arXiv subjects

Hideo Hosono

Publications and source records attributed to Hideo Hosono.

At least 37 records · Page 2Linked to original sources

arXiv2021

Fermi surface nesting, vacancy ordering and the emergence of superconductivity in IrSb compounds

Fermi surface nesting, as a peculiar reciprocal space feature, is not only closely correlated with the real space superstructure, but also directly modulates the underlying electronic behavior. In this work, we elucidate the Fermi surface nesting feature of the IrSb compound with buckled-honeycomb-vacancy (BHV) ordering through Rh and Sn doping, and its correlation with structure and electronic state evolution. The advantageous substitution of atom sites (i.e., Rh on the Ir sites, Sn on the Sb sites, respectively), rather than the direct occupation of vacancies, induces the collapse of BHV order and the emergence of superconductivity. The distinct superconducting behavior of Rh and Sn incorporated systems are ascribed to the mismatch of Fermi surface nesting in the Sn case.

cond-mat.supr-con↗

arXiv2021

High-entropy van der Waals materials formed from mixed metal dichalcogenides, halides and phosphorus trisulfides

The charge, spin, and composition degrees of freedom in high-entropy alloy endow it with tunable valence and spin states, infinite combinations and excellent mechanical performance. Meanwhile, the stacking, interlayer, and angle degrees of freedom in van der Waals material bring it with exceptional features and technological applications. Integration of these two distinct material categories while keeping their merits would be tempting. Based on this heuristic thinking, we design and explore a new range of materials (i.e., dichalcogenides, halides and phosphorus trisulfides) with multiple metallic constitutions and intrinsic layered structure, which are coined as high-entropy van der Waals materials. Millimeter-scale single crystals with homogeneous element distribution can be efficiently acquired and easily exfoliated or intercalated in this materials category. Multifarious physical properties like superconductivity, magnetic ordering, metal-insulator transition and corrosion resistance have been exploited. Further research based on the concept of high-entropy van der Waals materials will enrich the high-throughput design of new systems with intriguing properties and practical applications.

cond-mat.mtrl-sci↗

arXiv2020

Crystal structure built from a GeO$_6$-GeO$_5$ polyhedra network with high thermal stability: $β$-SrGe$_2$O$_5$

By tackling the challenge of extending transparent oxide semiconductors to Ge based oxides, we have found a not-yet-reported crystal structure, named $β$-SrGe$_2$O$_5$, which is composed of edge-sharing GeO$_6$ octahedra interconnected by GeO$_5$ bipyramids. Single crystals were successfully grown by the high-pressure flux method. $β$-SrGe$_2$O$_5$ has a band gap of 5.2 eV and a dispersive conduction band with an effective mass as small as 0.34 times the electron rest mass, which originates from the edge-sharing GeO$_6$ octahedra network. Although known compounds with octahedral GeO$_6$ coordination are commonly unstable at atmospheric pressure and elevated temperatures, $β$-SrGe$_2$O$_5$ exhibits thermal stability up to 700 $^\circ$C.

cond-mat.mtrl-sci↗

arXiv2020

Shallow Valence Band of Rutile GeO$_2$ and P-type Doping

GeO$_2$ has an $α$-quartz-type crystal structure with a very wide fundamental band gap of 6.6 eV and is a good insulator. Here we find that the stable rutile-GeO$_2$ polymorph with a 4.6 eV band gap has a surprisingly low $\sim$6.8 eV ionization potential, as predicted from the band alignment using first-principles calculations. Because of the short O$-$O distances in the rutile structure containing cations of small effective ionic radii such as Ge$^{4+}$, the antibonding interaction between O 2p orbitals raises the valence band maximum energy level to an extent that hole doping appears feasible. Experimentally, we report the flux growth of $1.5 \times 1.0 \times 0.8$ mm$^3$ large rutile GeO$_2$ single crystals and confirm the thermal stability for temperatures up to $1021 \pm 10~^\circ$C. X-ray fluorescence spectroscopy shows the inclusion of unintentional Mo impurities from the Li$_2$O$-$MoO$_3$ flux, as well as the solubility of Ga in the r-GeO$_2$ lattice as a prospective acceptor dopant. The resistance of the Ga- and Mo-codoped r-GeO$_2$ single crystals is very high at room temperature, but it decreases by 2-3 orders of magnitude upon heating to 300 $^\circ$C, which is attributed to thermally-activated p-type conduction.

