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We investigated the pressure dependence of electric transport in a superconducting sample, Ba0.77Na0.23Ti2Sb2O, to complete the phase diagram of superconducting transition temperature (Tc) against pressure (p). This superconducting sample exhibits a Tc value of 5.8 K at ambient pressure. Here, the superconductivity of the recently reported sample was investigated over a wide pressure range. The Tc value monotonously decreased with pressure below 8 GPa. Interestingly, the Tc value rapidly increased above 8 GPa and slowly declined with pressure above 11 GPa. Thus, a new superconducting phase was discovered above ∼9 GPa. The crystal structure of Ba0.77Na0.23Ti2Sb2O was also elucidated at 0-22.0 GPa with synchrotron X-ray powder diffraction. Consequently, an evident relation between the crystal structure and the superconductivity was revealed, namely, a clear structural phase transition was observed at 8-11 GPa, where the Tc value rapidly increased against pressure. This study provides detailed information on the superconductivity of Ba0.77Na0.23Ti2Sb2O under pressure, which will lead to a comprehensive understanding of pressure-driven superconductivity.

The application of an electric field can be a new technique to control the electronic properties of two-dimensional materials. In a conventional double-gate structure, an ionic liquid is used in th...

The interface between the single crystal and the Au source/drain electrodes in [7]phenacene single-crystal field-effect transistors (FETs) was modified using 14 electron acceptors with different redox potentials. The effective hole-injection barrier heights (ϕheffs) for [7]phenacene single-crystal FETs have been plotted as a function of the redox potential (Eredox) of the inserted electron acceptors, showing that the ϕheff decreases with increasing Eredox. The highest ϕheff occurs without inserted material (electron acceptors), and this deviates from the otherwise linear relationship between ϕheff and Eredox. We have investigated the temperature dependence of ϕheff in an attempt to determine why the ϕheff value without inserted material is so high, which suggests that no additional barrier, such as a tunneling barrier, is formed in the device. We conclude that the pure Schottky barrier in this FET is lowered very significantly by the insertion of an electron acceptor. The gate-voltage dependence of ϕheff ...

Picene is a phenacene-type aromatic hydrocarbon molecule with five benzene rings. We have fabricated picene single crystal (SC) field-effect transistors (FETs) with solid gate and ionic liquid gate dielectrics. Although the picene SC FET showed a large hole-injection barrier without any modification of interface between source/drain electrodes and picene SC, such a large hole-injection barrier could be effectively reduced by modifying the interface with tetracyanoquinodimethane (TCNQ). Picene SC FET with an HfO2 gate dielectric and TCNQ-coated electrodes shows p-channel characteristics with a smooth hole injection and a field-effect mobility more than 1 cm2 V–1 s–1 in two-terminal measurement. Picene SC FET could be operated even in bottom-contact structure by modifying the interface with octanethiol. Furthermore, picene SC FET operated with ionic liquid gate dielectric, [1-butyl-3-methylimidazolium][hexafluorophosphate], showing the field-effect mobility of 1.8 × 10–1 cm2 V–1 s–1 and low absolute value, ...