9,519 research outputs found
Quantum electric-dipole liquid on a triangular lattice
Geometric frustrations and quantum mechanical fluctuations may prohibit the
formation of long-range ordering even at the lowest temperature, and therefore
liquid-like ground states could be expected. A good example is the quantum spin
liquid in frustrated magnets that represents an exotic phase of matter and is
attracting enormous interests. Geometric frustrations and quantum fluctuations
can happen beyond magnetic systems. Here we propose that quantum
electric-dipole liquids, analogs to quantum spin liquids, could emerge in
frustrated dielectrics where antiferroelectrically coupled small electric
dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite
BaFe12O19, in which small electric dipoles originated from the off-center
displacement of Fe3+ in the FeO5 bipyramids constitute a two-dimensional
triangular lattice, represents a promising candidate to generate the
anticipated electric-dipole liquid. We present a series of experimental
evidences, including dielectric permittivity, heat capacity, and thermal
conductivity measured down to 66 mK, to reveal the existence of a nontrivial
ground state in BaFe12O19, characterized by itinerant low-energy excitations
with a small gap, to which we interpret as an exotic liquid-like quantum phase.
The quantum electric-dipole liquids in frustrated dielectrics open up a fresh
playground for fundamental physics and may find applications in quantum
information and computation as well.Comment: 13 pages, 6 figure
Train Your Own GNN Teacher: Graph-Aware Distillation on Textual Graphs
How can we learn effective node representations on textual graphs? Graph
Neural Networks (GNNs) that use Language Models (LMs) to encode textual
information of graphs achieve state-of-the-art performance in many node
classification tasks. Yet, combining GNNs with LMs has not been widely explored
for practical deployments due to its scalability issues. In this work, we
tackle this challenge by developing a Graph-Aware Distillation framework (GRAD)
to encode graph structures into an LM for graph-free, fast inference. Different
from conventional knowledge distillation, GRAD jointly optimizes a GNN teacher
and a graph-free student over the graph's nodes via a shared LM. This
encourages the graph-free student to exploit graph information encoded by the
GNN teacher while at the same time, enables the GNN teacher to better leverage
textual information from unlabeled nodes. As a result, the teacher and the
student models learn from each other to improve their overall performance.
Experiments in eight node classification benchmarks in both transductive and
inductive settings showcase GRAD's superiority over existing distillation
approaches for textual graphs
Jets in a Gamma-Ray Burst During its Prompt Emission: Evolution of Lorentz Factor
Knowledge about the Lorentz factor and its evolution of relativistic jets in
gamma-ray bursts (GRBs) is crucial to understand their physics. An exact value
of bulk Lorentz factor can be estimated based on a high-energy spectral cutoff,
which may appear in GRBs' prompt emission owing to the absorption of
photon-photon pair production. In this work, we focus on the investigation of
the bulk Lorentz factor evolution of jets in an individual burst. Based on
\textsl{Fermi} observations, we search for the bursts with multiple
-ray pulses characterized by a high-energy spectral cutoff, and nine
GRBs are obtained. Together with the estimation of the pulse duration and
radiation spectrum, the Lorentz factor of jets corresponding to different
pulses in an individual GRB are estimated. It is shown that the Lorentz factor
of jets in an individual GRB fluctuates within a certain range and without a
general trend in these nine GRBs. In addition, the Lorentz factors of the jets
in GRBs~130821A, 160509A and 160625B seem to increase with time. We also study
the relations among , , and for the pulses
in our sample, which is found to be consistent with that found in previous
works.Comment: Accepted for publication in Ap
- …