Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDisorder-enabled hydrodynamics of charge and heat transport in monolayer graphene
210
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Hydrodynamic behavior in electronic systems is commonly accepted to be associated with extremely clean samples such that electron-electron collisions dominate and total momentum is conserved. Contrary to this, we show that in monolayer graphene the presence of disorder is essential to enable an unconventional hydrodynamic regime which exists near the charge neutrality point and is characterized by a large enhancement of the Wiedemann-Franz ratio. Although the enhancement becomes more pronounced with decreasing disorder, the very possibility of observing the effect depends crucially on the presence of disorder. We calculate the maximum extrinsic carrier density $n_c$ below which the effect becomes manifest, and show that $n_c$ vanishes in the limit of zero disorder. For $n>n_c$ we predict that the Wiedemann-Franz ratio actually decreases with decreasing disorder. We complete our analysis by presenting a transparent picture of the physical processes that are responsible for the crossover from conventional to disorder-enabled hydrodynamics. Recent experiments on monolayer graphene are discussed and shown to be consistent with this picture.
rate research
Read More
We investigate the contribution of charge puddles to the non-vanishing conductivity minimum in disordered graphene flakes at the charge neutrality point. For that purpose, we study systems with a geometry that suppresses the transmission due to evanescent modes allowing to single out the effect of charge fluctuations in the transport properties. We use the recursive Greens functions technique to obtain local and total transmissions through systems that mimic vanishing density of states at the charge neutrality point in the presence of a local disordered local potential to model the charge puddles. Our microscopic model includes electron-electron interactions via a spin resolved Hubbard mean field term. We establish the relation between the charge puddle disorder potential and the electronic transmission at the charge neutrality point. We discuss the implications of our findings to high mobility graphene samples deposited on different substrates and provide a qualitative interpretation of recent experimental results.
Electrons behave like a classical fluid with a momentum distribution function that varies slowly in space and time when the quantum mechanical carrier-carrier scattering dominates over all other scattering processes. Recent experiments in monolayer and bilayer graphene have reported signatures of such hydrodynamic electron behavior in ultra-clean devices. In this theoretical work, starting from a microscopic treatment of electron-electron, electron-phonon and electron-impurity interactions within the Random Phase Approximation, we demonstrate that monolayer and bilayer graphene both host two different hydrodynamic regimes. We predict that the hydrodynamic window in bilayer graphene is stronger than in monolayer graphene, and has a characteristic `v-shape as opposed to a `lung-shape. Finally, we collapse experimental data onto a universal disorder-limited theory, thereby proving that the observed violation of Wiedemann-Franz law in monolayers occurs in a regime dominated by impurity-induced electron-hole puddles.
We have experimentally studied the nonlinear nature of electrical conduction in monolayer graphene devices on silica substrates. This nonlinearity manifests itself as a nonmonotonic dependence of the differential resistance on applied DC voltage bias across the sample. At temperatures below ~70K, the differential resistance exhibits a peak near zero bias that can be attributed to self-heating of the charge carriers. We show that the shape of this peak arises from a combination of different energy dissipation mechanisms of the carriers. The energy dissipation at higher carrier temperatures depends critically on the length of the sample. For samples longer than 10um the heat loss is shown to be determined by optical phonons at the silica-graphene interface.
We investigate theoretically thermal and electrical conductances for the system consisting of a quantum dot (QD) connected both to a pair of Majorana fermions residing the edges of a Kitaev wire and two metallic leads. We demonstrate that both quantities reveal pronounced resonances, whose positions can be controlled by tuning of an asymmetry of the couplings of the QD and a pair of MFs. Similar behavior is revealed for the thermopower, Wiedemann-Franz law and dimensionless thermoelectric figure of merit. The considered geometry can thus be used as a tuner of heat and charge transport assisted by MFs.
At high magnetic fields, monolayer graphene hosts competing phases distinguished by their breaking of the approximate SU(4) isospin symmetry. Recent experiments have observed an even denominator fractional quantum Hall state thought to be associated with a transition in the underlying isospin order from a spin-singlet charge density wave at low magnetic fields to an antiferromagnet at high magnetic fields, implying that a similar transition must occur at charge neutrality. However, this transition does not generate contrast in typical electrical transport or thermodynamic measurements and no direct evidence for it has been reported, despite theoretical interest arising from its potentially unconventional nature. Here, we measure the transmission of ferromagnetic magnons through the two dimensional bulk of clean monolayer graphene. Using spin polarized fractional quantum Hall states as a benchmark, we find that magnon transmission is controlled by the detailed properties of the low-momentum spin waves in the intervening Hall fluid, which is highly density dependent. Remarkably, as the system is driven into the antiferromagnetic regime, robust magnon transmission is restored across a wide range of filling factors consistent with Pauli blocking of fractional quantum hall spin-wave excitations and their replacement by conventional ferromagnetic magnons confined to the minority graphene sublattice. Finally, using devices in which spin waves are launched directly into the insulating charge-neutral bulk, we directly detect the hidden phase transition between bulk insulating charge density wave and a canted antiferromagnetic phases at charge neutrality, completing the experimental map of broken-symmetry phases in monolayer graphene.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
