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Electrical resistivity of the Fe X Mn 1−X S (0 ≤ X ≤ 0.29) single crystals based on the Mott insulator α-MnS is experimentally studied in the temperature range of 2–300 K at ambient pressure (P = 0) and at high (up to 30 GPa) hydrostatic pressures for x = 0.12. The electron subsystem of Fe X Mn 1−X S undergoes insulator-to-metal transitions indicated by a resistivity drop by a factor of 10 6 with an increase in the chemical pressure (X) due to the cation substitution under ambient conditions and at the hydrostatic pressure (P C = 27 ± 5 GPa) for x = 0.12. The results obtained show that the hydrostatic pressure - and cation-substitution induced insulator-to-metal transitions in the α-MnS-based Mott compounds have similar mechanisms. The dependence of the critical hydrostatic pressure P C on the Fe content in Fe X Mn 1−X S is established.

We have produced a superconducting binary-elements intercalated graphite, CaxSr1−xCy, with the intercalation of Sr and Ca in highly-oriented pyrolytic graphite; the superconducting transition temperature, Tc, was ~3 K. The superconducting CaxSr1−xCy sample was fabricated with the nominal x value of 0.8, i.e., Ca0.8Sr0.2Cy. Energy dispersive X-ray (EDX) spectroscopy provided the stoichiometry of Ca0.5(2)Sr0.5(2)Cy for this sample, and the X-ray powder diffraction (XRD) pattern showed that Ca0.5(2)Sr0.5(2)Cy took the SrC6-type hexagonal-structure rather than CaC6-type rhombohedral-structure. Consequently, the chemical formula of CaxSr1−xCy sample could be expressed as ‘Ca0.5(2)Sr0.5(2)C6’. The XRD pattern of Ca0.5(2)Sr0.5(2)C6 was measured at 0–31 GPa, showing that the lattice shrank monotonically with increasing pressure up to 8.6 GPa, with the structural phase transition occurring above 8.6 GPa. The pressure dependence of Tc was determined from the DC magnetic susceptibility and resistance up to 15 GPa, which exhibited a positive pressure dependence of Tc up to 8.3 GPa, as in YbC6, SrC6, KC8, CaC6 and Ca0.6K0.4C8. The further application of pressure caused the rapid decrease of Tc. In this study, the fabrication and superconducting properties of new binary-elements intercalated graphite, CaxSr1−xCy, are fully investigated, and suitable combinations of elements are suggested for binary-elements intercalated graphite.

We report the results of the X-ray absorption spectroscopy (XAS) on the intermediate valence compound SmB6. The XAS measurements were performed near the nonmagnetic-magnetic phase boundary. Mean Sm valence v Sm was estimated from absorption spectra, and we found that v Sm near the boundary ( P ≥ 10 GPa and T ∼ 12 K ) is far below a trivalent state with magnetic characteristics. Although the result is markedly different from the cases of pressure induced magnetic orders in Yb and Ce compounds, it is likely that the large deviation from the trivalent state seems to be common in some Sm compounds which possess electronic configuration between 4 f 5 and 4 f 6 with multi 4 f electrons.

Metal intercalation to graphite produces various types of superconductors. The highest superconducting transition temperature Tc (onset temperature, Tconset, of 11.5 K) was found in Ca intercalated graphite, denoted CaC6. Tconset increased up to 15.1 K at 7.5 GPa, implying a positive pressure dependence. However, no new metal-intercalated graphite superconductors with Tconset higher than 11.5 K at ambient pressure have so far been reported. To search for new graphite superconductors, we successfully synthesized binary-element-intercalated graphite, CaxK1−xCy. Their structure resembles that of KC8. Tc increased continuously with increasing x. Furthermore, the pressure dependence of Tc in Ca0.6K0.4C8 was investigated over a wide pressure range from 0–43 GPa. Tc (= 9.6 K at 0 GPa) increased to 11.6 K at 3.3 GPa, and decreased to 2.0 K at 41 GPa. This behavior is similar to that of CaC6, albeit with a lower maximum Tc. X-ray diffraction patterns were measured under high pressures of 0–24 GPa, and suggest a structural transition at 15 GPa. Evidence is given for superconducting graphite involving binary metal intercalation.

