Bias and temperature dependence of the noise in a single electron transistor

Models generalizing the su (2) XX spin-chain were recently introduced. These XXC models also have an underlying su (2) structure. Their construction method is shown to generalize to the chains based on the fundamental representations of the A_m Lie algebras. Integrability of the new models is shown in the context of the quantum inverse scattering method. Their R-matrix is found and shown to yield a representation of the Hecke algebra. The diagonalization of the transfer matrices is carried out using the algebraic Bethe Ansatz. I comment on eventual generalizations and possible links to reaction-diffusion processes. Received: 24 June 1998 / Received in final form: 8 September 1998 / Accepted: 10 September 1998     

Permittivity of BaTiO3 epitaxial films grown on the YBa2Cu3O7−δ(001) surface

The epitaxial heterostructures YBa₂Cu₃O_7?δ and YBa₂Cu₃O_7?δ/(5 nm)SrTiO₃/BaTiO₃/(5 nm)SrTiO₃/YBa₂Cu₃O_7?δ are grown by the laser evaporation method on an LaAlO₃(100) substrate. The permittivity of a BaTiO₃ layer is approximately doubled (T=300 K) when a SrTiO₃ thin layer is inserted between a ferroelectric layer and superconducting cuprate electrodes. A maximum in the temperature dependence of the permittivity for a barium titanate layer in the YBa₂Cu₃O_7?δ/(5 nm)SrTiO₃/BaTiO₃/(5 nm)SrTiO₃/YBa₂Cu₃O_7?δ heterostructure is shifted by 70–80 K toward the low-temperature range with respect to its location in the corresponding dependence for the BaTiO₃ bulk single crystal. The bias voltage dependence of the permittivity for the BaTiO₃ grown layers exhibits a clearly pronounced hysteresis (T=300 K). The superconducting transition temperature for the lower YBa₂Cu₃O_7?δ electrode in a superconductor/ferroelectric/superconductor heterostructure considerably depends on the rate of its cooling after the completion of the formation process.     

Transport parameters of granular La0.67Ca0.33MnO3 films grown on an R-plane sapphire

Precisely (100)-oriented, 200-nm thick La_0.67Ca_0.33MnO₃ films have been grown by laser ablation on a sapphire (R-plane) substrate covered by a (100)SrTiO₃/(001)Bi₂SrNb₂O₉/(001)CeO₂ trilayer buffer. The azimuthal misorientation of crystal grains (50–300 nm) in the La_0.67Ca_0.33MnO₃ films decreased by about 40% as the condensation temperature was increased ered from 760 to 810° C. The lattice parameter of the grown manganate films was reduced to 3.81–3.82 Å by enriching them with oxygen. The maximum in the temperature dependence of the electrical resistivity of the La_0.67Ca_0.33MnO₃ films grown was shifted toward lower temperatures by 20–50 K relative to its position for bulk ceramic samples of a stoichiometric composition. The largest magnetoresistance (MR=42% at H=0.4 T) was found in La_0.67Ca_0.33MnO₃ films with a Mn⁴⁺ concentration on the order of 50% (T=166 K).     

Response of the electrical resistivity and magnetoresistance of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> epitaxial films to biaxial compressive mechanical (001) or (110) strains

The behavior of the electrical resistivity and magnetoresistance of 40-to 120-nm-thick La_0.67Ca_0.33MnO₃ films grown on differently oriented lanthanum aluminate substrates was studied. The cell volume in thin (40 nm) La_0.67Ca_0.33MnO₃ films grown coherently on (001)LaAlO₃ was found to be substantially smaller. Mechanical stress relaxation in biaxially strained La_0.67Ca_0.33MnO₃ films is accompanied by an increase in the cell volume. The temperatures at which the electrical resistivity and magnetoresistance in biaxially strained La_0.67Ca_0.33MnO₃ films were maximum can differ by 60–70 K from those observed in bulk single crystals.     

Coulomb blockade electrometer with a high-T c island

We report on a successful attempt to fabricate a Coulomb blockade electrometer consisting of an ultrasmall YBa₂Cu₃O_7−δ (YBCO) island coupled to two gold electrodes through a high-resistance native surface tunnel barrier. A third electrode placed near the island was used as an electrostatic gate. Spectra typical for tunneling into the YBCO superconductor were reproducibly measured. At temperatures below 0.5 K the low-bias conductance was suppressed by the Coulomb blockade. The blockade could be periodically varied by the gate potential. An external magnetic field of up to 5 T strongly influenced the transport via the island but without any change in the period of the Coulomb oscillations. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 112–117 (25 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Superconductivity in ultrathin films I. Transition temperatures of amorphous Bi and Ga

Superconducting transition temperatures (T _c) and electron tunneling characteristics have been measured on amorphous, vapour quenched films of Ga and Bi in the thickness range 3 to 50 nm. TheT _c's are depressed and the tunnel densities of states are smeared as compared to bulk superconductors. A model considering the proximity effect between an extremely thin non-superconducting sheath (presumably due to the decrease of electron concentration at the surfaces) and a remaining bulk superconducting part gives good agreement withT _c measurements, while the predicted tunnel density of states is only in qualitative correspondence with experiments.     

Search for localized phonon modes inlead-based alloys by superconducting tunneling

To investigate the appearance of localized phonon modes, superconductive tunneling was performed into films of Pb_0·9M_0·1 (M = Ag, Cd, Ga, Ge, In, Mg, Mg, Sb, Sn, Te, Zn) and Pb_0·97Sn_0·03. The films were quench-condensed and later annealed at 30, 100 and 300°K. Structure in tunneling curves resulting from localized phonons was observed only for a well annealed In alloy film. For most of the impurities an absence of observable local phonon modes could be explained as due to a lack of solid solubility or of sufficient structural order in the film. For Na and Sn alloys, however, these arguments cannot be used. No modes could be seen for such alloys even in films condensed at room temperature, heat-treated slightly, and quenched directly into liquid helium.