cond-mat.mtrl-sci↗

arXiv2020

Superconductivity from buckled-honeycomb-vacancy ordering

Vacancies are prevalent and versatile in solid-state physics and materials science. The role of vacancies in strongly correlated materials, however, remains uncultivated until now. Here, we report the discovery of an unprecedented vacancy state forming an extended buckled-honeycomb-vacancy (BHV) ordering in Ir$_{16}$Sb$_{18}$. Superconductivity emerges by suppressing the BHV ordering through squeezing of extra Ir atoms into the vacancies or isovalent Rh substitution. The phase diagram on vacancy ordering reveals the superconductivity competes with the BHV ordering. Further theoretical calculations suggest that this ordering originates from a synergistic effect of the vacancy formation energy and Fermi surface nesting with a wave vector of (1/3, 1/3, 0). The buckled structure breaks the crystal inversion symmetry and can mostly suppress the density of states near the Fermi level. The peculiarities of BHV ordering highlight the importance of "correlated vacancies" and may serve as a paradigm for exploring other non-trivial excitations and quantum criticality.

cond-mat.supr-con↗

arXiv2020

Pressure-induced Topological and Structural Phase Transitions in an Antiferromagnetic Topological Insulator

Recently, natural van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n have been theoretically predicted and experimentally shown to host tunable magnetic properties and topologically nontrivial surface states. In this work, we systematically investigate both the structural and electronic responses of MnBi2Te4 and MnBi4Te7 to external pressure. In addition to the suppression of antiferromagnetic order, MnBi2Te4 is found to undergo a metal-semiconductor-metal transition upon compression. The resistivity of MnBi4Te7 changes dramatically under high pressure and a non-monotonic evolution of \r{ho}(T) is observed. The nontrivial topology is proved to persists before the structural phase transition observed in the high-pressure regime. We find that the bulk and surface states respond differently to pressure, which is consistent with the non-monotonic change of the resistivity. Interestingly, a pressure-induced amorphous state is observed in MnBi2Te4, while two high pressure phase transitions are revealed in MnBi4Te7. Our combined theoretical and experimental research establishes MnBi2Te4 and MnBi4Te7 as highly tunable magnetic topological insulators, in which phase transitions and new ground states emerge upon compression.

cond-mat.supr-con↗

arXiv2020

Higher-Order Topological Crystalline Insulating Phase and Quantized Hinge Charge in Topological Electride Apatite

In higher-order topological insulators, bulk and surface electronic states are gapped, while there appear gapless hinge states protected by spatial symmetry. Here we show by ab initio calculations that the La apatite electride is a higher-order topological crystalline insulator. It is a one-dimensional electride, in which the one-dimensional interstitial hollows along the $c$ axis support anionic electrons, and the electronic states in these one-dimensional channels are well approximated by the one-dimensional Su-Schrieffer-Heeger model. When the crystal is cleaved into a hexagonal prism, the 120$^\circ$ hinges support gapless hinge states, with their filling quantized to be 2/3. This quantization of the filling comes from a topological origin. We find that the quantized value of the filling depends on the fundamental blocks that constitute the crystal. The apatite consists of the triangular blocks, which is crucial for giving nontrivial fractional charge at the hinge.

cond-mat.mtrl-sci↗

arXiv2020

Phonon scattering limited mobility in the representative cubic perovskite semiconductors SrGeO$_3$, BaSnO$_3$ and SrTiO$_3$