We report a systematic study of Sm valence in the prototypical intermediate valence compound ${\mathrm{SmB}}_{6}$. Sm mean valence ${v}_{\mathrm{Sm}}$ was measured by x-ray absorption spectroscopy as a function of pressure $(1lPl13\phantom{\rule{0.28em}{0ex}}\mathrm{GPa})$ and temperature $(3lTl300\phantom{\rule{0.28em}{0ex}}\mathrm{K})$. Pressure-induced magnetic order was detected above ${P}_{c}=10\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ by resistivity measurements. A shift toward the localized $4f$ state with increasing $P$ and/or $T$ is evident from an increase in ${v}_{\mathrm{Sm}}$. However ${v}_{\mathrm{Sm}}$ at ${P}_{c}$ is anomalously far below 3, which differs from the general case of nonmagnetic-magnetic transition in Yb and Ce compounds. From the $T$ dependence of ${v}_{\mathrm{Sm}}(P,T)$, we found that ${v}_{\mathrm{Sm}}(P,T)$ consists of two different characteristic components: One is associated with low-energy electronic correlations involving Kondo-like behavior, and the other is associated with high-energy valence fluctuations.

‘Aromatic hydrocarbon’ implies an organic molecule that satisfies the (4 n + 2) π-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K x picene, five benzene rings). Its superconducting transition temperatures ( T c ’s) were 7 and 18 K. Recently, we found a new superconducting K x picene phase with a T c as high as 14 K, so we now know that K x picene possesses multiple superconducting phases. Besides K x picene, we discovered new superconductors such as Rb x picene and Ca x picene. A most serious problem is that the shielding fraction is ⩽15% for K x picene and Rb x picene, and it is often ∼1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metal-doped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T c that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects.

As a follow-up of our previous work on pressure-induced metallization of the 2H_{c}-MoS_{2} [Chi et al., Phys. Rev. Lett. 113, 036802 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.036802], here we extend pressure beyond the megabar range to seek after superconductivity via electrical transport measurements. We found that superconductivity emerges in the 2H_{a}-MoS_{2} with an onset critical temperature T_{c} of ca. 3 K at ca. 90 GPa. Upon further increasing the pressure, T_{c} is rapidly enhanced beyond 10 K and stabilized at ca. 12 K over a wide pressure range up to 220 GPa. Synchrotron x-ray diffraction measurements evidenced no further structural phase transition, decomposition, and amorphization up to 155 GPa, implying an intrinsic superconductivity in the 2H_{a}-MoS_{2}. DFT calculations suggest that the emergence of pressure-induced superconductivity is intimately linked to the emergence of a new flat Fermi pocket in the electronic structure. Our finding represents an alternative strategy for achieving superconductivity in 2H-MoS_{2} in addition to chemical intercalation and electrostatic gating.

As a follow-up of our previous work on pressure-induced metallization of the 2H_{c}-MoS_{2} [Chi et al., Phys. Rev. Lett. 113, 036802 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.036802], here we extend pressure beyond the megabar range to seek after superconductivity via electrical transport measurements. We found that superconductivity emerges in the 2H_{a}-MoS_{2} with an onset critical temperature T_{c} of ca. 3 K at ca. 90 GPa. Upon further increasing the pressure, T_{c} is rapidly enhanced beyond 10 K and stabilized at ca. 12 K over a wide pressure range up to 220 GPa. Synchrotron x-ray diffraction measurements evidenced no further structural phase transition, decomposition, and amorphization up to 155 GPa, implying an intrinsic superconductivity in the 2H_{a}-MoS_{2}. DFT calculations suggest that the emergence of pressure-induced superconductivity is intimately linked to the emergence of a new flat Fermi pocket in the electronic structure. Our finding represents an alternative strategy for achieving superconductivity in 2H-MoS_{2} in addition to chemical intercalation and electrostatic gating.

