Noise and electrical properties of YBCO nanostructures
Doctoral thesis, 2020

This thesis work deals with the investigation of noise properties in cuprate High critical Temperature Superconductor (HTS) YBCO nanoscale devices. Here the aim is to get a better understanding of nanoscale fluctuations in the normal state of HTS from which superconductivity evolves. The observation of fluctuations in the electronic properties might offer valuable clues toward the microscopic mechanism leading to superconductivity in HTS, which still represent one of the main unsolved problems in solid-state physics. In this respect, the YBCO nanodevices are implemented as tools to obtain new experimental signatures, which can deliver new insights about the complex properties of HTS materials. Since cuprate HTS undergo various nano-scale ordering transitions upon cooling and variation of hole doping, being able to study transport properties on the nanoscale is of utmost importance. In this respect, resistance noise properties of YBCO nanowires are studied as a function of temperature and hole doping. Indications of nematic fluctuations, that is local time dependent fluctuations of the in-plane conductivity anisotropy, have been observed in a wide temperature range above the superconducting transition. The observed fluctuations might be related to so-called charge stripe fluctuations, which represent a possible microscopic mechanism for superconductivity in these materials.

However, the interest in HTS nanostructures is not purely academic. The technological application of YBCO weak links in SQUID, is a major focus of research in the field. In this thesis, we present a novel fabrication process of HTS weak links: the nanoscale Grooved Dayem Bridge (GDB). Here, the layout of the bridge and the weak link inside the bridge are realized during one single lithography process on a YBCO film grown on a single crystal substrate. This results in high-quality weak links with IcRn products as high as 550 µV and differential resistances much larger than those observed in bare Dayem bridges at T=77 K. Moreover, the GDB greatly simplifies the fabrication procedure compared to grain boundary based JJs. We have used YBCO GDBs as novel nanoscale building blocks in HTS SQUID magnetometers coupled to an in plane pickup loop, which have been characterized via transport and noise measurements at T= 77 K. These devices exhibit large voltage modulations (ΔV =27-50 µV), low values of white magnetic flux noise, 6 µΦ0/\sqrt{Hz}, and corresponding magnetic field noise, 63 fT/\sqrt{Hz}, at T=77 K. Therefore, GDB based SQUIDs combine the nanofabrication advantages and the device reproducibility, which are typical of Dayem bridges, with the performances, i.e. low magnetic flux and field noise, of state-of-the-art SQUIDs based on grain boundary JJs. The achieved magnetic field noise paves the way for the realization of a single layer YBCO magnetometer with magnetic field noise below 20 fT/\sqrt(Hz).






Kollektorn, kemivägen 9, Chalmers
Opponent: Prof. Hans Hilgenkamp, University of Twente, The Netherlands


Edoardo Trabaldo

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

Improved noise performance of ultrathin YBCO Dayem bridge nanoSQUIDs

Superconductor Science and Technology,; Vol. 30(2017)

Journal article

Noise Properties of YBCO Nanostructures

IEEE Transactions on Applied Superconductivity,; Vol. 27(2017)

Journal article

Probing the phase diagram of cuprates with YBa2Cu3O7−δ thin films and nanowires

Physical Review Materials,; Vol. 2(2018)

Journal article

SQUID magnetometer based on Grooved Dayem nanobridges and a flux transformer

IEEE Transactions on Applied Superconductivity,; Vol. 30(2020)

Journal article

Transport and noise properties of YBCO nanowire based nanoSQUIDs

Superconductor Science and Technology,; Vol. 32(2019)

Review article

Noise anomalies in the resistive state of YBa2Cu3O7− nanostructures with varying doping

The discovery of High critical Temperature Superconductors (HTSs), more than 30 years ago, has given a tremendous boost to the field of superconductivity. However, the complexity of the system, with various intertwined degrees of freedom, simultaneously at play, makes this spectacular phenomenon one of the main unresolved puzzles in solid state physics that could be faced only with the constant development of new experimental techniques. A recent breakthrough, coming from the advances in X-ray scattering techniques, has unified the behavior of the various HTS compound families demonstrating that Charge Density Waves (CDWs) a modulation of charge carriers at the nanoscale are ubiquitous for all cuprate-based HTSs. The question now arises: What is the role of this nanoscale order in the formation of the superconducting state? Whereas static charge ordering is considered to compete with superconductivity, fluctuations of a charge order may hold the key to explain superconductivity in these materials. In this respect, the study of electronic noise, i.e. the temporal fluctuations of electrical properties, could be instrumental in uncovering the existence of a fluctuating charge order. In this thesis work, we present an extensive study  of resistance noise measurements performed on YBa2Cu3O7-d (YBCO) nanostructures as a function of temperature and oxygen doping. We find noise signatures, which can be connected to fluctuations of an electronic nematic order, which breaks rotational symmetry. The observed fluctuations might be related to so-called charge stripe fluctuations, which represent a possible microscopic mechanism for superconductivity in these materials.

At the same time nanoscale HTS devices might be instrumental for the development of  beyond state-of-the-art sensors, such as the nanoscale superconducting quantum interference device (nanoSQUID) for the ultra-sensitive detection of magnetic flux. The fact that YBCO-based devices are operational at temperatures above the boiling temperature of liquid nitrogen, an abundant and cheap resource as compared to sparse and expensive helium, makes YBCO nanoSQUIDs very promising candidates for applications ranging from bio-diagnostics to geophysical surveys. In this thesis work we have developed a new nanoscale weak link, a key ingredient in superconducting electronics. By introducing the nanoscale Grooved Dayem bridge (GDB) we have realized SQUID magnetometers with noise performance at par with the state-of-the-art HTS-based SQUID magnetometers. The rather simple fabrication procedure of GDBs could open the way to a range of future high-performance high-frequency applications, such as HTS rapid single flux quantum (RSFQ) circuits and superconducting quantum interference filters.

Areas of Advance

Nanoscience and Nanotechnology

Subject Categories

Nano Technology

Condensed Matter Physics


Nanofabrication Laboratory



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4735



Kollektorn, kemivägen 9, Chalmers


Opponent: Prof. Hans Hilgenkamp, University of Twente, The Netherlands

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