15 research outputs found
Equal-Spin Andreev Reflection in Junctions of Spin-Resolved Quantum Hall Bulk State and Spin-Singlet Superconductor
The recent development of superconducting spintronics has revealed the
spin-triplet superconducting proximity effect from a spin-singlet
superconductor into a spin-polarized normal metal. In addition recently
superconducting junctions using semiconductors are in demand for highly
controlled experiments to engineer topological superconductivity. Here we
report experimental observation of Andreev reflection in junctions of
spin-resolved quantum Hall (QH) states in an InAs quantum well and the
spin-singlet superconductor NbTi. The measured conductance indicates a sub-gap
feature and two peaks on the outer side of the sub-gap feature in the QH
plateau-transition regime increases. The observed structures can be explained
by considering transport with Andreev reflection from two channels, one
originating from equal-spin Andreev reflection intermediated by spin-flip
processes and second arising from normal Andreev reflection. This result
indicates the possibility to induce the superconducting proximity gap in the
the QH bulk state, and the possibility for the development of superconducting
spintronics in semiconductor devices
Weak antilocalization in quasi-two-dimensional electronic states of epitaxial LuSb thin films
Observation of large non-saturating magnetoresistance in rare-earth
monopnictides has raised enormous interest in understanding the role of its
electronic structure. Here, by a combination of molecular-beam epitaxy,
low-temperature transport, angle-resolved photoemssion spectroscopy, and hybrid
density functional theory we have unveiled the bandstructure of LuSb, where
electron-hole compensation is identified as a mechanism responsible for large
magnetoresistance in this topologically trivial compound. In contrast to bulk
single crystal analogues, quasi-two-dimensional behavior is observed in our
thin films for both electron and holelike carriers, indicative of dimensional
confinement of the electronic states. Introduction of defects through growth
parameter tuning results in the appearance of quantum interference effects at
low temperatures, which has allowed us to identify the dominant inelastic
scattering processes and elucidate the role of spin-orbit coupling. Our
findings open up new possibilities of band structure engineering and control of
transport properties in rare-earth monopnictides via epitaxial synthesis.Comment: 20 pages, 12 figures; includes supplementary informatio
Atomic structure of postgrowth annealed epitaxial Fe/(001)GaAs interfaces
The interfacial atomic structure of epitaxial Fe films grown by molecular beam epitaxy on c(4x4) reconstructed (001) GaAs was investigated using high-angle annular dark-field imaging in scanning transmission electron microscopy. No extended interfacial reaction phase is observed and the image contrast is discussed in terms of the interface atomic configuration. The images show an As-terminated semiconductor. The interface consists of a single partially occupied plane inserted between the Fe film and the GaAs, which most likely is occupied by Fe. This interface structure provides strong evidence for preferential Fe–As bonding across the interface
Growth and characterization of -Sn thin films on In- and Sb-rich reconstructions of InSb(001)
-Sn thin films can exhibit a variety of topologically non-trivial
phases. Both studying the transitions between these phases and making use of
these phases in eventual applications requires good control over the electronic
and structural quality of -Sn thin films. -Sn growth on InSb
often results in out-diffusion of indium, a p-type dopant. By growing
-Sn via molecular beam epitaxy on the Sb-rich c(44) surface
reconstruction of InSb(001) rather than the In-rich c(82), we
demonstrate a route to substantially decrease and minimize this indium
incorporation. The reduction in indium concentration allows for the study of
the surface and bulk Dirac nodes in -Sn via angle-resolved
photoelectron spectroscopy without the common approaches of bulk doping or
surface dosing, simplifying topological phase identification. The lack of
indium incorporation is verified in angle-resolved and -integrated ultraviolet
photoelectron spectroscopy as well as in clear changes in the Hall response
Tuning the Band Topology of GdSb by Epitaxial Strain
Rare-earth monopnictide (RE-V) semimetal crystals subjected to hydrostatic
pressure have shown interesting trends in magnetoresistance, magnetic ordering,
and superconductivity, with theory predicting pressure-induced band inversion.
Yet, thus far, there have been no direct experimental reports of interchanged
band order in RE-Vs due to strain. This work studies the evolution of band
topology in biaxially strained GdSb (001) epitaxial films using angle-resolved
photoemission spectroscopy (ARPES) and density functional theory (DFT). We find
that biaxial strain continuously tunes the electronic structure from
topologically trivial to nontrivial, reducing the gap between the hole and the
electron bands dispersing along the [001] direction. The conduction and valence
band shifts seen in DFT and ARPES measurements are explained by a tight-binding
model that accounts for the orbital symmetry of each band. Finally, we discuss
the effect of biaxial strain on carrier compensation and magnetic ordering
temperature
Epitaxial growth, magnetoresistance, and electronic band structure of GdSb magnetic semimetal films
Motivated by observations of extreme magnetoresistance (XMR) in bulk crystals
of rare-earth monopnictide (RE-V) compounds and emerging applications in novel
spintronic and plasmonic devices based on thin-film semimetals, we have
investigated the electronic band structure and transport behavior of epitaxial
GdSb thin films grown on III-V semiconductor surfaces. The Gd3+ ion in GdSb has
a high spin S=7/2 and no orbital angular momentum, serving as a model system
for studying the effects of antiferromagnetic order and strong exchange
coupling on the resulting Fermi surface and magnetotransport properties of
RE-Vs. We present a surface and structural characterization study mapping the
optimal synthesis window of thin epitaxial GdSb films grown on III-V
lattice-matched buffer layers via molecular beam epitaxy. To determine the
factors limiting XMR in RE-V thin films and provide a benchmark for band
structure predictions of topological phases of RE-Vs, the electronic band
structure of GdSb thin films is studied, comparing carrier densities extracted
from magnetotransport, angle-resolved photoemission spectroscopy (ARPES), and
density functional theory (DFT) calculations. ARPES shows hole-carrier rich
topologically-trivial semi-metallic band structure close to complete
electron-hole compensation, with quantum confinement effects in the thin films
observed through the presence of quantum well states. DFT predicted Fermi
wavevectors are in excellent agreement with values obtained from quantum
oscillations observed in magnetic field-dependent resistivity measurements. An
electron-rich Hall coefficient is measured despite the higher hole carrier
density, attributed to the higher electron Hall mobility. The carrier
mobilities are limited by surface and interface scattering, resulting in lower
magnetoresistance than that measured for bulk crystals
Tuning the band topology of GdSb by epitaxial strain
Rare-earth monopnictide (RE-V) semimetal crystals subjected to hydrostatic pressure have shown interesting trends in magnetoresistance, magnetic ordering, and superconductivity, with theory predicting pressure-induced band inversion. Yet, thus far, there have been no direct experimental reports of interchanged band order in RE-Vs due to strain. This work studies the evolution of band topology in biaxially strained GdSb(001) epitaxial films using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT). As biaxial strain is tuned from tensile to compressive strain, the gap between the hole and the electron bands dispersed along [001] decreases. The conduction and valence band shifts seen in DFT and ARPES measurements are explained by a tight-binding model that accounts for the orbital symmetry of each band. Finally, we discuss the effect of biaxial strain on carrier compensation and magnetic ordering temperature