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MYB12 is one of the key genes causing variation in anthocyanin colour in lily flowers. Nearly full-length sequences of the MYB12 gene were determined in 6 wild species and their 6 varieties, each of the Archelirion and Sinoartagon sections from the genus Lilium, and their sequences were compared with sequences of 20 cultivars of Oriental and Asiatic hybrid lilies. In total, 29 MYB12 sequences were detected. Most of the MYB12 sequences in full-pink-flowered cultivars of Oriental hybrid lilies were similar to those in Lilium speciosum and L. rubellum, and thus, should be derived from these two wild species. Lilium auratum had identical or similar MYB12 sequences to Oriental hybrid cultivars ‘Dizzy’ and ‘Casablanca’: These plants have a white tepal background with or without red raised spots and red centrelines. MYB12 genes from L. japonicum rarely appeared in Oriental hybrid lily cultivars. MYB12 sequences in Asiatic hybrid lily cultivars were identical or similar to those in L. cernuum, indicating that L. cernuum has contributed pink colouration to these cultivars.

To further enhance the critical current density ( J c ) and irreversibility field ( H irr ) of (Cu 1− x C x )Ba 2 Ca n −1 Cu n O 2 n +4− δ ( n =4; hereafter described as (Cu,C)-1234), pinning centers were introduced by heavy-ion irradiation. The polycrystalline samples were irradiated with Au 15+ ions (240 MeV energy) at various fluence of 3.5 × 10 10 , 6.5 × 10 10 , 1 × 10 11 , 2.5 × 10 11 and 5 × 10 11 ions/cm 2 . The intragrain J c was determined from M – H curves using Bean’s critical state model. With increase of the fluence, J c shows a rapid increase and reaches a maximum value, 4.1 × 10 6 A/cm 2 (77 K and 1 T) for the fluence of 1 × 10 11 ions/cm 2 and above which it decreases slowly. The maximum value of H irr (77 K), determined by extrapolating J c curves to a 10 3 A/cm 2 criterion, is about 14.5 T for the 2.5 × 10 11 ions/cm 2 . The α value in equation H irr ( T )= H irr (0)(1− T / T c ) α decreases from 2.97 for un-irradiated sample to 1.87 for the fluence of 1 × 10 11 ions/cm 2 . These results indicate the possibility of J c (77 K and 1 T) enhancement and reaching a high H irr (77 K) at the fluence of the 1.5 × 10 11 ions/cm 2 .

Anisotropic superconducting properties of inter-metallic compounds MgB2, Y2PdGe3, and CaAlSi with AlB2 structure are studied by detailed angular dependent transport measurements. MgB2 and CaAlSi shows appreciable anisotropy of the upper critical field, Hc2, with mass anisotropy parameter γ=3 and 2, respectively, while Y2PdGe3 is almost isotropic. In-plane anisotropy of Hc2 in these hexagonal superconductors is very small, consistent with the prediction based on GL theory.

TlBa2Ca2Cu3Oy (Tl-1223) superconducting films were prepared under identical conditions, on MgO substrates with different morphologies resulting from heat treatments at temperatures between 600 and 1350 °C. The superconducting films have almost the same morphology, in-plane alignment and composition, but different critical current densities Jc. Critical current density Jc determined at 77.3 K differs for films with various annealed MgO substrates, by a factor of 5 in zero field and 10 in 1 T. The behavior of Jc is discussed in relation with the flatness of the MgO surface, and with pinning effects induced by the Ca-segregates. For the present work, the best films were obtained for the un-annealed (as-received) substrates and for substrates treated at 1350 °C. In these samples, the substrate’s flatness and morphology with regular steps are essential for high quality of the superconducting films. In the films grown on MgO annealed between 800 and 1200 °C and showing rough surface and Ca-segregates, Jc was lower. However, Jc was increasing with heat treatment temperature of the substrate, possibly due to the Ca-segregates inducing or acting as pinning centers. The effects of Ca-segregates are of interest for maximization of the quality of the high-temperature superconducting films. In the literature, up to now, these effects have not been considered and therefore Ca-segregates removal has been recommended.

Temperature dependence of the Hall coefficient and the resistivity in Tl2Ba2CaCu2O y (TL-2212), Tl2Ba2Ca2Cu3O y (Tl-2223) and Cu0.7C0.3Ba2Ca3Cu4O y (Cu-1234) have been measured under high pressure up to 6 GPa. The values of the intrinsic T c enhancement not related to charge transfer by applied pressure were estimated to be ∼0.8K/GPa for the Tl system and ∼1.1K/GPa for Cu-1234.

We study the superconducting electronic structures of Nb 3 Al and MgB 2 using high-resolution spectroscopy. The obtained spectrum of Nb 3 Al measured below T c shows clear opening of the superconducting gap with a sharp pile up in the density of states and a shift of the leading edge. In addition, the spectrum shows a peak–dip–hump line shape expected from the strong-coupling theory. On the other hand, for MgB 2 , the superconducting-state spectrum measured at 5.4 K shows a coherent peak with a shoulder structure, in sharp contrast to that expected from a single isotropic gap. The superconducting spectral shape of MgB 2 can be explained in terms of a multicomponent gap.

