35 research outputs found
In-situ scattering studies of superconducting vacancy-ordered monoclinic TiO thin films
We investigate the structural and transport properties of vacancy-ordered
monoclinic superconducting thin films grown by molecular beam
epitaxy. The evolution of the crystal structure during growth is monitored by
in-situ synchrotron X-ray diffraction. Long-range ordering of Ti and O
vacancies in the disordered cubic phase stabilizes the vacancy-ordered
monoclinic TiO phase. The reduced structural disorder arising from
vacancy-ordering is correlated with a superconductor-metal transition (SMT) in
contrast to the superconductor-insulator transition (SIT) observed in cubic
TiO, orthorhombic , and the Magneli and
phase. Magnetoresistance measurements for the SIT phases
indicate superconducting fluctuations persisting in the normal phase. These
results confirm the role of disorder related to Ti and O vacancies and
structural inhomogeneity in determining the electronic properties of the normal
state of titanium oxide-based superconductors
Coexistence of superconductivity and weak anti-localization at KTaO3 (111) interfaces
The intersection of two-dimensional superconductivity and topologically
nontrivial states hosts a wide range of quantum phenomena, including Majorana
fermions. Coexistence of topologically nontrivial states and superconductivity
in a single material, however, remains elusive. Here, we report on the
observation of two-dimensional superconductivity and weak anti-localization at
the TiOx/KTaO3(111) interfaces. A remnant, saturating resistance persists below
the transition temperature as superconducting puddles fail to reach phase
coherence. Signatures of weak anti-localization are observed below the
superconducting transition, suggesting the coexistence of superconductivity and
weak anti-localization. The superconducting interfaces show roughly one order
of magnitude larger weak anti-localization correction, compared to
non-superconducting interfaces, alluding to a relatively large coherence length
in these interfaces
Structure of droplet-epitaxy-grown InAs/GaAs quantum dots
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98673/1/ApplPhysLett_98_243115.pd
Oxygen vacancy-induced anomalous Hall effect in a non-magnetic oxide
The anomalous Hall effect, a hallmark of broken time-reversal symmetry and
spin-orbit coupling, is frequently observed in magnetically polarized systems.
Its realization in non-magnetic systems, however, remains elusive. Here, we
report on the observation of anomalous Hall effect in nominally non-magnetic
KTaO3. Anomalous Hall effect emerges in reduced KTaO3 and shows an extrinsic to
intrinsic crossover. A paramagnetic behavior is observed in reduced samples
using first principles calculations and quantitative magnetometry. The observed
anomalous Hall effect follows the oxygen vacancy-induced magnetization
response, suggesting that the localized magnetic moments of the oxygen
vacancies scatter conduction electrons asymmetrically and give rise to
anomalous Hall effect. The anomalous Hall conductivity becomes insensitive to
scattering rate in the low temperature limit (T<5 K), implying that the Berry
curvature of the electrons on the Fermi surface controls the anomalous Hall
effect. Our observations describe a detailed picture of many-body interactions,
triggering anomalous Hall effect in a non-magnetic system
Exchange bias in La0.7Sr0.3CrO3/La0.7Sr0.3MnO3/La0.7Sr0.3CrO3 heterostructures
In the recent past, heterostructures of magnetic oxide thin films have attracted a great deal of research excitement due to very interesting physical properties such as antiferromagnetic interlayer coupling, tunable exchange-bias, interfacial driven magnetic properties and high mobility electron gas across the interfaces. In this work, we report on the comprehensive magnetic properties observed from the heterostructures of (2 unit cells) La0.7Sr0.3CrO3/(8 unit cells) La0.7Sr0.3MnO3/(2 unit cells) La0.7Sr0.3CrO3, which are epitaxially deposited on SrTiO3 substrate by plasma-assisted oxide molecular beam epitaxy. Using SQUID magnetometer, the magnetic properties are studied when the magnetic field was applied both in plane and out of plane. The Curie temperature of this structure is found to be at 290 K. Most significantly, at 2 K, we observed a complete up/down shift (along magnetization axis) of hysteresis loop when the sample was cooled under a magnetic field of ± 5000 Oe in the in-plane configuration. We believe that the strong antiferromagnetic (super) exchange coupling of Mn-Cr across the two interfaces is responsible for the observed exchange bias. We will present and discuss our in-detailed experimental findings collected on this heterostructure as a function of temperature and magnetic field