arXiv subjects

A. Rusydi

Publications and source records attributed to A. Rusydi.

25 records · Page 2Linked to original sources

arXiv2006

Experimental evidence of paired hole states in model high-$T_c$ compounds

The distribution of holes in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ (SCCO) is revisited with semi-emperical reanalysis of the x-ray absorption (XAS) data and exact-diagonalized cluster calculations. A new interpretation of the XAS data leads to much larger ladder hole densities than previously suggested. These new hole densities lead to a simple interpretation of the hole crystal (HC) recently reported with 1/3 and 1/5 wave vectors along the ladder. Our interpretation is consistent with paired holes in the rung of the ladders. Exact diagonalization results for a minimal model of the doped ladders suggest that the stabilization of spin structures consisting of 4 spins in a square plaquette as a result of resonance valence bond (RVB) physics suppresses the hole crystal with a 1/4 wave vector.

cond-mat.str-el↗

arXiv2005

Quantum melting of the hole crystal in the spin ladder of Sr14-xCaxCu24O41

The "spin ladder" is a reduced-dimensional analogue of the high temperature superconductors that was predicted to exhibit both superconductivity and an electronic charge density wave or "hole crystal" (HC). Both phenomena have been observed in the doped spin ladder system Sr14-xCaxCu24O41 (SCCO), which at x=0 exhibits a HC which is commensurate at all temperatures. To investigate the effects of discommensuration we used resonant soft x-ray scattering (RSXS) to study SCCO as a function of doped hole density, d. The HC forms only with the commensurate wave vectors L_L = 1/5 and L_L = 1/3 and exhibits a simple temperature scaling T_(1/3) / T_(1/5) = 5/3. For irrational wave vectors the HC "melts", perhaps through the motion of topological defects carrying fractional charge.

cond-mat.str-el↗

arXiv2005

Spatially modulated "Mottness" in La2-xBaxCuO4

Stripe phases were predicted to arise in doped antiferromagnets through competition between magnetism and the kinetic energy of mobile carriers (typically holes). In copper-oxides the main experimental evidence for stripes is neutron scattering from La1.48Nd0.4Sr0.12CuO4 (LNSCO) and La1.875Ba0.125CuO4 (LBCO) which reveals coexisting static spin and charge order whose wavelengths differ by a factor of two, reminiscent of charged rivers separating regions of oppositely-phased antiferromagnetism. A neutron is an electrically neutral object, however, so does not detect charge but rather its associated lattice distortion ; it is not known if the "stripe" phase in LNSCO and LBCO actually involves ordering of the doped holes. Here we present a study of the charge order in LBCO with resonant soft x-ray scattering (RSXS). We observe giant resonances at both the mobile carrier and upper-Hubbard band features in the OK edge. These demonstrate a substantial modulation in the doped hole density as well as the amount of spectral weight near the correlated gap, i.e. the degree of "Mottness". The peak-to-trough amplitude of the valence modulation is estimated to be 0.063 holes, which if interpreted with a model of the stripe form factor suggests an integrated area of 0.59 holes under a single stripe. While only an estimate, this number agrees with what is expected for half-filled stripes.

cond-mat.str-el↗

arXiv2005

Hole crystallization in the spin ladder of Sr14Cu24O41

One of the deepest questions in condensed matter physics concerns what other phases compete with superconductivity in high-transition-temperature (high-Tc) superconductors. One candidate is the "stripe" phase, in which the carriers (holes) condense into rivers of charge separating regions of antiferromagnetism. A related but lesser known system is the "spin ladder", which consists of two coupled chains of magnetic ions forming an array of rungs. A doped ladder can be thought of as a high-Tc material with lower dimensionality, and has been predicted to exhibit both superconductivity and an insulating "hole crystal" phase in which the carriers are localised through many-body interactions. The competition between the two resembles that between static stripes and superconductivity in high-Tc materials. Here we report evidence, from resonant x-ray scattering, for the existence of a hole crystal in the doped spin ladder of Sr14Cu24O41. This phase exists without a detectable distortion in the structural lattice, indicating it arises from many-body effects. Our measurements confirm theoretical predictions and support the picture that proximity to charge ordered states is a general property of superconductivity in copper-oxides.

cond-mat.str-el↗

arXiv2004

Zooming-in on the charge ordering in YBa2Cu3O6.5

We report direct evidence of charge/orbital ordering of low energy electronic states of $Cu$ in YBa$_2$Cu$_3$O$_{6+x}$ ortho-II phase in both the $CuO_3$ chain and the CuO$_2$ plane. Huge enhancement of the $({1/2},0,0)$ superstructure Bragg peak is observed when photon energy is tuned to the $Cu L_{2,3}$ absorption edge with large polarization dependence. The ordering in the $CuO_2$ plane discovered here sheds new light on how the one dimensional $Cu-O$ chains affect the $CuO_2$ plane, and why many normal and superconducting state properties of this system exhibit strong anisotropy.

cond-mat.supr-con↗

arXiv2003

Soft x-ray resonant diffraction study of magnetic and orbital correlations in a manganite near half-doping

We have utilized the resonant x-ray diffraction technique at the Mn L-edge in order to directly compare magnetic and orbital correlations in the Mn sub-lattice of Pr0.6Ca0.4MnO3. The resonant line shape is measured below T_OO ~ 240 K at the orbital ordering wave vector (0,1/2,0), and below T_N ~ 175 K at the antiferromagnetic wave vector (1/2,0,0). Comparing the width of the super-lattice peaks at the two wavevectors, we find that the correlation length of the magnetism exceeds that of the orbital order by nearly a factor of two. Furthermore, we observe a large (~ 3 eV) shift in spectral weight between the magnetic and orbital line shapes, which cannot be explained within the classic Goodenough picture of a charge-ordered ground state. To explain the large shift, we calculate the resonant line shapes for orbital and magnetic diffraction based on a relaxed charge-ordered model.

cond-mat.str-el↗

arXiv2002

A Structural Probe of the Doped Holes in Cuprate Superconductors

An unresolved issue concerning cuprate superconductors is whether the distribution of carriers in the CuO(2) plane is uniform or inhomogeneous. Because the carriers comprise a small fraction of the total charge density and may be rapidly fluctuating, modulations are difficult to detect directly. Here we demonstrate that in anomalous x-ray scattering at the oxygen K edge of the cuprates, the contribution of carriers to the scattering amplitude is selectively magnified 82 times. This enhances diffraction from the doped holes by more than 10^3, permitting direct structural analysis of the superconducting ground state. Scattering from thin films of La(2)CuO(4+x) (Tc = 39 K) at T=(50 +/- 5) K on the reciprocal space intervals (0,0,0.21) -> (0,0,1.21) and (0,0,0.6) -> (0.3,0,0.6) show a rounding of the carrier density near the substrate suggestive of a depletion zone or similar effect. The structure factor for off-specular scattering was less than 3x10-7 e, suggesting an absence of in-plane hole ordering in this material.

cond-mat.supr-con↗