arXiv subjects

Yuya Haraguchi

Publications and source records attributed to Yuya Haraguchi.

27 records · Page 2Linked to original sources

arXiv2022

Perfect kagome-lattice antiferromagnets with J$_{eff}$ = 1/2: The Co$^{2+}$-analogs of copper minerals volborthite and vesignieite

We report the synthesis, crystal structure, and magnetic properties of Co$^{2+}$ kagome magnets Co$_3$V$_2$O$_7$(OH)$_2$$\cdot$2H$_2$O and BaCo$_3$(VO$_4$)$_2$(OH)$_2$, which can be recognized as Co-analogues of the intensively researched quantum kagome magnet volborthite Cu$_3$V$_2$O$_7$(OH)$_2$$\cdot$2H$_2$O and vesignieite BaCu$_3$(VO$_4$)$_2$(OH)$_2$. For each compound, the ground state is seemingly A-type antiferromagnetic order. At low temperatures, applying a magnetic field causes a metamagnetic-like transition described by the transition in which antiferromagnetically-aligned canted moments change to ferromagnetically-aligned ones. These ground and field-induced states include a canted ferromagnetic component perpendicular to the kagome planes favored by Dzyaloshinskii-Moriya interactions. These magnetic properties are well characterized by the J$_{eff}$ = 1/2 physics. Our findings will be the first step toward clarifying the J$_{eff}$ = 1/2 kagome physics, which has been little studied experimentally or theoretically.

cond-mat.str-el↗

arXiv2022

Honeycomb lattice iridate on the verge of Mott-collapse

A new honeycomb lattice iridate (La,Na)IrO$_3$ ($\approx$ LaNaIr$_2$O$_6$) is successfully synthesized from the spin-orbit coupled Mott insulator Na$_2$IrO$_3$ by replacing the interlayer Na$^+$ ions with La$^{3+}$ ions. (La,Na)IrO$_3$ shows a finite Sommerfeld term in heat capacity and a $-\ln T$ dependence of resistivity, indicating a realization of a metallic state driven by a Mott collapse. Furthermore, crystal structure analysis reveals the formation of Ir zig-zag chains with metal-metal bonding, increasing kinetic energy resulting in the Mott collapse. This observation would be due to a Mott collapse induced in a $J_{\mathrm{eff}} = 1/2$ spin-orbit coupling Mott insulator with an Ir honeycomb lattice by topochemical control of the ionic configuration.

cond-mat.str-el↗

arXiv2022

Observation of topological flat bands in the kagome semiconductor Nb$_3$Cl$_8$

The destructive interference of wavefunctions in a kagome lattice can give rise to topological flat bands (TFBs) with a highly degenerate state of electrons. Recently, TFBs have been observed in several kagome metals, including Fe$_3$Sn$_2$, FeSn, CoSn, and YMn$_6$Sn$_6$. Nonetheless, kagome materials that are both exfoliable and semiconducting are lacking, which seriously hinders their device applications. Herein, we show that Nb$_3$Cl$_8$, which hosts a breathing kagome lattice, is gapped out because of the absence of inversion symmetry, while the TFBs survive because of the protection of the mirror reflection symmetry. By angle-resolved photoemission spectroscopy measurements and first-principles calculations, we directly observe the TFB and a moderate band gap in Nb$_3$Cl$_8$. By mechanical exfoliation, we successfully obtain monolayers of Nb$_3$Cl$_8$ and confirm that they are stable under ambient conditions. In addition, our calculations show that monolayers of Nb$_3$Cl$_8$ have a magnetic ground state, thus providing opportunities to study the interplay between geometry, topology, and magnetism.

cond-mat.mtrl-sci↗

arXiv2022

Quantum paramagnetism in the hyperhoneycomb Kitaev magnet $β$-ZnIrO$_3$

A polycrystalline sample of the hyperhoneycomb iridate $β$-ZnIrO$_3$ was synthesized via a topochemical reaction, and its structural, magnetic, and thermodynamic properties were investigated. The magnetization and heat capacity data show the absence of long-range magnetic order at least down to 2 K. A positive Curie-Weiss temperature $θ_W \sim 45$ K probed by the temperature dependence of magnetic susceptibility indicates that a Kitaev interaction is dominant. These observations suggest that a quantum spin liquid may have been realized. Furthermore, the observation of linear temperature-dependent contribution to the heat capacity with no magnetic field effect evidences gapless excitation. These facts are surprisingly contrary to the chemical disorder evidenced by the crystallographic analysis. By discussing the differences in the size effect of Z$_2$-fluxes in 2D and 3D Kitaev magnets, we propose that there is a hidden mechanism to protect the quantum spin liquid state from chemical disorder.

cond-mat.str-el↗

arXiv2021

Quantum antiferromagnet bluebellite comprising a maple-leaf lattice made of spin-1/2 Cu$^{2+}$ ions

