Commensurability effect on the charge ordering ofLa2−xSrxNiO

Abstract

Measurements of Hall coefficients, thermoelectric power, and optical conductivity spectra were done for single crystals of La 2Ϫx Sr x NiO 4 (xϭ0.27Ϫ0.50) showing prototypical charge ordering. We found that the character of the carriers in the charge-ordered state changes from electronlike to holelike when the hole concentration p crosses 1/3, and that the correlation gap in the optical spectrum for pϭ1/3 is collapsed when p is away from 1/3. These results indicate that the deviation of p from 1/3 can be regarded as electron or hole doping into the commensurate charge-ordered state at pϭ1/3. ͓S0163-1829͑99͒50732-7͔Charge ordering is a generic phenomenon for the strongly correlated electron system whose band filling deviates away from integer value. In this state, doped carriers are localized and order periodically ͑usually accompanied by spin order-ing͒ at low temperature. Recent studies on transition metal oxides have shown a variety of examples of charge ordering for two-dimensional ͑2D͒ nickelates ͑with K 2 NiF 4 structure͒, 1-5 2D and 3D ͑perovskite͒ manganites, 6-8 and perovskite ferrates. 9 Among them, La 2Ϫx Sr x NiO 4 is a prototypical example of charge ordering. In this compound, charge and spin ordering occurs over a wide holeconcentration ͑p͒ range (0Ͻpр0.5), and the wave vectors of the charge ordering, (Ϯ⑀,Ϯ⑀), and spin ordering, ( 1 2 Ϯ⑀/2, 1 2 Ϯ⑀/2), vary continuously with p, almost following the trend that ⑀ϳp. 1-4 These results suggest a picture in which doped holes in this 2D nickelate line up along the diagonal direction of the Ni square lattice, and the period of these ''charge stripes'' varies continuously in accordance with the hole concentration. 5 It should be noted that similar variations of the charge-stripes period with carrier concentration are also observed in perovskite manganites, 7 and that several theoretical studies 10,11 can reproduce this phenomenon and the relation of ⑀ϭp.Concerning such charge ordering over a wide carrierconcentration range, it is an interesting issue whether the commensurability effect exists for a specific carrier concentration. In fact, a previous study 12 reported an anomaly at p ϭ1/3, where the resistivity jumps most clearly at the transition temperature of the charge ordering (T co ), compared with other hole concentrations. This suggests the importance of the commensurate vs incommensurate issue in the charge and spin ordering of 2D nickelates. In this paper, we demonstrate that pϭ1/3 is a special hole concentration for this system and transport properties and electronic structures are critically affected by the deviation of the hole concentration from this value. We propose a picture in which the commensurate charge-ordered state for pϭ1/3 is analogous to a Mott insulator, and the deviation from pϭ1/3 (pϾ1/3 or p Ͻ1/3) can be regarded as hole or electron doping, respectively, into such a Mott insulator.All the samples studied in this work are single crystals grown by a floating-zone method. Taking account of the oxygen of stoichiometry (␦) in the sampl...

Neutron scattering studies on stripe phases in non-cuprate materials

“…2. This picture is further corroborated by the Hall effect measurements across this amount of doping which show a change in the sign of charge carriers just at x = 1/3 and suggest electron-and holelike charge carriers below and above this value, respectively [86]. The stability of the commensurate phase at x = 1/3 thus explains the slight deviations of the ε ch =n h rule that persist even at low temperatures, see Fig.…”

Bond-Stretching-Phonon Anomalies in Stripe-OrderedLa1.69Sr0.31NiO4

“…The maximum transition temperatures for charge-stripe and magnetic order occur at x = 1 3 [11,15]. Well below the charge-ordering temperature, T co , the nickelates have very large resistivities [16,17], consistent with all of the added holes being localized in charge stripes.We [110], a splitting of the same magnitude is observed over much of the zone and, in particular, at the zone boundary. These results are important for two reasons.…”

Charge ordering and charge dynamics inNd2−xSrxNiOIshizaka1, Taguchi2, Kajimoto3 et al. 2003Phys. Rev. BSelf Cite413460View full textAdd to dashboardCite

“…The incommensurate charge ordering transition at T CO IC ϳ240 K is detected as anomalies of transport, optical, and thermal properties in various kinds of measurements. [13][14][15] At xϭ1/2, which is another fixed point for commensurability, a rather complicated ordering process has been observed in a recent neutron diffraction measurement. 16 First, a commensurate checkerboard ͑CB͒-type charge order is observed to evolve below T CO C ϳ480 K, which is eventually taken over by, while coexisting with, an incommensurate (⑀ϳ0.44) stripe order with lowering temperature below T CO IC ϳ180 K. The low-T stripe order seems to subsist from the lower doped region with changing its ⑀ value.…”