711 research outputs found
Model-Based Reinforcement Learning with Isolated Imaginations
World models learn the consequences of actions in vision-based interactive
systems. However, in practical scenarios like autonomous driving,
noncontrollable dynamics that are independent or sparsely dependent on action
signals often exist, making it challenging to learn effective world models. To
address this issue, we propose Iso-Dream++, a model-based reinforcement
learning approach that has two main contributions. First, we optimize the
inverse dynamics to encourage the world model to isolate controllable state
transitions from the mixed spatiotemporal variations of the environment.
Second, we perform policy optimization based on the decoupled latent
imaginations, where we roll out noncontrollable states into the future and
adaptively associate them with the current controllable state. This enables
long-horizon visuomotor control tasks to benefit from isolating mixed dynamics
sources in the wild, such as self-driving cars that can anticipate the movement
of other vehicles, thereby avoiding potential risks. On top of our previous
work, we further consider the sparse dependencies between controllable and
noncontrollable states, address the training collapse problem of state
decoupling, and validate our approach in transfer learning setups. Our
empirical study demonstrates that Iso-Dream++ outperforms existing
reinforcement learning models significantly on CARLA and DeepMind Control.Comment: arXiv admin note: substantial text overlap with arXiv:2205.1381
Verification of Onsager reciprocal relation between anomalous transverse coefficients of an anisotropic antiferromagnet
Whenever two irreversible processes occur simultaneously, time-reversal
symmetry of microscopic dynamics gives rise, on a macroscopic level, to
Onsager's reciprocal relations, which impose constraints on the number of
independent components of any transport coefficient tensor. Here, we show that
in the antiferromagnetic YbMnBi, which displays a strong
temperature-dependent anisotropy, the Onsager's reciprocal relations are
strictly satisfied for anomalous electric, , and anomalous
thermoelectric, , conductivity tensors. In contradiction with
what was recently reported by Pan [1], we find that , and . This equality
holds in the whole temperature window irrespective of the relative weights of
the intrinsic or extrinsic mechanisms. The ratio
is close at room temperature, but peaks to an unprecedented magnitude
of 2.9 at 150 K, which may involve non-degenerate carriers of
small Fermi surface pockets.Comment: 6 pages, 4 figures,supplemental materials include
Phonon thermal Hall effect in strontium titanate
It has been known for more than a decade that phonons can produce an
off-diagonal thermal conductivity in presence of magnetic field. Recent studies
of thermal Hall conductivity, , in a variety of contexts, however,
have assumed a negligibly small phonon contribution. We present a study of
in quantum paraelectric SrTiO, which is a non-magnetic
insulator and find that its peak value exceeds what has been reported in any
other insulator, including those in which the signal has been qualified as
'giant'. Remarkably, and peak at the same
temperature and the former decreases faster than the latter at both sides of
the peak. Interestingly, in the case of LaCuO and -RuCl,
and peak also at the same temperature. We also
studied KTaO and found a small signal, indicating that a sizable
is not a generic feature of quantum paraelectrics. Combined to
other observations, this points to a crucial role played by antiferrodistortive
domains in generating of this solid.Comment: Main text: 6 pages, 4 figures, Supplemental Material is included.
Accepted by Phys. Rev. Let
Field-linear anomalous Hall effect and Berry curvature induced by spin chirality in the kagome antiferromagnet Mn3Sn
During the past two decades, it has been established that a non-trivial
electron wave-function topology generates an anomalous Hall effect (AHE), which
shows itself as a Hall conductivity non-linear in magnetic field. Here, we
report on an unprecedented case of field-linear AHE. In MnSn, a kagome
magnet, the out-of-plane Hall response, which shows an abrupt jump, was
discovered to be a case of AHE. We find now that the in-plane Hall response,
which is perfectly linear in magnetic field, is set by the Berry curvature of
the wavefunction. The amplitude of the Hall response and its concomitant Nernst
signal exceed by far what is expected in the semiclassical picture. We argue
that magnetic field induces out-of-plane spin canting and thereafter gives rise
to nontrivial spin chirality on the kagome lattice. In band structure, we find
that the spin chirality modifies the topology by gapping out Weyl nodal lines
unknown before, accounting for the AHE observed. Our work reveals intriguing
unification of real-space Berry phase from spin chirality and momentum-space
Berry curvature.Comment: 4 figures and 6 pages. The supplementary materials were attached to
the en
Finite-temperature violation of the anomalous transverse Wiedemann-Franz law
The Wiedemann-Franz (WF) law links the ratio of electronic charge and heat
conductivity to fundamental constants. It has been tested in numerous solids,
but the extent of its relevance to the anomalous transverse transport, which
represents the topological nature of the wave function, remains an open
question. Here we present a study of anomalous transverse response in the
noncollinear antiferromagnet MnGe extended from room temperature down to
sub-Kelvin temperature and find that the anomalous Lorenz ratio remains close
to the Sommerfeld value up to 100 K, but not above. The finite-temperature
violation of the WF correlation is caused by a mismatch between the thermal and
electrical summations of the Berry curvature, rather than the inelastic
scattering as observed in ordinary metals. This interpretation is backed by our
theoretical calculations, which reveals a competition between the temperature
and the Berry curvature distribution. The accuracy of the experiment is
supported by the verification of the Bridgman relation between the anomalous
Ettingshausen and Nernst effects. Our results identify the anomalous Lorenz
ratio as an extremely sensitive probe of Berry spectrum near the chemical
potential.Comment: 9 pages,6 figures, Supplemental Material include
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