| 1. |
- Campillo, E., et al.
(författare)
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Deviations from the extended London model at high magnetic fields in YBa2Cu3 O7
- 2022
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Ingår i: Physical Review B. - 2469-9950. ; 105:18
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Tidskriftsartikel (refereegranskat)abstract
- We report on the evolution with the magnetic field and the temperature of the vortex lattice (VL) in fully oxygenated YBa2Cu3O7 as studied by time-of-flight small-angle neutron scattering. Using the High Field Magnet/Extreme Environment Diractometer beamline at Helmholtz-Zentrum Berlin, we have obtained data up to 25.9 T - much higher than data available previously. Our VL structure results are consistent with the progressive suppression by the field of the superconductivity along the crystallographic b (CuO chain) direction and an accompanying shift of the nodal directions as the field is increased. The intensity of the diffracted signal reveals the spatial variation of magnetization caused by the VL (the "form factor"). Instead of a rapid falloff with the field, as seen in superconductors with smaller upper critical fields, we find that the form factor is almost constant with the field above ∼12 T. We speculate that this is due to Pauli paramagnetic effects.
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| 2. |
- Jellyman, E., et al.
(författare)
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Unconventional superconductivity in the nickel chalcogenide superconductor TlNi2Se2
- 2020
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Ingår i: Physical Review B. - 2469-9950. ; 101:13
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a study of the vortex lattice (VL) of the nickel chalcogenide superconductor TlNi2Se2, using small angle neutron scattering. This superconductor has the same crystal symmetry as the iron arsenide materials. Previous work points to it being a two-gap superconductor, with an unknown pairing mechanism. No structural transitions in the vortex lattice are seen in the phase diagram, arguing against d-wave gap symmetry. Empirical fits of the temperature dependence of the form factor and penetration depth rule out a simple s-wave model, supporting the presence of nodes in the gap function. The variation of the VL opening angle with field is consistent with earlier reports of multiple gaps
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| 3. |
- Shen, L., et al.
(författare)
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Magnetic phase diagram of the quantum spin chain compound SrCo2V2O8 : A single-crystal neutron diffraction study
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:7
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Tidskriftsartikel (refereegranskat)abstract
- We explore magnetic order in the quantum spin chain compound SrCo2V2O8 up to 14.9 T and down to 50 mK, using single-crystal neutron diffraction. Upon cooling in zero-field, commensurate antiferromagnetic (C-AFM) order with modulation vector=(0, 0, 1) develops below T N≃5.0K. Applying an external magnetic field (H∥c axis) destabilizes this C-AFM order, leading to an order-disorder transition between T N and ∼1.5 K. Below 1.5 K, a commensurate to incommensurate (IC-AFM) transition occurs at 3.9 T, above which the magnetic reflections can be indexed by=(0, 0, 1 ±δl). The incommensurability δl scales monotonically with H until the IC-AFM order disappears around 7.0 T. Magnetic reflections modulated by emerge again at higher fields. While the characters of the C-AFM, IC-AFM and the emergent AFM order in SrCo2V2O8 appear to fit the descriptions of the Néel, longitudinal spin density wave and transverse AFM order observed in the related compound BaCo2V2O8, our results also reveal several unique signatures that are not present in the latter, highlighting the inadequacy of mean-field theory in addressing the complex magnetic order in systems of this class.
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