BaBiO$_3$ is a mixed-valence perovskite which escapes the metallic state through a Bi valence (and Bi-O bond) disproportionation or CDW distortion, resulting in a semiconductor with a gap of 0.8 eV at zero pressure. The evolution of structural and electronic properties at high pressure is, however, largely unknown. Pressure, one might have hoped, could reduce the disproportionation, making the two Bi ions equivalent and bringing the system closer to metallicity or even to superconductivity, such as is attained at ambient pressure upon metal doping. We address the high-pressure phase diagram of pristine BaBiO$_3$ by ab initio DFT calculations based on GGA and hybrid functionals in combination with crystal structure prediction methods based on evolutionary algorithms, molecular dynamics and metadynamics. The calculated phase diagram from 0 to 50 GPa indicates that pristine BaBiO$_3$ resists metallization under pressure, undergoing instead at room temperature structural phase transitions from monoclinic \textit{I2/m} to nearly tetragonal \textit{P-1} at 7 GPa, possibly to monoclinic \textit{C2/m} at 27 GPa, and to triclinic \textit{P1} at 43 GPa. Remarkably, all these phases sustain and in fact increase the inequivalence of two Bi neighboring sites and of their Bi-O bonds and, in all cases except semimetallic \textit{C2/m}, the associated insulating character. We then present high-pressure resistivity data which generally corroborate these results, and show that the insulating character persists at least up to 80 GPa, suggesting that the \textit{C2/m} phase is probably an artifact of the small computational cell., Comment: 8 pages, 10 figures

Most of the Eu compounds are in the divalent (Eu) electronic state and order magnetically. On the other hand, the Eu-trivalent (Eu) compounds exist but are small in number. An energy difference between the Eu and Eu states is, however, not extremely large. Therefore, the valence transition occurs in some Eu compounds. We present the characteristic properties of the Eu compounds from several viewpoints: a canting magnetisation in the Eu-antiferromagnets, the Fermi surface property in the Eu-compounds of EuPd and EuCoSi, the heavy fermion state in EuNiP, the temperature-induced valence transition in EuPdSi, the pressure-induced valence transition in EuRhSi and EuRuP, and the heavy fermion state approaching to the quantum critical point with increasing pressure in EuNiGe .

A pressure-induced phase transition in the colossal magnetoresistance (CMR) material Fe0.18Mn0.82S was studied by using infrared (IR) reflection and X-ray diffraction (XRD) at pressures up to 40 GPa at room temperature. XRD shows that the crystal structure of this sample is a NaCl-type structure at ambient pressure, that a structural change starts around 17 GPa, and that a mixed phase mixed between the NaCl-type low-pressure phase and an unknown structure high pressure phase continues up to around 25 GPa. On the other hand, the IR reflectivity increases with increasing pressure from 15 GPa and becomes remarkably high around 20 GPa. The spectra do not show any changes from 30 GPa. From these results, we conclude that the phase transition of Fe0.18Mn0.82S at room temperature starts around 15 GPa and is completed around 30 GPa and that the high-pressure phase is not a band-overlapping semimetal but a true metal.

We present the results of the pressure dependence of the superconductivity of the inorganic electride 12CaO·7Al2O3:e− (C12A7:e−) single crystal through the ac-susceptibility measurement under high pressure. C12A7:e− has the cage structure and the density of states derived from the cages may play an important role in the superconductivity. The superconducting transition temperature (T c) is ∼ 0.2 K at ambient pressure and monotonically increases up to 1.79 K at 4.7 GPa. The upper critical field H c2 and −dH c2/dT at T c, in proportion to the density of states (DOS) at Fermi energy becomes larger under high pressure. The superconductivity in C12A7:e− is mediated by the electron-phonon interaction, and the increase of Tc with pressure may arise from a peak structure of the DOS of cage conduction band.

