arXiv subjects

Shinichiro Ideta

Publications and source records attributed to Shinichiro Ideta.

7 recordsLinked to original sources

arXiv2026

Topological Surface States and Anisotropic Magnetotransport in SnSb$_6$Te$_{10}$

We have investigated the electronic structure and magnetotransport properties of SnSb$_6$Te$_{10}$ single crystals using density functional theory (DFT), synchrotron-based angle-resolved photoemission spectroscopy (ARPES), and quantum transport measurements. Our DFT calculations reveal a clear spin-orbit coupling driven band inversion between the Sb-$p$ and Te-$p$ states together with a non-trivial $\mathbb{Z}_2$ topological invariant. The calculated surface-state dispersion and hexagonally warped Fermi surface contours agree well with the ARPES measurements. Temperature-dependent transport measurements indicate dominant electron-phonon scattering, while Hall measurements confirm hole-type carriers with carrier density of the order of $10^{21}$ cm$^{-3}$. Both transverse and longitudinal magnetotransport exhibit weak antilocalization behavior, while Shubnikov-de Haas oscillations observed for $H \parallel c$ yield a Berry phase close to $π$, consistent with Dirac-like surface states. Furthermore, angle-dependent magnetotransport measurements reveal pronounced anisotropy associated with an anisotropic Fermi surface topology and mixed bulk-surface transport behavior. Our combined theoretical and experimental results establish SnSb$_6$Te$_{10}$ as a strong topological insulator and a promising platform for investigating topological transport phenomena in layered telluride systems.

cond-mat.mtrl-sci↗

arXiv2026

Emergent surface resonance from charge density wave symmetry breaking in TiSe2

Surface confined electronic states provide a fertile ground for discovering emergent phenomena that have no counterpart in the bulk, offering new routes to manipulate correlations, symmetry breaking, and dimensionality at the atomic scale. Here, we show that charge density wave (CDW) symmetry breaking can yield a surface states in 1T-TiSe2. Micro angle resolved photoemission spectroscopy resolves a sharp, two dimensional surface resonant state (SRS) that emerges within the CDW reconstructed low energy spectrum. The SRS exhibits notable temperature dependence and its spectral weight collapses around 160 K, while CDW transition temperature TCDW is commonly reported as 202 K. Slab DFT+U calculations reproduce a surface localized resonance when CDW folding brings valence and conduction states into near degeneracy, suggesting a correlation tuned, surface selective origin. These results point to a form of correlation-tuned surface resonance in a layered CDW compound and suggest a framework for engineering low dimensional quantum states in van der Waals materials via symmetry breaking and electronic structure tuning.

cond-mat.mtrl-sci↗

arXiv2024

Electronic states in superconducting type-II Dirac semimetal: 1T-PdSeTe

We have investigated the surface and bulk electronic structures of the superconducting type-II Dirac semimetal 1T-PdSeTe. The superconducting transition temperature $T_C = 3.2$ K was almost twice as high as $T_C = 1.6$ K in 1T-PdTe$_2$. Scanning transmission electron microscopy measurements showed homogeneously mixed Se and Te atoms in the chalcogen layers, consistent with the CdI$_2$-type crystal structure. Angle-resolved photoemission spectroscopy measurements and density functional theory calculations indicated the existence of the topological surface states, and the overall band structures were similar to those of 1T-PdTe$_2$. These results suggest that CdI$_2$-type lattice symmetry dictates the band dispersion, regardless of atomic disorder in the chalcogen layers. As the electronic band dispersion and the local structures were persistent upon substitution, the enhancement of $T_C$ is likely associated with the chemical pressure. Our results provide insight into the effects of the solid solution on the surface and bulk electronic states as well as the superconducting transition temperature.

cond-mat.supr-con↗

arXiv2024

Coupling between electrons and charge density wave fluctuation and its possible role in superconductivity