Cubic perovskite oxides are emerging high-mobility transparent conducting oxides (TCOs), but Ge-based TCOs had not been known until the discovery of metastable cubic SrGeO$_3$. $0.5 \times 0.4 \times 0.2$-mm$^3$ large single crystals of the cubic SrGeO$_3$ perovskite were successfully synthesized employing the high-pressure flux method. The phonon spectrum is determined from the IR optical reflectance and Raman-scattering analysis to evaluate the electron transport governed by optical phonon scattering. A calculated room-temperature mobility on the order of $3.9 \times 10^2$ cm$^2$V$^{-1}$s$^{-1}$ is obtained, identifying cubic SrGeO$_3$ as one of the most promising TCOs. Employing classical phonon theory and a combined experimental-theoretical approach, a comprehensive analysis of the intrinsic electron mobility in the cubic perovskite semiconductors SrGeO$_3$, BaSnO$_3$, and SrTiO$_3$ is provided based on the magnitude of polarization and eigenfrequency of optically active phonons.

cond-mat.mtrl-sci↗

arXiv2020

Heavily Hydride-ion-doped 1111-type Iron-based Superconductors: Synthesis, Physical Properties and Electronic Structure

Iron-based superconductors have grown to be a new continent of high Tc superconductors comparable to cuprates. The optimal critical temperature (Tc) of 56 K in electron-doped 1111-type iron oxypnictides attracts considerable attention of physicists and chemists. Carrier doping is not only essential to induce superconductivity but also is a critical parameter that governs the electronic, magnetic, and crystallographic properties of ground states in high-Tc superconductors. Hydride ion (H-) which is an anionic state of hydrogen acts as an efficient electron donor in the 1111-type, leading to several important discoveries such as two-dome structure of superconducting phase and bipartite parent phase. This article summarizes the synthesis, physical properties, and electronic structure of the H- bearing 1111-type iron-based superconductors along with the relevant phenomena of other superconductors. We show several common characteristics of iron-based superconductors with high-Tc over 50 K and suggest a way to achieve higher Tc.

cond-mat.supr-con↗

arXiv2019

Negative-hydrogen-ion production from a nanoporous 12CaO $\cdot$ 7Al2O3 (C12A7) electride surface

A high production rate of negative hydrogen ion was observed from a nanoporous C12A7 electride surface immersed in hydrogen/deuterium low-pressure plasmas. The target was biased at 10-170 V negatively and the target surface was bombarded by H3 + ions from the plasma. The production rate was 1-2 orders higher than a clean molybdenum surface. The measured H-energy spectrum indicates that the major production mechanism is desorption by sputtering. This material has potential to be used as production surface of cesium-free negative ion sources for accelerators, heating beams in nuclear fusion, and surface modification for industrial applications.

physics.plasm-ph↗

arXiv2019

Natural van der Waals heterostructural single crystals with both magnetic and topological properties

Heterostructures having both magnetism and topology are promising materials for the realization of exotic topological quantum states while challenging in synthesis and engineering. Here, we report natural magnetic van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n that exhibit controllable magnetic properties while maintaining their topological surface states. The interlayer antiferromagnetic exchange coupling is gradually weakened as the separation of magnetic layers increases, and an anomalous Hall effect that is well coupled with magnetization and shows ferromagnetic hysteresis was observed below 5 K. The obtained homogeneous heterostructure with atomically sharp interface and intrinsic magnetic properties will be an ideal platform for studying the quantum anomalous Hall effect, axion insulator states, and the topological magnetoelectric effect.

cond-mat.mtrl-sci↗

arXiv2019

Topological semimetal phases manifested in transition metal dichalcogenides intercalated with 3d metals