Object: We assessed whether or not deep venous reflux (DVR) improved after short saphenous vein (SSV) stripping was performed in patients with SSV reflux and DVR. Materials and Methods: Sixty-eight patients with SSV reflux who underwent SSV striping every Monday between 2008 and 2011 at Ryougoku Ashino Clinic were enrolled in this study. Forty-six of the 68 patients were selected for the analysis because they underwent duplex ultrasound examinations before and after the operation. The DVR was classified into four categories: type 0, no reflux; type I, reflux in popliteal vein; type II, reflux from popliteal vein to the middle of the superficial femoral vein (SFV) and type III, reflux from the popliteal vein to the SFV. Results: There were 23, 13, 2 and 8 patients with type 0, I, II, III before operation, respectively. There were 33, 8, 1, 4 patients with type 0, I, II, III after operation, respectively. There were no changes in 29 patients, improvement in 15 and new DVR in three (type 0 to I). Conclusion: SSV stripping is feasible in patients with DVR and the DVR might not be deteriorated even though that is performed.

We report syntheses of new superconducting metal-doped MoSe2 materials (MxMoSe2). The superconducting MxMoSe2 samples were prepared using a liquid NH3 technique and can be represented as ‘(NH3)yMxMoSe2’. The Tcs of these materials were approximately 5.0 K, independent of x and the specific metal atom. X-ray diffraction patterns of (NH3)yNaxMoSe2 were recorded using polycrystalline powders. An increase in lattice constant c showed that the Na atom was intercalated between MoSe2 layers. The x-independence of c was observed in (NH3)yNaxMoSe2, indicating the formation of a stoichiometric compound in the entire x range, which is consistent with the x-independence of Tc. A metallic edge of the Fermi level was observed in the photoemission spectrum at 30 K, demonstrating its metallic character in the normal state. Doping of MoSe2 with Li and K also yielded superconductivity. Thus, MoSe2 is a promising material for designing new superconductors, as are other transition metal dichalcogenides.

Background Doppler ultrasound (US) has been widely used to evaluate the cervical venous system of multiple sclerosis patients according to the hypothesis of chronic cerebrospinal venous insufficiency with contradictory results. Venous anatomy and pathology can be examined with less operator-dependent magnetic resonance imaging (MRI). Our aim is to assess the interobserver agreement in measuring internal jugular vein (IJV) cross-sectional area (CSA) in MR images and to explore the agreement between US and MRI in the detection of calibers of ≤0.3 cm 2 in the IJV CSA in the prospective study. Methods Thirty-seven multiple sclerosis patients underwent MRI of the cervical venous system. Two independent neuroradiologists measured the CSA of IJV at the mid-thyroid level. Furthermore, the time from contrast enhancement of common carotid arteries to that of each IJV (transit time in seconds) was assessed, and recorded whether IJV or the vertebral plexus visualized first during the contrast passage. US examination had been performed earlier. Results Interobserver agreement for assessing IJV CSA in MR images was substantial: the measurements differed >0.5 cm 2 between the examiners in only 5 IJVs (7%), Cohen's kappa 0.79. Transit times from common carotid artery to IJV varied between 5.1 and 14.1 sec. Fifteen patients had left-to-right asymmetry in the speed of IJV contrast filling. IJV CSA ≤ 0.3 cm 2 was found in 51 IJVs on the basis of US. Ten of these IJVs (19.6%) showed IJV CSA ≤ 0.3 cm 2 also in MRI. All IJVs defined as CSA ≤ 0.3 cm 2 in MRI met this caliber criterion also in US. Conclusions Interobserver agreement at the thyroid level of the IJV was good at MRI measurements. The US defines more IJVs as narrow (CSA ≤ 0.3 cm 2 ) than MRI. The US measurements for IJV CSA are not comparable with these methods. The US seems too sensitive in terms of finding venous stenosis.

Pressure dependence of the electronic and crystal structures of KxFe2−ySe2, which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change of Fermi surface topology. Our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.