In most of charge density wave (CDW) systems of different material classes, ranging from traditional correlated systems in low-dimension to recent topological systems with Kagome lattice, superconductivity emerges when the system is driven toward the quantum critical point (QCP) of CDW via external parameters of doping and pressure. Despite this rather universal trend, the essential hinge between CDW and superconductivity has not been established yet. Here, the evidence of coupling between electron and CDW fluctuation is reported, based on a temperature- and intercalation-dependent kink in the angle-resolved photoemission spectra of 2H-PdxTaSe2. Kinks are observed only when the system is in the CDW phase, regardless of whether a long- or short-range order is established. Notably, the coupling strength is enhanced upon long-range CDW suppression, albeit the coupling energy scale is reduced. Interestingly, estimation of the superconducting critical temperature by incorporating the observed coupling characteristics into McMillan's equation yields result closely resembling the known values of the superconducting dome. Our results thus highlight a compelling possibility that this new coupling mediates Cooper pairs, which provides new insights on the competing relationship not only for CDW, but also for other competing orders.

cond-mat.supr-con↗

arXiv2023

Semiconducting Electronic Structure of the Ferromagnetic Spinel $\mathbf{Hg}\mathbf{Cr}_2\mathbf{Se}_4$ Revealed by Soft-X-Ray Angle-Resolved Photoemission Spectroscopy

We study the electronic structure of the ferromagnetic spinel $\mathrm{Hg}\mathrm{Cr}_2\mathrm{Se}_4$ by soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) and first-principles calculations. While a theoretical study has predicted that this material is a magnetic Weyl semimetal, SX-ARPES measurements give direct evidence for a semiconducting state in the ferromagnetic phase. Band calculations based on the density functional theory with hybrid functionals reproduce the experimentally determined band gap value, and the calculated band dispersion matches well with ARPES experiments. We conclude that the theoretical prediction of a Weyl semimetal state in $\mathrm{Hg}\mathrm{Cr}_2\mathrm{Se}_4$ underestimates the band gap, and this material is a ferromagnetic semiconductor.

cond-mat.mtrl-sci↗

arXiv2022

Large anomalous Hall effect induced by weak ferromagnetism in the noncentrosymmetric antiferromagnet $\mathrm{Co}\mathrm{Nb}_3\mathrm{S}_6$

We study the mechanism of the exceptionally large anomalous Hall effect (AHE) in the noncentrosymmetric antiferromagnet $\mathrm{Co}\mathrm{Nb}_3\mathrm{S}_6$ by angle-resolved photoemission spectroscopy (ARPES) and magnetotransport measurements. From ARPES measurements of $\mathrm{Co}\mathrm{Nb}_3\mathrm{S}_6$ and its family compounds ($\mathrm{Fe}\mathrm{Nb}_3\mathrm{S}_6$ and $\mathrm{Ni}\mathrm{Nb}_3\mathrm{S}_6$), we find a band dispersion unique to the Co intercalation existing near the Fermi level. We further demonstrate that a slight deficiency of sulfur in $\mathrm{Co}\mathrm{Nb}_3\mathrm{S}_6$ eliminates the ferromagnetism and the AHE simultaneously while hardly changing the band structure, indicating that the weak ferromagnetism is responsible for the emergence of the large AHE. Based on our results, we propose Weyl points near the Fermi level to cause the large AHE.

cond-mat.mtrl-sci↗

arXiv2020

Electronic Structure of $\mathrm{Sr}_{1-y}\mathrm{Ca}_{y}\mathrm{Fe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($x$ = 0.25, $y$ = 0.08) Revealed by Angle-Resolved Photoemission Spectroscopy

We have investigated the electronic structure of $\mathrm{Sr}_{1-y}\mathrm{Ca}_{y}\mathrm{Fe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($x$ = 0.25, $y$ = 0.08) by means of angle-resolved photoemission spectroscopy. From the comparison with the results of $\mathrm{BaFe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$, the effects of smaller structural anisotropy ($c/a$) on the Fermi surfaces (FSs) and the gap structures are discussed. The observed FSs have three dimensional shapes. One of the hole FSs is strongly warped between the $Γ$ and $Z$ points, and the innermost FS observed at the $Z$ point disappears at the $Γ$ point, which is similar to the FS features of $\mathrm{SrFe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($x$ = 0.35). In the superconducting state, the node like gap-minimum is present for the $d_{xy}$ electron FS near the $X$ point, while the gaps around the other high symmetry points are isotropic. Several theoretical models based on the spin and/or the orbital fluctuation are examined to explain all these experimental results.

cond-mat.supr-con↗