The local structure of Nb3Ge intermetallic superconductor has been studied by Ge K-edge absorption spectroscopy. Extended x-ray absorption fine structure (EXAFS) experiments show two Ge–Nb distances. In addition to the crystallographic distance of ~2.87 A, there exists a second Ge–Nb distance, shorter than the first by ~0.2 A, assigned to a phase with short-range symmetry related to local displacements in the Nb–Nb chains. The x-ray absorption near-edge structure (XANES) spectrum has been simulated by full multiple-scattering calculations considering the local displacements determined by the EXAFS analysis. The XANES spectrum has been well reproduced by considering a cluster of 99 atoms within a radius of about 7 A from the central Ge atom and introducing determined local displacements.

The superconductivity and the lattice properties of a sintered MgB2 material have been investigated under high pressure up to 10 GPa. The transition temperature was found to decrease linearly with increasing hydrostatic pressure at a rate of 1.03 K GPa−1, which can be explained with the classical Bardeen–Cooper–Shrieffer theory based on an electron–phonon coupling mechanism. The crystal lattice exhibits an anisotropic compressibility characterized by a larger compressibility along the c-direction than the a/b-directions. The anisotropy is attributed to a weaker inter-plane bonding along the c-axis in comparison with a stronger intra-plane bonding perpendicular to the c-axis. The bulk modulus of the measured material was deduced to be 172 GPa.

The oxygen isotope effect on T c in a four-CuO 2 -layer cuprate of (Cu,C)Ba 2 Ca 3 Cu 4 O y ( T c =117 K) has been investigated. The isotope-substituted samples of equivalent quality were successfully synthesized under high pressure directly from precursors which were prepared from the oxides obtained by heating metals of Ba, Ca and Cu in oxygen isotope ( 17 O and 18 O) atmosphere. We concluded that the oxygen isotope effect ( T c ∼ M − α : M is the oxygen mass) is small but finite ( α =0.021±0.006) in this compound. This result agrees with the previously reported isotope effects in optimally doped cuprates of Y-123 and (Bi,Pb)-2223.

Thin films of Cu m −1 Ba m (Sr,Ca) n Cu n +1 O 2 m +2 n +1 , i.e., [BaCuO 2 ] m /[(Sr,Ca)CuO 2 ] n superlattices have been grown by layer-by-layer growth method with rf magnetron sputtering on NdGaO 3 (1 1 0) substrate. Two targets with the compositions BaCuO 2 and (Sr,Ca)CuO 2 , which form the charge reservoir and superconducting layers, respectively, were used. [BaCuO 2 ] m /[(Sr,Ca)CuO 2 ] n superlattice was grown at 460–520 °C in a gas mixture of Ar and N 2 O by alternatively depositing the charge reservoir layer and superconducting layer. The superlattice modulation is close to that of high pressure synthesized bulk materials. By means of the layer-by-layer growth method, a system of Cu-based artificial lattice structures is formed. Electrical transport properties of these superlattices were also investigated.

Magnetic properties of single crystalline and dense polycrystalline MgB 2 prepared under high pressure have been investigated in a wide field range through local and global magnetization measurements using micro-Hall probe and SQUID magnetometer. The lower critical field, H c1 , measured by Hall probe shows a BCS-like temperature dependence and can be fitted by two-gap model. Field dependence of magnetic critical current density is quite different for single and polycrystalline samples. There is only one pinning force peak for bulk sample, whereas there are two pinning force peaks for single crystalline sample. The upper critical field, H c2 , and the irreversibility field, H irr , have been measured with magnetic field parallel and perpendicular to the boron sheets and the anisotropy ratio of H c2 is estimated to be about 3.

Superconducting samples have been synthesized from starting compositions Cu 0.5 Tl x Ba 2 Ca 3 Cu 4 O 12+ y , x Tl =0.35–1 in the sealed Au-tubes. Starting oxygen content was y =0 and/or y =±0.225. Samples contain non-superconducting phases and only one main superconducting phase, 1234. The energy dispersive spectroscopy grain composition was Tl 0.87–1.3 Ba 1.9–2.05 Ca 2.55–3.1 Cu 4 O x (normalized to Cu=4). The starting Tl and oxygen content do not influence the occurrence of the phases, grain size, morphology and composition. On the other hand the phase content strongly depends on Tl content and almost does not depend on oxygen content. Both Tl and oxygen content are important for the transport properties of the superconducting grains and it seems that also of the non-superconducting matrix. T c of the samples was in the range 119.1–111.3 K.

We report the growth of TlBa 2 Ca 2 Cu 3 O y superconducting thin film on CeO 2 buffered r-cut sapphire substrate by amorphous phase epitaxy method, wherein an amorphous phase of a composition, TlBa 2 Ca 3 Cu 4 O y was deposited by rf magnetron sputtering and subsequently crystallized by annealing at high temperatures in a closed system. There exists an optimum thickness of about 200 A of CeO 2 buffer layer that gives a smooth buffer layer surface. At the temperature around 840 °C we get only Tl-2212 phase and for a longer annealing time it results in Tl-1212 phase. At higher temperatures Ba reacts with Ce to form BaCeO 3 . To avoid this reaction process we introduced another amorphous buffer layer, TlSr 2 CaCu 2 O y onto CeO 2 layer. By this method we could prepare a good quality Tl-1223 thin film which showed a T c of 104 K and a J c = 0.3 MA/cm 2 at 77 K and 0.1 T field.

