Engineered Tunnel Barriers for a YBCO Single Electron Transistor
Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Van Veldhoven, Zenas
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Despite the great scienti c effort, the microscopic origin of superconductivity in the
high-temperature superconductor Y Ba2Cu3O7-8 is still not understood.
In recent work, Gustafsson, D. et al. discovered that the superconducting order parameter
in a Y Ba2Cu3O7-8 mesoscopic island did not have a purely d-wave symmetry,
as it is commonly assumed. By using a Single-Electron Transistor (SET) made
of a Y Ba2Cu3O7-8 source, mesoscopic island, drain and gate, they discovered that the
Y Ba2Cu3O7-8 island had a fully gapped superconductivity. This indicates the existance
of a subdominant imaginary order parameter in Y Ba2Cu3O7-8 that gaps the nodes of
the d-wave order parameter.
In order to investigate the doping dependence of this subdominant order parameter, one
should use a new design for the SET, with normal metal source, drain and gate. To have
a working SET, the tunnel resistance between the electrodes and the islands needs to be
higher than the quantum resistance.
The goal of this work is to engineer the Y Ba2Cu3O7-8-Au tunnel junction with a su -
ciently high tunnel resistance. For that, tunnel barriers between Y Ba2Cu3O7-8 and Au
were created by an Ar ion milling procedure of the surface using different etching times
and di erent voltages. The current-voltage characteristics of the Au-Y Ba2Cu3O7-8
junctions were investigated and the contact resistivity between Y Ba2Cu3O7-8 and Au
was measured.
The surface etching seems to create low transparency interfaces. In addition, a normal
Y Ba2Cu3O7-8 layer is formed at the surface, which can be turned superconducting by
ozone treatment. Suitable tunnel barriers for a Y Ba2Cu3O7-8 SET can be created using
mild surface etching and ozonation.