Charge ordering and charge dynamics inNd2−xSrxNiO

Abstract

Charge ordering phenomena and their effects on charge dynamics have been investigated for single crystals of R 2Ϫx Sr x NiO 4 (RϭLa, Nd͒ with xϭ0.5 for RϭLa and 0.33рxр0.70 for RϭNd by measurements of neutron diffraction and optical reflectivity spectra. The essential features of charge dynamics for 0.33рx р0.5 appear to be least affected by R species ͑La or Nd͒. In xу0.5, commensurate checkerboard ͑CB͒-type charge order shows up at such a high temperature as T CO C ϳ480 K. An incommensurate stripe order, that tends to take over the CB-type charge order at lower temperatures, is also clearly observed up to xϭ0.7. The remarkable evolution of the pseudogap feature as lowering temperature is observed in the optical conductivity spectrum. As x is increased, the energy scale (⌬ PG ), the onset T (T PG ) of the pseudogap, and the in-plane resistivity upturn T (T ab ) scale with each other and decrease monotonically after taking a maximum at x ϭ0.5, as T CO C is simultaneously reduced. The results indicate that the charge dynamics is significantly regulated by emergence of the CB-type charge correlation, and that the melting of the CB-type charge order must be playing a key role in driving the insulator-metal transition at xϳ0.9.

Unidirectional diagonal order and three-dimensional stacking of charge stripes in orthorhombicPr1.67Sr0.33NiO4andHücker1, Zimmermann2, Klingeler3 et al. 2006Phys. Rev. B

“…[1][2][3][4][5][6] Of particular interest is that, in both materials, incommensurate spin correlations and lattice modulations are observed which are consistent with the concept of charge and spin stripes. 7 Undoped, both systems are insulating antiferromagnets ͑AF͒.…”

“…5,36 As a result, the HTT/LTO phase boundary shifts to much higher temperatures and Sr concentrations so that even for x = 0.33, the transition takes place above room temperature ͓see Fig. 1͑a͔͒.…”

Microscopic origin of diagonal stripe phases in doped nickelates

“…39,40,41 Interestingly, above this doping, incommensurability tends to saturate rapidly with the value ǫ ≃ 0.44. 32 Apparently, CO itself induces commensurate values of ǫ and such a commensurability effect seems to be an intrinsic property of the stripe order. At the same time, the increased hole density at the DWs suppresses the superexchange energy gain, best optimized when all the holes are accommodated within stripes.…”

Electronic and Magnetic Nano Phase Separation in Cobaltates La2−x Sr x CoO4

“…Interestingly, nickelates around half-doping also exhibit CBCO at high temperatures (∼480 K) and become charge stripe ordered on cooling to low temperatures (∼180 K) [15,16]. This re-arrangement of charges into stripes at low temperatures seems to be hampered in the cobaltates which also have a much more robust CBCO with distinctly higher CBCO ordering temperatures than in the nickelates.…”