Kazuyuki Hamada

NMR study of local hole distribution, spin fluctuation and superconductivity in Tl2Ba2Ca2Cu3O10

Abstract 63Cu, 17O and 205Tl NMR have been performed in the high-Tc superconductor Tl2Ba2Ca2Cu3O10 whose Tc(max) is 127 K. The hole densities at Cu and oxygen sites in the CuO2 plane have been extracted from the nuclear quadrupole frequency νQ. The striking feature is that the Cu holes are significantly transferred to oxygen site due to strong hybridization between Cu and oxygen. From an analysis of T1 and T2G, it has been found that the spectral weight of the spin fluctuation is transferred to higher energy compared to YBa2Cu3O7, while the magnetic correlation length ξ does not differ much. Thus, it is suggested that the higher Tc is due to higher characteristic energy of spin fluctuations, i.e. the superconductivity is spin fluctuation mediated. The superconducting properties are consistently explained by a d-wave superconductivity model with a finite density of states (DOS) at the Fermi level. We show that the disorder of the Ca/TlO layer caused by the partial inter-substitution of Tl and Ca is responsible for the potential scattering to produce such a DOS. It is found that if such a potential scattering were absent, Tc would go up to 132 K which is quite close to the record Tc realized in the Hg based compound.

Characteristics of the spin fluctuation in Tl2Ba2Ca2Cu3O10

We report a 63 Cu and 17 O NMR study in the high- T c superconductor Tl 2 Ba 2 Ca 2 Cu 3 O 10 with T c (max)=127 K. The results of T 1 and T 2 G reveal that the characteristic energy of the antiferromagnetic spin fluctuation Γ Q is higher than that in YBa 2 Cu 3 O 7 , while the magnetic correlation lengths ξ do not differ much from each other. The high T c in this compound is thus related to large Γ Q , suggesting that the superconductivity is spin fluctuation mediated.

A method for doping Tl-based cuprate superconductors with holes

Abstract We previously demonstrated that the T c for a Tl-2223 superconductor was increased to above 125 K when the sample was encapsulated in an evaluated quartz tube and post-annealed at 750°C for 250 h. It was indicated by thermo-electric power measurements that the post-annealed Tl-2223 sample had a hole concentration higher than an as-sintered Tl-2223 sample. Moreover, when the same encapsulation-and-post-annealing (ECPA) technique was applied to a Tl-2212 phase and a Tl-2234 sample, the T c decreased in the case of Tl-2212 while it increased in the case of TL-2234 phase. This demonstrated that the ECPA technique was affective in increasing the hole concentration in both over-doped (i.e. Tl-2212) and under-doped (i.e. Tl-2223 and Tl-2234) phases. Judging from the changes in the lattice constants and the chemical composition, it was likely that the increases in hole concentration and the subsequent changes in T c were due to decreases in the Tl content during ECPA processes.

30-TW laser–plasma interactions at ILE, Osaka

The 30-TW GEKKO-MII short pulse laser is completed and is used for high field physics studies, including a basic fast ignitor research. The second harmonic (2ω) backscattering shows critical surface recession due to the laser photon pressure. A few hundred protons and deuterons are observed. The 100-TW GEKKO-XII short pulse laser, a petawatt laser module, is constructed to study a feasibility of fast ignition of an imploded target.

New Tl-based copper oxide containing double-MO2-unit fluorite block: (Tl, Cu) Sr2 (R, Ce)3Cu2O11 (R: rare earth element)

Abstract New Tl-based copper oxides. (Tl, Cu)Sr2(R, Ce)3Cu2O11 (R: rare earth element) (Tl-based “1232”), have been synthesized. These compounds have tetragonal unit cells with lattice constants approximately equal to a=3.8 A and c=17.3 A . A Rietveld analysis using X-ray powder diffraction data shows that the crystal structure of (Tl 4 5 Cu 1 5 )Sr2(Ho 1 3 Ce 2 3 )3Cu2O11 consists of a double-MO2-unit flouride block, i.e. [(Ho, Ce)O2]2 and a Tl-based “1212” block, i.e. (Tl, Cu)Sr2(Ho, Ce)Cu2O7. The temperature dependences of the electrical resistivity for all of these compounds are semiconductive. However, these compounds are considered to be candidates for parent materials for new high-Tc superconductors.

