@phdthesis{17881,
  abstract     = {This work can be broadly classified into the study of critical phenomena in a one dimensional
array of Josephson junctions. While we study quantum criticality when the array is in thermal
equilibrium at zero bias, the non-equilibrium study involves understanding the bistability of the
array at a critical non-zero bias. This work furthers our knowledge in understanding quantum
critical behaviour at finite temperatures in a one dimensional Josephson array, while also
establishing relaxation behaviour dual to that observed in a single Josephson junction.
Chapter 1 briefly introduces the model to understand superconductor-insulator phase transition
in a one dimensional Josephson array and points out the state of the field from where we
started our zero-bias experiments. In this context it discusses the phase-charge duality observed
in a Josephson array and its dual hysteretic behaviour to that of a single junction, setting the
ground for our non-equilibrium study of the array.
Chapter 2 shows the experimental setup and the chip layout of the device we measured.
In chapter 3 we show that, unlike the typical quantum-critical broadening scenario, in one dimensional Josephson arrays temperature dramatically shifts the critical region. This shift leads
to a regime of superconductivity at high temperature, arising from the melted zero-temperature
insulator. Our results quantitatively explain the low-temperature onset of superconductivity in
nominally insulating regimes, and the transition to the strongly insulating phase. We further
present, to our knowledge, the first understanding of the onset of anomalous-metallic resistance
saturation [30]. This work demonstrates a non-trivial interplay between thermal effects and
quantum criticality. A practical consequence is that, counterintuitively, the coherence of
high-impedance quantum circuits is expected to be stabilized by thermal fluctuations.
In chapter 4, we show relaxation oscillations in a current-biased one dimensional array of
Josephson junctions. These oscillations are well described by a circuit model, dual to the
ordinary Josephson relaxation oscillations [72]. Injection locking these oscillations results in
current plateaux. The relaxation step is found to obey a characteristic self-consistent relation,
suggesting that it is governed by overheating effects.
Chapter 5 describes the various checks and analysis we performed to support our conclusions
made in chapters 3 and 4.
Finally, chapter 6 describes the nanofabrication steps and the finite element electromagnetic
simulations we performed to fabricate our devices.},
  author       = {Mukhopadhyay, Soham},
  isbn         = {978-3-99078-043-5},
  issn         = {2663-337X},
  pages        = {82},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Thermal effects in one dimensional Josephson chains}},
  doi          = {10.15479/at:ista:17881},
  year         = {2024},
}