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Effects of hole doping on magnetic and lattice excitations inSr2Ir1−xRuxO4(x=0-0.2)
Glamazda, A.,Lee, W.-J.,Choi, K.-Y.,Lemmens, P.,Choi, H. Y.,Lee, N.,Choi, Y. J. American Physical Society 2014 Physical review. B, Condensed matter and materials Vol.89 No.10
Raman scattering is employed to explore the effects of hole doping in single crystals of Sr2Ir1-xRuxO4 (x = 0, 0.01, 0.03, 0.05, 0.1, and 0.2). Introducing a few percentages of holes has a strong impact on magnetic excitations and lattice dynamics. With increasing x the well structured two-magnon continuum turns into diffusive magnetic scattering. Furthermore one-and two-phonon scatterings are rapidly suppressed. Remarkably, the two Ir(Ru)-O-Ir(Ru) bond angle modes with different Ir(Ru)O-6 octahedral rotations coexist and compete upon hole doping. This is ascribed to the difference of electronic properties between Ir4+ and Ru4+ ions. The doping and temperature dependence of the bond angle modes suggests that an electronically phase separated state develops upon Ru doping.
Relation between Kitaev magnetism and structure in α−RuCl3
Glamazda, A.,Lemmens, P.,Do, S.-H.,Kwon, Y. S.,Choi, K.-Y. American Physical Society 2017 Physical review. B Vol.95 No.17
<P>Raman scattering has been employed to investigate lattice and magnetic excitations of the honeycomb Kitaev material alpha-RuCl3 and its Heisenberg counterpart CrCl3. Our phonon Raman spectra give evidence for a first-order structural transition from a monoclinic to a rhombohedral structure for both compounds. Significantly, only alpha-RuCl3 features a large thermal hysteresis, consistent with the formation of a wide phase of coexistence. In the related temperature interval of 70-170 K, we observe a hysteretic behavior of magnetic excitations as well. The stronger magnetic response in the rhombohedral compared to the monoclinic phase evidences a coupling between the crystallographic structure and low-energymagnetic response. Our results demonstrate that the Kitaev magnetism concomitant with fractionalized excitations is susceptible to small variations of bonding geometry.</P>
Quantum criticality in the coupled two-leg spin ladder Ba2CuTeO6
Glamazda, A.,Choi, Y. S.,Do, S.-H.,Lee, S.,Lemmens, P.,Ponomaryov, A. N.,Zvyagin, S. A.,Wosnitza, J.,Sari, Dita Puspita,Watanabe, I.,Choi, K.-Y. American Physical Society 2017 Physical Review B Vol.95 No.18
<P>We report on zero-field muon spin rotation, electron-spin resonance, and polarized Raman scattering measurements of the coupled quantum spin ladder Ba2CuTeO6. Zero-field muon spin rotation and electron-spin resonance probes disclose a successive crossover from a paramagnetic through a spin-liquid-like into a magnetically ordered state with decreasing temperature. More significantly, the two-magnon Raman response obeys a T-linear scaling relation in its peak energy, linewidth, and intensity. This critical scaling behavior presents an experimental signature of proximity to a quantum-critical point from an ordered side in Ba2CuTeO6.</P>
Structural instability of the CoO<sub>4</sub> tetrahedral chain in SrCoO<sub>3−δ</sub> thin films
Glamazda, A.,Choi, K.-Y.,Lemmens, P.,Choi, Woo Seok,Jeen, Hyoungjeen,Meyer, Tricia L.,Lee, Ho Nyung American Institute of Physics 2015 Journal of Applied Physics Vol.118 No.8
<P>Raman scattering experiments together with detailed lattice dynamic calculations are performed to elucidate crystallographic and electronic peculiarities of SrCoO3-delta films. We observe that the 85 cm(-1) phonon mode involving the rotation of a CoO4 tetrahedron undergoes a huge hardening by 21 cm(-1) with decreasing temperature. In addition, new phonon modes appear at 651.5 and 697.6 cm(-1). The latter modes are attributed to the Jahn-Teller activated modes. Upon cooling from room temperature, all phonons exhibit an exponential-like increase of intensity with a characteristic energy of about 103-107 K. We attribute this phenomenon to an instability of the CoO4 tetrahedral chain structure, which constitutes a key ingredient to understand the electronic and structural properties of the brownmillerite SrCoO2.5. (C) 2015 AIP Publishing LLC.</P>