Nanoscale YBa2Cu3O7-δ devices -Searching for a subdominant order parameter using a single electron transistor
Doctoral thesis, 2012

The microscopic origin of High critical Temperature Superconductivity (HTS) is still an open issue in condensed matter physics. It is believed that by exlporing the quasiparticle energy spectrum one can learn about the mechanism promoting the superconducting state. In this thesis we have developed a nanoscale spectroscopic tool, an all superconducting YBa2Cu3O7−δ (YBCO) Single Electron Transistor, allowing us to obtain information from the quasiparticle spectrum of an entire nanometer scale island. In this experiment we find a fully gapped superconductivity which strongly depends on the externally applied magnetic field. This finding shows that the order parameter is not purely dx2−y2 with nodes, instead it has an additinal subdominant imaginary component which lifts the zero energy quasiparticles. The realization of the transistor has required the engineering of nanaoscale YBCO Josephson grain boundary (GB) junctions with stringent demands on the transport properties. Part of the work in this thesis has been devoted to the development and characterization of two methods to fabricate nanoscale GB junctions. A conventional method based on e-beam lithography and ion milling and a new soft nanopatterning technique. The new method is based on the phase competition between superconducting YBCO and insulating greenphase at the grain boundary. This has allowed the creation of junctions with minimal damage in the fabrication process. Together, the two methods create grain boundaries that span a large range of critical current densities and normal resistivities, which can be employed in various applications.

grain boundary

Josephson junctions

YBCO

single electron transistors

high temperature superconductivity

Kollektorn, Institutionen för Mikroteknologi och Nanovetenskap, Chalmers tekniska högskola
Opponent: Prof. Reinhold Kleiner, Physikalisches Institut, University of Tübingen, Germany

Author

David Gustafsson

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

High critical temperature superconductor Josephson junctions for quantum circuit applications

Physica Scripta,; Vol. T137(2009)p. 014006-

Paper in proceedings

Low capacitance HTS junctions for single electron transistors

Physica C: Superconductivity and its Applications,; Vol. 470(2009)p. S188-S190

Paper in proceedings

Noise properties of nanoscale YBa2Cu3O7- δ Josephson junctions

Physical Review B - Condensed Matter and Materials Physics,; Vol. 84(2011)

Journal article

Soft Nanostructuring of YBCO Josephson Junctions by Phase Separation

Nano Letters,; Vol. 10(2010)p. 4824-4829

Journal article

Areas of Advance

Nanoscience and Nanotechnology (2010-2017)

Infrastructure

Nanofabrication Laboratory

Subject Categories

Condensed Matter Physics

ISBN

978-91-7385-680-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3361

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: 228

Kollektorn, Institutionen för Mikroteknologi och Nanovetenskap, Chalmers tekniska högskola

Opponent: Prof. Reinhold Kleiner, Physikalisches Institut, University of Tübingen, Germany

More information

Created

10/8/2017