For further enhancement of critical currents density Jc and irreversibility field Hirr of (Cu1−xCx) Ba2Can−1CunO2n+4−δ ((Cu,C)-(n−1)n, n=3, 4 and 5) family, pinning centers were introduced by ion and neutron irradiation in these compounds. The polycrystalline samples were irradiated with 3.6×1017 neutrons/cm2 or with Au15+ ions (240 MeV energy) at a fluence of 1×1011 ions/cm2. Jc and Hirr were determined for the irradiated samples as well as unirradiated samples. The intragrain Jc was evaluated from M–H curves using Bean's critical state model. In (Cu,C)-12(n−1)n, Jc (77 K, 1 T) shows a remarkable increase from 3.9×104 to 9.1×105 A/cm2 for neutron irradiated (Cu,C)-1234 and from 3.9×104 to 4.1×106 A/cm2 for heavy-ion irradiated (Cu,C)-1234. These results indicate the possibility of further enhancement of Jc and of achieving a very high Hirr of (Cu,C)-1234 in (Cu,C)-12(n−1)n family.

A 50 μm thick slice of (Cu,C)Ba 2 Ca 3 Cu 4 O y (Cu:1234) bulk superconductor grown by high-pressure synthesis technique was irradiated with high-energy (240 MeV) Au 15+ ions (10 11 cm −2 ). Complimentary DC magnetization measurements up to 5 T showed an increase in critical current density by two orders of magnitude. AC susceptibility studies were performed in DC magnetic fields up to 14 T and at various temperatures, using various AC field amplitudes (up to 15 Oe) and frequencies (up to 10 kHz). Critical current densities at various temperatures and fields were estimated from critical state model. Using the third harmonic response of the sample we were able to separate different contributions to the dissipation: inter-grain regions, grains without columnar defects (heavy-ions penetration depth is about one quarter of sample’s thickness), and grains with columnar defects. In irradiated grains, we could observe a peak-effect in the field dependence of critical current density at high DC fields and temperatures between 85 and 105 K, suggesting the possibility of the highest irreversibility field at liquid nitrogen temperature.

The Raman spectrum of (Cu x C 1− x )Ba 2 Ca 3 Cu 4 O y was measured. Two successive anomalies with decreasing temperature were attributed to two superconducting gaps having different magnitude. Anomaly also includes features of phonons interacting with an inter-band charge fluctuation. The interaction between two gaps and a phonon is discussed.

Cu1−xTlxBa2Ca2Cu3O10−y(Cu1−xTlx-1223) superconductor thin films has been proven to be very promising candidate in the cuprate family due to their ability to carry very high current densities (2×107 A/cm2). The detailed characterization of these films has been carried out, however, their growth kinetics have not been studied yet. In this paper we have reported the mechanism of growth kinetics of Cu1−xTlx-1223 superconductor thin films. The amorphous phase of Cu1−xTlx-1223 films was deposited on SrTiO3(1 0 0) substrate by rf-sputtering. The sputtered deposited films were placed in a gold capsule along with a precursor pellet containing thallium. The mouth of the Au capsule was closed and was heated at different temperatures by keeping the thallium treatment time identical in each experiment (70 min). It was observed from the heat treatment experiments that the growth of Cu1−xTlx-1212 was started around 850 ° C and completed at 860 ° C. The partial growth of Cu1−xTlx-1223 started around 870 ° C and was completed around 890 ° C. A mix of Cu1−xTlx-1212 and Cu1−xTlx-1223 was produced at the temperature in between 860 and 890 ° C. However, at the elevated temperatures (above ∼890 °C) a mix of Cu1−xTlx-1223, Cu1−xTlx-1234 and Cu1−xTlx-1245 was formed. These observations manifested that the growth of Cu1−xTlx-1223 was accomplished via Cu1−xTlx-1212 by the introduction of an additional CuO2 plane in Cu1−xTlx-1212. The fabrication of Cu1−xTlx-1223 at various temperatures showed the synthesis temperature to be 890 ° C, at the elevated temperatures a mix of Cu1−xTlx-1223, Cu1−xTlx-1234 and Cu1−xTlx-1245 was formed. By using different target compositions it is observed that a predominant single phase of higher CuO2 planes (such as Cu1−xTlx-1234 and Cu1−xTlx-1245) could not be prepared from the target containing Sr. However, the phases with higher CuO2 planes could be synthesized from the targets containing only barium in the compound. From the resistivity measurements the Tc of Cu1−xTlx-1212 was 78 K and Cu1−xTlx-1223 was 104 K. The pole figure measurements of (1 0 3) reflection showed these films to be oriented along a and c axes.

CuBa 2 Ca 3 Cu 4 O 12-y (Cu:1234) high-temperature superconductors (HTS) doped with up to 2% Zn were grown using the high-pressure synthesis technique. Magnetization loops of the samples were measured at various temperatures between 5 and 77.3 K and magnetic fields up to 14 T. Critical current densities J c of the samples were estimated using the critical state model. The results show that Zn-induced pinning centers increase Jc of Cu:1234 several times, depending on field and temperature. From the experimentally determined field-temperature region in which a higher Zn concentration lead to a higher J c , we suggest the existence of a cross-over from quite efficient, extended (in the c-axes direction) pinning centers to point-like (inefficient) pinning centers at a certain temperature, depending on field. This effect can be attributed to the fact that, unlike other HTS, in Cu:1234 there is a second critical temperature T c2 of about 70-80 K (in zero field, and 50-60 K in 15 T), related to the over-doping of pyramidal basal plane (outer CuO 2 plane).

