626 research outputs found
Twistable electronics with dynamically rotatable heterostructures
The electronic properties of two-dimensional materials and their
heterostructures can be dramatically altered by varying the relative angle
between the layers. This makes it theoretically possible to realize a new class
of twistable electronics in which device properties can be manipulated
on-demand by simply rotating the structure. Here, we demonstrate a new device
architecture in which a layered heterostructure can be dynamically twisted, in
situ. We study graphene encapsulated by boron nitride where at small rotation
angles the device characteristics are dominated by coupling to a large
wavelength Moir\'e superlattice. The ability to investigate arbitrary rotation
angle in a single device reveals new features in the optical, mechanical and
electronic response in this system. Our results establish the capability to
fabricate twistable electronic devices with dynamically tunable properties
High quality electrostatically defined hall bars in monolayer graphene
Realizing graphene's promise as an atomically thin and tunable platform for
fundamental studies and future applications in quantum transport requires the
ability to electrostatically define the geometry of the structure and control
the carrier concentration, without compromising the quality of the system.
Here, we demonstrate the working principle of a new generation of high quality
gate defined graphene samples, where the challenge of doing so in a gapless
semiconductor is overcome by using the insulating state, which emerges
at modest applied magnetic fields. In order to verify that the quality of our
devices is not compromised by the presence of multiple gates we compare the
electronic transport response of different sample geometries, paying close
attention to fragile quantum states, such as the fractional quantum Hall (FQH)
states, that are highly susceptible to disorder. The ability to define local
depletion regions without compromising device quality establishes a new
approach towards structuring graphene-based quantum transport devices
Competing Fractional Quantum Hall and Electron Solid Phases in Graphene
We report experimental observation of the reentrant integer quantum Hall
effect in graphene, appearing in the N2 Landau level. Similar to
high-mobility GaAs/AlGaAs heterostructures, the effect is due to a competition
between incompressible fractional quantum Hall states, and electron solid
phases. The tunability of graphene allows us to measure the - phase
diagram of the electron-solid phase. The hierarchy of reentrant states suggest
spin and valley degrees of freedom play a role in determining the ground state
energy. We find that the melting temperature scales with magnetic field, and
construct a phase diagram of the electron liquid-solid transition
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