In the search for stable topological semimetals with clean band profiles, we have screened all the 3$d$ metal-intercalated transition-metal dichalcogenides (3dI-TMDCs) by performing hybrid-functional-based ab initio calculations. Two classes of topological materials featuring twelve Weyl nodes in the $k_z=0$ plane (without spin-orbit interactions) are identified: (a) time-reversal-breaking Weyl semimetals VT$_3$X$_6$ (ferromagnetic) and (b) spinless Weyl semimetals MnT$_3$X$_6$ (nonmagnetic), where T=Nb, Ta; X=S, Se. VNb$_3$S$_6$, prototypical of class (a), is half-metallic with only two bands crossing at the Fermi level to form Weyl nodes. MnNb$_3$S$_6$ in the nonmagnetic phase is essentially a spinless version of VNb$_3$S$_6$ featuring an equally clean and simple band profile. Although the space group symmetry (P6$_3$22) implies that the degeneracy between the two bands is lifted for $k$ away from the Weyl nodes, the gap remains extremely small ($\ll$ 0.1 meV) along a loop connecting the Weyl nodes. This quasi-nodal-line degeneracy is explained in terms of the quasi-mirror symmetry of the lattice, induced by the in-plane twofold rotation axes, and the specific orbital nature of the bands. 3dI-TMDCs are chemically and thermally stable stoichiometric compounds containing no toxic elements and are a viable platform for the study of topological condensed-matter physics.

cond-mat.str-el↗

arXiv2019

Superconductivity at 48 K of heavily hydrogen-doped SmFeAsO epitaxial films grown by topotactic chemical reaction using CaH2

High-critical-temperature (Tc) superconductivity at 48 K is reported for hydrogen-doped SmFeAsO epitaxial films on MgO single-crystal substrates. The key processes are pulsed laser deposition to grow undoped SmFeAsO epitaxial films and subsequent topotactic chemical reaction using CaH2 powders under evacuated silica-glass ampule atmosphere. Based on this post-deposition thermal annealing treatment that we have developed, a maximum hydrogen concentration x = ~0.35 was realized in SmFeAs(O1-xHx). Disordered hydrogen-substitution at O sites is experimentally confirmed directly by atomic-scale microstructural observations. Magnetization measurement validates the bulk nature of the high-Tc superconductivity in the films. This method will become an effective and general method to fabricate various high-quality oxyhydride epitaxial films.

cond-mat.supr-con↗

arXiv2019

Heteroepitaxial Thin-Film Growth of a Ternary Nitride Semiconductor CaZn2N2

Zinc-based nitride CaZn2N2 films grown by molecular beam epitaxy (MBE) with a plasma-assisted active nitrogen-radical source are promising candidates of next-generation semiconductors for light-emitting diodes and solar cells. This nitride compound has previously only been synthesized in a bulk form by ultrahigh-pressure synthesis at 5 GPa. Three key factors have been found to enable heteroepitaxial film growth: (i) precise tuning of the individual flux rates of Ca and Zn, (ii) the use of GaN template layers on sapphire c-plane as substrates, and (iii) the application of MBE with an active N-radical source. Because other attempts at physical vapor deposition and thermal annealing processes have not produced CaZn2N2 films of any phase, this rf-plasma-assisted MBE technique represents a promising way to stabilize CaZn2N2 epitaxial films. The estimated optical band gap is ~1.9 eV, which is consistent with the value obtained from bulk samples. By unintentional carrier doping, n- and p-type electronic conductions are attained with low carrier densities of the order of 1013 /cm3. These features represent clear advantages when compared with Zn-based oxide semiconductors, which usually have much higher carrier densities irrespective of their intentionally undoped state. The carrier mobilities at room temperature are 4.3 cm2/(Vs) for electrons and 0.3 cm2/(Vs) for hole carriers, which indicates that transport properties are limited by grain boundary scattering, mainly because of the low-temperature growth at 250 °C, which realizes a high nitrogen chemical potential.

cond-mat.mtrl-sci↗

arXiv2019

Quantum dynamics of hydrogen in iron-based superconductor LaFeAsO0.9D0.1 measured with inelastic neutron spectroscopy

