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The stacking fault formation during physical vapor transport growth of heavily nitrogen-doped (mid-10 19 cm -3 ) 4H-SiC crystals was investigated. Low-voltage scanning electron microscopy (LVSEM) observations detected the stacking fault formation on the (000-1) facet of heavily nitrogen-doped 4H-SiC crystals. Stacking faults showed characteristic morphologies, and atomic force microscopy (AFM) studies revealed that these morphologies of stacking faults stemmed from the interaction between surface steps and stacking faults. Based on these results, the stacking fault formation mechanism in heavily nitrogen-doped 4H-SiC crystals is discussed.

Basal plane bending and stress distribution in physical vapor transport-grown n-type 4H-SiC crystals were investigated. High resolution X-ray diffraction measurements were performed on commercially available 3-inch-diameter 4H-SiC substrates and along the growth front surface of as-grown 1-inch-diameter 4H-SiC boules. The measurements revealed that structural parameters such as the c-lattice constant, basal plane tilting, and FWHM showed characteristic variations across the substrates and as-gown boules, indicating that the crystals had a non-uniform distribution of dislocations comprising domain structures. Residual stress measured by micro Raman spectroscopy showed a similar behavior, which was an oscillatory spatial variation. On the basis of these results, defect structures in the crystals are elucidated.

Titanium dioxide is one of the most popular compounds among simple oxides. Except for the fully oxidized titanate, titanium oxides have partially filled d states and their exotic properties have captured attention. Here, we report on the discovery of superconductivity in Ti 4 O 7 and γ- Ti 3 O 5 in a thin film form. The epitaxial Ti 4 O 7 and γ- Ti 3 O 5 thin films were grown using pulsed-laser deposition on (LaAlO 3 ) 0.3 –(SrAl 0.5 Ta 0.5 O 3 ) 0.7 and α -Al 2 O 3 substrates, respectively. The highest superconducting transition temperatures are 3.0 K and 7.1 K for Ti 4 O 7 and γ- Ti 3 O 5 , respectively. The mechanism behind the superconductivity is discussed on the basis of electrical measurements and previous theoretical predictions. We conclude that the superconductivity arises from unstabilized bipolaronic insulating states with the assistance of oxygen non-stoichiometry and epitaxial stabilization.

Transition metal oxides display various electronic and magnetic phases such as high-temperature superconductivity. Controlling such exotic properties by applying an external field is one of the biggest continuous challenges in condensed matter physics. Here, we demonstrate clear superconductor-insulator transition of LiTi 2 O 4 films induced by Li-ion electrochemical reaction. A compact electrochemical cell of pseudo-Li-ion battery structure is formed with a superconducting LiTi 2 O 4 film as an anode. Li content in the film is controlled by applying a constant redox voltage. An insulating state is achieved by Li-ion intercalation to the superconducting film by applying reduction potential. In contrast, the superconducting state is reproduced by applying oxidation potential to the Li-ion intercalated film. Moreover, superconducting transition temperature is also recovered after a number of cycles of Li-ion electrochemical reactions. This complete reversible transition originates in difference in potentials required for deintercalation of initially contained and electrochemically intercalated Li + ions.

The early-stage pathologies of frontotemporal lobal degeneration (FTLD) remain largely unknown. In VCP T262A -KI mice carrying VCP gene mutation linked to FTLD, insufficient DNA damage repair in neural stem/progenitor cells (NSCs) activated DNA-PK and CDK1 that disabled MCM3 essential for the G1/S cell cycle transition. Abnormal neural exit produced neurons carrying over unrepaired DNA damage and induced early-stage transcriptional repression-induced atypical cell death (TRIAD) necrosis accompanied by the specific markers pSer46-MARCKS and YAP. In utero gene therapy expressing normal VCP or non-phosphorylated mutant MCM3 rescued DNA damage, neuronal necrosis, cognitive function, and TDP43 aggregation in adult neurons of VCP T262A -KI mice, whereas similar therapy in adulthood was less effective. The similar early-stage neuronal necrosis was detected in PGRN R504X -KI, CHMP2B Q165X -KI, and TDP N267S -KI mice, and blocked by embryonic treatment with AAV–non-phospho-MCM3. Moreover, YAP-dependent necrosis occurred in neurons of human FTLD patients, and consistently pSer46-MARCKS was increased in cerebrospinal fluid (CSF) and serum of these patients. Collectively, developmental stress followed by early-stage neuronal necrosis is a potential target for therapeutics and one of the earliest general biomarkers for FTLD.