Synthesis of Tl‐based ‘‘2234’’ superconductors

Nearly single‐phase samples of superconducting Tl–Ba–Ca–Cu–O ‘‘2234’’ were successfully synthesized. The sample sintered in air had Tc of 112 K. Post‐annealing of the sintered sample in a high‐pressure oxygen gas made its Tc increase up to 115 K. The sample sintered in argon gas had Tc of 90 K. The thermoelectric power (TEP) of the sample was also measured. All the samples showed positive TEP signals. The magnitude of TEP signal decreased as Tc increased. Thus, it was likely that the as‐sintered 2234 phase was in an under‐doped state with respect to the optimum carrier concentration.

Mobile Intrinsic Localized Modes of a Spatially Periodic and Articulated Structure

The intrinsic localized mode (ILM) in a spatially periodic and articulated structure is examined in detail numerically. The structure is composed of identical, uniform and rigid members connected with neighboring ones at junctions through couplers giving nonlinear restoring moments. The system, with both free ends, constitutes a constrained Hamiltonian system subject to holonomic constraints by continuity of displacements at junctions. The formulation of flexural motions of the system has been already given in the previous paper [Y. Watanabe, K. Hamada, and N. Sugimoto: Wave Motion 45 (2007) 100], where the existence and properties of the stationary ILMs were examined in detail. In this paper, it is revealed by calculations under asymmetrical initial conditions with respect to the center of the structure, that there are two types of mobile ILMs: one is a trapped type at either end of the structure and the other is a propagating type at a constant speed, but subject to reflections at both ends. It is the former that shows the general behavior of the ILMs in the structure and the stationary type of ILM found in the previous paper should be regarded as a special case.

Effect of structural disorder on the superconductivity in Tl2Ba2Ca2Cu3O10

The 63 Cu spin-lattice relaxation rate has been measured in an annealed sample of Tl 2 Ba 2 Ca 2 Cu 3 O 10 with T c =123 K, and compared with that in the previously reported as-grown sample with T c = 115 K. We found, for the first time, that T c increases as a result of a decrease in the residual density of states (DOS), N res , at the Fermi level due to the improvement of crystal ordering by annealing . Based on the T 1 result, N res normalized by the value at T c , N res / N 0 , was found to be reduced from 0.30 to 0.18 after annealing. A 2-dimensional d-wave superconductivity model accounts for the increase of T c in terms of the change in potential scattering due to crystal imperfection, which is probably caused by Ca/Tl inter-substitution.

Nearly single-phase Tl-based “2223” superconductor with Tc =125 K

Abstract A nearly single-phase Tl-based “2223” superconductor was obtained from the nominal composition of Tl 1.7 Ba 2 Ca 2.3 Cu 3 O z . The as-sintered samples had T c mag (diamagnetic onset temperature) at 122.5 K. These samples were annealed in various atmospheres such as nitrogen, argon and high-pressure oxygen gases. When the samples was heated in a reduced atmosphere, e.g. N 2 gas, the sample weight decreased. Om the contrary when heated in a high pressure oxygen gas, the sample weight increased. Therefore, the change in the sample weight was considered to be arisen by the change in the oxygen content of the sample. We obtained the highest T c mag of 124.7 K by annealing sample in weakly reduced atmosphere. The dependence of the oxygen content on T c mag demonstrated an over- convex curve that had the maximum value of 124.7 K at 0.06 wt% loss in the sample weight.

Synthesis and Properties of Tl-Based “2223” Superconductor with T c R=0 =127 K

Single phase superconducting Tl-Based “2223” material with a Tc higher than 125 K, i.e. Tc R=0 (zero-resistance temperature) = 127 K and Tc mag (diamagnetic onset temperature) = 130 K, was obtained using Ca-rich nominal composition of Tl1.7Ba2Ca2.3Cu3Oz. After sintering at 890 Ti the critical temperature of the samples were around 120 K, but post-annealing with an encapsulation in an evacuated quartz tube effectively improved the Tc values. The critical temperature correlated with the post-annealing time, and for the samples annealed at 750 °C for longer than 80 h, the Tc values exceeded 125 K. As a structure change connected with the improvement of the Tc an increase in the c — axis was observed while the a — axis was not affected by post-annealing.