26 research outputs found
Direct Observation of an Incommensurate Charge Density Wave in the BiS2-based Superconductor NdO1-xFxBiS2
The nature of superconductivity in BiS-based superconductors has been
controversial while ab-initio calculations proposed this system in close
proximity to a charge-density-wave (CDW) phase. Using high-energy high-flux
X-ray diffraction, we reveal an intrinsic and long-range CDW phase coexisting
with superconductivity in NdOFBiS superconductor ( = 0.37
and 0.3). The CDW wavevector in NdOFBiS correspond
Q = (0.17, 0.17, 0.5) and is associated with transverse atomic
displacements. Interestingly, this wavevector does not match theoretical
expectations based on either phonon softening or Fermi surface nesting. In
NdOFBiS, where the superconducting transition temperature
is highest, the CDW satellites are slightly broader and weaker compared to
NdOFBiS, possibly suggesting the competition with the
superconductivity. Lastly, we measure a thermal diffuse scattering across the
superconducting transition temperature and find no meaningful changes in favor
of the unconventional pairing mechanism. Our result suggests the importance of
understanding CDW which might hold a key to the superconductivity in the
BiS-based superconductor.Comment: 7 pages, 3 figures, Supplementary to be uploade
The dual nature of magnetism in a uranium heavy fermion system
The duality between localized and itinerant nature of magnetism in
electron systems has been a longstanding puzzle. Here, we report
inelastic neutron scattering measurements, which reveal both local and
itinerant aspects of magnetism in a single crystalline system of
UPtSi. In the antiferromagnetic state, we observe broad continuum
of diffuse magnetic scattering with a resonance-like gap of 7 meV,
and surprising absence of coherent spin-waves, suggestive of itinerant
magnetism. While the gap closes above the Neel temperature, strong dynamic spin
correlations persist to high temperature. Nevertheless, the size and
temperature dependence of the total magnetic spectral weight can be well
described by local moment with . Furthermore, polarized neutron
measurements reveal that the magnetic fluctuations are mostly transverse, with
little or none of the longitudinal component expected for itinerant moments.
These results suggest that a dual description of local and itinerant magnetism
is required to understand UPtSi, and by extension, other 5
systems in general.Comment: see supplementary material for more detail
Event-based processing of neutron scattering data at the Spallation Neutron Source
The Spallation Neutron Source at Oak Ridge National Laboratory, USA, ushered in a new era of neutron scattering experiments through the use of event-based data. Tagging each neutron event allows pump–probe experiments, measurements with a parameter asynchronous to the source, measurements with continuously varying parameters and novel ways of testing instrument components. This contribution will focus on a few examples. A pulsed magnet has been used to study diffraction under extreme fields. Continuous ramping of temperature is becoming standard on the POWGEN diffractometer. Battery degradation and phase transformations under heat and stress are often studied on the VULCAN diffractometer. Supercooled Al2O3 was studied on NOMAD. A study of a metallic glass through its glass transition was performed on the ARCS spectrometer, and the effect of source variation on chopper stability was studied for the SEQUOIA spectrometer. Besides a summary of these examples, an overview is provided of the hardware and software advances to enable these and many other event-based measurements
Event-based processing of neutron scattering data at the Spallation Neutron Source
The Spallation Neutron Source at Oak Ridge National Laboratory, USA, ushered in a new era of neutron scattering experiments through the use of event-based data. Tagging each neutron event allows pump–probe experiments, measurements with a parameter asynchronous to the source, measurements with continuously varying parameters and novel ways of testing instrument components. This contribution will focus on a few examples. A pulsed magnet has been used to study diffraction under extreme fields. Continuous ramping of temperature is becoming standard on the POWGEN diffractometer. Battery degradation and phase transformations under heat and stress are often studied on the VULCAN diffractometer. Supercooled Al2O3 was studied on NOMAD. A study of a metallic glass through its glass transition was performed on the ARCS spectrometer, and the effect of source variation on chopper stability was studied for the SEQUOIA spectrometer. Besides a summary of these examples, an overview is provided of the hardware and software advances to enable these and many other event-based measurements
Direct observation of an incommensurate charge density wave in the BiS2 -based superconductor NdO1-x FxBiS2
© 2021 American Physical Society.The nature of superconductivity in BiS2-based superconductors has been controversial while ab initio calculations proposed this system in close proximity to a charge-density-wave (CDW) phase. Using high-energy high-flux x-ray diffraction, we reveal an intrinsic and long-range CDW phase coexisting with superconductivity in NdO1-xFxBiS2 superconductor (x=0.37 and 0.3). The CDW wave vector in NdO0.63F0.37BiS2 correspond QCDW=(0.17, 0.17, 0.5) and is associated with transverse atomic displacements. Interestingly, this wave vector does not match theoretical expectations based on either phonon softening or Fermi surface nesting. In NdO0.7F0.3BiS2, where the superconducting transition temperature is highest, the CDW satellites are slightly broader and weaker compared to NdO0.63F0.37BiS2, possibly suggesting the competition with the superconductivity. Last, we measure a thermal diffuse scattering across the superconducting transition temperature and find no meaningful changes. Our result suggests the importance of understanding CDW which might hold a key to the superconductivity in the BiS2-based superconductor.11Nsciescopu
High temperature tetragonal crystal structure of UPt2Si2
â“’ Walter de Gruyter GmbH High temperature crystal structure of UPt2Si2 determined using single-crystal neutron diffraction at 400 K is reported. It is found that the crystal structure remains of the primitive tetragonal CaBe2Ge2 type with the space group P4/nmm. Anisotropic displacement factors of the Pt atoms at the 2a (3/4 1/4 0) and Si atoms at the 2c (1/4 1/4 z) Wyckoff sites are found to be anomalously large11sci
Dual Nature of Magnetism in a Uranium Heavy-Fermion System
The duality between the localized and itinerant nature of magnetism in 5f-electron systems has been a long-standing puzzle. Here, we report inelastic neutron scattering measurements, which reveal both local and itinerant aspects of magnetism in a single-crystalline system of UPt2Si2. In the antiferromagnetic state, we observe a broad continuum of diffuse magnetic scattering with a resonancelike gap of ≈7 meV and the surprising absence of coherent spin waves, suggestive of itinerant magnetism. While the gap closes above the N´eel temperature, strong dynamic spin correlations persist to a high temperature. Nevertheless, the size and temperature dependence of the total magnetic spectral weight can be well described by a local moment with J ¼ 4. Furthermore, polarized neutron measurements reveal that the magnetic fluctuations are mostly transverse, with little or none of the longitudinal component expected for itinerant moments. These results suggest that a dual description of local and itinerant magnetism is required to understand UPt2Si2 and, by extension, other 5f systems, in general. © 2018 American Physical Societ