arXiv subjects

Hiromi Tanaka

Publications and source records attributed to Hiromi Tanaka.

17 recordsLinked to original sources

arXiv2022

Tower-Complete Problems in Contraction-Free Substructural Logics

We investigate the non-elementary computational complexity of a family of substructural logics without contraction. With the aid of the technique pioneered by Lazić and Schmitz (2015), we show that the deducibility problem for full Lambek calculus with exchange and weakening ($\mathbf{FL}_{\mathbf{ew}}$) is not in Elementary (i.e., the class of decision problems that can be decided in time bounded by an elementary recursive function), but is in PR (i.e., the class of decision problems that can be decided in time bounded by a primitive recursive function). More precisely, we show that this problem is complete for Tower, which is a non-elementary complexity class forming a part of the fast-growing complexity hierarchy introduced by Schmitz (2016). The same complexity result holds even for deducibility in BCK-logic, i.e., the implicational fragment of $\mathbf{FL}_{\mathbf{ew}}$. We furthermore show the Tower-completeness of the provability problem for elementary affine logic, which was proved to be decidable by Dal Lago and Martini (2004).

math.LO↗

arXiv2021

Pressure-induced superconductivity in TiGeTe$_{6}$

Layered ternary transition-metal chalcogenides have been focused as a vein of exploration for superconductors. In this study, TiGeTe$_{6}$ single crystals were synthesized and characterized by structural and valence state analyses and electrical transport measurements. The transport properties were measured under various pressures up to 71 GPa. The activation energy gets smaller as the applied pressure increases, and a signature of a pressure-induced metallization was observed under around 8.4 GPa. Under 13 GPa, pressure-induced superconductivity was discovered in this compound for the first time, with successive drops at 3 K and 6 K in the resistance, indicating the presence of multiple superconducting transitions. The superconducting transition temperature kept increasing as we further applied the pressure to the TiGeTe$_{6}$ single crystal in the performed pressure range, reaching as high as 8.1 K under 71 GPa.

cond-mat.supr-con↗

arXiv2020

Pressure-Induced Superconductivity in Layered Transition-metal Chalcogenides (Zr,Hf)GeTe$_{4}$ Explored by Data-driven Approach

Layered transition-metal chalcogenides (Zr,Hf)GeTe$_{4}$ were screened out from database of Atomwork as a candidate for pressure-induced superconductivity due to their narrow band gap and high density of state near the Fermi level. The (Zr,Hf)GeTe$_{4}$ samples were synthesized in single crystal and then the compositional ratio, crystal structures, and valence states were investigated via energy dispersive spectrometry, single crystal X-ray diffraction, and X-ray photoelectron spectroscopy, respectively. The pressure-induced superconductivity in both crystals were first time reported by using a diamond anvil cell with a boron-doped diamond electrode and an undoped diamond insulating layer. The maximum superconducting transition temperatures of ZrGeTe$_{4}$ and HfGeTe$_{4}$ were 6.5 K under 57 GPa and 6.6 K under 60 GPa, respectively.

cond-mat.supr-con↗

arXiv2020

Decision Problems for Propositional Non-associative Linear Logic and Extensions

In our previous work, we proposed the logic obtained from full non-associative Lambek calculus by adding a sort of linear-logical modality. We call this logic non-associative non-commutative intuitionistic linear logic ($\mathbf{NACILL}$, for short). In this paper, we establish the decidability and undecidability results for various extensions of $\mathbf{NACILL}$. Regarding the decidability results, we show that the deducibility problems for several extensions of $\mathbf{NACILL}$ with the rule of left-weakening are decidable. Regarding the undecidability results, we show that the provability problems for all the extensions of non-associative non-commutative classical linear logic by the rules of contraction and exchange are undecidable.

math.LO↗

arXiv2019

Crystal Size Improvement of Bi-based Superconducting Whiskers under Stress-controlled Condition

Using stress-controlled amorphous precursors, we have successfully grown large $Bi_{2}$$Sr_{2}$$Ca_{\textit{n}-1}$$Cu_{\textit{n}}$$O_{\textit{y}}$ (Bi-based) high-transition temperature superconducting whiskers. Especially, under a high compressive stress attained by 1 GPa pelletizing, the crystal size of a whisker was significantly enhanced up to 9.5 mm length (growth period: 96 h) which is 2.4 times larger than that of the conventional amorphous-precursors method. In addition, by using the stress-controlled precursors, the number of the obtained Bi-based whiskers were also increased by a factor of 1.8.

cond-mat.supr-con↗

arXiv2019

Pressure-induced superconductivity in layered pnictogen diselenide NdO$_{0.8}$F$_{0.2}$Sb$_{1-x}$Bi$_x$Se$_2$ (x = 0.3 and 0.7)

