8 research outputs found
SU(4) Symmetry Breaking and Induced Superconductivity in Graphene Quantum Hall Edges
In graphene, the approximate SU(4) symmetry associated with the spin and
valley degrees of freedom in the quantum Hall (QH) regime is reflected in the
4-fold degeneracy of graphene's Landau levels (LL's). Interactions and the
Zeeman effect break such approximate symmetry and lift the corresponding
degeneracy of the LLs. We study how the breaking of the approximate SU(4)
symmetry affects the properties of graphene's QH edge modes located in
proximity to a superconductor. We show how the lifting of the 4-fold degeneracy
qualitatively modifies the transport properties of the QH-superconductor
heterojunction. For the zero LL, by placing the edge modes in proximity to a
superconductor, it is in principle possible to realize a 1D topological
superconductor supporting Majoranas in the presence of sufficiently strong
Zeeman field. We estimate the topological gap of such a topological
superconductor and relate it to the properties of the QH-superconductor
interface.Comment: 12 pages, 7 figure
Andreev reflection of quantum Hall states through a quantum point contact
We investigate the interplay between the quantum Hall (QH) effect and
superconductivity in InAs surface quantum well (SQW)/NbTiN heterostructures
using a quantum point contact (QPC). We use QPC to control the proximity of the
edge states to the superconductor. By measuring the upstream and downstream
resistances of the device, we investigate the efficiency of Andreev conversion
at the InAs/NbTiN interface. Our experimental data is analyzed using the
Landauer-Buttiker formalism, generalized to allow for Andreev reflection
processes. We show that by varying the voltage of the QPC, , the
average Andreev reflection, , at the QH-SC interface can be tuned from 50%
to 10%. The evolution of with extracted from the measurements
exhibits plateaus separated by regions for which varies continuously with
. The presence of plateaus suggests that for some ranges of
the QPC might be pinching off almost completely from the QH-SC interface some
of the edge modes. Our work shows a new experimental setup to control and
advance the understanding of the complex interplay between superconductivity
and QH effect in two-dimensional gas systems
Reemergence of missing Shapiro steps in the presence of in-plane magnetic field
In the presence of a 4-periodic contribution to the current phase
relation, for example in topological Josephson junctions, odd Shapiro steps are
expected to be missing. While missing odd Shapiro steps have been observed in
several material systems and interpreted in the context of topological
superconductivity, they have also been observed in topologically trivial
junctions. Here, we study the evolution of such trivial missing odd Shapiro
steps in Al-InAs junctions in the presence of an in-plane magnetic field
. We find that the odd steps reappear at a crossover
value, exhibiting an in-plane field angle anisotropy that depends on spin-orbit
coupling effects. We interpret this behavior by theoretically analyzing the
Andreev bound state spectrum and the transitions induced by the non-adiabatic
dynamics of the junction. Our results highlight the complex phenomenology of
missing Shapiro steps and the underlying current phase relations in planar
Josephson junctions designed to realize Majorana states
Prolyl-4-hydroxylase 3 maintains β-cell glucose metabolism during fatty acid excess in mice
The α-ketoglutarate–dependent dioxygenase, prolyl-4-hydroxylase 3 (PHD3), is an HIF target that uses molecular oxygen to hydroxylate peptidyl prolyl residues. Although PHD3 has been reported to influence cancer cell metabolism and liver insulin sensitivity, relatively little is known about the effects of this highly conserved enzyme in insulin-secreting β cells in vivo. Here, we show that the deletion of PHD3 specifically in β cells (βPHD3KO) was associated with impaired glucose homeostasis in mice fed a high-fat diet. In the early stages of dietary fat excess, βPHD3KO islets energetically rewired, leading to defects in the management of pyruvate fate and a shift from glycolysis to increased fatty acid oxidation (FAO). However, under more prolonged metabolic stress, this switch to preferential FAO in βPHD3KO islets was associated with impaired glucose-stimulated ATP/ADP rises, Ca(2+) fluxes, and insulin secretion. Thus, PHD3 might be a pivotal component of the β cell glucose metabolism machinery in mice by suppressing the use of fatty acids as a primary fuel source during the early phases of metabolic stress
Leggett Modes in Dirac Semimetals
In recent years experimentalists have been able to clearly show that several
materials, such as MgB2, iron-based superconductors3, monolayer NbSe2, are
multiband superconductors. Superconducting pairing in multiple bands can give
rise to novel and very interesting phenomena. Leggett modes are exemplary of
the unusual effects that can be present in multiband superconductors. A Leggett
mode describes the collective periodic oscillation of the relative phase
between the phases of the superconducting condensates formed by electrons in
different bands. It can be thought of as the mode arising from an inter-band
Josephson effect. The experimental observation of Leggett modes is challenging
for several reasons: (i) Multiband superconductors are rare; (ii) they describe
charge fluctuations between bands and therefore are hard to probe directly;
(iii) their mass gap is often larger than the superconducting gaps and
therefore are strongly overdamped via relaxation processes into the
quasiparticle continuum. In this work we show that Leggett modes, and their
frequency, can be detected unambigously in a.c. driven superconducting quantum
interference devices (SQUIDs). We then use the results to analyze the
measurements of a SQUID based on Cd3As2, an exemplar Dirac semimetal, in which
superconductivity is induced by proximity to superconducting Al. The
experimental results show the theoretically predicted unique signatures of
Leggett modes and therefore allow us to conclude that a Leggett mode is present
in the two-band superconducting state of Dirac semimetal (DSM) Cd3As2.Comment: 13 pages, 8 figure
Discovery of a Potent Class of PI3Kα Inhibitors with Unique Binding Mode via Encoded Library Technology (ELT)
In the search of PI3K p110α
wild type and H1047R mutant selective small molecule leads, an encoded
library technology (ELT) campaign against the desired target proteins
was performed which led to the discovery of a selective chemotype
for PI3K isoforms from a three-cycle DNA encoded library. An X-ray
crystal structure of a representative inhibitor from this chemotype
demonstrated a unique binding mode in the p110α protein