Spin-1/2 maple leaf lattice antiferromagnets are expected to show interesting phenomena originating from frustration effects and quantum fluctuations. We report the hydrothermal synthesis of a powder sample of bluebellite Cu$_6$IO$_3$(OH)$_{10}$Cl as a first potential candidate. Magnetization and heat capacity measurements reveal moderate frustration with a Curie-Weiss temperature of $-35$ K, and a magnetic transition at $T_N$ = 17 K. Surprisingly, the magnetic susceptibility and heat capacity above $T_N$ are well reproduced by the Bonner-Fisher model, which suggests that a one-dimensional spin correlation with a magnetic interaction of 25 K occurs in the apparently two-dimensional lattice. This emergent one-dimensionality cannot be explained by orbital ordering or dimensional reduction due to geometrical frustration. We believe that there is an unknown mechanism to cause one-dimensionality in the spin-1/2 maple leaf lattice antiferromagnet.

cond-mat.str-el↗

arXiv2021

Metallic state in the vicinity of molecular orbital crystallization in the d$^1$ thiospinel ZnTi$_2$S$_4$ prepared via a reductive ion-exchange reaction

A novel Ti3+-based thiospinel ZnTi2S4 is successfully synthesized via a low-temperature ion-exchange reaction. ZnTi2S4 shows a signature of metallic ground state evidenced by a contribution of conduction electrons in the heat capacity and Pauli-like paramagnetic susceptibility. These observations contrast to the electronic state of similar Ti3+-based spinel MgTi2O4 exhibiting the metal-insulator transition associated with a molecular orbital crystallization (MOC). Furthermore, the magnetic susceptibility of ZnTi2S4 shows a pseudogap-like behavior indicated by a vast peak in the magnetic susceptibility around 110 K, likely originating from the MOC fluctuation. The origin of the difference in the electronic states of MgTi2O4 and ZnTi2S4 would be due to the different magnitude of overlap between Ti 3d and p orbitals (O: 2p and S: 3p). The presence of a MOC state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in a MOC.

cond-mat.str-el↗

arXiv2020

Strong antiferromagnetic interaction owing to a large trigonal distortion in the spin-orbit-coupled honeycomb lattice iridate CdIrO$_3$

We investigated the magnetic properties of the ilmenite-type iridate CdIrO$_3$ with a honeycomb lattice formed by Ir$^{4+}$ ions prepared via a solid-state metathesis. The magnetization measurements with using the powder sample reveal a large effective magnetic moment and a fairly strong antiferromagnetic interaction, indicating a deviation from the Kitaev model. Considering the relationship between magnetism and crystal structure in CdIrO$_3$ with comparing with the other ilmenite-type iridates ZnIrO$_3$ and MgIrO$_3$, we conclude that insulating CdIrO$_3$ cannot be describe as a $J_{\rm eff} = 1/2$ Mott state owing to a metathetically-stabilized large trigonal distortion of IrO$_6$ octahedra.

cond-mat.str-el↗

arXiv2018

Frustrated Magnetism of the Maple-Leaf-Lattice Antiferromagnet MgMn$_3$O$_7$$\cdot$3H$_2$O

We present a novel hydrated layered manganate MgMn$_3$O$_7$$\cdot$3H$_2$O as a maple-leaf-lattice (MLL) antiferromagnet candidate. The MLL is obtained by regularly depleting 1/7 of the lattice points from a triangular lattice so that the magnetic connectivity $z = 5$ and is thus intermediately frustrated between the triangular ($z = 6$) and kagomé ($z = 4$) lattices. In MgMn$_3$O$_7$$\cdot$3H$_2$O, the Mn$^{4+}$ ions, carrying Heisenberg spin 3/2, form a regular MLL lattice in the quasi-two-dimensional structure. Magnetization and heat capacity measurements using a hydrothermally-prepared powder sample reveal successive antiferromagnetic transitions at 5 and 15 K. A high-field magnetization curve up to 60 T at 1.3 K exhibits a multi-step plateau-like anomaly. We discuss the unique frustration of the MLL antiferromagnet in which the chiraldegree of freedom may play an important role.

cond-mat.mtrl-sci↗

arXiv2018

Magnetic ordering with an XY-like anisotropy in the honeycomb lattice iridates ZnIrO$_3$ and MgIrO$_3$ synthesized via a metathesis reaction

We have successfully synthesized the novel antiferromagnets with Ir$^{4+}$ honeycomb lattice ZnIrO$_3$ and MgIrO$_3$ and investigated their magnetic and thermodynamic properties. The two iridates are isomorphic but exhibit qualitatively different magnetic properties. ZnIrO$_3$ shows antiferromagnetic ordering below 46.6 K, whereas MgIrO$_3$ displays weak ferromagnetic behavior below 31.8 K owing to formation of a canted antiferromagnetic ordering. The measurement of magnetic susceptibility with using an oriented powder sample revealed the presence of an XY-like magnetic anisotropy and a tilting magnetic structure which is possibly stabilized by the Kitaev interaction. Moreover, magnetization curves of MgIrO3 and ZnIrO3 up to 60 T show different behaviors, demonstrating that each magnetic ground state is different with each other. We discuss the difference in the ground state between MgIrO$_3$ and ZnIrO$_3$ from the viewpoint a magnetic model consisting of the Kitaev and Dzyaloshinskii-Moriya interactions with the spin frustration effect on the honeycomb lattice.

cond-mat.str-el↗