Reshaping the phase diagram of YBa2Cu3O7-δ through strain in ultrathin films and nanowires
Doctoral thesis, 2021
This thesis describes new experiments that are able to highlight the physics of the strange metal by studying the physical mechanisms that lead to its breakdown, using nanoscale \newline YBa2Cu3O7-δ (YBCO) thin films and devices.
So far, a detailed temperature-doping phase diagram describing the complex properties of the HTS cuprates was available only for single crystals. The first part of the thesis shows that we can reproduce all the main features of the HTS phase diagram for YBCO thin films and nanowires. By reconstructing the surface of the substrates, with high temperature annealing, we are able to grow highly strained, untwinned films. These films are instrumental for studying anisotropic transport properties of both the strange metal and the superconducting state.
In the second part of the thesis we have studied the evolution of the $T$-linear resistivity in the strained films as a function of the thickness and of the doping. In ultrathin and underdoped YBCO films the strange metal phase is restored when the CDW order, detected by resonant inelastic X-ray scattering, is suppressed. This observation points towards an intimate connection between the onset of CDW and the breakdown of the $T$-linear resistivity in underdoped cuprates, a link that was missing until now.
Finally, the thesis describes how the phase diagram of YBCO is reshaped for thin films and devices at the nanoscale, and in particular how the superconducting transition is enhanced by the suppression of CDW order in the underdoped regime. We also show that the dynamics of the phase-slip phenomenon in ultrathin nanowires becomes very different in the direction where the CDW order is suppressed. These results highlight the competing nature of superconductivity and charge order.
Overall, the research presented in the thesis work, demonstrates how strain control and nanoscale dimensions allow to manipulate the ground state of HTS which is an important step to disclose the mechanism for high critical temperature superconductivity.
charge density wave
Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics
Fabrication and electrical transport characterization of high quality underdoped YBa2Cu3O7-δ nanowires
Superconductor Science and Technology,; Vol. 33(2020)
Untwinned YBa2Cu3O7-delta thin films on MgO substrates: A platform to study strain effects on the local orders in cuprates
Physical Review Materials,; Vol. 3(2019)
Probing the phase diagram of cuprates with YBa2Cu3O7−δ thin films and nanowires
Physical Review Materials,; Vol. 2(2018)
Restored strange metal phase through suppression of charge density waves in underdoped YBa2Cu3O7–δ
Science,; Vol. 373(2021)p. 1506-1510
Wahlberg, E., Arpaia, R.,Trabaldo, E.,Brookes, N.B., Ghiringhelli, G., Bauch, T., Lombardi, F. Reshaping the phase diagram of strained, ultrathin YBa2Cu3O7-δ by a unidirectional charge density wave
In this thesis we use YBa2Cu3O7-δ thin films and nanowires to study the evolution of the strange metal, CDW and HTS phases with strain and nanoscale dimensions. The aim is to get new insights about their intertwining by tuning the electronic ground state of the material. We show that the CDW plays an active role in breaking down the strange metal state and that transport measurements in thin films and nanostructures can give new hints about the competing nature of the CDW and superconducting state. These results add an important piece to the puzzle of high temperature superconductivity.
Oxide Nanoelectromechanical Systems for Ultrasensitive and Robust Sensing of Biomagnetic Fields (Oxinems)
European Commission (EC) (828784), 2019-05-01 -- 2023-04-30.
Functional Dirac Materials
Knut and Alice Wallenberg Foundation (KAW.2013.0096), 2014-07-01 -- 2019-06-30.
Areas of Advance
Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)
Condensed Matter Physics
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5026
Chalmers University of Technology
Kollektorn (A423), MC2, Kemivägen 9
Opponent: Dr. Cyril Proust, Laboratoire National des Champs Magnétiques Intenses Toulouse, France