Engineering of ultrathin barriers in high T C, trilayer Josephson junctions

Abstract

Josephson junctions with ultrathin (25–40 Å) barriers were fabricated using high TC, trilayer films grown by atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The films consisted of top and bottom electrodes of Bi2Sr2CaCu2O8, separated by a single molecular layer of a metastable compound, Bi2Sr2(Ca, Sr, Bi, Dy)n−1CunO2n+4, with n=5 to 11. Systematic variation of Bi or Dy doping on Ca sites in the barrier layer provided four orders of magnitude of tuning of both the junction critical current and the normal state resistance, while keeping their product approximately constant, near 0.5 mV. Barrier and junction engineering, on an atomic length scale, has been demonstrated for the first time.

Epitaxial Growth and Properties of Doped Transition Metal and Complex Oxide Films

“…Atomic absorption (AA) has proven to be useful for this purpose. [131,132] However, new levels of AA sensitivity and stability are needed when monitoring dopants and host metals at low growth rates and, therefore, low metal fluxes. [103] MBE has been used to investigate the properties of oxide films that are useful for fundamental studies of environmental surface geochemistry, [89][90][91][92][93][94] thermal catalysis, [95,96] photocatalysis, [97][98][99][100][101] chemical sensors, [79][80][81][82][83][84][85][86][87][88] epitaxial oxides on Si, [19][20][21][22][23][24][25][26][27] and high-T c superconductivity.…”

Real-time in-situ flux monitoring by wavelength-modulated atomic absorption spectroscopy in molecular beam epitaxy: Application to Ga flux measurement

“…For short, AAS provides a useful absorption for real fluxes; it is element dependent and multiple elements might be monitored simultaneously. It then took almost twenty years to solve the noise and drift problems with dual-beam systems [2][3][4][5][6][7][8], finally leading to flux monitoring tools usable for MBE growth. The main drawback of these direct absorption measurements comes from the low absorption induced by the usual atomic beams: typical experiments involve detecting a small loss of a large transmitted photon flux.…”

Molecular beam epitaxy of SrTiO3 with a growth window

“…Therefore, conventional MBE of SrTiO 3 and related materials, such as many high-temperature superconductors or ferroelectrics, requires precise flux control and stability to obtain a stoichiometric oxide. Flux control is possible on the order of 0.1 -1% [8,9], which corresponds to defect concentrations of 10 20 cm -3 or higher. This sharply contrasts with high-quality 4 semiconductor films, where defect concentrations are in the ppm range or better (corresponding to concentrations of less than 10 17 cm -3 ).…”