arXiv subjects

Ikuma Tateishi

Publications and source records attributed to Ikuma Tateishi.

10 recordsLinked to original sources

arXiv2025

Orbital paramagnetism without density of states enhancement in nodal-line semimetal ZrSiS

Unconventional orbital paramagnetism without enhanced density of states was recently discovered in the nodal-line semimetal ZrSiS. We propose a novel interband mechanism, linked to the negative curvature of energy dispersions, which successfully accounts for the observed anomalous response. This negative curvature originates from energy variation along the nodal line, inherent in realistic nodal-line materials. Our results suggest that such orbital paramagnetism provides strong evidence for the presence of nodal lines in ZrSiS, and serves as a hallmark of other nodal-line materials.

cond-mat.mes-hall↗

arXiv2024

Ideal Spin-Orbit-Free Dirac Semimetal and Diverse Topological Transitions in Pr$_8$CoGa$_3$ Family

Topological semimetals, known for their intriguing properties arising from band degeneracies, have garnered significant attention. However, the discovery of a material realization and the detailed characterization of spinless Dirac semimetals have not yet been accomplished. Here, we propose from first-principles calculations that the $RE_8\mathrm{Co}X_3$ group ($RE$ = rare earth elements, $X$ = Al, Ga, or In) contains ideal spinless Dirac semimetals whose Fermi surfaces are fourfold degenerate band-crossing points (without including spin degeneracy). Despite the lack of space inversion symmetry in these materials, Dirac points are formed on the rotation-symmetry axis due to accidental degeneracies of two bands corresponding to different 2-dimensional irreducible representations of $C_{6v}$ group. We also investigate, through first-principles calculations and effective model analysis, various phase transitions caused by lattice distortion or elemental substitutions from the Dirac semimetal phase to distinct topological semimetallic phases such as nonmagnetic linked-nodal-line and Weyl semimetals (characterized by the second Stiefel-Whitney class) and ferromagnetic Weyl semimetals.

cond-mat.mtrl-sci↗

arXiv2022

Topological invariant and domain connectivity in moiré materials

Recently, a moiré material has been proposed in which multiple domains of different topological phases appear in the moiré unit cell due to a large moiré modulation. Topological properties of such moiré materials may differ from that of the original untwisted layered material. In this paper, we study how the topological properties are determined in moiré materials with multiple topological domains. We show a correspondence between the topological invariant of moiré materials at the Fermi level and the topology of the domain structure in real space. We also find a bulk-edge correspondence that is compatible with a continuous change of the truncation condition, which is specific to moiré materials. We demonstrate these correspondences in the twisted Bernevig-Hughes-Zhang model by tuning its moiré periodic mass term. These results give a feasible method to evaluate a topological invariant for all occupied bands of a moiré material, and contribute to the design of topological moiré materials and devices.

cond-mat.mes-hall↗

arXiv2022

Electronic topological transition of 2D boron by the ion exchange reaction

We systematically investigated electronic evolutions of non-symmorphic borophene with chemical environments that were realized by the ion exchange method. Electronic structures can be characterized by the topological $Z_2$ invariant. Spectroscopic experiments and DFT calculations unveiled that a sheet of hydrogenated borophene (borophane) is the Dirac nodal loop semimetal ($Z_2=-1$), while a layered crystal of YCrB$_4$ is an insulator ($Z_2=1$). The results demonstrate the electronic topological transition by replacement of the counter atoms on the non-symmorphic borophene layer.

cond-mat.mtrl-sci↗

arXiv2022

Quantum spin Hall effect from multi-scale band inversion in twisted bilayer Bi$_2$(Te$_{1-x}$Se$_x$)$_3$

Moiré materials have become one of the most active fields in material science in recent years due to their high tunability, and their unique properties emerge from the Moiré-scale structure modulation. Here, we propose twisted bilayer Bi$_2$(Te$_{1-x}$Se$_x$)$_3$ as a new Moiré material where the Moiré-scale modulation induces a topological phase transition. We show, in twisted bilayer Bi$_2$(Te$_{1-x}$Se$_x$)$_3$, a topological insulator domain and a normal insulator domain coexist in the Moiré lattice structure, and edge states on the domain boundary make nearly flat bands that dominate the material properties. The edge states further contribute to a Moiré-scale band inversion, resulting in Moiré-scale topological states. There are corresponding Moiré-scale edge states and they are so to speak "edge state from edge state", which is a unique feature of twisted bilayer Bi$_2$(Te$_{1-x}$Se$_x$)$_3$. Our result not only proposes novel quantum phases in twisted bilayer Bi$_2$Te$_3$-family, but also suggests the twisting of stacking sensitive topological materials paves an avenue in the search for novel quantum materials and devices.

