278 research outputs found
Quota and Risk Sharing among Fishermen
Pooling and exchange of random resources may offer the owners insurance and substitution. Greater efficiency and more stable revenues thereby obtain. These good properties derive from a sharing rule that complies with the core concept from cooperative production games. It is applied here to fisheries with stochastic yield.Resource management; randomization; risk; insurance; cooperative games; core allocations; mutual exchange; stochastic programming; communal fisheries.
Strongly angle-dependent magnetoresistance in Weyl semimetals with long-range disorder
The chiral anomaly in Weyl semimetals states that the left- and right-handed
Weyl fermions, constituting the low energy description, are not individually
conserved, resulting, for example, in a negative magnetoresistance in such
materials. Recent experiments see strong indications of such an anomalous
resistance response; however, with a response that at strong fields is more
sharply peaked for parallel magnetic and electric fields than expected from
simple theoretical considerations. Here, we uncover a mechanism, arising from
the interplay between the angle-dependent Landau level structure and long-range
scalar disorder, that has the same phenomenology. In particular, we ana-
lytically show, and numerically confirm, that the internode scattering time
decreases exponentially with the angle between the magnetic field and the Weyl
node separation in the large field limit, while it is insensitive to this angle
at weak magnetic fields. Since, in the simplest approximation, the internode
scattering time is proportional to the anomaly-related conductivity, this
feature may be related to the experimental observations of a sharply peaked
magnetoresistance.Comment: 8 pages, 4 figure
Quantized Fermi-arc-mediated transport in Weyl semimetal nanowires
We study longitudinal transport in Weyl semimetal nanowires, both in the
absence and in the presence of a magnetic flux threading the nanowires. We
identify two qualitatively different regimes of transport with respect to the
chemical potential in the nanowires. In the "surface regime", for low doping,
most of the conductance occurs through the Fermi-arc surface states, and it
rises in steps of one quantum of conductance as a function of the chemical
potential; furthermore, with varying flux the conductance changes in steps of
one quantum of conductance with characteristic Fabry-P\'erot interference
oscillations. In the "bulk-surface regime", for highly-doped samples, the
dominant contribution to the conductance is quadratic in the chemical
potential, and mostly conditioned by the bulk states; the flux dependence shows
clearly that both the surface and the bulk states contribute. The two
aforementioned regimes prove that the contribution of the Fermi-arc surface
states is salient and, therefore, crucial for understanding transport
properties of finite-size Weyl semimetal systems. Last but not least, we
demonstrate that both regimes are robust to disorder.Comment: 13 pages, 6 figure
Tenfold way and many-body zero modes in the Sachdev-Ye-Kitaev model
The Sachdev-Ye-Kitaev (SYK) model, in its simplest form, describes k Majorana fermions with random all-to-all four-body interactions. We consider the SYK model in the framework of a many-body Altland-Zirnbauer classification that sees the system as belonging to one of eight (real) symmetry classes depending on the value of k mod 8. We show that, depending on the symmetry class, the system may support exact many-body zero modes with the symmetries also dictating whether these may have a nonzero contribution to Majorana fermions, i.e., single-particle weight. These zero modes appear in all but two of the symmetry classes. When present, they leave clear signatures in physical observables that go beyond the threefold (Wigner-Dyson) possibilities for level spacing statistics studied earlier. Signatures we discover include a zero-energy peak or hole in the single-particle spectral function, depending on whether symmetries allow or forbid zero modes to have single-particle weight. The zero modes are also shown to influence the many-body dynamics, where signatures include a nonzero long-time limit for the out-of-time-order correlation function. Furthermore, we show that the extension of the four-body SYK model by quadratic terms can be interpreted as realizing the remaining two complex symmetry classes; we thus demonstrate how the entire tenfold Altland-Zirnbauer classification may emerge in the SYK model
Defining a bulk-edge correspondence for non-Hermitian Hamiltonians via singular-value decomposition
We address the breakdown of the bulk-boundary correspondence observed in
non-Hermitian systems, where open and periodic systems can have distinct phase
diagrams. The correspondence can be completely restored by considering the
Hamiltonian's singular value decomposition instead of its eigendecomposition.
This leads to a natural topological description in terms of a flattened
singular decomposition. This description is equivalent to the usual approach
for Hermitian systems and coincides with a recent proposal for the
classification of non-Hermitian systems. We generalize the notion of the
entanglement spectrum to non-Hermitian systems, and show that the edge physics
is indeed completely captured by the periodic bulk Hamiltonian. We exemplify
our approach by considering the chiral non-Hermitian Su-Schrieffer-Heger and
Chern insulator models. Our work advocates a different perspective on
topological non-Hermitian Hamiltonians, paving the way to a better
understanding of their entanglement structure.Comment: 6+5 pages, 8 figure
Creatively Capturing Structure and Energy: Zero Balancing\u27s Essential Elements (Article & Video)
Through the creative use of coloring, I am devising a way to document Zero Balancingâs two foundational elements, structure and energy and the changes that occur following a ZB session. I believe this experiential activity will be a creative fulcrum, helping the client connect more effectively with the deepest part of themselves thereby experiencing greater ease and freedom from their issues. As the activity of coloring is a âright brainâ/ creative endeavor, I believe it can serve to enhance a clientâs expanded state of consciousness, one of the hallmarks of a Zero Balancing session, as well as improve their overall sense of well-being. The documents that emerge from these sessions will also serve to enhance the practitionerâs insight into the clientâs frame of mind and physical state. Please read the article and view the video
Mesoscopic Spin Hall Effect
We investigate the spin Hall effect in ballistic chaotic quantum dots with
spin-orbit coupling. We show that a longitudinal charge current can generate a
pure transverse spin current. While this transverse spin current is generically
nonzero for a fixed sample, we show that when the spin-orbit coupling time is
large compared to the mean dwell time inside the dot, it fluctuates universally
from sample to sample or upon variation of the chemical potential with a
vanishing average. For a fixed sample configuration, the transverse spin
current has a finite typical value ~e^2 V/h, proportional to the longitudinal
bias V on the sample, and corresponding to about one excess open channel for
one of the two spin species. Our analytical results are in agreement with
numerical results in a diffusive system [W. Ren et al., Phys. Rev. Lett. 97,
066603 (2006)] and are further confirmed by numerical simulation in a chaotic
cavity.Comment: 4 pages, 2 figure
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