•La-doped SrTiO3/TiO2 eutectic crystals were grown by a micro-pulling-down method.•Grown crystals were composed of the TiO2 rod phase in the SrTiO3 matrix phase.•Diameter of TiO2 rods systematically ...decreased as the growth rate was increased.•Grown crystal exhibited a lower thermal conductivity than the SrTiO3 single crystal.•ZTs of crystals grown at 0.02 and 0.5 mm/min were 0.015 and 0.025, respectively.
La-doped SrTiO3/TiO2 (La:STO/TO) eutectic crystals were grown by a micro-pulling-down method at various growth rates to control the eutectic morphology and thermoelectric properties. The La:STO/TO eutectic crystals were composed of a TiO2 (TO) rod phase in the SrTiO3 (STO) matrix phase for all growth rates. The diameter of the TO rod phase systematically decreased as the growth rate was increased, according to the Jackson–Hunt model, and the diameter reached approximately 1 μm at a growth rate of 1 mm/min. The La:STO/TO eutectic crystal exhibited a lower thermal conductivity than the Nb:STO single crystal, owing to the decrease in the lattice thermal conductivity by phonon scattering at boundaries in the eutectic morphology. The figures of merit, ZTs, of the La:STO/TO eutectic crystals grown at 0.02 and 0.5 mm/min growth rates were 0.015 and 0.025, respectively. The faster growth rate led to an increased ZT, owing to the decrease in electrical resistivity.
We fabricated (Ba,Na)Fe2As2 superconducting wires using the powder-in-tube method and hot isostatic pressing. By improving powder synthesis processes compared with previous studies, highly pure raw ...materials for the wire fabrication were obtained. The largest transport critical current density (Jc) reached 40 kA cm−2 at T = 4.2 K under a magnetic field of 100 kOe. This value exceeds not only the value of transport Jc of the previous (Ba,Na)Fe2As2 wire but also those of all iron-based superconducting round wires. Improvements of polycrystalline powder synthesis play a key role for the enhancement of Jc. Furthermore, it was clarified that higher densification by high-pressure sintering and the texturing of grains in the core of the wire due to drawing also increased Jc effectively. Advantages of (Ba,Na)Fe2As2 wires compared with (Ba,K)Fe2As2 wires are also discussed.
Obtaining semiconducting properties that meet practical standards for p-type transparent oxide semiconductors is challenging due to the balance between the defects that generate hole and electron ...carriers. Here, we demonstrate that modulating the individual thermodynamic and kinetic conditions during the growth of p-type oxide SnO films is beneficial in tailoring their semiconducting properties. By tuning the growth temperature and laser fluence for pulsed laser deposition, the hole carrier density dramatically changes from approximately 4 × 1016 to 6 × 1018 cm–3 at room temperature. The room-temperature hole mobility (μ) strongly depends on the carrier density (n), and their relationship is like a “volcano-shaped” curve. This suggests the competition between several scattering sources, such as the ionized impurity scattering (μ ∝ n –1), and grain boundary and/or dislocation scattering (μ ∝ n 0.5) for higher and lower n, respectively. The hole mobility is enhanced to approximately 21 cm2 V–1 s–1 at room temperature, which is the highest recorded for SnO films to date. These findings provide important guidelines for designing all-oxide transparent electronic devices.
Stannous oxide, SnO, is a promising material for practical applications as a p-type transparent oxide semiconductor. However, in its thin-film form, the reported semiconducting properties of SnO are ...unfortunately insufficient for the development of oxide devices. In this work, we report that the hole mobility of SnO epitaxial films grown by pulsed laser deposition can be improved by reducing the growth temperature. The hole mobility is estimated to be approximately 10 cm
2
V
−1
s
−1
at room temperature, which is nearly four times higher than the one originally reported for epitaxial films fabricated at the conventional growth temperature. In addition, the observed carrier density of the fabricated SnO films is slightly lower compared with that of the ones fabricated at the conventional growth temperature. This suggests that the Sn vacancy formation as a hole carrier dopant is suppressed by the reduction in the growth temperature. This result offers the key for the improvement of the performance of oxide thin-film devices.
Stannous oxide, SnO, is a promising material for practical applications as a p-type transparent oxide semiconductor. The hole mobility of SnO epitaxial films grown by pulsed laser deposition can be improved by reducing the growth temperature.
A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials, such as the cuprate high-temperature superconductors. Because of its ...unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates, where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping- and temperature-dependence ARPES study of spectral gaps in Bi ₂Sr ₂CaCu ₂O ₈₊δ, covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p = 0.19 for the pseudogap phase and p = 0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below T c and exists p > 0.19 at higher temperatures. Our data imply a revised phase diagram that reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome.
(La0.5–x Na0.5+x )Fe2As2 ((La,Na)122) is an interesting system in the sense that either electrons (x < 0) or holes (x > 0) can be doped into the Fe2As2 layers, simply by changing the composition ...value x. However, only nonbulk superconducting samples (single crystals) with x = 0.1 have been synthesized to date. Here, we successfully synthesize polycrystalline samples with a wide hole-doping composition range of 0 ≤ x ≤ 0.35 via a conventional solid-state reaction, by tuning the reaction temperature according to x. The parent compound, (La0.5Na0.5)Fe2As2 (x = 0), is a nonsuperconductor with a resistivity anomaly at 130 K due to structural and antiferromagnetic transitions. We find that the temperature of the resistivity anomaly decreases with increasing x and that bulk superconductivity emerges for 0.15 ≤ x ≤ 0.35. The maximum transition temperature is 27.0 K, for x = 0.3. An electronic phase diagram for the hole-doping side is constructed. However, electron-doped samples (x < 0) cannot be synthesized; thus, the other half of the electronic phase diagram of (La,Na)122 requires resolution to study the electron–hole symmetry in Fe-based superconductors.