Temperature and time dependence of the phase formation in the (Cu0.5,Tl0.5)-1234 composition have been studied. The liquid–vapour deposition mechanism for the formation of 12(n − 1)n superconducting phases is presented. XRD, SEM, EDS and weight loss data are discussed. Samples were superconducting with maximum Tc and Jc (at 60 K and 0.5 T), determined from M(H) loops of 118 K and 4 × 105 A cm−2, respectively.

Thin films of Tl(Ba, Sr)2Ca2Cu3Oy superconductor have been grown on CeO2 buffered r-cut sapphire substrate with the use of a template TlSr2CaCu2Oy by the amorphous phase epitaxy method. By using this template containing Sr, we have overcome the problem of chemical reactions between Ba and Ce present in the superconducting and buffer layers, respectively, at the normal processing temperatures of 840–890 °C. Films grown by this method have an excellent c-axis orientation as well as in-plane alignment with the TlSr2CaCu2Oy template, which in turn is aligned with the CeO2 layers. These films have superconducting critical temperature values up to 104 K and critical current density values as high as 1 MA cm−2 at 77.3 K and 0 T.

We report on the precise determination of the lower critical field ( H c1 ) of the newly discovered superconductor MgB 2 measured by Hall probe. Two polycrystalline samples with different grain sizes and one single crystalline sample are compared. By setting a small criterion for the first flux penetration into the sample, H c1 was determined. Based on our measurements, MgB 2 seems more similar to borocarbides and low- T c superconductors, which follow BCS temperature dependence, than to high- T c superconductors. Comparison with two-gap superconductivity is also made.

Cu1−xTlxBa2Ca3Cu4O12−y (Cu1−xTlx-1234) thin films have been found to be very attractive candidates in the cuprate family due to their low superconductor anisotropy, long coherence length and, consequently, high Jc. The method of preparation has been reported previously, however the kinetics of their formation has not yet been studied. In this paper, we report on the growth kinetics of superconducting Cu1−xTlxBa2Ca3Cu4O12−y thin films. In the preparation, we use the amorphous phase epitaxy method, which is a thallium treatment of the amorphous phase at elevated temperatures. The amorphous phase was deposited on a SrTiO3 substrate by rf-sputtering from a stoichiometric target with a composition of CuBa2Ca3Cu4Oy. The thallium treatment of the amorphous phase was carried out in a gold capsule for 45 min. The mechanism of the growth kinetics has shown that the formation of Cu1−xTlxBa2Ca3Cu4O12−y thin films was accomplished from Cu1−xTlxBa2Ca1Cu2O8−y (Cu1−xTlx-1212) and Cu1−xTlxBa2Ca2Cu3O10−y (Cu1−xTlx-1223) by the successive introduction of CuO2 planes in these phases. We also studied the effect of the time and temperature of the thallium treatment on the growth of Cu1−xTlx-1234 films. The best synthesis temperature for Cu1−xTlx-1234 films was found to be 910 °C, but this phase could also be isolated as a single phase at lower temperatures (~890 °C). However, the low-temperature synthesis results in a higher thallium content in the final compound. From the x-ray diffraction measurements the c-axis length was found to increase with the increase of the thallium content. The pole figure measurements of the (103) reflection of the films have shown a-axis oriented crystals with Δ = 0.8°. The observed critical temperature (Tc) for Cu1−xTlx-1212, Cu1−xTlx-1223 and Cu1−xTlx-1234 are 78 K, 103 K and 110 K respectively. Current density measurements have shown a maximum Jc ~ 2 × 106 A cm−2.

Superconducting compounds of Ba2Can−1CunO2n(O,F)2 (n=2–5) whose apical oxygen is partially substituted by fluorine have been synthesized under high pressure. The nearly single-phase samples of n=3 and 4 were prepared from almost stoichiometric compositions (δ is small) of Ba2Ca2Cu3O6(O1−y±δFy)2 (y=0.6–0.8) and Ba2Ca3Cu4O8(O1−y±δFy)2 (y=0.5–0.7), respectively. The samples showed sharp superconducting transitions in both resistivity and susceptibility measurements. The samples showed typical under-doped behavior (S-shape) in the temperature dependence of resistivity. The Tc for the n=3 phase monotonically increased with decreasing a nominal fluorine content y, which shows the electronic state shifts from under-doped toward optimally one with increasing hole density by substitution of apical O2− for F−. The highest Tc measured so far for n=2, 3, 4 and 5 phases were 90, 120, 105 and 90 K, respectively. This compound shows a maximum Tc at n=3 like in many other homologous series. In spite of a short spacing between superconducting blocks (≈7.36 A), the critical current density (Jc) and irreversibility field (Hirr) of the n=3 phase decreased rapidly with increasing temperature provably due to the small carrier (holes) density.

We prepared two MgB 2 bulks by applying conventional sintering and high-pressure sintering methods, and compared the current carrying properties. J c obtained by the resistive method was larger than that obtained by the magnetic method. J c – B curves obtained by the resistive method showed no history effect. These results indicate that most of the superconducting currents flowing in the MgB 2 bulks were intergrain (transport) currents and intragrain currents were negligibly small. The high-pressure sintered sample with smaller grain size showed smaller field dependence of J c and higher B irr than the conventionally sintered sample with larger grain size. This behavior can be explained by the grain boundary flux pinning.

