From Nature
Nikolay Kardjilov1, Ingo Manke1,2, Markus Strobl1,3, André Hilger1, Wolfgang Treimer1,4, Michael Meissner1, Thomas Krist1 & John Banhart1,2
Neutrons are highly sensitive to magnetic fields owing to their magnetic moment, whereas their charge neutrality enables them to penetrate even massive samples. The combination of these properties with radiographic and tomographic imaging1, 2, 3, 4 enables a technique that is unique for investigations of macroscopic magnetic phenomena inside solid materials. Here, we introduce a new experimental method yielding two- and three-dimensional images that represent changes of the quantum-mechanical spin state of neutrons caused by magnetic fields in and around bulk objects. It opens up a way to the detection and imaging of previously inaccessible magnetic field distributions, hence closing the gap between high-resolution two-dimensional techniques for surface magnetism5, 6 and scattering techniques for the investigation of bulk magnetism7, 8, 9. The technique was used to investigate quantum effects inside a massive sample of lead (a type-I superconductor).
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From Nature
Hyungje Woo1,2, Pengcheng Dai1,2, S. M. Hayden3, H. A. Mook2, T. Dahm4, D. J. Scalapino5, T. G. Perring6 and F. Doan7
Understanding the magnetic excitations in high-temperature (high-Tc) copper-oxide superconductors is important because they may mediate the electron pairing for superconductivity1, 2. By determining the wavevector (Q) and energy () dependence of the magnetic excitations, it is possible to calculate the change in the exchange energy available to the superconducting condensation energy3, 4, 5. For the high-Tc superconductor YBa2Cu3O6+x, the most prominent feature in the magnetic excitations is the resonance6, 7, 8, 9, 10, 11, 12. Suggestions that the resonance contributes a major part of the superconducting condensation4, 13 have not gained acceptance because the resonance is only a small portion of the total magnetic scattering12, 13, 14. Here, we report an extensive mapping of magnetic excitations for YBa2Cu3O6.95(Tc93 K). Absolute intensity measurements of the full spectra allow us to estimate the change in the magnetic exchange energy between the normal and superconducting states, which is about 15 times larger than the superconducting condensation energy15, 16—more than enough to provide the driving force for high-Tc superconductivity in YBa2Cu3O6.95.
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We demonstrate that delta doping can be used to create a dimensionally confined region of metallic ferromagnetism in an antiferromagnetic (AFM) manganite host, without introducing any explicit disorder due to dopants or frustration of spins. Theoretical consideration of these additional carriers shows that they cause a local enhancement of ferromagnetic double exchange with respect to AFM superexchange, resulting in local canting of the AFM spins. This leads to a highly modulated magnetization, as measured by polarized neutron reflectometry. The spatial modulation of the canting is related to the spreading of charge from the doped layer and establishes a fundamental length scale for charge transfer, transformation of orbital occupancy, and magnetic order in these manganites. Furthermore, we confirm the existence of the canted, AFM state as was predicted by de Gennes [Phys. Rev. 118, 141 (1960)] but had remained elusive.