74 research outputs found
Carrier concentration-tuned phase transitions in high-Tc cuprates and perovskite oxide interfaces
Ph.DDOCTOR OF PHILOSOPH
Self-passivated freestanding superconducting oxide film for flexible electronics
The integration of high-temperature superconducting YBa2Cu3O6+x (YBCO) into
flexible electronic devices has the potential to revolutionize the technology
industry. The effective preparation of high-quality flexible YBCO films
therefore plays a key role in this development. We present a novel approach for
transferring water-sensitive YBCO films onto flexible substrates without any
buffer layer. Freestanding YBCO film on a polydimethylsiloxane substrate is
extracted by etching the Sr3Al2O6 sacrificial layer from the LaAlO3 substrate.
In addition to the obtained freestanding YBCO thin film having a Tc of 89.1 K,
the freestanding YBCO thin films under inward and outward bending conditions
have Tc of 89.6 K and 88.9 K, respectively. A comprehensive characterization
involving multiple experimental techniques including high-resolution
transmission electron microscopy, scanning electron microscopy, Raman and X-ray
Absorption Spectroscopy is conducted to investigate the morphology, structural
and electronic properties of the YBCO film before and after the extraction
process where it shows the preservation of the structural and superconductive
properties of the freestanding YBCO virtually in its pristine state. Further
investigation reveals the formation of a YBCO passivated layer serves as a
protective layer which effectively preserves the inner section of the
freestanding YBCO during the etching process. This work plays a key role in
actualizing the fabrication of flexible oxide thin films and opens up new
possibilities for a diverse range of device applications involving thin-films
and low-dimensional materials.Comment: 22 pages,4 figures,references adde
Unconventional quantum oscillations and evidence of non-trivial electronic states in quasi-two-dimensional electron system at complex oxide interfaces
The simultaneous occurrence of electric-field controlled superconductivity
and spin-orbit interaction makes two-dimensional electron systems (2DES)
constructed from perovskite transition metal oxides promising candidates for
the next generation of spintronics and quantum computing. It is, however,
essential to understand the electronic bands thoroughly and verify the
predicted electronic states experimentally in these 2DES to advance
technological applications. Here, we present novel insights into the electronic
states of the 2DES at oxide interfaces through comprehensive investigations of
Shubnikov-de Haas oscillations in two different systems: EuO/KTaO (EuO/KTO)
and LaAlO/SrTiO (LAO/STO). To accurately resolve these oscillations, we
conducted transport measurements in high magnetic fields up to 60 T and low
temperatures down to 100 mK. For 2D confined electrons at both interfaces, we
observed a progressive increase of oscillations frequency and cyclotron mass
with the magnetic field. We interpret these intriguing findings by considering
the existence of non-trivial electronic bands, for which the dispersion
incorporates both linear and parabolic dispersion relations. In addition to
providing experimental evidence for topological-like electronic states in
KTO-2DES and STO-2DES, the unconventional oscillations presented in this study
establish a new paradigm for quantum oscillations in 2DES based on perovskite
transition metal oxides, where the oscillations frequency exhibits quadratic
dependence on the magnetic field
Competition of electronic correlation and reconstruction in La1-xSrxTiO3/SrTiO3 heterostructures
Electronic correlation and reconstruction are two important factors that play
a critical role in shaping the magnetic and electronic properties of correlated
low-dimensional systems. Here, we report a competition between the electronic
correlation and structural reconstruction in La1-xSrxTiO3/SrTiO3
heterostructures by modulating material polarity and interfacial strain,
respectively. The heterostructures exhibit a critical thickness (tc) at which a
metal-to-insulator transition (MIT) abruptly occurs at certain thickness,
accompanied by the coexistence of two- and three-dimensional (2D and 3D)
carriers. Intriguingly, the tc exhibits a V-shaped dependence on the doping
concentration of Sr, with the smallest tc value at x = 0.5. We attribute this
V-shaped dependence to the competition between the electronic reconstruction
(modulated by the polarity) and the electronic correlation (modulated by
strain), which are borne out by the experimental results, including
strain-dependent electronic properties and the evolution of 2D and 3D carriers.
Our findings underscore the significance of the interplay between electronic
reconstruction and correlation in the realization and utilization of emergent
electronic functionalities in low-dimensional correlated systems
Optical Properties of Superconducting Nd0.8Sr0.2NiO2 Nickelate
The intensive search for alternative non-cuprate high-transition-temperature
() superconductors has taken a positive turn recently with the discovery
of superconductivity in infinite layer nickelates. This discovery is expected
to be the basis for disentangling the puzzle behind the physics of high
in oxides. In the unsolved quest for the physical conditions necessary for
inducing superconductivity, we report an optical study of a
NdSrNiO film measured using optical spectroscopy, at
temperatures above and below the critical temperature K. The
normal-state electrodynamics of NdSrNiO, is described by
the Drude model characterized by a scattering time just above ( s) and a plasma frequency cm in
combination with an absorption band in the Mid-Infrared (MIR) around cm. The MIR absorption indicates the presence of strong
electronic correlation effect in the NiO plane similarly to cuprates. Below
, a superconducting energy gap () of meV is extracted
from the Terahertz reflectivity using the the Mattis-Bardeen model. From the
Ferrel-Glover-Thinkam Rule applied to the real part of the optical
conductivity, we also estimate a London penetration depth of about 490 nm, in
agreement with a type-II superconductivity in NdSrNiO
Nickelate
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