12 research outputs found
Impact of disorder on dynamics and ordering in the honeycomb-lattice iridate Na2IrO3
Kitaev's honeycomb spin-liquid model and its proposed realization in materials such as α-RuCl3, Li2IrO3, and Na2IrO3 continue to present open questions about how the dynamics of a spin liquid are modified in the presence of non-Kitaev interactions as well as the presence of inhomogeneities. Here we use Na23 nuclear magnetic resonance to probe both static and dynamical magnetic properties in single-crystal Na2IrO3. We find that the NMR shift follows the bulk susceptibility above 30 K but deviates from it below; moreover below TN the spectra show a broad distribution of internal magnetic fields. Both of these results provide evidence for inequivalent magnetic sites at low temperature, suggesting inhomogeneities are important for the magnetism. The spin-lattice relaxation rate is isotropic and diverges at TN, suggesting that the Kitaev cubic axes may control the critical quantum spin fluctuations. In the ordered state, we observe gapless excitations, which may arise from site substitution, emergent defects from milder disorder, or possibly be associated with nearby quantum paramagnetic states distinct from the Kitaev spin liquid
Fermi-surface reconstruction by stripe order in cuprate superconductors
Quantum oscillations have revealed the presence of a small pocket in the
Fermi surface of the cuprate superconductor YBCO, whose nature and origin are
the subject of much debate. Interpretations include electron and hole pockets;
scenarios include Fermi-surface reconstruction by antiferromagnetism,
d-density-wave order, and stripe order. Here we report quantum oscillations in
the Seebeck and Nernst coefficients of YBCO and show, from the magnitude and
sign of the Seebeck coefficient, that they come from an electron pocket. Using
measurements of the Seebeck coefficient as a function of hole doping p, we show
that the evolution of the Fermi surface in YBCO is the same as in Eu-LSCO, a
cuprate where stripe order (a modulation of spin and charge densities) is well
established. The electron pocket is most prominent where stripe order is
strongest, at p = 1/8. This shows that Fermi-surface reconstruction is a
generic mechanism of underdoped cuprates, intimately related to stripe order.Comment: 15 pages, 5 figures, Supplementary information now integrated into
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Impact of disorder on dynamics and ordering in the honeycomb-lattice iridate Na2IrO3
Kitaev's honeycomb spin-liquid model and its proposed realization in materials such as α-RuCl3, Li2IrO3, and Na2IrO3 continue to present open questions about how the dynamics of a spin liquid are modified in the presence of non-Kitaev interactions as well as the presence of inhomogeneities. Here we use Na23 nuclear magnetic resonance to probe both static and dynamical magnetic properties in single-crystal Na2IrO3. We find that the NMR shift follows the bulk susceptibility above 30 K but deviates from it below; moreover below TN the spectra show a broad distribution of internal magnetic fields. Both of these results provide evidence for inequivalent magnetic sites at low temperature, suggesting inhomogeneities are important for the magnetism. The spin-lattice relaxation rate is isotropic and diverges at TN, suggesting that the Kitaev cubic axes may control the critical quantum spin fluctuations. In the ordered state, we observe gapless excitations, which may arise from site substitution, emergent defects from milder disorder, or possibly be associated with nearby quantum paramagnetic states distinct from the Kitaev spin liquid
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Magnetism and superconductivity in heavy fermion superconductor CeCo (In0.97 Cd0.03)5
Zero field (ZF) and transverse field (TF) muon spin relaxation and rotation (μ SR) experiments have been carried out in the Cd-doped heavy fermion superconductor CeCoIn5 to investigate its superconducting state. The ZF-μ SR results in CeCo (In0.97 Cd0.03)5 revealed that no spontaneous magnetic field was induced below its superconducting transition temperature (Tc), indicating no evidence for time reversal symmetry breaking. The muon Knight shifts obtained from TF-μ SR measurements decrease significantly below Tc, consistent with a spin-singlet state as in the parent compound CeCoIn5, which is a d-wave superconductor. © 2008 Elsevier B.V