Year: 2011
Type: article
Abstract: Sessions C513In NSNO, diagonal-stripe charge ordering is observed at x=1/3 [1] in contrast to LSCO with vertical-stripe charge ordering at x=1/8 [2].NSNO also shows checkerboard (CB) charge ordering at x=1/2 [3].This system undergoes an insulator-metal transition with melting of its charge ordered state but shows no superconductivity up to x = 1.6 [4].Hitherto there has been no study of the electronic structure in the insulator-metal critical region.The comparison between these layered nickelate and cuprate Mott transition systems will be of benefit for understanding the uniqueness of high-T c cuprates.We have investigated the resonant x-ray diffraction (RXD) at Ni Kedge (~8.3 keV) photon energy to clarify the electric structure in CBtype charge order phase in Nd 1.5 Sr 0.5 NiO 4 (x=0.5).In the present case, we consider a dipole transition between Ni 1s and 4p.The 4p-level are influenced by their interaction with the e g electrons.In CB-type order phase, we have succeeded in observing the non-zero RXD signal at (100) for an incident x-ray polarization E||a, whereas there is no RXD signal for E||c.The polarization dependence of (100) diffraction suggests that the (x 2 -y 2 )-type hole orbital order of e g -state is realized in x=0.5.The charge disproportionation is estimated less than 0.2, thus the CB-type modulation of electronic structure should be originated from the orbital order rather than the charge order.As decreasing temperature, the material undergoes a tetragonalorthorhombic structural transition at around 250 K. Upon the transition the polarization dependence of the RXD signal changes, that is, the intensity of RXD for E||c becomes greater than that for E||a.The behavior is consist with the (3z 2 -r 2 )-type hole orbital order of e g -state.Therefore the (x 2 -y 2 )-type hole orbital order transmutes into the (3z 2r 2 )-type order in accordance with the orthorhombic transition.The tilting of NiO 6 -cage should affect the e g orbital state.We consider that the (3z 2 -r 2 )-type orbital order plays an important role in the insulatormetal transition.
Authors: M. Kubicki, K. Brzeziński, M. Jaskólski, Z. Dauter, B. Guillot
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W2317662290