2,445 research outputs found
Berry phase jumps and giant nonreciprocity in Dirac quantum dots
We predict that a strong nonreciprocity in the resonance spectra of Dirac
quantum dots can be induced by the Berry phase. The nonreciprocity arises in
relatively weak magnetic fields and is manifest in anomalously large
field-induced splittings of quantum dot resonances which are degenerate at
due to time-reversal symmetry. This exotic behavior, which is governed by
field-induced jumps in the Berry phase of confined electronic states, is unique
to quantum dots in Dirac materials and is absent in conventional quantum dots.
The effect is strong for gapless Dirac particles and can overwhelm the
-induced orbital and Zeeman splittings. A finite Dirac mass suppresses the
effect. The nonreciprocity, predicted for generic two-dimensional Dirac
materials, is accessible through Faraday and Kerr optical rotation measurements
and scanning tunneling spectroscopy.Comment: 6 pages, 6 figure
Resonant Tunneling and Intrinsic Bistability in Twisted Graphene Structures
We predict that vertical transport in heterostructures formed by twisted
graphene layers can exhibit a unique bistability mechanism. Intrinsically
bistable - characteristics arise from resonant tunneling and interlayer
charge coupling, enabling multiple stable states in the sequential tunneling
regime. We consider a simple trilayer architecture, with the outer layers
acting as the source and drain and the middle layer floating. Under bias, the
middle layer can be either resonant or non-resonant with the source and drain
layers. The bistability is controlled by geometric device parameters easily
tunable in experiments. The nanoscale architecture can enable uniquely fast
switching times.Comment: 7 pages, 4 figure
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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