Two “superconducting transition temperatures” ( T c s) of Cu x Ba 2 Ca 3 Cu 4 O y were examined by the specific heat measurement. Comparing the specific heat under magnetic field (14 T) and that without field, two anomalies were observed in the electronic specific heat. When there are more than two Fermi surfaces (FSs) and the superconducting gaps do not develop simultaneously in these FSs, we can expect two anomalies. Strictly speaking the second anomaly at lower temperature ( T c2 ) is not due to the real phase transition but its vestige. A theoretical inspection indicates the second anomaly means the inter-FS interaction is very weak. If the symmetry of the superconducting gap on one FS is different from that on the other, one can expect a drastic suppression of the inter-FS interaction.

TlBa 2 Ca n −1 Cu n O y ( n =3: Tl-1223 and n =4: Tl-1234) have been found to have comparable T c with Hg-system which is known to show the highest T c in superconductors. Samples were synthesized under a pressure of 3.5 GPa using precursors with small residual carbon concentrations. We found that starting composition of Tl and synthesis temperature also affect the T c . Polycrystalline samples showed T c of 133.5 (Tl-1223) and 127 K (Tl-1234) after the post-annealing in nitrogen flow, respectively. Composition analysis suggested that suppression of the substitution of Tl for Ba- and Ca-site enhances the T c .

The electronic structure of TlCa 2 Ba 2 Cu 3 O 9 (Tl1223) and its change by oxygen reduction or anion substitution is investigated by using the scalar-relativistic full-potential linearized augmented-plane-wave method. Electronic structure of Tl1223 is almost similar to the homologous system, Tl1212. However, reduction of oxygen, or substitution of flourine by oxygen induce a great change for Tl6s band, and this band crosses the Fermi level and additional carriers are introduced onto this new band. This behavior is confirmed by the X-ray photoemission spectroscopy.

The Sr x Ca 1− x CuO 2 thin films and [CaCuO 2 ] m /[SrCuO 2 ] n superlattices (SLs) have been prepared by multi-target off-axis rf magnetron sputtering on treated SrTiO 3 (1 0 0) with periodic step arrays of atomic control on substrate surfaces. X-ray diffraction analyses have confirmed the formation of the tetragonal, infinite layer crystal structure with c -axis orientation. The obtained SLs and the Sr x Ca 1− x CuO 2 thin films showed semiconducting behavior. The Sr x Ca 1− x CuO 2 thin films with x =0.7 had remarkable resistive anomalies around 90 K and clear Meissner signals at temperature below 45 K. For the CaCuO 2 /SrCuO 2 artificial SLs, SL chemical modulation was observed for structures with individual layers as thin as two unit cells. The peak attributed to the SL periodicity was also observed, indicating good control of the film growth.

We report on the epitaxial growth of 1:2:0:1 type CuBa 2 CuO y layer, an infinite layer CaCuO 2 and their superlattice (1×3) by self-assembling epitaxy method, involving rf magnetron sputtering, on (1 0 0) SrTiO 3 substrate. Excellent (0 0 1) films of both the CuBa 2 CuO y and CaCuO 2 with c ∼8.4 and 3.2 A, respectively, were obtained. A superlattice with a period of about 18.5 A which corresponds to the formula CuBa 2 Ca 3 Cu 4 O y was prepared by growing alternatively the 1:2:0:1 and CaCuO 2 at about 500°C in a gas mixture 10–20 mTorr of Ar+N 2 O. The as-grown superlattice film showed a superconducting diamagnetic signal at about 20 K.

Superconducting thin films with a predominant single phase of Cu1-xTlxBa2Ca3Cu4O12-y [Cu1-xTlx-1234] have been prepared for the first time by employing a two-step method. In this method the crystalline material was prepared from the sputtered amorphous phase by thallium treatment. This process was carried out at 900 °C for 1 h in an Au capsule. The amorphous phase was prepared by sputter deposition onto an SrTiO3 substrate from a stoichiometric target of composition CuBa2Ca3Cu4Ox. The films achieved after thallium treatment were aligned bi-axially along the a- and c-axes. XRD (x-ray diffraction) measurements showed a single-phase material with a c-axis lattice constant of 18.74 A. The c-axis lattice constant of Cu1-xTlx-1234 films is in between that of Cu-1234 (17.99 A) and Tl-1234 (19.11 A) superconductors. The pole figure measurements of 103 reflection of the films showed a-axis-oriented crystals with Δ = 0.8°. The composition of the films after EDX (energy dispersive x-ray spectroscopy) measurements was Cu0.3Tl0.7Ba2Ca3Cu4O12-y. From the resistivity measurements Tc was 110 K and Jc measurements showed a current density of 2.0×106 A cm-2 (77 K, 0 T). The preparation of Cu1-xTlx-1234 superconductor films by this method was highly reproducible.

