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Kazuhiko Ikeuchi

Publications and source records attributed to Kazuhiko Ikeuchi.

23 records · Page 2Linked to original sources
arXiv2016

Spin excitations in optimally P-doped BaFe2(As0.7P0.3)2superconductor

We use inelastic neutron scattering to study temperature and energy dependence of spin excitations in optimally P-doped BaFe2(As0.7P0.3)2 superconductor (Tc = 30 K) throughout the Brillouin zone. In the undoped state, spin waves and paramagnetic spin excitations of BaFe2As2 stem from antiferromagnetic (AF) ordering wave vector QAF= (1/-1,0) and peaks near zone boundary at (1/-1,1/-1) around 180 meV. Replacing 30% As by smaller P to induce superconductivity, low-energy spin excitations of BaFe2(As0.7P0.3)2form a resonance in the superconducting state and high-energy spin excitations now peaks around 220 meV near (1/-1,1/-1). These results are consistent with calculations from a combined density functional theory and dynamical mean field theory, and suggest that the decreased average pnictogen height in BaFe2(As0.7P0.3)2 reduces the strength of electron correlations and increases the effective bandwidth of magnetic excitations.

cond-mat.supr-con↗
arXiv2013

Phonons and Spin Excitations in Fe-Based Superconductor Ca10Pt4As8(Fe1-xPtxAs)10 (x ~ 0.2)

By means of neutron inelastic scattering, magnetic excitations and phonons were measured for a single crystal of slightly overdoped superconductor Ca10Pt4As8(Fe1-xPtxAs)10 (x ~ 0.2) with the transition temperature Tc of ~33 K. Below Tc, magnetic excitation spectra \{chi}"(Q, ω) measured at Q = QM [magnetic Γ points] are gapped, and in the relatively higher ω region, the \{chi}"(QM, ω)-increase was observed with decreasing T, where the maximum of the increase was found at ~18 meV at 3 K (<< Tc). These characteristics are favorable to orbital-fluctuation-mediated superconductivity with the so-called S++symmetry of the order parameter. The energy dependence of δQ-temperature(T) curve of the magnetic excitations seems to have anomalous behavior in rather wide T region above Tc, δQ being the width of the Q scan profile. In the phonon measurements, we observed softening of the in-plane TA mode, which corresponds to the elastic constant C66. This softening seems to start at rather high temperature T, as T is lowered. Additionally, anomalous increase in spectral weights of the TO-phonons at around QM in the region 35 < ω < 40 meV was found even above Tc, as T is lowered from ambient T . Because the spectral weights in this ω region mainly correspond to the in-plane motions of Fe atoms and because orbital fluctuations are expected to be strong at around QM, the result may present clues to investigate a possible coupling between the fluctuations of the orbitals and lattice system.

cond-mat.supr-con↗
arXiv2013

Switching of intra-orbital spin excitations in electron-doped iron pnictide superconductors

We investigate the doping dependence of the magnetic excitations in two-superconducting-dome-system LaFeAsO1-xDx. Using inelastic neutron scattering, spin fluctuations at different wavenumbers were observed under both superconducting domes around x = 0.1 and 0.4, but vanished at x = 0.2 corresponding to the Tc valley. Theoretical calculations indicate that the characteristic doping dependence of spin fluctuations is rationally explained as a consequence of the switching of the two intra-orbital nestings within Fe-3dYZ, ZX and 3dX2-Y2 by electron doping. The present results imply that the multi-orbital nature plays an important role in the doping and / or material dependence of the Tc of the iron pnictide superconductors.

cond-mat.supr-con↗
arXiv2012

Disentangling a quantum antiferromagnet with resonant inelastic X-ray scattering

Low-dimensional copper oxide lattices naturally manifest electronic states with strong short range quantum entanglement, which are known to lead to remarkable emergent material properties. However the nanometer scale many-body wavefunction is challenging to measure or manipulate in a simple way. In this study, X-ray induced $dd$ electronic transitions are used to suppress spin entanglement across a single lattice site in the spin-1/2 antiferromagnetic chain compound SrCuO$_2$, revealing a class of cuprate magnetic excitations that result from breaking the spin chain. These measurements are the first to employ two closely spaced X-ray resonances of copper (M$_2$ and M$_3$) as a form of natural 2-slit interferometer to distinguish between different types of electronic transition and resolve how they influence the dynamics of nearby spin-entangled electrons.

cond-mat.str-el↗