Magnetotransport study of the charged stripes in high-T_c cuprates

We present a study of the in-plane and out-of-plane magnetoresistance (MR) in heavily-underdoped, antiferromagnetic YBa_{2}Cu_{3}O_{6+x}, which reveals a variety of striking features. The in-plane MR demonstrates a "d-wave"-like anisotropy upon rotating the magnetic field H within the ab plane. With decreasing temperature below 20-25 K, the system acquires memory: exposing a crystal to the magnetic field results in a persistent in-plane resistivity anisotropy. The overall features can be explained by assuming that the CuO_2 planes contain a developed array of stripes accommodating the doped holes, and that the MR is associated with the field-induced topological ordering of the stripes.Comment: 4 pages, 5 figures, invited paper at M2S-HTSC-VI, to be published in Physics C (Proceedings of the International Conference on Materials and Mechanisms of Superconductivity, High Temperature Superconductors VI (M2S-HTSC-VI), Houston, Feb 20-25, 2000

Interplay of superconductivity and magnetism in cuprates

High temperature superconductivity : new materials and properties : joint symposium of the SB RAS and the CNEAS TU / edited by Kyosuke Terayam

c-Axis Transport and Resistivity Anisotropy of Lightly- to Moderately-Doped La_{2-x}Sr_{x}CuO_{4} Single Crystals: Implications on the Charge Transport Mechanism

Both the in-plane and the out-of-plane resistivities (\rho_{ab} and \rho_{c}) are measured in high-quality La_{2-x}Sr_{x}CuO_{4} (LSCO) single crystals in the lightly- to moderately-doped region, x = 0.01 to 0.10, and the resistivity anisotropy is determined. In all the samples studied, the anisotropy ratio \rho _{c}/\rho_{ab} quickly increases with decreasing temperature, although in non-superconducting samples the strong localization effect causes \rho _{c}/\rho_{ab} to decrease at low temperatures. Most notably, it is found that \rho_{c}/\rho_{ab} at moderate temperatures (100 - 300 K) is almost completely independent of doping in the non-superconducting regime (x = 0.01 to 0.05); this indicates that the same charge confinement mechanism that renormalizes the c-axis hopping rate is at work down to x = 0.01. It is discussed that this striking x-independence of \rho_{c}/\rho_{ab} is consistent with the idea that holes form a self-organized network of hole-rich regions, which also explains the unusually metallic in-plane transport of the holes in the lightly-doped region. Furthermore, the data for x > 0.05 suggest that the emergence of the superconductivity is related to an increase in the c-axis coupling.Comment: 7 pages, 5 figures, submitted to Phys. Rev.

Flux growth of superconducting crystals RBa2Cu3Ox

High temperature superconductivity : new materials and properties : joint symposium of the SB RAS and the CNEAS TU / edited by Kyosuke Terayam

Thermodynamic and transport properties of underdoped cuprates from ARPES data

he relationship between photoemission spectra of high-$T_{\textrm{c}}$ cuprates and their thermodynamic and transport properties are discussed. The doping dependence of the expected quasi-particle density at the Fermi level ($E_\mathrm{F}$) are compared with the electronic specific heat coefficient $\gamma$ and that of the spectral weight at $E_\mathrm{F}$ with the in-plane and out-of-plane superfluid density. We have estimated the electrical resistivity of underdoped cuprates from the momentum distribution curve (MDC) at $E_\mathrm{F}$ in the nodal direction. The temperature dependence of the MDC width is also consistent with that of the electrical resistivity.Comment: 14 pages, 4 figures, proceeding of International Symposium on Synchrotron Radiatin Research for Spin and Electronic States in d and f Electron Systems(SRSES2003

Magnetotransport Mechanisms in Strongly Underdoped YBa_2Cu_3O_x Single Crystals

We report magnetoresistivity measurements on strongly underdoped YBa_2Cu_3O_x (x=6.25, 6.36) single crystals in applied magnetic fields H || c-axis. We identify two different contributions to both in-plane and out-of-plane magnetoresistivities. The first contribution has the same sign as the temperature coefficient of the resistivity \partial ln(\rho_i)/\partial T (i={c,ab}). This contribution reflects the incoherent nature of the out-of-plane transport. The second contribution is positive, quadratic in field, with an onset temperature that correlates to the antiferromagnetic ordering.Comment: 4 pages, 3 figure

