54 research outputs found
On the \alpha-Invariants of Cubic Surfaces with Eckardt Points
In this paper, we show that the \alpha_{m,2}-invariant of a smooth cubic
surface with Eckardt points is strictly bigger than 2/3. This can be used to
simplify Tian's original proof of the existence of Kaehler-Einstein metrics on
such manifolds. We also sketch the computations on cubic surfaces with one
ordinary double points, and outline the analytic difficulties to prove the
existence of orbifold Kaehler-Einstein metrics.Comment: 22 pages. We add a new section discussing singular stable cubic
surface
A Rapid Method for Detection of Salmonella in Milk Based on Extraction of mRNA Using Magnetic Capture Probes and RT-qPCR
Magnetic separation is an efficient method for target enrichment and elimination of inhibitors in the molecular detection systems for foodborne pathogens. In this study, we prepared magnetic capture probes by modifying oligonucleotides complementary to target sequences on the surface of amino-modified silica-coated magnetic nanoparticles and optimized the conditions and parameters of probe synthesis and hybridization. We innovatively put the complexes of magnetic capture probes and target sequences into qPCR without any need for denaturation and purification steps. This strategy can reduce manual steps and save time. We used the magnetic capture probes to separate invA mRNA from Salmonella in artificially contaminated milk samples. The detection sensitivity was 104Â CFU/ml, which could be increased to 10Â CFU/ml after a 12Â h enrichment step. The developed method is robust enough to detect live bacteria in a complex environmental matrix
Observation of first-order quantum phase transitions and ferromagnetism in twisted double bilayer graphene
Twisted graphene multilayers are highly tunable flatband systems for
developing new phases of matter. Thus far, while orbital ferromagnetism has
been observed in valley polarized phases, the long-range orders of other
correlated phases as well as the quantum phase transitions between different
orders mostly remain unknown. Here, we report an observation of Coulomb
interaction driven first-order quantum phase transitions and ferromagnetism in
twisted double bilayer graphene (TDBG). At zero magnetic field, the transitions
are revealed in a series of step-like abrupt resistance jumps with prominent
hysteresis loop when either the displacement field (D) or the carrier density
(n) is tuned across symmetry-breaking boundary near half filling, indicating a
formation of ordered domains. It is worth noting that the good turnability and
switching of these states gives a rise to a memory performance with a large
on/off ratio. Moreover, when both spin and valley play the roles at finite
magnetic field, we observe abundant first-order quantum phase transitions among
normal metallic states from charge neutral point, orbital ferromagnetic states
from quarter filling, and spin-polarized states from half filling. We interpret
these first-order phase transitions in the picture of phase separations and
spin domain percolations driven by multi-field tunable Coulomb interactions, in
agreement with Lifshitz transition from Hartree-Fock calculations. The observed
multi-filed tunable domain structure and its hysteresis resembles the
characteristics of multiferroics, revealing intriguing magnetoelectric
properties. Our result enriches the correlated phase diagram in TDBG for
discovering novel exotic phases and quantum phase transitions, and it would
benefit other twisted moir\'e systems as well
Room-temperature correlated states in twisted bilayer MoS
Moir\'e superlattices have emerged as an exciting condensed-matter quantum
simulator for exploring the exotic physics of strong electronic correlations.
Notable progress has been witnessed, but such correlated states are achievable
usually at low temperatures. Here, we report the transport evidences of
room-temperature correlated electronic states and layer-hybridized SU(4)
Hubbard model simulator in AB-stacked MoS homo-bilayer moir\'e
superlattices. Correlated insulating states at moir\'e band filling factors v =
1, 2, 3 are unambiguously established in twisted bilayer MoS. Remarkably,
the correlated electronic states can persist up to a record-high critical
temperature of over 285 K. The realization of room-temperature correlated
states in twisted bilayer MoS can be understood as the cooperation effects
of the stacking-specific atomic reconstruction and the resonantly enhanced
interlayer hybridization, which largely amplify the moir\'e superlattice
effects on electronic correlations. Furthermore, extreme large non-linear Hall
responses up to room-temperature are uncovered near correlated insulating
states, demonstrating the quantum geometry of moir\'e flat conduction band.Comment: 13 pages, 3 figure
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