A TlBa2Ca2Cu3Oy (Tl-1223) superconductor with an ideal composition has a much higher Tc than the established value (~120 K). The intrinsic Tc arises by suppression of Tl substitution for Ba and Ca sites, which inherently occurs in samples prepared by conventional methods. The substitution of Tl was suppressed by preserving the samples in a heavily over-doped state (Tc~100 K) which was realized by a high-pressure (solid and oxygen) synthesis method. In addition, we found several synthesis conditions for which we could obtain high-Tc samples with good reproducibility. Residual carbon in the precursor was found to be harmful for superconductivity, so that it had to be reduced as much as possible before the high-pressure synthesis. The synthesis temperature and starting concentration of Tl, which also affect Tc, had to be controlled properly to enhance Tc. Samples show that Tc≥130 K by post-annealing in a reducing atmosphere at 650-700 °C for 0.5 h to 12 h. The sample prepared with the starting composition of Tl0.75Ba2Ca2Cu3.25Oy had an almost ideal grain composition and showed a Tc of 133.5 K. This Tc is comparable with that of HgBa2Ca2Cu3Oy (Hg-1223) which is known to have the highest Tc in superconductors.

We measured for the first time the fundamental and higher harmonic components of AC susceptibility of CuBa 2 Ca 3 Cu 4 O y superconductor produced by the high-pressure technique, in various experimental conditions (temperature, DC magnetic field, AC field amplitude and frequency). The results are discussed qualitatively in the frame of the critical state and other models in the literature. By using a very simple frequency-dependent critical state model, we estimated the parameters of practical interest, critical current density and pinning potential at various DC fields and temperatures and the irreversibility field. We also extrapolated our estimations to both practical temperature of 77 K and longer time scale as of DC magnetization and transport measurements. The results appeared to be quite self-consistent.

A change of electronic structure and chemical bond nature of high pressure synthesized (Cu,Tl)Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9-/spl delta// [(Cu,Tl)-1223] and TlBa/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9-/spl delta// [Tl-1223] with reduction-annealing, which leads to a significant rise of their superconducting transition temperature T/sub c/ above 130 K, has been investigated by in-situ photoemission spectroscopy. Their intrinsic surface nature has been achieved by fracturing in vacuum. In (Cu,Tl)-1223, a Fermi edge is observed for the first time. Trivalent Tl and heavily over-doped states of Cu-O clusters are dominant in as-grown specimens of both systems. The annealing resulted in remarkable shifts of photoemission spectra of Ba and Tl core levels towards higher binding energy with an increase of the annealing temperature, which means a selective oxygen-depletion around their charge-reservoirs and a decrease of valency of Tl. In contrast, there are quite little shape-changes and movements in valence band spectra and core signals of Cu and O. These results reveal that, in the high temperature-treated specimens, major portions of the electrons left should be absorbed into the cations in their charge reservoir, which consequently should cause a much more moderate change of the hole-concentration of the CuO/sub 2/ planes. It suggests that the utilization of this charge-redistribution mechanism in over-doped specimens should be an advantageous way to optimize the electronic structure of the 1223 phases for high T/sub c/.

Specific heat anomaly was studied on Cu x Ba 2 Ca 3 Cu 4 O y . ΔC/ T c , a height of peak of the specific heat at the superconducting transition ( T c ) divided by T c , is less than 60% of that of optimally doped YBa 2 Cu 3 O 7-δ . This suggests that a large density of states (DOS) remains to prohibit the creation of Bardeen-Cooper-Schrieffer (BCS) pairs at T c . It is much larger than the residual DOS at 0 K. We interpret that the “ missing DOS ” start to become BCS pairs at a temperature lower than T c , as proposed by an NMR study [Phys. Rev. B 61 (2000) 9707], though we have not yet seen clear evidence of this.

The single phase of TlCu-1234 superconductor thin films is prepared for the first time by the amorphous phase epitaxy (APE) method, which is thallium treatment of sputtered amorphous phase at 900°C for 1 h. The amorphous phase is prepared by sputtering from the stoichiometric target composition CuBa 2 Ca 3 Cu 4 O 12− y . The films on the SrTiO 3 substrate are aligned biaxially after the thallium treatment. Highly reproducible TlCu-1234 films are prepared by this method. The XRD reflected a predominant single phase with the c -axis lattice constant of 18.74 A. This lattice constant value is in between that of Cu-1234 (17.99 A) and Tl-1234 (19.11 A). The pole figure measurements of (103) reflection of the films showed a -axis-oriented crystals with Δ φ =0.8°. The composition of the films after Energy Dispersive X-ray (EDX) measurements is Tl 0.8 Cu 0.2 Ba 2 Ca 3 Cu 4 O 12− y . From the resistivity measurements, the T c is 113 K. Preliminary J c measurements showed a current density of 1.0×10 6 A/cm 2 (77 K, 0 T).

The bi-axially-oriented thin films of Cu/sub 1-x/Tl/sub x/(Ba,Sr)/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10-y/(Cu/sub 1-x/Tl/sub x/-1223: x=0.2-1.0) were prepared by an amorphous phase epitaxy (APE) technique on SrTiO/sub 3/ substrates. The amorphous phase was deposited by sputtering on the substrate and annealed in a thallium atmosphere at /spl sim/885/spl deg/C for /spl sim/50 min. Their T/sub c/ values were 100-113 K and higher than those of the YBa/sub 2/Cu/sub 3/O/sub 7-y/ (Y-123, that is, Cu-1212) system. Their J/sub c/ values were 2/spl times/10/sup 7/ A/cm/sup 2/ (77 K, 0 T) and 4/spl times/10/sup 5/ A/cm/sup 2/ (77 K, 10 T) at their maximum for x/spl sim/0.5. The J/sub c/ values were higher than the maximum values of Y-123 thin films by a factor of 2. The high J/sub c/ values are consistent with the low superconducting anisotropy (/spl gamma/=/spl xi//sub ab///spl xi//sub c/=2.5-4) of Cu/sub 1-x/Tl/sub x/-1223 and its high T/sub c/.