cond-mat.mes-hall↗

arXiv2021

Thin Films of Topological Nodal Line Semimetals as a Candidate for Efficient Thermoelectric Converters

Thermoelectric materials intrigue much interest due to their wide range of application such as power generators and refrigerators. The efficiency of thermoelectric materials is quantified by the figure of merit, and a figure greater than unity is desired. To achieve this, a large Seebeck coefficient and low phonon thermal conductivity are required. We show that this can be achieved with a thin film of topological nodal line semimetals. We also discusses the correlation effect and spin current induced by a temperature gradient. The obtained results provide insight for the improvement of thermoelectric materials.

cond-mat.mes-hall↗

arXiv2021

Characteristic singular behaviors of nodal line materials emerging in orbital magnetic susceptibility and Hall conductivity

The bulk properties of nodal line materials have been an important research topic in recent years. In this paper, we study the orbital magnetic susceptibility and the Hall conductivity of nodal line materials using the formalism with thermal Green's functions and find characteristic singular behaviors of them. It is shown that, in the vicinity of the gapless nodal line, the orbital magnetic susceptibility shows a $δ$-function singularity and the Hall conductivity shows a step function behavior in their chemical potential dependences. Furthermore, these singular behaviors are found to show strong field angle dependences corresponding to the orientation of the nodal line in the momentum space. These singular behaviors and strong angle dependences will give clear evidence for the presence of the nodal line and its orientation and can be used to experimentally detect nodal line materials.

cond-mat.mes-hall↗

arXiv2020

Nodal lines and mapping to mirror Chern numbers in Ca$_2$As family

We study topological properties of materials in the Ca$_2$As family without spin-orbit coupling (SOC) by combining the first-principles calculation and a tight-binding model calculation. As a result of the calculation, we reveal that the Ca$2_$As family consists of one insulator phase and three nodal line phases including an intersecting nodal ring phase, though one of the phases is not found with realistic material parameters. Additionally, we discuss what kind of nontrivial topological invariants will emerge from each nodal line phase when SOC is introduced. We also find a mapping from a nodal line semimetal without SOC to a topological crystalline insulator with SOC. This mapping can be used to specify the realized topological phase from the candidates given by the previous phase classification method.

cond-mat.mes-hall↗

arXiv2020

Mapping rules from nodal line semimetal to topological crystalline insulator in face centered cubic lattice

We study what kind of topological crystalline insulator phase emerges from nodal line semimetal phases in the face-centered cubic system which is not indicated by topological indices when spin-orbit coupling (SOC) is introduced. We construct an effective model which hosts two different nodal lines phases, and calculated mirror Chern numbers in it by introducing SOC. As a result, we find that the two nodal line phases with different nodal line configurations are mapped to different topological crystalline insulator phases. This result shows that turning off SOC and checking the nodal line configuration can distinguish the two topological crystalline insulator phases, which have not been distinguished by previous methods.

cond-mat.mes-hall↗

arXiv2018

Face centered cubic SnSe as a $\mathbb{Z}_2$ trivial Dirac nodal line material

The presence of a Dirac nodal line in a time-reversal and inversion symmetric system is dictated by the $\mathbb{Z}_2$ index when spin-orbit interaction is absent. In a first principles calculation, we show that a Dirac nodal line can emerge in $\mathbb{Z}_2$ trivial material by calculating the band structure of SnSe in a face centered cubic lattice as an example. We qualitatively show that it becomes a topological crystalline insulator when spin-orbit interaction is taken into account. We clarify the origin of the Dirac nodal line by obtaining irreducible representations corresponding to bands and explain the triviality of the $\mathbb{Z}_2$ index. We construct an effective model representing the Dirac nodal line using the {\bf k}$\cdot${\bf p} method, and discuss the Berry phase and a surface state expected from the Dirac nodal line.

cond-mat.mes-hall↗