Charge Excitations in the Stripe-OrderedLa5/3Sr1/3NiO4andLa

Abstract

Charge excitations were studied for stipe-ordered 214 compounds, La 5/3 Sr 1/3 NiO4 and 1/8-doped La2(Ba, Sr)xCuO4 using resonant inelastic x-ray scattering in hard x-ray regime. We have observed charge excitations at the energy transfer of ∼ 1 eV with the momentum transfer corresponding to the charge stripe spatial period both for the diagonal (nikelate) and parallel (cuprates) stripes. These new excitations can be interpreted as a collective stripe excitation or charge excitonic mode to a stripe-related in-gap state.There is accumulation of theoretical and experimental implications that the inhomogeneous charge state, such as a charge stripe state, occurring as a result of the carrier doping into the strongly correlated electron system is intimately related to the realization of high temperature superconductivity in cuprates [1,2]. Understanding the dynamics of the charge stripe state is one of the basic problems. To date, whereas the dynamics in spin sector has been studied extensively by neutron scattering [3,4,5,6], the dynamics in charge sector is yet to be understood.The 214 type nickelates and cuprates, family compounds of the firstly discovered high temperature superconductor La 2−x Ba x CuO 4 , exhibit charge stripe order when holes are doped. The stripe order has been comprehensively studied by diffraction techniques [7,8,9,10] and characterized by antiphase antiferromagnetic domains divided by one dimensional charge stripes where doped holes are confined. Upon carrier doping, La 2−x Sr x NiO 4 (LSNO) shows ordered state of "diagonal" stripes, where the charge stripes run along the diagonal direction of the NiO 2 square lattice [7] (Fig. 1 a). Holedoped 214 cuprates La 2−x (Ba, or Sr) x CuO 4 (LBCO or LSCO) show diagonal stripe order in the low doping insulating region [11], whereas in the superconducting dome the systems, particularly LBCO, show static order of "parallel" stripes only in the vicinity of x = 0.125 [12,13] where the superconductivity is suppressed [14]. This is frequently quoted as 1/8 anomaly. Here the charge stripes are parallel to the Cu-O-Cu bond (Fig. 1 b). Consequently, relation between the dynamical fluctuation of parallel stripes and the superconductivity is of interest.Resonant inelastic x-ray scattering (RIXS) in hard xray regime, a recently developed experimental probe, have revealed various types of charge excitations in the strongly correlated electron systems, such as the charge RIXS is an ideal probe for detecting charge excitations associated with the stripe having a specific momentum

Electronic structure of doped lanthanum cuprates studied with resonant inelastic x-ray scattering

“…It should be noted that we did not observe an obvious enhancement of the NIR peak at the stripe-ordering wave-vector; the peak was still observed at q=(π/2,0), but the background was higher (our measurements of momentum dependence will be presented elsewhere, but our low-energy elastic tails were too high to verify the result of Ref. 37). …”

Charge and Orbital Order in Transition Metal Oxides

“…Stripe order was found in doped manganites [152] and also discovered in doped La 2−x Sr x NiO 4 nickelates about the same time as in the cuprates [153]. However, in contrast to the cuprates the stripes in La 5/3 Sr 1/3 NiO 4 are diagonal and contain one (and not half) hole per unit cell [154]. Intriguing features seen in the spin excitation spectra of La 2 NiO 4+δ nickelates were reported recently [155] which suggest that the inward dispersion, seen also in cuprates, has a common origin in stripe phases.…”

Determination of the optical properties of La2−xBaxCuO4Homes1, Hücker2, Li3 et al. 2012Phys. Rev. B498500View full textAdd to dashboardCite

“…Recently, large single crystals of La 2−x Ba x CuO 4 have become available that have allowed a much more detailed investigation of the electronic [26][27][28][29][30][31][32][33][34][35] and structural [36][37][38][39][40][41][42][43][44][45][46][47] properties of the 1/8 phase. With the onset of the LTT phase both long-range charge-stripe order, followed by spin-stripe order at a slightly lower temperature, are observed.…”