arXiv subjects

Jun Fujioka

Publications and source records attributed to Jun Fujioka.

6 recordsLinked to original sources

arXiv2026

Carrier-density dependence of magnetotransport in correlated Dirac semimetal CaIrO$_3$

We report the carrier density dependence of the magnetotransport property in the correlated Dirac semimetal CaIrO$_3$. In the dilute carrier density region ($n_{\rm H}$ $\sim 2.2 \times 10^{16} \,$$\rm{cm}^{-3}$) at $2 \, \mathrm{K}$, the mobility exceeds $1.0 \times 10^{5} \,$$\rm{cm}^{2}/\rm{Vs}$ at $2 \, \mathrm{K}$, and the transverse magnetoresistance (MR) reaches $2,000 \,$\% at $12 \, \mathrm{T}$. The analysis of quantum oscillations and Hall conductivity shows that the Fermi velocity is nearly independent of the cross-sectional area of the Fermi surface, or equivalently the carrier density, supporting a $k$-linear dispersion of the Dirac node. The field dependence of magnetoresistivity is nearly $B$-linear in the moderate carrier density region ($n_\mathrm{H} \geq 4 \times 10^{16}\,$cm$^{-3}$), but scales with $B^{\alpha}$ ($\alpha > 2$) in the lower carrier density region. The variation of magnetoresistivity is likely affected by the enhanced long-range Coulomb interaction in the quantum limit, where Dirac electrons are subject to the magnetic confinement.

cond-mat.mtrl-sci↗

arXiv2025

Stark difference in the in-plane anomalous Hall response in Zintl compounds EuA2Sb2 (A = Zn, Cd) thin films

Recent observation of the in-plane anomalous Hall effect in magnetic Weyl semimetal EuCd2Sb2 has drawn attention to out-of-plane orbital magnetization induced by an in-plane field component. Here we study EuZn2Sb2, a sister compound of EuCd2Sb2, to demonstrate sensitive changes of the in-plane anomalous Hall effect on the band modulation. The Hall resistivity measured with rotating the magnetic field within the (001) principal plane of EuZn2Sb2 films exhibits a clear three-fold component corresponding to the in-plane anomalous Hall effect, which is distinct from the two-fold component of the planar Hall effect. The in-plane anomalous Hall effect of EuZn2Sb2 is highly contrasting to EuCd2Sb2, especially in terms of its opposite sign and field dependence, which can be explained by model calculations with different band inversion parameters. Our results pave the way for systematically controlling the in-plane anomalous Hall effect and orbital magnetization through elaborate band engineering.

cond-mat.mtrl-sci↗

arXiv2023

On Ultrafast X-ray Methods for Magnetism

With the introduction of x-ray free electron laser sources around the world, new scientific approaches for visualizing matter at fundamental length and time-scales have become possible. As it relates to magnetism and "magnetic-type" systems, advanced methods are being developed for studying ultrafast magnetic responses on the time-scales at which they occur. We describe three capabilities which have the potential to seed new directions in this area and present original results from each: pump-probe x-ray scattering with low energy excitation, x-ray photon fluctuation spectroscopy, and ultrafast diffuse x-ray scattering. By combining these experimental techniques with advanced modeling together with machine learning, we describe how the combination of these domains allows for a new understanding in the field of magnetism. Finally, we give an outlook for future areas of investigation and the newly developed instruments which will take us there.

cond-mat.mtrl-sci↗

arXiv2023

Spin-lattice and magnetoelectric couplings enhanced by orbital degrees of freedom in polar magnets

Orbital degrees of freedom mediating an interaction between spin and lattice were predicted to raise strong magnetoelectric effect, i.e. realize an efficient coupling between magnetic and ferroelectric orders. However, the effect of orbital fluctuations have been considered only in a few magnetoelectric materials, as orbital degeneracy driven Jahn-Teller effect rarely couples to polarization. Here, we explore the spin-lattice coupling in multiferroic Swedenborgites with mixed valence and Jahn-Teller active transition metal ions on a stacked triangular/Kagome lattice using infrared and dielectric spectroscopy. On one hand, in CaBa$M_4$O$_7$ ($M$ = Co, Fe), we observe strong magnetic order induced shift in the phonon frequencies and a corresponding large change in the dielectric response. Remarkably, as an unusual manifestation of the spin-phonon coupling, the spin-fluctuations reduce the phonon life-time by an order of magnitude at the magnetic phase transitions. On the other hand, lattice vibrations, dielectric response, and electric polarization show no variation at the Néel temperature of CaBaFe$_2$Co$_2$O$_7$, which is built up by orbital singlet ions. Our results provide a showcase for orbital degrees of freedom enhanced magnetoelectric coupling via the example of Swedenborgites.

cond-mat.str-el↗

arXiv2020

Evolution of possible Weyl semimetal states across the hole-doping induced Mott transition in pyrochlore iridates

We study possible Weyl semimetals of strongly-correlated electrons by investigating magnetotransport properties in pyrochlore R2Ir2O7 (R=rare-earth ions), choosing three types of R ions to design the exchange coupling scheme between R 4f and Ir 5d moments; non-magnetic Eu (4f6), isotropic Gd (4f7), and anisotropic Tb (4f8). In the doping-induced semimetallic state, distinctive features of magnetoresistance and Hall effect are observed in R=Gd and Tb compounds due to the effects of the exchange-enhanced isotropic and anisotropic Zeeman fields, respectively, exemplifying the double Weyl semimetal and the 2-in 2-out line-node semimetal as predicted by theories. In particular, a Hall angle of R=Gd compound is strongly enhanced to 1.5 % near above the critical doping for the Mott transition. Furthermore, an unconventional Hall contribution is discerned for a lower doping regime of R=Gd compound, which can be ascribed to the emergence of Weyl points with the field-distorted all-in all-out order state. These findings indicate that the hole-doping induced Mott transition as well as the characteristic f-d exchange interaction stabilizes versatile topological semimetal states in a wide range of material parameter space.

cond-mat.str-el↗

arXiv2020

Robust ferromagnetism in highly strained SrCoO3 thin films

Epitaxial strain provides important pathways to control the magnetic and electronic states in transition metal oxides. However, the large strain is usually accompanied by a strong reduction of the oxygen vacancy formation energy, which hinders the direct manipulation of their intrinsic properties. Here using a post-deposition ozone annealing method, we obtained a series of oxygen stoichiometric SrCoO3 thin films with the tensile strain up to 3.0%. We observed a robust ferromagnetic ground state in all strained thin films, while interestingly the tensile strain triggers a distinct metal to insulator transition along with the increase of the tensile strain. The persistent ferromagnetic state across the electrical transition therefore suggests that the magnetic state is directly correlated with the localized electrons, rather than the itinerant ones, which then calls for further investigation of the intrinsic mechanism of this magnetic compound beyond the double-exchange mechanism.

cond-mat.str-el↗