C. C. Tsuei

MOTT TRANSITION FIELD EFFECT TRANSISTOR

A field effect transistor fabricated with an oxide channel has been shown to demonstrate switching characteristics similar to conventional siliconmetal oxide field effect transistors. This device is believed to operate via a Mott metal-insulator transition induced by the gate field, and offers a potential technology alternative for the regime beyond silicon scaling limitations.

Phase-sensitive evidence for d-wave pairing symmetry in electron-doped cuprate superconductors

We present phase-sensitive evidence that the electron-doped cuprates Nd(1.85)Ce(0.15)CuO(4-y) (NCCO) and Pr(1.85)Ce(0.15)CuO(4-y) (PCCO) have d-wave pairing symmetry. This evidence was obtained by observing the half-flux quantum effect, using a scanning SQUID microscope, in c-axis-oriented films of NCCO or PCCO epitaxially grown on tricrystal [100] SrTiO3 substrates designed to be frustrated for a d(x(2)-y(2)) order parameter. Samples with two other configurations, designed to be unfrustrated for a d-wave superconductor, do not show the half-flux quantum effect.

Pairing Symmetry in Single-Layer Tetragonal Tl2Ba2CuOβ+δ Superconductors

A high-resolution scanning superconducting quantum interference device microscopy study of tetragonal single-layer Tl2Ba2CuOβ+δ films, deposited on tricrystal SrTiO3 substrates, demonstrates the effect of spontaneously generated half flux quanta. This observation shows that in addition to YBa2Cu3O7, the order parameter symmetry in Tl2Ba2CuOβ+δ is consistent with that of a dx2-y2 pair state. This result also rules out any bilayer or twinning effects and any pairing that is incompatible with the fourfold rotational symmetry as in the Tl2Ba2CuOβ+δ superconducting system.

Superconducting mercury-based cuprate films with a zero-resistance transition temperature of 124 Kelvin.

The synthesis of high-quality films of the recently discovered mercury-based cuprate films with high transition temperatures has been plagued by problems such as the air sensitivity of the cuprate precursor and the volatility of Hg and HgO. These processing difficulties have been circumvented by a technique of atomic-scale mixing of the HgO and cuprate precursors, use of a protective cap layer, and annealing in an appropriate Hg and O2 environment. With this procedure, a zero-resistance transition temperature as high as 124 kelvin in c axis-oriented epitaxial HgBa2CaCu2O6+δ films has been achieved.

Layer dependence of the superconducting transition temperature of HgBa2Can−1CunO2n+2+δ

Abstract High-pressure methods have been used to synthesize multiphase compositions in the Hg12{ n −1} n homologous series. The phase assemblages were examined by optical, electron diffraction and X-ray diffraction techniques, and their stoichiometries verified by electron microprobe. Transport and magnetic susceptibility measurements were combined with the results of the phase analysis to establish superconducting transition temperatures for both as-prepared and O 2 - or Ar-annealed materials. It was found that the transition temperature peaks at T c = 134 K for n = 3 and then decreases abruptly for n >4, reaching T c K for n ⪖7.

Design and realization of an all d-wave dc π-superconducting quantum interference device

The predominantly dx2−y2-pairing symmetry in most high-Tc superconductors provides the opportunity to fabricate Josephson junction circuits in which part of the junctions are biased by a phase difference of the superconducting order parameter of π. We present fabrication and measurements of an all high-Tc dc superconducting quantum interference device (dc SQUID) realized with thin-film technology, of which the Josephson junctions consist of one standard junction and one junction with a π-phase shift. The characteristics of the π-SQUID are compared with the properties of a standard high-Tc SQUID.

Quadratic temperature dependence of the in-plane resistivity in superconducting Nd1.85CuO4 — Evidence for Fermi-liquid normal state

Abstract The in-plane normal-state resistivity, ϱ|;( T ), of the electron-doped superconductor Nd 1.85 Ce 0.15 CuO 4 has been measured and analyzed as a function of temperature in the range of T c to 300 K where T c ( R =0)=20 K. A dominant T 2 temperature dependence of ϱ|( T ) for T T 200 K, the data indicate a logarithmic correction to the quadratic temperature dependence. These findings are consistent with the Fermi-liquid model for electron-electron scattering, which is greatly enhanced in the CuO 2 -layered oxides. The experimental results of this work lend strong support to the validity of a Fermi-liquid description for the normal-state of electron-doped Cu-oxide superconductors.

Magnetron sputtering and laser patterning of high transition temperature Cu oxide films

High Tc Y‐Ba‐Cu‐O films have been prepared by dc magnetron sputtering of metal alloy targets. To circumvent the negative ion effect, two alloy targets, YCu and BaCu, are sputtered in an argon atmosphere with an oxygen spray near the substrate. Films deposited on sapphire with onsets at 92 K and a 6° transition width (10–90%) have been achieved using this technique. These films have been successfully patterned with the technique of laser ablation.

Integer and half-integer flux-quantum transitions in a niobium-iron pnictide loop

Measurements of integer and half-integer transitions of the quantized magnetic flux through a superconducting niobium–iron pnictide ring provide strong evidence to support predictions that the Cooper pairs within iron-based superconductors show an unconventional ‘reversed s-wave symmetry’.

Diffusion of oxygen in superconducting YBa2Cu3O7−δ oxide upon annealing in helium and oxygen ambients

Superconducting YBa2Cu3O7−δ oxide specimens (Tc∼91 K) formed by sintering were annealed in He gas ambient at constant temperatures ranging from 300 to 440 °C. Outdiffusion of oxygen during the annealing procedure was monitored by in situ electrical resistivity measurement. Below 350 °C, no resistivity changes were observed with time. From 370 to 440 °C, resistivity increased linearly with annealing time except the very initial period. Indiffusion of oxygen monitored by switching He to O2 (or air) during the annealing occurred extremely rapidly as indicated by a precipitous drop of resistivity. Assuming that the outdiffusion of oxygen is interfacial‐reaction limited, an activation energy of 1.7 eV was measured. The effects of oxygen diffusion on resistivity indicate that oxygen atoms mediate majority carriers in the oxide.