Tadashi Adachi

The ability to efficiently control charge and spin in the cuprate high-temperature superconductors is crucial for fundamental research and underpins technological development. Here, we explore the tunability of magnetism, superconductivity, and crystal structure in the stripe phase of the cuprate La Ba CuO , with = 0.115 and 0.135, by employing temperature-dependent (down to 400 mK) muon-spin rotation and AC susceptibility, as well as X-ray scattering experiments under compressive uniaxial stress in the CuO plane. A sixfold increase of the three-dimensional (3D) superconducting critical temperature and a full recovery of the 3D phase coherence is observed in both samples with the application of extremely low uniaxial stress of 0.1 GPa. This finding demonstrates the removal of the well-known 1/8-anomaly of cuprates by uniaxial stress. On the other hand, the spin-stripe order temperature as well as the magnetic fraction at 400 mK show only a modest decrease under stress. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. However, strain produces an inhomogeneous suppression of the spin-stripe order at elevated temperatures. Namely, a substantial decrease of the magnetic volume fraction and a full suppression of the low-temperature tetragonal structure is found under stress, which is a necessary condition for the development of the 3D superconducting phase with optimal . Our results evidence a remarkable cooperation between the long-range static spin-stripe order and the underlying crystalline order with the three-dimensional fully coherent superconductivity. Overall, these results suggest that the stripe- and the SC order may have a common physical mechanism.

To investigate proposed ferromagnetic fluctuations in the so-called single-layer Bi-2201 and La-214 high-Tc cuprates, we performed magnetization and electrical resistivity measurements using single-layer Tl-2201 cuprates Tl2Ba2CuO6+δ and La-214 La2−xSrxCuO4 in the heavily overdoped regime. Magnetization of Tl2Ba2CuO6+δ and La2−xSrxCuO4 exhibited the tendency to be saturated in high magnetic fields at low temperatures, suggesting the precursor behavior toward the formation of a ferromagnetic order. It was found that the power of temperature n obtained from the temperature dependence of the electrical resistivity is ~4/3 and ~5/3 for Bi-2201 and La2−xSrxCuO4, respectively, and is ~4/3 at high temperatures and ~5/3 at low temperatures in Tl2Ba2CuO6+δ. These results suggest that two- and three-dimensional ferromagnetic fluctuations exist in Bi-2201 and La2−xSrxCuO4, respectively. In Tl2Ba2CuO6+δ, it is suggested that the dimension of ferromagnetic fluctuations is two at high temperatures and three at low temperatures, respectively. The dimensionality of ferromagnetic fluctuations is understood in terms of the dimensionality of the crystal structure and the bonding of atoms in the blocking layer.

The magnetic hysteresis curve can provide information about magnetic properties, particle size, and its distribution. For superparamagnetic materials, the characteristics of the hysteresis curve are very typical, that is, Hc is equal to zero with a certain Ms value related to particle size in the order of nanometers. Here, we report the analysis of the magnetization hysteresis curve by applying a modified Langevin equation with and without a log-normal distribution for nearly superparamagnetic Fe3O4 and Fe3O4 encapsulated by SiO2 (Fe3O4–SiO2). To study the reliability of the modified Langevin equation, we compared the particle size values obtained from fittings analysis of the modified Langevin equation with those obtained from the TEM measurement. It was found that particle size from TEM measurement for Fe3O4 and Fe3O4–SiO2 is 11 and 14 nm, respectively. These values had a very high match with the particle size obtained from fitting analysis of the modified Langevin equation with or without a log-normal distribution, which is 12.6 and 12.9 nm for Fe3O4 and 13.8 and 14.5 nm for Fe3O4–SiO2, respectively. The fitting results of the modified Langevin equation with a log-normal distribution showed a value closer to the measurement results. By using the modified Langevin equation with a log-normal distribution, it was also obtained that the probability density function for Fe3O4 was 20.69% and that for Fe3O4–SiO2 was 0.55%. It was concluded that the modified Langevin equation with and without log-normal distribution was able to be used to obtain the particle size and its distribution for nearly superparamagnetic samples.

Abstract A small-momentum-width muon beam, so-called ultra-slow muon beam, can be generated by laser ionization of muonium. To realize efficient ultra-slow muon generation, the Lyman-alpha and below 360 nm coherent light are required to resonantly excite the muonium from the ground state to 2p and sequentially ionizes excited muonium to the unbound state. At the J-PARC MLF Ultra-Slow Muon beamline, we have successfully generated Lyman-alpha coherent light exceeding 10 μJ using an all-solid-state laser and high-efficiency vacuum ultraviolet light generation technologies. In this paper, we will describe the intense Lyman-alpha light source.

