Magnetic and Charge Dynamics in a Doped One-Dimensional Transition Metal Oxide

Abstract

We have measured the electrical resistivity, polarized x-ray absorption, and magnetic neutron scattering for Y~"Ca,BaNi 1,zn, 05 to determine how doping affects the charge and spin dynamics of a Haldane chain compound. While Zn doping, which severs the NiO chains, increases the resistivity beyond that of the pure material, Ca doping introduces holes, residing mainly in the 2p, orbital of the oxygens in the NiO chains. Both dopants lead to simple finite size effects above the Haldane gap. In addition, we have discovered that Ca doping yields substantial magnetic states below the Haldane gap.PACS numbers: 75.25.+z, 71.30.+h, 72.80.6a Doping of two-and three-dimensional (3D) transition metal oxides yields phenomena ranging from strongly renormalized Fermi liquid behavior in the vanadates to high temperature superconductivity in the cuprates [1,2]. In view of the enhanced quantum fluctuations in 1D systems, doping of transition metal chain oxides could well lead to equally surprising discoveries. Furthermore, because the theory of 1D systems is less speculative than that of 2D and 3D materials, tests of theory should be simpler than for the cuprates and vanadates. Thus motivated, we have performed transport, x-ray absorption, and neutron scattering experiments to determine how doping affects Y2BaNi05, a charge transfer insulator [3] containing Ni2+ (S = 1) chains with a quantum disordered, Haldane ground state [4 -7]. To the best of our knowledge these experiments are the first on any carrier-doped 1D transition metal oxide, and Y2BaNi05 provides the first gapped spin liquid, of any dimension, to which carriers can be added. The key result is that while substitution of nonmagnetic Zn + for magnetic Ni + on the chains simply produces effects one can associate with chain cutting, replacing the off-chain Y3+ by Ca2+ has far more dramatic consequences. In particular, holes appear in oxygen orbitals along the NiO chains radically changing the temperature dependence of the resistivity from the simple insulating behavior of the parent. In both the parent and doped compounds, electrical conduction is 1D. Carrier doping also yields new magnetics states below the Haldane gap.The specimens were large (-5 cm3) polycrystalline pellets as well as small (0.5 X 1.0 X 3.0 mm3) single crystals. %e prepared the pellets using a standard solid state reaction, while we grew the crystals from Baand Ni-rich melts [8 -10]. The stoichiometry of Y, Ca, Ba, Zn, and Ni in each of these samples was determined by analysis of the y rays produced upon cold neutron capture at the National Institute of Standards and Technology (NIST) research reactor. All four pellets had compositions in agreement with the nominal values. The magnetic susceptibilities of the pellets were consistent with those obtained previously for the same compositions [8,11]. Figure 1 displays the four-terminal dc resistivity (p) [12] for single crystals with silver paste contacts. The conduction in pure Y2BaNi05 is remarkably 1D with p along the chain (a axis) 3 orders of magni...

Low-temperature heat transport of spin-gapped quantum magnets

“…But a lot of researches have shown that there is a spin gap in the excitation spectrum [10,11]. This result is now well supported by numerical calculations on spin-1 1D HAFM ring.…”

Finite-size spectrum, magnon interactions, and magnetization ofS=1Heisenberg spin chains

“…[4][5][6][7][8][9] Many low-energy features of the model can be understood using an approximate mapping onto the nonlinear model (NL M). In particular, the low-lying excited states are constructed from a triplet of interacting bosons ͑magnons͒.…”

Spin Dynamics of Hole DopedY2−xCaxBaNiO5

“…In another approach dynamics was provided to the holes [6] but the Ni-Ni exchange J was assumed larger than both the hole hopping amplitude and the short-bond NiO exchange. While studying these limits is instructive since gap states are produced, the drastic reduction in ρ dc observed experimentally upon doping [4] suggests that holes are likely mobile over several lattice spacings. [7] Thus, in this paper we propose a new model for Y 2−x Ca x BaNiO 5 with fully mobile S=1/2 holes interacting with S=1 spins, which is studied using realistic values for the couplings.…”

“…Two remarkable experimental features were observed upon doping, namely (i) the reduction of the resistivity ρ dc by several orders of magnitude leading to a one dimensional conductor, and (ii) the creation of states inside the Haldane gap as revealed by inelastic neutron scattering (INS) data. [4] To understand these in-gap states, spin systems with site or bond impurities have been recently proposed. [5] Holes are assumed to be so strongly localized that their mobility is neglected.…”