Yasuhide Tomioka

Bio: Yasuhide Tomioka is an academic researcher from National Institute of Advanced Industrial Science and Technology. The author has contributed to research in topics: Antiferromagnetism & Charge ordering. The author has an hindex of 42, co-authored 190 publications receiving 6928 citations. Previous affiliations of Yasuhide Tomioka include Japanese Ministry of International Trade and Industry.

Control of the electronic phase of a manganite by mode-selective vibrational excitation

Abstract: Controlling a phase of matter by coherently manipulating specific vibrational modes has long been an attractive (yet elusive) goal for ultrafast science. Solids with strongly correlated electrons, in which even subtle crystallographic distortions can result in colossal changes of the electronic and magnetic properties, could be directed between competing phases by such selective vibrational excitation. In this way, the dynamics of the electronic ground state of the system become accessible, and new insight into the underlying physics might be gained. Here we report the ultrafast switching of the electronic phase of a magnetoresistive manganite via direct excitation of a phonon mode at 71 meV (17 THz). A prompt, five-order-of-magnitude drop in resistivity is observed, associated with a non-equilibrium transition from the stable insulating phase to a metastable metallic phase. In contrast with light-induced and current-driven phase transitions, the vibrationally driven bandgap collapse observed here is not related to hot-carrier injection and is uniquely attributed to a large-amplitude Mn-O distortion. This corresponds to a perturbation of the perovskite-structure tolerance factor, which in turn controls the electronic bandwidth via inter-site orbital overlap. Phase control by coherent manipulation of selected metal-oxygen phonons should find extensive application in other complex solids--notably in copper oxide superconductors, in which the role of Cu-O vibrations on the electronic properties is currently controversial.

Nonlinear phononics as an ultrafast route to lattice control

Abstract: Light can interact with the electrons in a crystalline solid, which in turn generates lattice vibrations or phonons. A related phenomenon was proposed 40 years ago in which it is the ions in the crystal rather than the electrons that mediate the interaction. This effect, known as ionic Raman scattering, is now observed experimentally.

Visualization of the Local Insulator-Metal Transition in Pr0.7Ca0.3MnO3

Abstract: The light-induced insulator-metal transition in the “colossal magnetoresistance” compound Pr0.7Ca0.3MnO3 is shown to generate a well-localized conducting path while the bulk of the sample remains insulating. The path can be visualized through a change of reflectivity that accompanies the phase transition. Its visibility provides a tool for gaining insight into electronic transport in materials with strong magnetic correlations. For example, a conducting path can be generated or removed at an arbitrary position just because of the presence of another path. Such manipulation may be useful in the construction of optical switches.

High-magnetic-field study of the phase transitions of R 1 − x Ca x MnO 3 ( R = Pr , Nd)

Abstract: We have investigated the magnetic-field-induced phase transitions of ${R}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ ($R=\mathrm{Pr}$ and Nd, $x=0.50,$ 0.45 and 0.50, 0.45, 0.40) by measurements of magnetization, magnetoresistance, and magnetostriction utilizing a nondestructive long-pulse magnet (generating up to 40 T). We observed processes where magnetic fields destroy the real-space ordering of the charge carriers and cause insulator-to-metal phase transitions over the whole temperature region below about 250 K. We found that the destruction of the charge ordering is accompanied with a structural phase transition as well as with the magnetic phase transition and the colossal magnetoresistance effect. The different profiles of the temperature vs transition field curve depending on the carrier concentration $x$ may be ascribed to the difference in the entropy between the commensurate and the discommensurate charge-ordered state. It turned out that the stability of the charge-ordered state is strongly correlated with the colinear antiferromagnetic ordering of the localized Mn moments.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Anomalous hall effect

Abstract: We present a review of experimental and theoretical studies of the anomalous Hall effect (AHE), focusing on recent developments that have provided a more complete framework for understanding this subtle phenomenon and have, in many instances, replaced controversy by clarity. Synergy between experimental and theoretical work, both playing a crucial role, has been at the heart of these advances. On the theoretical front, the adoption of Berry-phase concepts has established a link between the AHE and the topological nature of the Hall currents which originate from spin-orbit coupling. On the experimental front, new experimental studies of the AHE in transition metals, transition-metal oxides, spinels, pyrochlores, and metallic dilute magnetic semiconductors, have more clearly established systematic trends. These two developments in concert with first-principles electronic structure calculations, strongly favor the dominance of an intrinsic Berry-phase-related AHE mechanism in metallic ferromagnets with moderate conductivity. The intrinsic AHE can be expressed in terms of Berry-phase curvatures and it is therefore an intrinsic quantum mechanical property of a perfect cyrstal. An extrinsic mechanism, skew scattering from disorder, tends to dominate the AHE in highly conductive ferromagnets. We review the full modern semiclassical treatment of the AHE together with the more rigorous quantum-mechanical treatments based on the Kubo and Keldysh formalisms, taking into account multiband effects, and demonstrate the equivalence of all three linear response theories in the metallic regime. Finally we discuss outstanding issues and avenues for future investigation.