1,625 research outputs found
Berryogenesis: self-induced Berry flux and spontaneous non-equilibrium magnetism
Spontaneous symmetry breaking is central to the description of interacting
phases of matter. Here we reveal a new mechanism through which a driven
interacting system subject to a time-reversal symmetric driving field can
spontaneously magnetize. We show that the strong internal ac fields of a metal
driven close to its plasmon resonance may enable Berryogenesis: the spontaneous
generation of a self-induced Bloch band Berry flux. The self-induced Berry flux
supports and is sustained by a circulating plasmonic motion, which may arise
even for a linearly polarized driving field. This non-equilibrium phase
transition occurs above a critical driving amplitude, and may be of either
continuous or discontinuous type. Berryogenesis relies on feedback due to
interband coherences induced by internal fields, and may readily occur in a
wide variety of multiband systems. We anticipate that graphene devices, in
particular, provide a natural platform to achieve Berryogenesis and
plasmon-mediated spontaneous non-equilibrium magnetization in present-day
devices
Plasmon geometric phase and plasmon Hall shift
The collective plasmonic modes of a metal comprise a pattern of charge
density and tightly-bound electric fields that oscillate in lock-step to yield
enhanced light-matter interaction. Here we show that metals with non-zero Hall
conductivity host plasmons with a fine internal structure: they are
characterized by a current density configuration that sharply departs from that
of ordinary zero Hall conductivity metals. This non-trivial internal structure
dramatically enriches the dynamics of plasmon propagation, enabling plasmon
wavepackets to acquire geometric phases as they scatter. Strikingly, at
boundaries these phases accumulate allowing plasmon waves that reflect off to
experience a non-reciprocal parallel shift along the boundary displacing the
incident and reflected plasmon trajectories. This plasmon Hall shift, tunable
by Hall conductivity as well as plasmon wavelength, displays the chirality of
the plasmon's current distribution and can be probed by near-field photonics
techniques. Anomalous plasmon dynamics provide a real-space window into the
inner structure of plasmon bands, as well as new means for directing plasmonic
beams
Energy-driven Drag at Charge Neutrality in Graphene
Coulomb coupling between proximal layers in graphene heterostructures results
in efficient energy transfer between the layers. We predict that, in the
presence of correlated density inhomogeneities in the layers, vertical energy
transfer has a strong impact on lateral charge transport. In particular, for
Coulomb drag it dominates over the conventional momentum drag near zero doping.
The dependence on doping and temperature, which is different for the two drag
mechanisms, can be used to separate these mechanisms in experiment. We predict
distinct features such as a peak at zero doping and a multiple sign reversal,
which provide diagnostics for this new drag mechanism.Comment: 6 pgs, 3 fg
Large optical conductivity of Dirac semimetal Fermi arc surfaces states
Fermi arc surface states, a hallmark of topological Dirac semimetals, can
host carriers that exhibit unusual dynamics distinct from that of their parent
bulk. Here we find that Fermi arc carriers in intrinsic Dirac semimetals
possess a strong and anisotropic light matter interaction. This is
characterized by a large Fermi arc optical conductivity when light is polarized
transverse to the Fermi arc; when light is polarized along the Fermi arc, Fermi
arc optical conductivity is significantly muted. The large surface spectral
weight is locked to the wide separation between Dirac nodes and persists as a
large Drude weight of Fermi arc carriers when the system is doped. As a result,
large and anisotropic Fermi arc conductivity provides a novel means of
optically interrogating the topological surfaces states of Dirac semimetals.Comment: 8 pages, 3 figure
Chiral plasmons without magnetic field
Plasmons, the collective oscillations of interacting electrons, possess
emergent properties that dramatically alter the optical response of metals. We
predict the existence of a new class of plasmons -- chiral Berry plasmons
(CBPs) -- for a wide range of two-dimensional metallic systems including gapped
Dirac materials. As we show, in these materials the interplay between Berry
curvature and electron-electron interactions yields chiral plasmonic modes at
zero magnetic field. The CBP modes are confined to system boundaries, even in
the absence of topological edge states, with chirality manifested in split
energy dispersions for oppositely directed plasmon waves. We unveil a rich CBP
phenomenology and propose setups for realizing them, including in anomalous
Hall metals and optically-pumped 2D Dirac materials. Realization of CBPs will
offer a new paradigm for magnetic field-free, sub-wavelength optical
non-reciprocity, in the mid IR-THz range, with tunable splittings as large as
tens of THz, as well as sensitive all-optical diagnostics of topological bands.Comment: 10 pgs, 3 fg
Linear magnetoresistance in metals: guiding center diffusion in a smooth random potential
We predict that guiding center (GC) diffusion yields a linear and
non-saturating (transverse) magnetoresistance in 3D metals. Our theory is
semi-classical and applies in the regime where the transport time is much
greater than the cyclotron period, and for weak disorder potentials which are
slowly varying on a length scale much greater than the cyclotron radius. Under
these conditions, orbits with small momenta along magnetic field are
squeezed and dominate the transverse conductivity. When disorder potentials are
stronger than the Debye frequency, linear magnetoresistance is predicted to
survive up to room temperature and beyond. We argue that magnetoresistance from
GC diffusion explains the recently observed giant linear magnetoresistance in
3D Dirac materials
Topological Bloch Bands in Graphene Superlattices
We outline an approach to endow a plain vanilla material with topological
properties by creating topological bands in stacks of manifestly nontopological
atomically thin materials. The approach is illustrated with a model system
comprised of graphene stacked atop hexagonal-boron-nitride. In this case, the
Berry curvature of the electron Bloch bands is highly sensitive to the stacking
configuration. As a result, electron topology can be controlled by crystal axes
alignment, granting a practical route to designer topological materials. Berry
curvature manifests itself in transport via the valley Hall effect and
long-range chargeless valley currents. The non-local electrical response
mediated by such currents provides diagnostics for band topology
Enhanced thermionic-dominated photoresponse in graphene Schottky junctions
Vertical heterostructures of van der Waals materials enable new pathways to
tune charge and energy transport characteristics in nanoscale systems. We
propose that graphene Schottky junctions can host a special kind of
photoresponse which is characterized by strongly coupled heat and charge flows
that run vertically out of the graphene plane. This regime can be accessed when
vertical energy transport mediated by thermionic emission of hot carriers
overwhelms electron-lattice cooling as well as lateral diffusive energy
transport. As such, the power pumped into the system is efficiently extracted
across the entire graphene active area via thermionic emission of hot carriers
into a semiconductor material. Experimental signatures of this regime include a
large and tunable internal responsivity with a non-monotonic
temperature dependence. In particular, peaks at electronic
temperatures on the order of the Schottky potential and has a large
upper limit ( when ). Our proposal opens up new approaches for engineering the
photoresponse in optically-active graphene heterostructures.Comment: 6 pages, 2 figure
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