Inelastic neutron scattering was performed for an iron-based superconductor LaFeAsO0.9D0.1, where most of D (deuterium) replaces oxygen, while a tiny amount goes into interstitial sites. By first-principle calculation, we characterize the interstitial sites for D (and for H slightly mixed) with four equivalent potential minima. Below the superconducting transition temperature Tc = 26 K,new excitations emerge in the range 5-15 meV, while they are absent in the reference system LaFeAsO0.9F0.1. The strong excitations at 14.5 meV and 11.1 meV broaden rapidly around 15 K and 20 K, respectively, where each energy becomes comparable to twice of the superconducting gap. The strong excitations are ascribed to a quantum rattling, or a band motion of hydrogen, which arises only if the number of potential minima is larger than two.

cond-mat.supr-con↗

arXiv2019

Near-room-temperature giant topological Hall effect in antiferromagnetic kagome metal YMn6Sn6

The kagome lattice, consisting of interconnected triangles and hexagons uniquely, is an excellent model system for study frustrated magnetism, electronic correlation and topological electronic structure. After an intensive investigation on frustrated magnetism in insulating magnetic kagome lattices, the interplay between charge and spin degrees of freedom via spin-orbital coupling in metallic systems (kagome metals) has become an attractive topic recently. Here, we study centrosymmetric YMn6Sn6 with Mn kagome lattice. We discover that it exhibits giant topological Hall effect near room temperature, ascribed to the field-induced non-collinear spin texture, possibly a skyrmion lattice (SkL) state. Combined with the large intrinsic anomalous Hall effect, YMn6Sn6 shows a synergic effect of real- and momentum-space Berry phase on physical properties. Since the features of tunable magnetic interaction and flexible structure in this large homologous series, it provides a novel platform for understanding the influence of electronic correlations on topological quantum states in both real and momentum spaces.

cond-mat.str-el↗

arXiv2019

Pressure-induced quantum critical point in a heavily hydrogen-doped iron-based superconductor LaFeAsO

An iron-based superconductor LaFeAsO$_{1-x}$H$_x$ (0 $\leq x \leq$ 0.6) undergoes two antiferromagnetic (AF) phases upon H doping. We investigated the second AF phase ($x$=0.6) using NMR techniques under pressure. At pressures up to 2 GPa, the ground state is a spin-density-wave state with a large gap; however, the gap closes at 4.0 GPa, suggesting a pressure-induced quantum critical point. Interestingly, the gapped excitation coexists with gapless magnetic fluctuations at pressures between 2 and 4 GPa. This coexistence is attributable to the lift up of the $d_{xy}$ orbital to the Fermi level, a Lifshitz transition under pressure.

cond-mat.supr-con↗

arXiv2019

Stabilization and heteroepitaxial growth of metastable tetragonal FeS thin films by pulsed laser deposition

Pulsed laser deposition, a non-equilibrium thin-film growth technique, was used to stabilize metastable tetragonal iron sulfide (FeS), the bulk state of which is known as a superconductor with a critical temperature of 4 K. Comprehensive experiments revealed four important factors to stabilize tetragonal FeS epitaxial thin films: (i) an optimum growth temperature of 300 °C followed by thermal quenching, (ii) an optimum growth rate of ~7 nm/min, (iii) use of a high-purity bulk target, and (iv) use of a single-crystal substrate with small in-plane lattice mismatch (CaF2). Electrical resistivity measurements indicated that none of all the films exhibited superconductivity. Although an electric double-layer transistor structure was fabricated using the tetragonal FeS epitaxial film as a channel layer to achieve high-density carrier doping, no phase transition was observed. Possible reasons for the lack of superconductivity include lattice strain, off-stoichiometry of the film, electrochemical etching by the ionic liquid under gate bias, and surface degradation during device fabrication.

cond-mat.mtrl-sci↗