Polycrystalline samples of layered pnictogen diselenide NdO0.8F0.2Sb1-xBixSe2 (x = 0 to 0.8) were successfully synthesized by solid-state reactions. Electrical resistivity in the synthesized samples was systematically decreased with an increase in Bi content x. Crystal structure analysis using synchrotron X-ray diffraction suggests that insulator to metal transition upon Bi doping correlates with anomalous change in c-axis length and/or corrugation in conducting layer. The emergence of superconductivity under high pressure is demonstrated using diamond anvil cell (DAC) with boron-doped diamond electrodes, for x = 0.3 and 0.7 as the representative samples. For Sb-rich one (x = 0.3), we observed a superconducting transition with Tconset = 5.3 K at 50 GPa, which is the first-ever report of the superconductivity in layered SbCh2-based (Ch: chalcogen) compounds. The Tconset of x = 0.3 increased with increasing pressure and reached 7.9 K at 70.8 GPa, followed by the gradual decrease in Tc up to 90 GPa. For Bi-rich one (x = 0.7), a superconducting transition with Tconset = 5.9 K was observed at 43.5 GPa, which is the almost comparable to that of x = 0.3; besides, upper critical field (Hc2) is evaluated to be ~10 T for x = 0.7, which is higher than that of x = 0.3 (Hc2 = 6.7 T at 50 GPa).

cond-mat.supr-con↗

arXiv2019

A note on undecidability of propositional non-associative linear logics

We introduce a non-associative and non-commutative version of propositional intuitionistic linear logic, called propositional non-associative non-commutative intuitionistic linear logic (NACILL for short). We prove that NACILL and any of its extensions by the rules of exchange and/or contraction are undecidable. Furthermore, we introduce two types of classical versions of NACILL, i.e., an involutive version of NACILL and a cyclic and involutive version of NACILL. We show that both of these logics are also undecidable.

cs.LO↗

arXiv2019

Crystal Growth of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ Whiskers from Pulverized Amorphous Precursors

High-transition temperature superconducting whiskers of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ were successfully grown from pulverized amorphous precursors. The obtained whiskers revealed a typical composition and diffraction patterns of a superconducting Bi-2212 phase. The whiskers from tiny precursors exhibit a spiral feature, suggesting a contribution from the growth mechanism of both vapor-liquid-solid and compressive stress models. The proposed method provides longer whiskers against the growth period, compared with that from conventional root-growth method.

cond-mat.supr-con↗

arXiv2019

Direct Patterning of Boron-doped Amorphous Carbon Using Focused Ion Beam-assisted Chemical Vapor Deposition

The deposition of boron-doped amorphous carbon thin films on SiO2 substrate was achieved via a focused ion beam-assisted chemical vapor deposition of triphenyl borane (C18H15B) and triphenyl borate (C18H15BO3). The existence of boron in the deposited film from triphenyl borane, with a precursor temperature of 90 °C, was confirmed by a core level X-ray photoelectron spectroscopy analysis. The film exhibited a semiconducting behavior with a band gap of 285 meV. Although the band gap was decreased to 197 meV after an annealing process, the film was still semiconductor. Additionally, a drastic reduction of the resistance on the deposited film by applying pressures was observed from an in-situ electrical transport measurements using a diamond anvil cell.

cond-mat.mtrl-sci↗

arXiv2019

Mask-less Patterning of Gallium-irradiated Superconducting Silicon Using Focused Ion Beam

A direct patterning technique of gallium-irradiated superconducting silicon has been established by focused gallium-ion beam without any mask-based lithography process. The electrical transport measurements for line and square shaped patterns of gallium-irradiated silicon were carried out under self-field and magnetic field up to 7 T. Sharp superconducting transitions were observed in both patterns at temperature of 7 K. The line pattern exhibited a signature of higher onset temperature above 10 K. A critical dose amount to obtain the superconducting gallium-irradiated silicon was investigated by the fabrication of various samples with different doses. This technique can be used as a simple fabrication method for superconducting device.

physics.app-ph↗

arXiv2019

Data-driven Exploration of Pressure-Induced Superconductivity in AgIn$_{5}$Se$_{8}$

Candidates compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by a high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on AgIn$_{5}$Se$_{8}$ which has high density of state near the Fermi level. AgIn$_{5}$Se$_{8}$ was successfully synthesized as single crystals using a melt and slow cooling method. The single-crystal X-ray diffraction analysis revealed the obtained crystal is high quality without deficiencies. The valence states in AgIn$_{5}$Se$_{8}$ were determined to be Ag1+, In3+ and Se2- in accordance with a formal charge by the core level X-ray photoelectron spectroscopy analysis. The electrical resistance was evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. Although the sample was insulator with a resistance of above 40 MΩ at ambient pressure, the resistance markedly decreased with increase of the pressure, and a pressure-induced superconducting transition was discovered at 3.4 K under 52.5 GPa. The transition temperature increased up to 3.7 K under further pressure of 74.0 GPa.

cond-mat.supr-con↗

arXiv2019

Pressure-induced Superconductivity in Tin Sulfide

Tin sulfide (SnS) was successfully synthesized in single crystals by a melt and slow-cooling method. The obtained sample was characterized by an X-ray diffraction, an energy dispersive spectrometry, and an X-ray photoelectron spectroscopy. Electrical transport properties in SnS were investigated under high pressure using a diamond anvil cell with boron-doped metallic diamond electrodes and undoped diamond insulating layer. We successfully observed an insulator to metal transition from 12.5 GPa and pressure-induced superconductivity at 5.8 K under 47.8 GPa as predicted by a theoretical calculation.