The emergence of superconductivity with strong correlation is one of the most attracted issues in condensed-matter physics, as seen in various unconventional superconductors. Here we show a new strongly correlated superconductor Li1-xNbO2 with rich characteristics such as two-dimensional, geometrically frustrated, and triangular NbO2 lattice and correlated flat-band-like electronic states. We revealed the electronic phase diagram by implementing Li-ion electrochemical cells with LiNbO2 epitaxial films. The Li-ion deintercalation increased the hole-doping level in NbO2 layer, along which a band insulator LiNbO2 underwent to a Fermi-liquid (FL) metal and superconductor associated with non-Fermi liquid (NFL) characters. The evolution of the NFL state coincided with the suppression of the Kondo-singlet formation near the superconducting dome, which linked superconductivity with quantum criticality. The obtained phase diagram involves general aspects of strongly correlated superconductors and bridges the gap between various systems.

We investigated systematic evolutions of structural and electronic properties of LixWO3 films, induced by Li-ion electrochemical reactions. Chronoamperometric Li-ion intercalation could control the amount of Li content up to x ~ 0.5. The resistivity abruptly decreased with increasing x and the films underwent an insulator to metal transition (IMT) within a range of 0.2 < x < 0.24, which was consistent with IMT of cubic NaxWO3. The X-ray diffraction analyses revealed the coexistence of tetragonal and cubic phases across IMT, suggesting that the alkaline-ion content was a primary factor for metallic conductivity in the ReO3-type WO3 system.

We report epitaxial synthesis of superconducting CsxWO3 (x = 0.11, 0.20, 0.31) films on Y-stabilized ZrO2 (111) substrates. The hexagonal crystal structure was verified not only for composition within the stable region of bulk (x = 0.20, 0.31), but also for the out-of-range composition (x = 0.11). The onset of superconducting transition temperature (TC) was recorded 5.8 K for x = 0.11. We found strong correlation between TC and c-axis length, irrespective of the Cs content. The results indicate that hidden superconducting phase region of hexagonal tungsten bronze is accessible by using epitaxial synthesis of lightly doped films.

In CsW2O6, which undergoes a metal-insulator transition (MIT) at 213 K, the emergence of exotic properties associated with rattling motion of Cs is expected owing to its characteristic \\beta-pyrochlore-type structure. However, a hurdle for crystal growth hampers elucidation of detailed properties and mechanisms of the MIT. Here we report on the epitaxial growth of \\beta-pyrochlore-type CsW2O6 films and their electronic properties across the MIT. Using pulsed-laser deposi-tion technique, we grew single-crystalline CsW2O6 films exhibiting remarkably lower resistivity compared with a poly-crystalline bulk and sharp MIT around 200 K. Negative magnetoresistance and positive Hall coefficient were found, which became pronounced below 200 K. The valence-band and core-levels photoemission spectra indicated the drastic changes across the MIT. In the valence band photoemission spectrum, the finite density of states was observed at the Fermi level in the metallic phase. In contrast, an energy gap appeared in the insulating phase. The split of W 4f core-level spectrum suggested the charge disproportionation of W5+ and W6+ in the insulating phase. The change of spectral shape in the Cs 4d core levels reflected the rattling motion of Cs+ cations. These results strongly suggest that CsW2O6 is a novel material, in which MIT is driven by the charge disproportionation associated with the rattling motion.