A high-density atomic oxygen beam generated by thermal nonequilibrium high-temperature plasma has been used to control the surface nature of high-T/sub c/ superconducting YBCO epitaxial films and Cu-1234 ceramics. We report characterization of the electronic structure of the cleaned surfaces by in-situ ultraviolet and X-ray photoemission spectroscopy (UPS,XPS) and study of the relationship between the surface natures controlled and transport properties of multilayer structures fabricated over them. For both kinds of materials, exposure of the surface at a temperature of 300/spl sim/500/spl deg/C to the atomic oxygen beam yields highly ordered surface structures and a metallic feature with high electron density of states at the Fermi level. Owing to the improvement, the contact resistance between a cleaned YBCO[100] film and in-situ deposited gold, and a cleaned Cu-1234 and gold were found to be in the range of 10/sup -10//spl sim/10/sup -9/ and /spl sim/10/sup -8/ /spl Omega/.cm/sup 2/, respectively. The realization of an intrinsic Au/YBCO interface resulted in direct observation of the superconducting proximity effect in the gold layer from the YBCO. The control of the electrical connection also led to an enhancement of interlayer superconducting coupling in Pb/Ag/Au/YBCO[100] junctions. A positive correlation was found between the critical current density of the junction J/sub c/ and the height of photoelectron Fermi edge of YBCO, which corresponds to the electron density of states at the surface. A high J/sub c/, of the order of 10/sup 4/ A/cm/sup 2/, was achieved on the junctions fabricated on the YBCO surface with a Fermi edge height of 10% relative to that of Cu 3d UPS-signal.

Single phase samples with the composition of (Cu, M)Ba2Ca3Cu4Oy(CuM-1234; M=C,Al,Tl,Mg,Zn) have been synthesized using high pressure technique. We have measured the pressure dependence of superconducting transition temperature (Tc) through insitu resistivity measurements up to 8 GPa for these samples, reproducibly. These samples indicated almost the same Tc-enhancement by applied pressure, in spite of their different ambient Tcvalues. The enhancement values of 8-10 K at 8 GPa pressure for these samples are found to be comparable to those of Hg-system and (B,C)-system.

The carrier distribution among the inequivalent CuO 2 planes in multilayer cuprates is investigated by 63 Cu Knight shift measurement with varying the carrier concentration, δ and the number of CuO 2 plane in a unit cell, n. We found that 70 (60)% of total carriers are doped selectively into two outer CuO 2 planes in n = 3 (4). This indicates resultantly that the inhomogeneity of carrier distribution increases with increasing δ and n in multilayer cuprates.

We have synthesized the single phase samples of CuxC0.1Ba2Ca3Cu4Oz(x=0.2∼0.9). Transport and magnetic measurements and iodometric titration analysis were carried out for these materials. From these results we discuss the correlation between Tc, the Hall number, copper valence and oxygen content. The effect of the substituted M ions on Tcin (CuC, M)-l234 (M=Ni,Zn,Al,TI,Mg) is also discussed. We propose a unique selective carrier-doping mechanism in (Cu,C)- and (CuC,Mg)-1234 systems.

A superconducting gap resonating with a phonon makes a structure in the phonon spectral function even in the d-wave pairing. This is demonstrated by a theoretical calculation. The conditions employed in our calculations are q→0 and the clean limit where q is the momentum of the phonon. The difference in the line shape of the phonon between the s-wave model and d-wave mode is noticeable. The resonance structure would be observed in the Raman spectrum when the phonon propagates in ab-plane, i.e., the directions of the incident light and scattered light are perpendicular to c-axis. We propose a new method to investigate the symmetry of superconducting gap function in the cuprate superconductor through this resonance structure.

Synthesis of ${\mathrm{CuBa}}_{2}{\mathrm{Ca}}_{3}{\mathrm{Cu}}_{4}{\mathrm{O}}_{12\ensuremath{-}y}$ (Cu-1234) with Mg doping at the Ca sites, hitherto unexplored, is attempted and reported here. Different samples with 5%, 10%, 20%, and 33% Mg (in nominal stoichiometry) have been prepared in gold capsules under 3.5 GPa pressure and at about 1000 \ifmmode^\circ\else\textdegree\fi{}C temperature using a cubic anvil-type high-pressure machine. The samples were characterized through x-ray diffractometry, resistivity, dc susceptibility, and Hall effect measurements. The samples were then aligned along their c axis under 10 T field at room temperature. Magnetization (both in $H\ensuremath{\parallel}\mathrm{ab}$ and $H\ensuremath{\parallel}c$) was measured between 120 and 5 K in different field values up to 5 T. The superconducting anisotropy (defined as ${\ensuremath{\xi}}_{\mathrm{ab}}/{\ensuremath{\xi}}_{c}{=H}_{c2}^{\mathrm{ab}}{/H}_{c2}^{c}$), estimated in the reversible magnetization regime, comes out to be about 1.4, and is lower than that of the pristine sample. Improvement in the anisotropy factor obtained has been discussed in light of the observed changes in the lattice parameters and the hole concentration, emanating from Mg doping in the Cu-site vacancies in charge reservoir blocks of the 1234 structure.