cond-mat.supr-con↗

arXiv2018

Pressure-induced Insulator to Metal Transition of Mixed Valence Compound Ce(O,F)SbS$_{2}$

Transport properties of Ce$_{0.85}$F0.15SbS$_{2}$ and undoped CeOSbS$_{2}$ under high pressure were investigated experimentally and theoretically. Electrical resistivity measurements of the Ce$_{0.85}$F0.15SbS$_{2}$ single crystals were performed under various high pressures using a diamond anvil cell with boron-doped diamond electrodes. The samples showed the insulator to metal transition by applying high pressure up to 30-40 GPa. On the other hand, the undoped CeOSbS$_{2}$ showed almost same transport property with the F-doped sample under high pressure. The valence state analysis using X-ray photoelectron spectroscopy revealed a simple valence state of Ce3+ in Ce$_{0.85}$F0.15SbS$_{2}$ and mixed valence state between Ce3+ and Ce4+ in undoped CeOSbS$_{2}$. The valence fluctuation in Ce carried out the comparable transport nature in the both samples. A band calculation suggests that the undoped CeOSbS$_{2}$ could be metallic under high pressure of 30 GPa in accordance with the experimental results. A superior thermoelectric property of power factor in CeOSbS$_{2}$ was estimated under high pressure around 20 GPa in comparison with that of ambient pressure.

cond-mat.mtrl-sci↗

arXiv2018

Data-driven Exploration of New Pressure-induced Superconductivity in PbBi$_2$Te$_4$ with Two Transition Temperatures

Candidates compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by the high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on PbBi$_2$Te$_4$ which has the similar electronic band structure and the same crystal structure with those of a pressure-induced superconductor SnBi2Se4 explored by the same data-driven approach. The PbBi$_2$Te$_4$ was successfully synthesized as single crystals using a melt and slow cooling method. The core level X-ray photoelectron spectroscopy analysis revealed Pb2+, Bi3+ and Te2- valence states in PbBi$_2$Te$_4$. The thermoelectric properties of the PbBi$_2$Te$_4$ sample were measured at ambient pressure and the electrical resistivity was also evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. The resistivity decreased with increase of the pressure, and two pressure-induced superconducting transitions were discovered at 3.4 K under 13.3 GPa and at 8.4 K under 21.7 GPa. The data-driven approach shows promising power to accelerate the discovery of new thermoelectric and superconducting materials.

cond-mat.supr-con↗

arXiv2018

Pressure-induced Superconductivity in Sulfur-doped SnSe Single Crystal Using Boron-doped Diamond Electrode-prefabricated Diamond Anvil Cell

Sulfur-doped SnSe single crystal was successfully synthesized using a melt and slow-cooling method. The chemical composition and valence state of the obtained sample were analyzed by X-ray photoelectron spectroscopy. The pressure range of a diamond anvil cell with boron-doped diamond electrodes was upgraded to 104 GPa using nano-polycrystalline diamond anvil to investigate a pressure effect for the sample. Electrical resistivity measurements of sulfur-doped SnSe single crystal showed the insulator-metal-superconductor transition by applying high pressure up to 75.9 GPa.

cond-mat.supr-con↗

arXiv2017

Electronic Transport Properties of Carrier Controlled SnSe Single Crystals

We found that the electronic transport property of SnSe single crystals was sensitive to oxygen content. Semiconducting SnSe single crystals were obtained by using Sn of grain form as a starting material while powder Sn resulted in metallic SnSe. X-ray photoelectron spectroscopy analysis revealed that the surfaces of raw Sn were oxidized, where the volume fraction was relatively low in grain Sn. This demonstrates that contamination of oxygen causes metallic behavior in grown SnSe single crystals.

cond-mat.mtrl-sci↗

arXiv2017

Superconductivity and its Enhancement under High Pressure in "F-free" Single Crystals of CeOBiS$_2$

"F-free" CeOBiS$_2$ single crystals have successfully grown, thoroughly eliminating a concern about F-contamination by using a high-purity CsCl flux. The obtained crystals have a plate-like shape with a size of 1.0-3.0 mm in the well-developed plane. Single crystal X-ray structural analysis clearly revealed that the CeOBiS$_2$ crystallizes with a space group $P4/nmm$ (with lattice parameters of $a$ = 4.0189(6) Å, $c$ = 13.573(2) Å). The bond valence sum estimation and X-ray photoelectron spectroscopy analysis showed that the chemical state of Ce was in the mixed valence of Ce$^{3+}$ and Ce$^{4+}$. The single crystals show superconductivity with zero resistivity at $\sim$1.3 K. This is the first conclusive evidence of superconductivity driven by Ce valence fluctuation in surely non-doped CeOBiS$_2$. The superconducting transition temperature was enhanced up to $\sim$3.8 K by applying hydrostatic pressure.

cond-mat.supr-con↗