Three of four (75%) vein biopsy samples from four patients (all male, mean onset: age 33.0, mean biopsy: age 59.7) of chronic phase phlebitis migrans showed positive periodontal bacteria DNA under the PCR (polymerase chain reaction) method. Of the 24 cases of Buerger disease (22 males, 2 females, mean onset: age 31.9, mean examination: age 62.6) that were investigated in our vascular laboratory, 65% of the patients suffered from moderate to severe varicose veins. Eight cases had a history of phlebitis migrans and three had an active ulcer or uncontrollable erosion in the foot. The rate of incidence was significantly higher than that of the well-matched control group. Other findings included one instance of deep vein thrombosis, and one instance of deep vein reflux. We could suggest that some intractable ulcer or erosion cases of Buerger disease may be complicated by superficial vein incompetence or other deep vein insufficiency. We also we need to check Buerger disease patients with duplex for vein reflux and other insufficiencies. Treatment of the varicose veins (including elastic stockings) was effective for all of the patients. (English Translation of Jpn J Phlebology 2011; 22: 25–31.)

In this article, we have developed pressure loading technique to extend the loading density of guest alkali metals in nanoporous crystals of zeolites. Zeolite crystals have solid framework and open regular nanospace. In the nanocages of zeolite crystals, s-electrons provided by the guest alkali metals occupy quantum electronic states of clusters successively. Under the pressure by the use of the pressure medium of alkali metals, we have observed significant change in the magnetic properties, indicating that the pressure loading increases loading densities which are closely related to the s-electron occupation at the quantum states of clusters.

大伏在静脈本幹硬化療法の高位結紮を併用する方法，高位結紮をしない方法の両者において，術後1年の経過を報告する．【方法】HL+法48例：高位結紮およびGSV根部を部分切除し，GSV断端から末梢側へ硬化剤を注入した．HL－法43例：下腿のGSV分枝から硬化剤を注入し，エコーでフォームをGSV本幹内，SFJまで誘導した．硬化剤は3%または1%POL：CO2=1 : 3，Tessari法で作製した．術後1，3，6，12カ月後に超音波検査にて経過を追った．【結果】大腿部の閉塞率はHL+法：6カ月後80.4%，12カ月後75.5%，HL－法：6カ月後63.4%，12カ月後52.8%であった．深部静脈血栓症などの有害事象は認めなかった．【結語】フォーム硬化療法は大伏在静脈不全に対する治療として，安全に施行できる．HL－法はHL+法に比べ，閉塞率は劣るが，治療としての有用性が示唆された．

The ternary iron chalcogenide, Fe(1.03)Se(0.57)Te(0.43) is a member of the recently discovered family of Fe-based superconductors with an ambient pressure T(c) of 13.9 K and a simple structure comprising layers of edge-sharing distorted Fe(Se/Te)(4) tetrahedra separated by a van der Waals gap. Here we study the relationship between its structural and electronic responses to the application of pressure. T(c) depends sensitively on applied pressure attaining a broad maximum of 23.3 K at approximately 3 GPa. Further compression to 12 GPa leads to a metallic but nonsuperconducting ground state. High-resolution synchrotron X-ray diffraction shows that the superconducting phase is metrically orthorhombic at ambient pressure but pressurization to approximately 3 GPa leads to a structural transformation to a more distorted structure with monoclinic symmetry. The exact coincidence of the crystal symmetry crossover pressure with that at which T(c) is maximum reveals an intimate link between crystal and electronic structures of the iron chalcogenide superconductors.

We have succeeded to electromagnetically excite and detect MHz-frequency-range ultrasound shear wave in polycrystalline Al under high pressures. The noncontact thickness-resonant electromagnetic acoustic resonance technique enables us to excite and detect polarized pure shear waves in an Al polycrystalline specimen in a pressurizing liquid through the Lorentz-force mechanism. Shear-mode resonance spectra have been successfully obtained up to 0.55 GPa at ambient temperature. Quasiharmonic analysis for the pressure dependence of shear modulus yields the zone-center shear-mode Gruneisen parameter γS to be 2.683, which agrees well with previously reported values calculated from the third-order elastic constants.

The electrical and structural properties of yttrium hydride YH x (x ∼ 3) were studied by the in situ measurements of the electrical resistance and X-ray diffraction up to 86 GPa. The electrical resistivity ρ increased with applying pressure up to 10 GPa and showed a maximum, which was accompanied with the structural transition of metal lattice from hcp into fcc structure. In fcc phase the ρ decreased significantly, however, the value was still high as 75×10−2 (Ω cm), which is larger by four orders of magnitude than that of pure yttrium metal. We could not confirm the insulator to metal transition up to 85 GPa. The ρ showed another maximum in the large pressure region 40–60 GPa without the structural phase transition of the metal lattice.