The pressure dependence of the superconducting transition temperature, T c ( P ) has been measured up to 8 GPa for (B 1− x C x )(Ba 1− y Sr y ) 2 Ca 2 Cu 3 O z ( x =0.3, y =0.25; x =0.35, y =0.3) and B 0.8 C 0.2 (Ba 0.75 Sr 0.25 ) 2 Ca 3 Cu 4 O z . Large enhancement of T c under pressure was observed in the BC-1223 system. In nearly optimally doped B 0.65 C 0.35 (Ba 0.7 Sr 0.3 ) 2 Ca 2 Cu 3 O z , T c ( P ) is observed to increase from 119.6 K at ambient pressure to 133.0 K at 8 GPa. The enhancement of T c under pressure in BC-1234 was observed to be smaller than that in BC-1223. The results were discussed compared with those in the Hg-based system.

The c -axis-oriented films of Bi 2 (La 1− x Sr x ) 2 CuO y (BLSCO) with a composition region 0.5≤ x ≤1.0 were grown on a single crystal MgO (100) substrate using the spin-coating pyrolysis method. Transmittance and reflectivity spectra were taken in the photon energy region from 2.5 to 13 meV and from 0.12 to 2.5 eV at room temperature. The absorption coefficient α was calculated from the film thickness, transmittance and reflectivity. The absorption spectra exhibited a constant edge of 1.2 eV which did not vary with strontium content x . This phenomenon demonstrates that the CT gap of BLSCO remains unchanged with the substitution of Sr for La. The absorption spectra in the infrared to visible light region were insensitive to the excess oxygen content, while those in the mid- and far-infrared regions showed strong dependence on the excess oxygen content. The absorption coefficient in the far-infrared region from 2.5 to 13 meV was very close to that calculated from the dc conductivity. The effective hole number calculated using the sum rule agreed with that calculated, assuming that one excess oxygen atom creates two holes in the composition region 0.5≤ x ≤0.8. The temperature dependence of conductivity showed the existence of an energy gap between the valence band and the acceptor level originated from the excess oxygen. An electronic model where the excess oxygen acts as the acceptor was proposed to interpret the observed results.

The hot press method was employed for the synthesis of a new family of the high T c superconductor (CuTl)Ba 2 Ca n −1 Cu n O 2 n +4− y . By varying the starting composition of the samples, the optimum preparation conditions for the Cu 1− x Tl x Ba 2 Ca 2 Cu 3 O 10− y ( x =0.25–0.75) phases were studied. The highest T c (121 K) sample of (Cu 0.3 Tl 0.7 )-1223 was obtained by hot press sintering at 1000°C for 3 h. Highly oriented (Cu 0.3 Tl 0.7 )-1223 samples along the c -axis were obtained by the same way.

Single crystals of CuBa 2 Ca 3 Cu 4 O y (Cu-1234) with dimensions up to 200×100×20 μ m 3 have been synthesized under high pressure using a belt type anvil apparatus. The impurity of Au, emanating from Au capsule, was found in the crystals by SEM–EDS analysis. These crystals showed superconducting transition temperature ( T c ) ranging from 105 K to 68 K and are lower than that of Au-free polycrystals ( T c =118 K). The T c values are found to decrease linearly with Au content at a substantially high rate of 7.0±0.4 K%, indicating the substitution of Au ions for Cu-sites. Superconducting anisotropy γ as estimated from the resistivity data of Cu-1234 single crystal just above T c (=102 K) has been found to be higher ( γ =5.8) than that for the Au-free polycrystals.

A new solid-solution superconductor, (Cu,Hg)Ba2Ca4Cu5Oy, with the tetragonal lattice parameters a = 3.849(2) A and c = 21.496(3) A , has been synthesized by the high-temperature and high-pressure technique. The structure refinement of the as-prepared (Cu,Hg)-1245 by the single-crystal X-ray diffraction method confirmed the substitutional composition (Cu0.76Hg0.24)Ba2Ca4Cu5O12.45, whose cationic composition was close to that obtained by chemical analysis. The additional Cu atoms at the mercury site construct the chain-like oxygen coordination. The superstructure observed in Cu-1245 disappeared by the partial substitution of mercury for copper in the present (Cu,Hg)-1245. The structure refinement of the as-prepared Hg-1245 revealed the mercury-site deficiency of about 20%.

Surface-cleaning using 100% ozone beams or atomic oxygen beams has been applied for the fabrication of high quality [110]- and (100)-axis oriented YBCO epitaxial films. The treatment recovers metallic surfaces in spite of the semiconducting properties of the as-received surfaces. High quality [110]- and (100)-oriented films with high T/sub c/ and high orientation were deposited by temperature-gradient self-template method. On both kinds of film clear photoelectron Fermi edges, evidence of a metallic feature, were observed at room temperature. For the [110] films, well-defined photoelectron Fermi edges are observed for the first time, For the (100) surface, the rather high electron density of states Fermi edge is as high as about 15% of Cu 3d signal in valence band, On the other hand, the edge-height of the [110] surface was less than 5% of the Cu 3d and it was reduced as a function of time. Detailed electronic structures and the origin of the difference of the surface-stabilities is discussed.