We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes.

Abstract We present the results of the investigations of high conducting area and superconductivity at the interfaces between ferroelectric oxide and insulating oxide in heterostructures, isostructural to BaTiO₃/La₂CuO₄. The performed numerical simulations of BaTiO₃/La₂CuO₄ heterostructure show the possibility of high conductivity state at the interface. The temperature dependence of the measured electrical resistance of the Ba_0.8Sr_0.2TiO₃/La₂CuO₄ heterostructure interface have been studied and the superconducting behaviour with transition temperature T_c about 30K has been found. Therefore, the transition to the state with 2DEG at the interface is demonstrated. The results offer the possibility to design novel electronic devices.

Abstract The results of the investigations of high conducting and superconducting areas at the interfaces between ferroelectric oxide and insulating oxide are presented. The numerical simulations of BaTiO₃/LaMnO₃ and BaTiO₃/La₂CuO₄ heterostructures have been performed. It is found that in the samples of the Ba_0.8Sr_0.2TiO₃/LaMnO₃ heterostructure the electrical resistance decreases significantly and exhibits metallic behaviour at low temperatures for the case when the c axis of ferroelectric film is directed along the normal to the surface of the single crystal. The superconducting behaviour with transition temperature T_c about 30K has been found at the interface of the Ba_0.8Sr_0.2TiO₃/La₂CuO₄ heterostructure. The proposed concept promises the ferroelectrically controlled interface conductivity and superconductivity.

To investigate the relationship between the so-called stripe correlations and the high-<italic>T</italic>_csuperconductivity, we have carried out magnetic susceptibility and zero-field muon spin relaxation measurements in partially Fe-substituted La₂₋<italic>_x</italic>Sr<italic>_x</italic>Cu₁₋<italic>_y</italic>Fe<italic>_y</italic>O₄(LSCFO). It has been found that the Fe substitution induces successive magnetic transitions in the overdoped regime: a spin-glass transition of Fe³⁺spins due to the Ruderman–Kittel–Kasuya–Yosida interaction based on itinerant spins at high temperatures and a stripe-order transition of localized Cu²⁺spins at low temperatures. The stripe-order transition disappears at the hole concentration per Cu of ∼0.28 which coincides with the endpoint of the superconductivity in pristine La₂₋<italic>_x</italic>Sr<italic>_x</italic>CuO₄, suggesting that the stripe correlations are closely related to the high-<italic>T</italic>_csuperconductivity in the overdoped regime as well as in the underdoped regime. For the spin-glass state, it has been found that the contribution of polarized itinerant spins to the muon-spin depolarization is not negligible. Taking into account neutron-scattering results obtained by He et al. [<ext-link ext-link-type="uri" xlink:href="http://doi.org/10.1103/PhysRevLett.107.127002" xlink:type="simple">Phys. Rev. Lett. <bold>107</bold>, 127002 (2011)</ext-link>] that a spin density wave (SDW) order has been observed in overdoped LSCFO, the present results demonstrate the presence of a novel coexistent state of an SDW order of itinerant spins and a spin-glass state of Fe³⁺spins.

To investigate the electronic state of Ce-free and Ce-underdoped high-<italic>T</italic>_ccuprates with the so-called T′ structure, we have performed muon spin relaxation (μSR) and specific heat measurements of Ce-free T′-La_1.8Eu_0.2CuO_4+δ(T′-LECO) polycrystals and Ce-underdoped T′-Pr_1.3−<italic>_x</italic>La_0.7Ce<italic>_x</italic>CuO_4+δ(T′-PLCCO) single crystals with <italic>x</italic>= 0.10. The μSR spectra of the reduced superconducting samples of both T′-LECO with <italic>T</italic>_c= 15 K and T′-PLCCO with <italic>x</italic>= 0.10 and <italic>T</italic>_c= 27 K have revealed that a short-range magnetic order coexists with the superconductivity in the ground state. The formation of a short-range magnetic order due to a very small amount of excess oxygen in the reduced superconducting samples strongly suggests that the Ce-free and Ce-underdoped T′-cuprates are strongly correlated electron systems.