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- ItemQuantum fluctuations of charge order induce phonon softening in a superconducting cuprate(College Park, Md. : APS, 2021) Huang, H.Y.; Singh, A.; Mou, C.Y.; Johnston, S.; Kemper, A.F.; van den Brink, J.; Chen, P.J.; Lee, T.K.; Okamoto, J.; Chu, Y.Y.; Li, J.H.; Komiya, S.; Komarek, A.C.; Fujimori, A.; Chen, C.T.; Huang, D.J.Quantum phase transitions play an important role in shaping the phase diagram of high-temperature cuprate superconductors. These cuprates possess intertwined orders which interact strongly with superconductivity. However, the evidence for the quantum critical point associated with the charge order in the superconducting phase remains elusive. Here we show the short-range charge orders and the spectral signature of the quantum fluctuations in La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) near the optimal doping using high-resolution resonant inelastic X-ray scattering. On performing calculations through a diagrammatic framework, we discovered that the charge correlations significantly soften several branches of phonons. These results elucidate the role of charge order in the LSCO compound, providing evidence for quantum critical scaling and discommensurations associated with charge order.
- ItemCharge-transfer energy in iridates: A hard x-ray photoelectron spectroscopy study(College Park, ML : American Physical Society, 2020) Takegami, D.; Kasinathan, D.; Wolff, K.K.; Altendorf, S.G.; Chang, C.F.; Hoefer, K.; Melendez-Sans, A.; Utsumi, Y.; Meneghin, F.; Ha, T.D.; Yen, C.H.; Chen, K.; Kuo, C.Y.; Liao, Y.F.; Tsuei, K.D.; Morrow, R.; Wurmehl, S.; Büchner, B.; Prasad, B.E.; Jansen, M.; Komarek, A.C.; Hansmann, P.; Tjeng, L.H.We have investigated the electronic structure of iridates in the double perovskite crystal structure containing either Ir4+ or Ir5+ using hard x-ray photoelectron spectroscopy. The experimental valence band spectra can be well reproduced using tight-binding calculations including only the Ir 5d, O 2p, and O 2s orbitals with parameters based on the downfolding of the density-functional band structure results. We found that, regardless of the A and B cations, the A2BIrO6 iridates have essentially zero O 2p to Ir 5d charge-transfer energies. Hence double perovskite iridates turn out to be extremely covalent systems with the consequence being that the magnetic exchange interactions become very long ranged, thereby hampering the materialization of the long-sought Kitaev physics. Nevertheless, it still would be possible to realize a spin-liquid system using the iridates with a proper tuning of the various competing exchange interactions.