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Register a new userDeviations from Matthiessens Rule for ${rm SrRuO_3}$ and ${rm CaRuO_3}$
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We have measured the change in the resistivity of thin films of ${rm SrRuO_3}$ and ${rm CaRuO_3}$ upon introducing point defects by electron irradiation at low temperatures, and we find significant deviations from Matthiessens rule. For a fixed irradiation dose, the induced change in resistivity {it decreases} with increasing temperature. Moreover, for a fixed temperature, the increase in resistivity with irradiation is found to be {it sublinear}. We suggest that the observed behavior is due to the marked anisotropic scattering of the electrons together with their relatively short mean free path (both characteristic of many metallic oxides including cuprates) which amplify effects related to the Pippard ineffectiveness condition.
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$rm SrRuO_3$ is an itinerant ferromagnet with $T_c sim 150 rm K$. When $rm SrRuO_3$ is cooled through $T_c$ in zero applied magnetic field, a stripe domain structure appears whose orientation is uniquely determined by the large uniaxial magnetocrystalline anisotropy. We find that the ferromagnetic domain walls clearly enhance the resisitivity of $rm SrRuO_3$ and that the enhancement has different temperature dependence for currents parallel and perpendicular to the domain walls. We discuss possible interpretations of our results.
We report properties of topological insulator - ferromagnet - superconductor trilayers comprised of thin films of 20 nm thick $rm Bi_2Se_3$ on 10 nm $rm SrRuO_3$ on 30 nm $rm YBa_2Cu_3O_x$. As deposited trilayers are underdoped and have a superconductive transition with $rm T_c$ onset at 75 K, zero resistance at 65 K, $rm T_{Cueri}$ at 150 K and $rm T^*$ of about 200 K. Further reannealing under vacuum yields the 60 K phase of $rm YBa_2Cu_3O_x$ which still has zero resistance below about 40 K. Only when $10times 100$ micro-bridges were patterned in the trilayer, some of the bridges showed resistive behavior all the way down to low temperatures. Magnetoresistance versus temperature of the superconductive ones showed the typical peak due to flux flow against pinning below $rm T_c$, while the resistive ones showed only the broad leading edge of such a peak. All this indicates clearly weak-link superconductivity in the resistive bridges between superconductive $rm YBa_2Cu_3O_x$ grains via the topological and ferromagnetic cap layers. Comparing our results to those of a reference trilayer with the topological $rm Bi_2Se_3$ layer substituted by a non-superconducting highly overdoped $rm La_{1.65}Sr_{0.35}CuO_4$, indicates that the superconductive proximity effect as well as ferromagnetism in the topological trilayer are actually strongly suppressed compared to the non-topological reference trilayer. This strong suppression is likely to originate in strong proximity induced edge currents in the SRO/YBCO layer that can lead to Majorana bound states, a possible signature of which is observed in the present study as zero bias conductance peaks.
We report the crystal field levels of several newly-discovered rare-earth kagome compounds: $rm{Nd_3Sb_3Mg_2O_{14}}$, $rm{Nd_3Sb_3Zn_2O_{14}}$, and $rm{Pr_3Sb_3Mg_2O_{14}}$. We determine the CEF Hamiltonian by fitting to neutron scattering data using a point-charge Hamiltonian as an intermediate fitting step. The fitted Hamiltonians accurately reproduce bulk susceptibility measurements, and the results indicate easy-axis ground state doublets for $rm{Nd_3Sb_3Mg_2O_{14}}$ and $rm{Nd_3Sb_3Zn_2O_{14}}$, and a singlet ground state for $rm{Pr_3Sb_3Mg_2O_{14}}$. These results provide the groundwork for future investigations of these compounds and a template for CEF analysis of other low-symmetry materials.
A unified approach is presented for investigating coupled spin-orbital fluctuations within a realistic three-orbital model for strongly spin-orbit coupled systems with electron fillings $n=3,4,5$ in the $t_{2g}$ sector of $d_{yz},d_{xz},d_{xy}$ orbitals. A generalized fluctuation propagator is constructed which is consistent with the generalized self-consistent Hartree-Fock approximation where all Coulomb interaction contributions involving orbital diagonal and off-diagonal spin and charge condensates are included. Besides the low-energy magnon, intermediate-energy orbiton and spin-orbiton, and high-energy spin-orbit exciton modes, the generalized spectral function also shows other high-energy excitations such as the Hunds coupling induced gapped magnon modes. We relate the characteristic features of the coupled spin-orbital excitations to the complex magnetic behavior resulting from the interplay between electronic bands, spin-orbit coupling, Coulomb interactions, and structural distortion effects, as realized in the compounds $rm NaOsO_3$, $rm Ca_2RuO_4$, and $rm Sr_2IrO_4$.
The temperature dependence of the hexagonal lattice parameter $c$ of single crystal $rm LaCoO_3$ (LCO) with $H=0$ and $800$Oe, as well as LCO bulk powders with $H=0$, was measured using high-resolution x-ray scattering near the transition temperature $T_oapprox 35$K. The change of $c(T)$ is well characterized by a power law in $T-T_o$ for $T>T_o$ and by a temperature independent constant for $T<T_o$ when convoluted with a Gaussian function of width $8.5$K. This behavior is discussed in the context of the unusual magnetic behavior observed in LCO as well as recent generalized gradient approximation calculations.
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