Aiming to introduce NbTi alloy superconducting joints for REBa
Cu
O
(REBCO, RE: rare-earth element) superconducting wires, NbTi alloy thin films were deposited at room temperature on SrTiO
(STO) ...(001) single-crystal substrates, which have a high lattice matching with REBCO (001). The strain, crystallinity, surface morphology, and superconducting property of the films with various thicknesses were investigated. The NbTi films grew in the orientation with (110)NbTi//(001)STO:001NbTi and 11-0 NbTi//100STO; that is, the NbTi lattices had two directions in the (110) of NbTi. The strain decreased and the crystallinity improved as the film thickness increased. The films were found to crystallize immediately at the interface between the films and substrates by cross-sectional scanning transmission electron microscopy. The flat surfaces of the films have mesh-like morphologies due to the growth of elongated NbTi grains along the 100 and 010 of the STO, reflecting the in-plane two directions of the NbTi lattices. The superconducting transition temperature of the films increased with improvement in the crystallinity of the films. The preparation of superconducting NbTi alloy thin films with sufficient crystallinity at room temperature suggested the possibility of forming the films on REBCO and the applicability of the films as superconducting joints.
In the recently discovered antiperovskite phosphide (Ca,Sr)Pd3P, centrosymmetric (CS) and non-centrosymmetric (NCS) superconducting phases appear depending on the Sr concentration, and their ...transition temperatures (Tc) differ by as much as one order of magnitude. In this study, we investigated the superconducting properties and electronic band structures of CS orthorhombic (CSo) (Ca0.6Sr0.4)Pd3P (Tc = 3.5 K) and NCS tetragonal (NCSt) (Ca0.25Sr0.75)Pd3P (Tc = 0.32 K) samples with a focus on explaining their large Tc difference. Specific heat measurements indicated that CSo (Ca0.6Sr0.4)Pd3P was an s-wave superconductor in a moderate-coupling regime with a 2Δ0/kBTc value of 4.0. Low-lying phonons leading to the strong coupling in the structurally analogous SrPt3P were unlikely to be present in CSo (Ca0.6Sr0.4)Pd3P. Given that CSo (Ca0.6Sr0.4)Pd3P and NCSt (Ca0.25Sr0.75)Pd3P exhibited similar Debye temperatures (ΘD) of approximately 200 K, the large Tc difference could not be attributed to ΘD. Tc of each phase was accurately reproduced based on the Bardeen–Cooper–Schrieffer (BCS) theory using experimental data and the density of states of the Fermi level N(0) calculated from their band structures. We concluded that the considerable suppression of Tc in NCSt (Ca0.25Sr0.75)Pd3P can be primarily attributed to the decrease in N(0) associated with the structural phase transition without considering the lack of inversion symmetry.
•Superconducting parameters have been clarified for centrosymmetric and non-centrosymmetric phases emerging in antiperovskite (Ca,Sr)Pd3P.•Centrosymmetric CSo (Ca,Sr)Pd3P is an s-wave superconductor in a moderate-coupling regime, in contrast to the analogous strong-coupling superconductor SrPt3P.•The weaker electron-phonon coupling in centrosymmetric (Ca,Sr)Pd3P compared to SrPt3P can be attributed to the absence of low-lying phonons.•The different Tc of both phases is accurately reproduced based on the BCS theory using experimentally and theoretically obtained parameters.
In this study, we succeeded in synthesizing new antiperovskite phosphides MPd3P (M = Ca, Sr, Ba) and discovered the appearance of a superconducting phase (0.17 ≤ x ≤ 0.55) in a solid solution (Ca1–x ...Sr x )Pd3P. Three perovskite-related crystal structures were identified in (Ca1–x Sr x )Pd3P, and a phase diagram was built on the basis of experimental results. The first phase transition from centrosymmetric (Pnma) to noncentrosymmetric orthorhombic (Aba2) occurred in CaPd3P near room temperature. The phase transition temperature decreased as Ca2+ was replaced with a larger-sized isovalent Sr2+. Bulk superconductivity at a critical temperature (T c) of approximately 3.5 K was observed in a range of x = 0.17–0.55; this was associated with the centrosymmetric orthorhombic phase. Thereafter, a noncentrosymmetric tetragonal phase (I41 md) remained stable for 0.6 ≤ x ≤ 1.0, and superconductivity was significantly suppressed as samples with x = 0.75 and 1.0 showed T c values as low as 0.32 K and 57 mK, respectively. For further substitution with a larger-sized isovalent Ba2+, namely, (Sr1–y Ba y )Pd3P, the tetragonal phase continued throughout the composition range. BaPd3P no longer showed superconductivity down to 20 mK. Since the inversion symmetry of structure and superconductivity can be precisely controlled in (Ca1–x Sr x )Pd3P, this material may offer a unique opportunity to study the relationship between inversion symmetry and superconductivity.
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