arXiv subjects

Jobu Matsuno

Publications and source records attributed to Jobu Matsuno.

24 records · Page 2Linked to original sources

arXiv2018

Electric-field control of anomalous and topological Hall effects in oxide bilayer thin films

One of the key technologies in spintronics is to tame spin-orbit coupling (SOC) that links spin and motion of electrons, giving rise to intriguing magneto-transport properties in itinerant magnets. Prominent examples of such SOC-based phenomena are anomalous and topological Hall effects. However, controlling them by electric field has remained unachieved since electric field tends to be screened in itinerant magnets. Here we demonstrate that both anomalous and topological Hall effects can be modulated by electric field in oxide heterostructures consisting of ferromagnetic SrRuO$_{3}$ and nonmagnetic SrIrO$_{3}$. We observed clear electric-field effect only when SrIrO$_{3}$ is inserted between SrRuO$_{3}$ and a gate dielectric. Our results establish that strong SOC of nonmagnetic materials such as SrIrO$_{3}$ is essential in electrical tuning of these Hall effects and possibly other SOC-related phenomena.

cond-mat.str-el↗

arXiv2015

Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices; a designed playground for honeycomb physics

We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically-resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.

cond-mat.str-el↗

arXiv2015

Semimetallic transport properties of epitaxially stabilized perovskite CaIrO3 films

We report on the synthesis and transport properties of perovskite (Pv) CaIrO3 thin films. The Pv phase of CaIrO3 was stabilized by epitaxial growth on SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and LaAlO3 substrates with strong tensile, weak tensile, and compressive strains, respectively. The resistivity of these films showed a poorly metallic behavior. The Hall resistivity exhibited a sign change as a function of temperature and a nonlinear magnetic-field dependence, which clearly indicated the coexistence of electrons and holes and hence supported that Pv CaIrO3 films are semimetallic. The observed robustness of the semimetallic ground state against tensile and compressive strains is consistent with the presence of symmetry-protected Dirac points (nodes) around the Fermi level that prohibits the system from becoming a band insulator.

cond-mat.supr-con↗

arXiv2014

Engineering spin-orbital magnetic insulator by tailoring superlattices

Novel interplay of spin-orbit coupling and electron correlations in complex Ir oxides recently emerged as a new paradigm for correlated electron physics. Because of a large spin-orbit coupling of ~0.5 eV, which is comparable to the transfer energy t and the crystal field splitting $Δ$ and Coulomb U, a variety of ground states including magnetic insulator, band insulator, semimetal and metal, shows up in a narrow materials phase space. Utilizing such subtle competition of the ground states, we successfully tailor a spin-orbital magnetic insulator out of a semimetal SrIrO$_3$ by controlling dimensionality using superlattice of [(SrIrO$_3$)$_m$, SrTiO$_3$] and show that a magnetic ordering triggers the transition to magnetic insulator. Those results can be described well by a first-principles calculation. This study is an important step towards the design and the realization of topological phases in complex Ir oxides with very strong spin-orbit coupling.

cond-mat.str-el↗

arXiv2013

5d transition metal oxide IrO2 as a material for spin current detection

Devices based on a pure spin current (a flow of spin angular momentum) have been attracting increasing attention as key ingredients for low-dissipation electronics. To integrate such spintronics devices into charge-based technologies, an electric detection of spin current is essential. Inverse spin Hall effect converts a spin current into an electric voltage through spin-orbit coupling. Noble metals such as Pt and Pd, and also Cu-based alloys, owing to the large direct spin Hall effect, have been regarded as potential materials for a spin-current injector. Those materials, however, are not promising as a spin-current detector based on inverse spin Hall effect. Their spin Hall resistivity rho_SH, representing the performance as a detector, is not large enough mainly due to their low charge resistivity. Here we demonstrate that heavy transition metal oxides can overcome such limitations inherent to metal-based spintronics materials. A binary 5d transition metal oxide IrO2, owing to its large resistivity as well as a large spin-orbit coupling associated with 5d character of conduction electrons, was found to show a gigantic rho_SH ~ 38 microohm cm at room temperature, one order of magnitude larger than those of noble metals and Cu-based alloys and even comparable to those of atomic layer thin film of W and Ta.

cond-mat.mes-hall↗

arXiv2010

Epitaxially stabilized iridium spinel oxide without cations in the tetrahedral site

Single-crystalline thin film of an iridium dioxide polymorph Ir2O4 has been fabricated by the pulsed laser deposition of LixIr2O4 precursor and the subsequent Li-deintercalation using soft chemistry. Ir2O4 crystallizes in a spinel (AB2O4) without A cations in the tetrahedral site, which is isostructural to lambda-MnO2. Ir ions form a pyrochlore sublattice, which is known to give rise to a strong geometrical frustration. This Ir spinel was found to be a narrow gap insulator, in remarkable contrast to the metallic ground state of rutile-type IrO2. We argue that an interplay of strong spin-orbit coupling and a Coulomb repulsion gives rise to an insulating ground state as in a layered perovskite Sr2IrO4.

cond-mat.str-el↗