2,321 research outputs found
Superconductivity in undoped T' cuprates with Tc over 30 K
Undoped cuprates have long been considered to be antiferromagnetic
insulators. In this article, however, we report that superconductivity is
achieved in undoped T'-RE2CuO4 (RE = Pr, Nd, Sm, Eu, and Gd). Our discovery was
performed by using metal-organic decomposition (MOD), an inexpensive and
easy-to-implement thin-film process. The keys to prepare the superconducting
films are firing with low partial-pressure of oxygen and reduction at low
temperatures. The highest Tc of undoped T'-RE2CuO4 is over 30 K, substantially
higher than "electron-doped" analogs. Remarkably, Gd2CuO4, even the derivatives
of which have not shown superconductivity so far, gets superconducting with
Tconset as high as ~ 20 K. The implication of our discovery is briefly
discussed.Comment: 22 pages, 5 figures, submitted to Physical Review Letter
Efficient method for simulating quantum electron dynamics under the time dependent Kohn-Sham equation
A numerical scheme for solving the time-evolution of wave functions under the
time dependent Kohn-Sham equation has been developed. Since the effective
Hamiltonian depends on the wave functions, the wave functions and the effective
Hamiltonian should evolve consistently with each other. For this purpose, a
self-consistent loop is required at every time-step for solving the
time-evolution numerically, which is computationally expensive. However, in
this paper, we develop a different approach expressing a formal solution of the
TD-KS equation, and prove that it is possible to solve the TD-KS equation
efficiently and accurately by means of a simple numerical scheme without the
use of any self-consistent loops.Comment: 5 pages, 3 figures. Physical Review E, 2002, in pres
Two Sizes of Superconducting Gaps on an Under-doped Bi2.1Sr1.9Ca2Cu3O10+δ with TC ∼ 101K by Tunneling Spectroscopy
AbstractWe measured tunneling conductances on an under-doped trilayer cuprate Bi2.1Sr1.9Ca2Cu3O10+≏ (Bi2223) with TC ∼ 101K by a point contact method, which has three CuO2 planes in a unit cell. The tunneling conductances on Bi2223 exhibited two sizes of gaps originated from outer and inner CuO2 plane (OP and IP). The estimated size of superconducting gap from OP ΔOP is 34 ± 6 meV, and the ΔIP from IP is 51 ± 5 meV, respectively. We also observed tunneling conductances which simultaneously displayed two superconducting peaks of OP and IP. Moreover, we propose the model of two superconductor-insulator-normal metal junctions which exhibit two sizes gaps of OP and IP
Large magneto-thermal effect and the spin-phonon coupling in a parent insulating cuprate Pr_{1.3}La_{0.7}CuO_4
The magnetic-field (H) dependence of the thermal conductivity \kappa of
Pr_{1.3}La_{0.7}CuO_4 is found to show a pronounced minimum for in-plane fields
at low temperature, which is best attributed to the scattering of phonons by
free spins that are seen by a Schottky-type specific heat and a Curie-Weiss
susceptibility. Besides pointing to a strong spin-phonon coupling in cuprates,
the present result demonstrates that the H-dependence of the phonon heat
transport should not be naively neglected when discussing the \kappa(H)
behavior of cuprates, since the Schottky anomaly is ubiquitously found in
cuprates at any doping.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.
Theory of double resonance magnetometers based on atomic alignment
We present a theoretical study of the spectra produced by
optical-radio-frequency double resonance devices, in which resonant linearly
polarized light is used in the optical pumping and detection processes. We
extend previous work by presenting algebraic results which are valid for atomic
states with arbitrary angular momenta, arbitrary rf intensities, and arbitrary
geometries. The only restriction made is the assumption of low light intensity.
The results are discussed in view of their use in optical magnetometers
Observation of Andreev bound states in bicrystal grain-boundary Josephson junctions of the electron doped superconductor LaCeCuO
We observe a zero-bias conductance peak (ZBCP) in the ab-plane quasiparticle
tunneling spectra of thin film grain-boundary Josephson junctions made of the
electron doped cuprate superconductor LaCeCuO. An applied magnetic field
reduces the spectral weight around zero energy and shifts it non-linearly to
higher energies consistent with a Doppler shift of the Andreev bound states
(ABS) energy. For all magnetic fields the ZBCP appears simultaneously with the
onset of superconductivity. These observations strongly suggest that the ZBCP
results from the formation of ABS at the junction interfaces, and,
consequently, that there is a sign change in the symmetry of the
superconducting order parameter of this compound consistent with a d-wave
symmetry.Comment: 9 pages, 7 figures; December 2004, accepted for publication in Phys.
Rev.
Andreev bound states at a cuprate grain boundary junction: A lower bound for the upper critical field
We investigate in-plane quasiparticle tunneling across thin film grain
boundary junctions (GBJs) of the electron-doped cuprate
LaCeCuO in magnetic fields up to T, perpendicular to
the CuO layers. The differential conductance in the superconducting state
shows a zero bias conductance peak (ZBCP) due to zero energy surface Andreev
bound states. With increasing temperature , the ZBCP vanishes at the
critical temperature K if B=0, and at K for B=16 T. As
the ZBCP is related to the macroscopic phase coherence of the superconducting
state, we argue that the disappearance of the ZBCP at a field
must occur below the upper critical field of the superconductor. We
find T which is at least a factor of 2.5 higher than
previous estimates of .Comment: 4 pages, 4 figure
Two-stage spin-flop transitions in S = 1/2 antiferromagnetic spin chain BaCu_2Si_2O_7
Two-stage spin-flop transitions are observed the in quasi-one-dimensional
antiferromagnet, BaCuSiO. A magnetic field applied along the
easy axis induces a spin-flop transition at 2.0 T followed by a second
transition at 4.9 T. The magnetic susceptibility indicates the presence of
Dzyaloshinskii-Moriya (DM) antisymmetric interactions between the intrachain
neighboring spins. We discuss a possible mechanism whereby the geometrical
competition between DM and interchain interactions, as discussed for the
two-dimensional antiferromagnet LaCuO, causes the two-stage
spin-flop transitions.Comment: 5 pages, 3 figures (included), accepted for publication in Phys. Rev.
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