N-type Cuprate Superconductors Research Articles

A New Bipolar Type Transistor Created Based on Interface Effects of Integrated All Perovskite Oxides

Oxide transistor is the basic device to construct the oxide electronic circuit that is the backing to develop integrated oxide electronics with high efficiency and low power consumption. By growing the perovskite oxide integrated layers and tailoring them to lead semiconducting functions at their interfaces, the development of oxide transistors may be able to perform. We realize a kind of p-i-n type integrated layers consisting of an n-type cuprate superconductor, p-type colossal magnetoresistance manganite, and a ferroelectric barrier (i). From this, bipolar transistors were fabricated at the back-to-back p-i-n junctions, for which the Schottky emission and p-n junction barriers, as well as the ferroelectric polarization, were integrated into the interfaces to control the transport properties; a preliminary but distinct current gain greater than 1.6 at input current of microampers order was observed. These results present a real possibility to date for developing bipolar all perovskite oxide transistors.

The origin of superconductivity in nominally ‘undoped’T′-La2−xYxCuO4 films

We have systematically studied the transport properties ofLa2−xYxCuO4 (LYCO)films with T′-phase (0.05≤x≤0.30). In this nominally ‘undoped’ system, superconductivity was acquired in a certain Y doping range(0.10≤x≤0.20). Measurements of resistivity, Hall coefficient in normal states and resistive critical field(Hc2ρ) in superconductingstates of the T′-LYCO films show similar behavior as the known Ce-doped n-type cuprate superconductors,indicating the intrinsic electron doping nature. The charge carriers are thought to beinduced by oxygen deficiency. Non-superconducting Y-doped Pr- or Nd-basedT′-phase cuprate films were also investigated for comparison, suggesting a crucial role of theradii of A-site cations in the origin of superconductivity in the nominally ‘undoped’cuprates. A reasonable scenario is put forward for the microscopic reduction process toexplain the experimental observations.

Intrinsic electron doping in nominal “nondoped” superconducting (La,Y)2CuO4 thin films grown by magnetron sputtering

The superconducting nominal “nondoped” La1.85Y0.15CuO4 (LYCO) thin films are prepared by magnetron sputtering. The best TC0 of more than 13K is achieved in the optimal films with highly pure c-axis oriented T′-type structure. The quasiquadratic temperature dependence of resistivity and the negative Hall coefficient in the normal state, effect of oxygen content are all quite similar to the known Ce-doped n-type cuprate superconductors, suggesting the electron-doping nature in T′-LYCO. The charge carriers are considered to arise from oxygen deficiency.

The band structure of n-type cuprate superconductors with the T′(T) structure taking into account strong electron correlation

The spectral density, dispersion relations, and the position of the Fermi level for n-doped compositions based on NCO and LCO were calculated within the framework of the generalized tight binding method. As distinguished from LCO, the dielectric gap in NCO is nonlinear in character. We observe a virtual level both at the bottom of the conduction band and at the top of the valence band in both compounds. However, its position corresponds to the extreme bottom of the conduction band in LCO and is 0.1–0.2 eV above the bottom in NCO. This explains why we observe Fermi level pinning in n-LCO as the concentration of the doping component grows and reproduce its absence in NCCO at low doping values. We also found both compositions to be unstable in a narrow concentration range with respect to a nonuniform charge density distribution. The relation between the phase diagram for NCCO and the calculated electronic structure is discussed.

Doping dependence of an n-type cuprate superconductor investigated by angle-resolved photoemission spectroscopy.

We present an angle-resolved photoemission doping dependence study of the n-type cuprate superconductor Nd(2-x)Ce(x)CuO(4+/-delta), from the half-filled Mott insulator to the T(c) = 24 K superconductor. In Nd2CuO4, we reveal the charge-transfer band for the first time. As electrons are doped into the system, this feature's intensity decreases with the concomitant formation of near- E(F) spectral weight. At low doping, the Fermi surface is an electron-pocket (with volume approximately x) centered at (pi,0). Further doping leads to the creation of a new holelike Fermi surface (volume approximately 1+x) centered at (pi,pi). These findings shed light on the Mott gap, its doping evolution, as well as the anomalous transport properties of the n-type cuprates.

A photoemission investigation of the superconducting gap in an electron-doped cuprate superconductor

We have performed angle resolved photoelectron spectroscopy (ARPES) on the electron-doped cuprate superconductor Nd Ce CuO . Evidence is found for an anisotropic superconducting gap that is consistent with the existence of a 1.85 0.15 4 d-wave superconducting order parameter in the n-type cuprate superconductors. © 2001 Elsevier Science B.V. All rights reserved.

Magnetic ordering in Nd2-xCexCuO4-y

The n-type cuprate superconductor and closely related samples of the general form Nd2−xCe x CuO4−y have been studied with the muon spin relaxation technique. Non-super-conducting samples display antiferromagnetism (AFM) withTN below 150 K, the value being dependent upon both Ce concentration and oxygen depletion. The results are interpreted in terms of carrier concentration.

Electronic structure of P-type and N-type cuprate superconductors

In previously known high- Tc copper oxide superconductors the charge carriers have been electron vacancies or holes. By contrast, we have recently discovered a class of superconducting copper oxides with the formula Ln 2 − x Ce x CuO 4 in which the doped carriers are electrons. we describe here how we created the new superconductors and discuss the effect of carrier doping various physical properties.

Doping effect on the transport and optical properties of P-type and N-type cuprate superconductors

We discuss the physical meaning of the doping high Tc oxides, P-type La2−xSrxCuO4 and recently discovered N-type Nd2−xCexCuO4−y, based on the experimental results of the Hall effect and the optical reflectivity spectrum. It is suggested that for light doping the Mott-Hubbard picture gives proper description of the transport properties whereas for heavy doping or for higher frequencies the Fermi lquid picture seems more appropriate for both N- and P-type materials.