Stephen W. Lovesey

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Orbital currents are proposed to be the order parameter of the pseudo-gap phase of cuprate high-temperature superconductors. We used resonant x-ray diffraction to observe orbital currents in a copper-oxygen plaquette, the basic building block of cuprate superconductors. The confirmation of the existence of orbital currents is an important step toward the(More)
Subtleties in the electronic structure of complex materials can be directly observed, in great detail, by means of the Bragg diffraction of x-rays whose energy matches an atomic resonance. Strange atomic multipoles can be encountered in the interpretation of measured Bragg intensities, e.g., chirality and magnetic charge. Additionally, the x-ray technique(More)
There is general agreement within the community of researchers that investigate high-Tc materials that it is most important to understand the pseudo-gap phase. To this end, many experiments on various cuprates have been reported. Two prominent investigations-Kerr effect and neutron Bragg diffraction-imply that underdoped YBCO samples possess long-range(More)
In the past decade, synchrotron radiation has triggered a surge in studies of the polarization dependence of X-ray beams passing through non-isotropic materials. A vast range of experimental results concerning polarization-dependent absorption (dichroism) and dispersion (birefringence, for example) are available from materials which are either magnetic or(More)
Analysis of published data gathered on a sample of Na(2)IrO(3), held deep inside the antiferromagnetic phase at 1.58 K, shows that iridium magnetic dipole moments, measured in resonant x-ray Bragg diffraction, lie in the a-c plane of the monoclinic crystal and enclose an angle ≈118° with the c-axis. These findings, together with bulk measurements, are(More)
We investigate how the order parameter of a continuous phase transition can be protected from view by symmetry in a magnetic crystal. The symmetry in question forbids atomic displacements and formation of magnetic dipoles, rendering the order parameter invisible in standard x-ray and magnetic neutron Bragg diffraction. Analysis of the allowed magnetic(More)
We succeed in deriving an exact expression for the magnetic interaction of neutrons and electrons including magneto-electric operators, allowed in the absence of a centre of inversion symmetry. Central characters are a spin anapole and an orbital (toroidal) analogue, in addition to familiar parity-even operators like the magnetic moment. A simulation of(More)
From the dawn of modern electromagnetism it has been known that a magnetic field is not handed (chiral). Arima and Saito (2009 J. Phys.: Condens. Matter 21 498001) persist with unwisdom in their repeated claim to have observed control of chirality using a magnetic field by and in itself. In our reply to their claim, we demonstrate damning errors in all(More)
Electronic and magnetic properties of ferric ions (3d 5) in multiferroic ScFeO3 are puzzling, in part because they are different from the only other multiferroic known to possess the same polar chemical structure, BiFeO3. Open questions about ScFeO3 can be addressed by confronting observations with results for G-type antiferromagnetism allowed by the(More)
A systematic analysis of resonant x-ray Bragg diffraction data for UPd(3), with signal enhancement at the U M(IV) edge, including possible structural phase transitions leads to a new determination of the space groups of the material in the phases between T(0)=7.8 K and T(+1)=6.9 K, as P 222(1), and between T(-1)=6.7 K and T(2)=4.4 K, as P2(1). In addition,(More)