The electrical resistivity ρ(T) of Y1−xUxPd3 (x = 0,0.05 and 0.2) and the lattice constants for x = 0 have been measured at high pressure. It is found that the cubic Cu3Au structure is stable up to 12 GPa at room temperature. The Kondo temperature TK was extracted from the ρ(T) curve and it was found that it increases with pressure. A logarithmic temperature dependence characteristic of the Kondo effect was found for x = 0.2 in the temperature range above about 0.5TK. Fermi liquid behaviour in ρ(T) for x = 0.05, i.e., , is observed and its stability at high pressure is discussed. The pressure dependence of the Kondo temperature TK is discussed using the Gruneisen parameters at TK, ΓK. It appears that the values of ΓK are the same for these two compounds (x = 0.05 and 0.2): ΓK = 12. The T-linear behaviour in ρ(T) for x = 0.2, which is characteristic behaviour for non-Fermi liquids, is collapsed by an application of pressure and typical Fermi liquid quadratic temperature dependence recovers at high pressure. From the result for x = 0.2, the power n of the temperature in is determined as 1.0 at ambient pressure and 1.9 at 5.8 GPa. It is pointed out that the hybridization effect due to the application of pressure gives rise to a crossover from a non-Fermi liquid state to Fermi liquid state. But the crossover temperature Tcr shows a pressure dependence different from that predicted by the two-channel Kondo model.

The electrical resistivity of single crystalline HoNi 2 B 2 C has been measured at high pressure and magnetic fields. The three anomalies in the magnetoresistance due to metamagnetic transitions are observed both at ambient and high pressures. It is found that the metamagnetic transition fields increase with increasing pressure. The temperature dependence of electrical resistivity is strongly dependent on magnetic field. Non Fermi liquid behavior is observed near the metamagnetic transition fields. But the normal Fermi liquid behavior recovers after completing the phase transition. The Grüneisen parameters are also calculated to examine the stability of electronic state.

Pressure dependence of the charge distribution along the columns of tetracyanoquinodimethane (TCNQ) molecules in Cs2TCNQ3, which is a semiconducting 1/3-filled Hubbard system with the optical energy gap of 0.3 eV at ambient conditions, has been studied by the infrared and visible absorption experiments. An electronic phase transition is found to occur at around 3.5 GPa, in accordance with the previously reported insulator-to-metal transition. Our result suggests that this phase transition accompanies a symmetry change in the relative position of the TCNQ− radical molecules sandwiching the TCNQ0 neutral molecule. In addition, the π* electrons, which are localized on the TCNQ− molecules in the low-pressure phase, are delocalized significantly in the high-pressure phase. However, in the high-pressure phase the π* electrons still maintain the localizing character. The charge-transfer degree of the neutral-like and radical-like molecules of the high-pressure phase is estimated to be ρ = 0.46-0.50 and 0.75-0.77, respectively.

The electrical resistivity of YbBe13 has been measured at high pressure up to 2 GPa and magnetic field up to 5 T. It is found that the electrical resisitivity shows a maximum near 25K (=Tmax) and has -logT term in temperature range above Tmax, indicating Kondo scattering of conduction electrons. The temperature of the resistivity maximum is only weakly affected by pressure but the gradients of the-logT term decrease with increasing pressure. The results is discussed in connection with the interplay between the Kondo effect and crystalline electric field.

Pressure dependence of several molecular vibration modes in Cs2TCNQ3 has been observed through the infrared absorption measurements. The behavior of the C-CN and C-H stretching modes suggests that phase transition takes place at around 3.6 GPa. The π* electrons, which are localized on TCNQ- molecules in the low-pressure phase, are delocalized significantly in the high-pressure phase. However, the radical-like and neutral-like molecules still coexist in the high-pressure phase indicating that the electrons are not completely delocalized. The electron-molecular-vibration (emv) coupled mode disappears in the high-pressure phase in coincident with the disappearance of the inter-radical charge transfer band S1, proving the strong coupling between them.

