electrons, Recently, experimental and theoretical investigations point out a localized and delocalized dual nature in actinide compounds, where itinerant quasiparticles account for the unconventional superconductivity in the vicinity of a magnetic instability. Here we report the strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2. The coupling is nearly antiferromagnetic. As embedded in the ferromagnetic matrix of localized 5f moments below Tc ~ 52 K, this coupling leads to short-range dynamic correlations of heavy quasiparticles, characterized by fluctuations of magnetic clusters. Those cluster-like spins of itinerant quasiparticles show a broad hump of magnetization at Tx≈28 K, which is typical for the spin-glass freezing. Thus, our results present the direct observation of itinerant quasiparticles coexisting with localized 5f moments by conventional magnetic measurements, providing a new route into the coexistence between ferromagnetism and superconductivity in heavy fermion systems.展开更多
It is of great importance to understand the origin of UG2 chromitite reefs and reasons why some chromitite reefs contain relatively high contents of platinum group elements（PGEs： Os, Ir, Ru, Rh,Pt, Pd） or highly si...It is of great importance to understand the origin of UG2 chromitite reefs and reasons why some chromitite reefs contain relatively high contents of platinum group elements（PGEs： Os, Ir, Ru, Rh,Pt, Pd） or highly siderophile elements（HSEs： Au, Re, PGE）. This paper documents sulphide-silicate assemblages enclosed in chromite grains from the UG2 chromitite. These are formed as a result of crystallisation of sulphide and silicate melts that are trapped during chromite crystallisation. The inclusions display negative crystal shapes ranging from several micrometres to 100 μm in size.Interstitial sulphide assemblages lack pyrrhotite and consist of chalcopyrite, pentlandite and some pyrite. The electron microprobe data of these sulphides show that the pentlandite grains present in some of the sulphide inclusions have a significantly higher iron（Fe） and lower nickel（Ni） content than the pentlandite in the rock matrix. Pyrite and chalcopyrite show no difference. The contrast in composition between inter-cumulus plagioclase（An_（68）） and plagioclase enclosed in chromite（An_（13））, as well as the presence of quartz, is consistent with the existence of a felsic melt at the time of chromite saturation.Detailed studies of HSE distribution in the sulphides and chromite were conducted by LA-ICP-MS（laser ablation-inductively coupled plasma-mass spectrometry）, which showed the following.（Ⅰ） Chromite contained no detectable HSE in solid solution.（Ⅱ） HSE distribution in sulphide assemblages interstitial to chromite was variable. In general, Pd, Rh, Ru and Ir occurred dominantly in pentlandite, whereas Os,Pt and Au were detected only in matrix sulphide grains and were clearly associated with Bi and Te.（Ⅲ）In the sulphide inclusions,（a） pyrrhotite did not contain any significant amount of HSE,（b） chalcopyrite contained only some Rh compared to the other sulphides,（c） pentlandite was the main host for Pd,（d）pyrite contained most of the Ru, Os, Ir and Re,（e） Pt and Rh were closely associated with Bi forming a continuous rim between pyrite and pentlandite and（f） no Au was detected. These results show that the use of ArF excimer laser to produce high-resolution trace element maps provides information that cannot be obtained by conventional（spot） LA-ICP-MS analysis or trace element maps that use relatively large beam diameters.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11404297)the Science Challenge Project(Grant No.TZ2016004)the Science and Technology Foundation of China Academy of Engineering Physics(Grant Nos.2013B0301050 and 2014A0301013)
文摘The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band- like ones, yielding heavy quasiparticles with an effective mass about 100 times （or more） of the bare electrons, Recently, experimental and theoretical investigations point out a localized and delocalized dual nature in actinide compounds, where itinerant quasiparticles account for the unconventional superconductivity in the vicinity of a magnetic instability. Here we report the strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2. The coupling is nearly antiferromagnetic. As embedded in the ferromagnetic matrix of localized 5f moments below Tc ~ 52 K, this coupling leads to short-range dynamic correlations of heavy quasiparticles, characterized by fluctuations of magnetic clusters. Those cluster-like spins of itinerant quasiparticles show a broad hump of magnetization at Tx≈28 K, which is typical for the spin-glass freezing. Thus, our results present the direct observation of itinerant quasiparticles coexisting with localized 5f moments by conventional magnetic measurements, providing a new route into the coexistence between ferromagnetism and superconductivity in heavy fermion systems.
基金granted by Laurentian UniversityNational Key R&D Program of China(Grant No.2016YFC0600207)
文摘It is of great importance to understand the origin of UG2 chromitite reefs and reasons why some chromitite reefs contain relatively high contents of platinum group elements（PGEs： Os, Ir, Ru, Rh,Pt, Pd） or highly siderophile elements（HSEs： Au, Re, PGE）. This paper documents sulphide-silicate assemblages enclosed in chromite grains from the UG2 chromitite. These are formed as a result of crystallisation of sulphide and silicate melts that are trapped during chromite crystallisation. The inclusions display negative crystal shapes ranging from several micrometres to 100 μm in size.Interstitial sulphide assemblages lack pyrrhotite and consist of chalcopyrite, pentlandite and some pyrite. The electron microprobe data of these sulphides show that the pentlandite grains present in some of the sulphide inclusions have a significantly higher iron（Fe） and lower nickel（Ni） content than the pentlandite in the rock matrix. Pyrite and chalcopyrite show no difference. The contrast in composition between inter-cumulus plagioclase（An_（68）） and plagioclase enclosed in chromite（An_（13））, as well as the presence of quartz, is consistent with the existence of a felsic melt at the time of chromite saturation.Detailed studies of HSE distribution in the sulphides and chromite were conducted by LA-ICP-MS（laser ablation-inductively coupled plasma-mass spectrometry）, which showed the following.（Ⅰ） Chromite contained no detectable HSE in solid solution.（Ⅱ） HSE distribution in sulphide assemblages interstitial to chromite was variable. In general, Pd, Rh, Ru and Ir occurred dominantly in pentlandite, whereas Os,Pt and Au were detected only in matrix sulphide grains and were clearly associated with Bi and Te.（Ⅲ）In the sulphide inclusions,（a） pyrrhotite did not contain any significant amount of HSE,（b） chalcopyrite contained only some Rh compared to the other sulphides,（c） pentlandite was the main host for Pd,（d）pyrite contained most of the Ru, Os, Ir and Re,（e） Pt and Rh were closely associated with Bi forming a continuous rim between pyrite and pentlandite and（f） no Au was detected. These results show that the use of ArF excimer laser to produce high-resolution trace element maps provides information that cannot be obtained by conventional（spot） LA-ICP-MS analysis or trace element maps that use relatively large beam diameters.
