Thermodynamic properties of excess-oxygen-doped La2CuO4.11 near a simultaneous transition to superconductivity and long-range magnetic order

We have measured the specific heat and magnetization {\it versus} temperature in a single crystal sample of superconducting La$_{2}$CuO$_{4.11}$ and in a sample of the same material after removing the excess oxygen, in magnetic fields up to 15 T. Using the deoxygenated sample to subtract the phonon contribution, we find a broad peak in the specific heat, centered at 50 K. This excess specific heat is attributed to fluctuations of the Cu spins possibly enhanced by an interplay with the charge degrees of freedom, and appears to be independent of magnetic field, up to 15 T. Near the superconducting transition $T_{c}$($H$=0)= 43 K, we find a sharp feature that is strongly suppressed when the magnetic field is applied parallel to the crystallographic c-axis. A model for 3D vortex fluctuations is used to scale magnetization measured at several magnetic fields. When the magnetic field is applied perpendicular to the c-axis, the only observed effect is a slight shift in the superconducting transition temperature.Comment: 8 pages, 8 figure

Orbital Kuantum Pengantar Teori dan Contoh Aplikasinya

Xii.; 400 hal.;ill.; 14,5x20,5 c

Magnetic field dependence of the transverse plasmon in SmLa0.8Sr0.2CuO4-delta

The magnetic field and temperature dependence of the transverse and longitudinal plasmons in SmLa_0.8Sr_0.2CuO_{4-\delta} have been measured for frequencies 5 < nu < 30 cm^{-1} and magnetic fields 0 < B < 7 T. A transition between a vortex glass and a vortex liquid regime, which revealed different field dependencies of the resonance frequencies, could be clearly observed. The positions and the spectral weights of the plasmons were successfully described using the multilayer model (Phys. Rev. B 64, 024530, 2001), which takes the compressibility of the electronic liquid into account. The compressibility is shown to remain constant in the broad range of field and temperature, which strongly supports the applicability of the model. The absolute value of the compressibility is close to that of a two-dimensional noninteracting electron gas.Comment: 5 pages, 4 figure