Indications of coherence-incoherence crossover in layered transport

For many layered metals the temperature dependence of the interlayer resistance has a different behavior than the intralayer resistance. In order to better understand interlayer transport we consider a concrete model which exhibits this behavior. A small polaron model is used to illustrate how the interlayer transport is related to the coherence of quasi-particles within the layers. Explicit results are given for the electron spectral function, interlayer optical conductivity and the interlayer magnetoresistance. All these quantities have two contributions: one coherent (dominant at low temperatures) and one incoherent (dominant at high temperatures).Comment: 6 pages, 4 figures, REVTEX

Normal-state conductivity in underdoped La_{2-x}Sr_xCuO_4 thin films: Search for nonlinear effects related to collective stripe motion

We report a detailed study of the electric-field dependence of the normal-state conductivity in La_{2-x}Sr_xCuO_4 thin films for two concentrations of doped holes, x=0.01 and 0.06, where formation of diagonal and vertical charged stripes was recently suggested. In order to elucidate whether high electric fields are capable of depinning the charged stripes and inducing their collective motion, we have measured current-voltage characteristics for various orientations of the electric field with respect to the crystallographic axes. However, even for the highest possible fields (~1000 V/cm for x=0.01 and \~300 V/cm for x=0.06) we observed no non-linear-conductivity features except for those related to the conventional Joule heating of the films. Our analysis indicates that Joule heating, rather than collective electron motion, may also be responsible for the non-linear conductivity observed in some other 2D transition-metal oxides as well. We discuss that a possible reason why moderate electric fields fail to induce a collective stripe motion in layered oxides is that fairly flexible and compressible charged stripes can adjust themselves to the crystal lattice and individual impurities, which makes their pinning much stronger than in the case of conventional rigid charge-density waves.Comment: 10 pages, 10 figures, accepted for publication in Phys. Rev.

Magnetic field effects and magnetic anisotropy in lightly doped La_{2-x}Sr_xCuO_4

The effects of the application of a magnetic field on the diagonal stripe spin-glass phase is studied in lightly doped La_{2-x}Sr_xCuO_4 (x=0.014 and 0.024). With increasing magnetic field, the magnetic elastic intensity at the diagonal incommensurate (DIC) positions (1,\pm\epsilon,0) decreases as opposed to the increase seen in superconducting samples. This diminution in intensity with increasing magnetic field originates from a spin reorientation transition, which is driven by the antisymmetric exchange term in the spin Hamiltonian. On the other hand, the transition temperature, the incommensurability, and the peak width of the diagonal incommensurate correlations are not changed with magnetic field. This result suggests that the magnetic correlations are determined primarily by the charge disproportionation and that the geometry of the diagonal incommensurate magnetism is also determined by effects, that is, stripe formation which are not purely magnetic in origin. The Dzyaloshinskii-Moriya antisymmetric exchange is nevertheless important in determining the local spin structure in the DIC stripe phase.Comment: 7 pages, 5 figures, to appear in Phys. Rev.

Coexistence of ferro- and antiferromagnetic order in Mn-doped Ni2_2MnGa

Ni-Mn-Ga is interesting as a prototype of a magnetic shape-memory alloy showing large magnetic field induced strains. We present here results for the magnetic ordering of Mn-rich Ni-Mn-Ga alloys based on both experiments and theory. Experimental trends for the composition dependence of the magnetization are measured by a vibrating sample magnetometer (VSM) in magnetic fields of up to several tesla and at low temperatures. The saturation magnetization has a maximum near the stoichiometric composition and it decreases with increasing Mn content. This unexpected behaviour is interpreted via first-principles calculations within the density-functional theory. We show that extra Mn atoms are antiferromagnetically aligned to the other moments, which explains the dependence of the magnetization on composition. In addition, the effect of Mn doping on the stabilization of the structural phases and on the magnetic anisotropy energy is demonstrated.Comment: 4 pages, 3 figure