A high-pressure apparatus which we can use at low temperature and high magnetic field has been designed for making measurements of thermal and transport properties of condensed matter. The details of the apparatus and some examples of the measurements are described and briefly discussed. It is proved that the apparatus is suitable for use up to hydrostatic pressure of ~ 3.5 GPa, down to ~ 2.0 K and up to ~ 11 T.

Crystals of the organic semiconductor Cs 2 TCNQ 3 have been grown under the influence of magnetic field of 5 T and their optical properties have been compared with the crystals grown without magnetic field. The magnetic field effect manifests itself as the enhancement of the intradimer charge transfer band S 1 , which appears at around 1.3 eV in the E//a polarization. The high-pressure optical absorption measurements have shown that the S 1 band of the crystal grown at 5 T contains a new component, which is significantly intensified with increasing pressure up to 1 GPa, but diminishes as pressure increases further up to 4 GPa, and remains constant at higher pressures. This new component is additional to the component of S 1 band which has similar properties to that of the crystals grown without magnetic filed, which continuously grows up to 3 GPa and abruptly broadens out at higher pressures. The new component of S 1 is strongly linked to the ferromagnetism in this substance.

The pressure dependence of the superconducting transition temperature (Tc) and unit cell metrics of tetragonal (NH3)yCs0.4FeSe were investigated in high pressures up to 41 GPa. The Tc decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The Tcvs. c plot is compared with those of various (NH3)yMxFeSe (M: metal atoms) materials exhibiting different Tc and c, showing that the Tc is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the Tc. No superconductivity was observed down to 4.3 K in (NH3)yCs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the Tc reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, Tc slowly decreased with increasing pressure above 21 GPa and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

The electrical resistivity in the Kondo semiconductor shows a metallic behavior at higher temperature region than the Kondo temperature TK and becomes semiconducting one in the low temperature region due to open the temperature-dependent energy gap [1]. YbB12, which crystalizes in the cubic NaCl type crystal structure, has two energy gaps whose sizes were estimated as E1 = 28 K and E2 = 78 K from the transport measurement [2]. SmB6 also forms cubic crystal structure of CsCl type [3] and is called as Kondo semiconductor [4]. YbB12 and SmB6 show similar transport behaviors [5]. A previous electrical resistivity measurement up to 14 GPa by Derr et al. shows that SmB6 was metalized at 10.5 GPa and a magnetic order appeared at about 10 K [4]. In case of YbB12, the electrical resistivity had been measured up to 8 and 20 GPa [2,6], however, has shown a semiconducting behavior. The pressure dependence of the activation energy estimated from the electrical resistivity suggests that the semiconductor to metal transition occurs at 100 GPa in YbB12. We are interested in metallic ground state of YbB12 that may exist above 100 GPa. In this paper, we report the results of electrical resistance measurement under ultra high pressures of up to 195 GPa with the diamond-anvil cell.

We studied the electronic state of UGa3 by measuring the electrical resistivity under pressure. When pressure is applied to UGa3, the Neel temperature TN = 67 K decreases steeply and becomes zero around 2.6 GPa. Correspondingly, the coefficient A in the electrical resistivity ρ = ρ0 + AT2, which is characteristic for Fermi liquid, increases steeply with increasing pressure. Around a magnetic quantum critical point of 2.6 GPa, a non-Fermi-liquid behaviour is found, showing a linear T-dependence of the resistivity, although the Fermi-liquid behaviour recovers above 4 GPa and the A-value decreases with increasing pressure. Furthermore, a resistivity drop, which might be related to superconductivity, was found below 0.3 K at 1.5 GPa, where the residual resistivity ρ0 has a maximum.

