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Orbital-driven nematicity in FeSe
Baek, S-H.,Efremov, D. V.,Ok, J. M.,Kim, J. S.,van den Brink, Jeroen,Bü,chner, B. Nature Publishing Group, a division of Macmillan P 2015 NATURE MATERIALS Vol.14 No.2
A fundamental and unconventional characteristic of superconductivity in iron-based materials is that it occurs in the vicinity of two other instabilities. In addition to a tendency towards magnetic order, these Fe-based systems have a propensity for nematic ordering: a lowering of the rotational symmetry while time-reversal invariance is preserved. Setting the stage for superconductivity, it is heavily debated whether the nematic symmetry breaking is driven by lattice, orbital or spin degrees of freedom. Here, we report a very clear splitting of NMR resonance lines in FeSe at T<SUB>nem</SUB> = 91 K, far above the superconducting T<SUB>c</SUB> of 9.3 K. The splitting occurs for magnetic fields perpendicular to the Fe planes and has the temperature dependence of a Landau-type order parameter. Spin–lattice relaxation rates are not affected at T<SUB>nem</SUB>, which unequivocally establishes orbital degrees of freedom as driving the nematic order. We demonstrate that superconductivity competes with the emerging nematicity.
Reinier W. A. Spek,Lotje A. Hoogervorst,Rob C. Brink,Jan W. Schoones,Derek F.P. van Deurzen,Michel P.J. van den Bekerom 대한견주관절학회 2024 대한견주관절의학회지 Vol.27 No.1
The aim of this systematic review was to collect evidence on the following 10 technical aspects of glenoid baseplate fixation in reverse total shoulder arthroplasty (rTSA): screw insertion angles; screw orientation; screw quantity; screw length; screw type; baseplate tilt; baseplate position; baseplate version and rotation; baseplate design; and anatomical safe zones. Five literature libraries were searched for eligible clinical, cadaver, biomechanical, virtual planning, and finite element analysis studies. Studies including patients >16 years old in which at least one of the ten abovementioned technical aspects was assessed were suitable for analysis. We excluded studies of patients with: glenoid bone loss; bony increased offset-reversed shoulder arthroplasty; rTSA with bone grafts; and augmented baseplates. Quality assessment was performed for each included study. Sixty-two studies were included, of which 41 were experimental studies (13 cadaver, 10 virtual planning, 11 biomechanical, and 7 finite element studies) and 21 were clinical studies (12 retrospective cohorts and 9 case-control studies). Overall, the quality of included studies was moderate or high. The majority of studies agreed upon the use of a divergent screw fixation pattern, fixation with four screws (to reduce micromotions), and inferior positioning in neutral or anteversion. A general consensus was not reached on the other technical aspects. Most surgical aspects of baseplate fixation can be decided without affecting fixation strength. There is not a single strategy that provides the best outcome. Therefore, guidelines should cover multiple surgical options that can achieve adequate baseplate fixation.
Nematicity and magnetism in LaFeAsO single crystals probed by As75 nuclear magnetic resonance
Ok, J. M.,Baek, S.-H.,Efremov, D. V.,Kappenberger, R.,Aswartham, S.,Kim, J. S.,van den Brink, Jeroen,Bü,chner, B. American Physical Society 2018 Physical review. B Vol.97 No.18
<P>We report a As-75 nuclear magnetic resonance study in LaFeAsO single crystals, which undergoes nematic and antiferromagnetic transitions at T-nem similar to 156 K and T-N similar to 138 K, respectively. Below T-nem, the As-75 spectrum splits sharply into two for an external magnetic field parallel to the orthorhombic a or b axis in the FeAs planes. Our analysis of the data demonstrates that the NMR line splitting arises from an electronically driven rotational symmetry breaking. The As-75 spin-lattice relaxation rate as a function of temperature shows that spin fluctuations are strongly enhanced just below T-nem. These NMR findings indicate that nematic order promotes spin fluctuations in magnetically ordered LaFeAsO, as observed in nonmagnetic and superconducting FeSe. We conclude that the origin of nematicity is identical in both FeSe and LaFeAsO regardless of whether or not a long-range magnetic order develops in the nematic state.</P>
Evidence for a Field-Induced Quantum Spin Liquid in α - RuCl3
Baek, S.-H.,Do, S.-H.,Choi, K.-Y.,Kwon, Y. S.,Wolter, A. U. B.,Nishimoto, S.,van den Brink, Jeroen,Bü,chner, B. American Physical Society 2017 Physical Review Letters Vol.119 No.3
<P>We report a Cl-35 nuclear magnetic resonance study in the honeycomb lattice alpha-RuCl3, a material that has been suggested to potentially realize a Kitaev quantum spin liquid (QSL) ground state. Our results provide direct evidence that alpha-RuCl3 exhibits a magnetic-field-induced QSL. For fields larger than similar to 10 T, a spin gap opens up while resonance lines remain sharp, evidencing that spins are quantum disordered and locally fluctuating. The spin gap increases linearly with an increasing magnetic field, reaching similar to 50 K at 15 T, and is nearly isotropic with respect to the field direction. The unusual rapid increase of the spin gap with increasing field and its isotropic nature are incompatible with conventional magnetic ordering and, in particular, exclude that the ground state is a fully polarized ferromagnet. The presence of such a field-induced gapped QSL phase has indeed been predicted in the Kitaev model.</P>
Hozoi, L.,Gretarsson, H.,Clancy, J. P.,Jeon, B.-G.,Lee, B.,Kim, K. H.,Yushankhai, V.,Fulde, Peter,Casa, D.,Gog, T.,Kim, Jungho,Said, A. H.,Upton, M. H.,Kim, Young-June,van den Brink, Jeroen American Physical Society 2014 Physical review. B, Condensed matter and materials Vol.89 No.11
In the search for topological phases in correlated electron systems, materials with 5d transition-metal ions, in particular the iridium-based pyrochlores A2Ir2O7, provide fertile grounds. Several topological states have been predicted but the actual realization of such states is believed to critically depend on the strength of local potentials arising from distortions of the IrO6 cages. We test this hypothesis by measuring with resonant inelastic x-ray scattering the electronic level splittings in the A = Y, Eu systems, which we show to agree very well with ab initio quantum chemistry electronic-structure calculations for the series of materials with A = Sm, Eu, Lu, and Y. We find, however, that the primary source for quenching the spin-orbit interaction is not a distortion of the IrO6 octahedra but longer-range lattice anisotropies which inevitably break the local cubic symmetry.