385,774 research outputs found
Slow L\'evy flights
Among Markovian processes, the hallmark of L\'evy flights is superdiffusion,
or faster-than-Brownian dynamics. Here we show that L\'evy laws, as well as
Gaussians, can also be the limit distributions of processes with long range
memory that exhibit very slow diffusion, logarithmic in time. These processes
are path-dependent and anomalous motion emerges from frequent relocations to
already visited sites. We show how the Central Limit Theorem is modified in
this context, keeping the usual distinction between analytic and non-analytic
characteristic functions. A fluctuation-dissipation relation is also derived.
Our results may have important applications in the study of animal and human
displacements.Comment: 6 pages, 2 figure
Cyclotron resonance inside the Mott gap: a fingerprint of emergent neutral fermions
A major obstacle to identify exotic quantum phases of matter featuring
spin-charge separation above one-dimension is the lack of tailored probes
allowing to establish their presence in correlated materials. Here we propose
an optoelectronic response that could allow to pinpoint the presence of certain
spin-charge separated states with emergent neutral gapless fermions in two and
three-dimensional materials. We show that even though these states behave like
insulators under static electric fields, they can display clear cyclotron
resonance peaks in their light absorption spectrum under static magnetic
fields, but typically the principal Kohn mode will be missing in comparison to
ordinary metals. This distinctive phenomena could be tested in materials such
as triangular lattice organics, three-dimensional mixed valence insulators
YbB and SmB, and transition metal dichalcogenides 1T-TaS and
1T-TaSe
Quantum nonlinear Hall effect induced by Berry curvature dipole in time-reversal invariant materials
It is well-known that a non-vanishing Hall conductivity requires
time-reversal symmetry breaking. However, in this work, we demonstrate that a
Hall-like transverse current can occur in second-order response to an external
electric field in a wide class of time-reversal invariant and inversion
breaking materials, at both zero and twice the optical frequency. This
nonlinear Hall effect has a quantum origin arising from the dipole moment of
the Berry curvature in momentum space, which generates a net anomalous velocity
when the system is in a current-carrying state. We show that the nonlinear Hall
coefficient is a rank-two pseudo-tensor, whose form is determined by point
group symmetry. We discus optimal conditions to observe this effect and propose
candidate two- and three-dimensional materials, including topological
crystalline insulators, transition metal dichalcogenides and Weyl semimetals.Comment: 5 pages, 1 figur
Anomalous stabilization in a spin-transfer system at high spin polarization
Switching diagrams of nanoscale ferromagnets driven by a spin-transfer torque
are studied in the macrospin approximation. We consider a disk-shaped free
layer with in-plane easy axis and external magnetic field directed in-plane at
90 degrees to that axis. It is shown that this configuration is sensitive to
the angular dependence of the spin-transfer efficiency factor and can be used
to experimentally distinguish between different forms of , in
particular between the original Slonczewski form and the constant
approximation. The difference in switching diagrams is especially pronounced at
large spin polarizations, with the Slonczewski case exhibiting an anomalous
region.Comment: 3 pages, 4 figure
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