The pressure dependence of the optical absorption spectra of (NMe4)2TCNQ3 and Cs2TCNQ3 has been measured at room temperature in the spectral range from mid-infrared to the visible. At ambient pressure the optical energy gap is observed at around 0.5 and 0.3 eV in (NMe4)2TCNQ3 and Cs2TCNQ3, respectively. The energy gap in (NMe4)2TCNQ3 decreases by 0.05 eV with increasing pressure up to 2 GPa, followed by an abrupt decrease towards 0.2 eV between 2 and 3 GPa. At higher pressures up to 5.5 GPa the gap remains almost unchanged. The intra- and inter-molecular optical absorption bands in the near-infrared to visible region are intensified by pressure and broaden out at 2.5 GPa. The absorption spectrum in Cs2TCNQ3 exhibits a similar behavior under pressure. These results suggest that an electronic phase transition is induced by pressure at around 2.5 GPa in both substances. This transition resembles the charge order-disorder (Verwey) transition in Fe3O4.

Magnetostriction and magnetoresistance of single-crystalline HoNi 2 B 2 C have been measured at ambient pressure. A large anisotropy was found in the field dependence of these properties. The magnetoresistance was also measured at high pressure up to 2 GPa at low temperature below the superconducting transition temperature (9 K). Several anomalies were found due to the metamagnetic transitions, in which the transition fields increased with increasing pressure. These results will be discussed from a thermodynamical point of view and compared with the anisotropy in the lattice compression.

A new high pressure apparatus using Ti-Ni shape memory alloy as an actuator has been developed. It is found that the high pressure around 10 GPa is easily obtained when we use the Bridgman type anvil having a face of 3 mm in diameter. Some other properties of this high pressure apparatus are reported briefly.

Ground state properties of intermetallic YCo 9 Si 4 are investigated by means of temperature-dependent electrical resistivity measurements under pressure using both a diamond-anvil cell and a piston-cylinder cell. At ambient pressure, YCo 9 Si 4 shows weak itinerant ferromagnetism below 25 K with an ordered moment of about 1.6 μ B / f . u . The temperature-dependent electrical resistivity exhibits below 10 K a power-law behavior R ( T ) = R 0 + AT n . The exponent n changes from n ≃ 1.7 at ambient pressure to about 1.5 at 6 GPa, referring to non-Fermi liquid behavior. The characteristic temperature decreases with pressure, implying a decrease of the ferromagnetic transition with pressure as well. The initial decrease of the ordering temperature is d T C / d p ≃ - 2 K / GPa . Both, the pressure-dependent evolution of T C as well as of the coefficients A and n indicate that a ferromagnetic quantum critical point will be reached under pressure of the order of 6 GPa.

We have studied the effect of pressure in the filled skutterudite PrRu4P12, which shows a metal–insulator (MI) transition at T MI = 63 K , via simultaneous measurements of electrical resistivity ( ρ ) and AC-calorimetry ( C AC ). Schottky-like anomalies in C AC disappear under pressure, suggesting a change of the ground state. The resistivity below T MI is strongly suppressed with increasing pressure, in contrast to the weak pressure dependence of T MI . Above 10 GPa, ρ ( T ) shows metallic behavior with small anomalies at T MI . We discuss the likely change of ground state in PrRu4P12 with pressure from triplet to singlet.

Electrical resistance and lattice parameters of the intermetallic compounds Ce(In 1− x Sn x ) 3 have been measured at high pressure. It is found that the Kondo temperature T K , which is estimated from the temperature showing the maximum in the ρ ( T ) curve, is increased and the Neel temperature of CeIn 3 ( x =0) is decreased by the application of pressure. The compression curves show a continuous decrease in volume with pressure, without any discontinuity. This fact indicates that the valence transition occurs continuously with pressure. The results are discussed briefly by using Gruneisen parameters.

The influence of pressure and magnetic field on strain gauge (SG) has been investigated in order to clarify the behaviors of SG under these conditions. It is found that the electrical resistance of SG mounted on Cu changes largely above a critical pressure Pc, at which the pressure transmitting medium is frozen due to solidification. However, no significant change in electrical resistance of SG above Pc was observed for that on WC and Mo. The magnetoresistance of SG at 4.2 K shows a hysteresis between an increasing and decreasing magnetic field at ambient pressure, which is suppressed by an application of pressure. On the basis of these data, a suitable reference and the relationship between the arrangement of SG and direction of load are briefly discussed.