Probing electronic nematicity and anisotropic electron-phonon coupling in strained YBCO nanowires
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Nanotechnology (MPNAT), MSc
Publicerad
2024
Författare
Rongrueangkul, Karn
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Despite nearly 40 years since its discovery in 1986, the underlying mechanism behind
the high-temperature superconductivity (HTS) in cuprates remains a significant enigma in
condensed matter physics. The existence of multiple intertwined local orders, originating
from the strongly correlated electrons, further complicates the study of these materials.
Such complexity of the normal state is depicted in a very intricate temperature-doping
phase diagram. A way to advance the knowledge of these materials is to tune the local
orders, both in the superconducting and in the normal state, to disentangle them for
individual study. One way to achieve such an effect is to apply strain to the cuprates
in nm-thick films. Previously, it was discovered that the unidirectional strain, induced
by few-unit-cell-thick films deposited on a nanostructured surface, can modify the charge
order and cause the in-plane resistivity of the films to become much more anisotropic
than in bulk materials. According to the Boltzmann transport model, such anisotropy
in the in-plane resistivity is due to the directional modification of the Fermi velocity
in which the velocity along one crystallographic in-plane direction is much higher than
another. This results in an anisotropic Fermi surface that connects to the presence of
an electronic nematicity, wherein the electronic structure retains translational symmetry
while spontaneously breaking rotational symmetry.
In earlier reports on the archetypal HTS YBa2Cu3O7−δ (YBCO) superconductor,
the photoemission and transport measurements appear to show that electron-phonon
coupling (EPC) can become directionally suppressed if the Fermi surface becomes nematic
(as in our sample). This should strongly affect the heat transport in nm-thick YBCO
films. Hence, the focus of this thesis work is to investigate the anisotropic EPC through
the study of electrical and heat transport properties of YBCO nanowires oriented along
different crystallographic axes. The nanowires are fabricated from YBCO thin films
epitaxially grown by the Pulsed Laser Deposition technique, and the strain is tuned by
modifying the film thickness.
Beskrivning
Ämne/nyckelord
High-Temperature Superconductors, YBCO, Electronic Nematicity