Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCurrent noise and higher order fluctuations in semiconducting bilayer systems
102
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We analyze the transport properties of a semiconductor based bilayer system under non-equilibrium conditions with special emphasis on the charge transfer statistics in the regime dominated by the exciton transport. We consider two different models. In one of them the transport occurs incoherently and is dominated by incoherent tunneling processes of individual excitons, while in the other system no disorder is present and transport processes are fully coherent. We find that the strength of cross correlations of currents in different layers is only insignificantly affected by the disorder and shows up similar behaviour in both systems. We discuss possible experimental realizations and make predictions for measurable quantities.
rate research
Read More
Higher-order topological insulators are newly proposed topological phases of matter, whose bulk topology manifests as localized modes at two- or higher-dimensional lower boundaries. In this work, we propose the twisted bilayer graphenes with large angles as higher-order topological insulators, hosting topological corner charges. At large commensurate angles, the intervalley scattering opens up the bulk gap and the corner states occur at half filling. Based on both first-principles calculations and analytic analysis, we show the striking results that the emergence of the corner states do not depend on the choice of the specific angles as long as the underlying symmetries are intact. Our results show that the twisted bilayer graphene can serve as a robust candidate material of two-dimensional higher-order topological insulator.
We propose an extension of the Landauer-Buttiker scattering theory to include effects of interaction in the active region of a mesoscopic conductor structure. The current expression obtained coincides with those derived by different methods. A new general expression for the noise is also established. These expressions are then discussed in the case of strongly sequential tunneling through a double-barrier resonant tunneling structure.
Higher order topological insulators are a new class of topological insulators in dimensions $rm d>1$. These higher-order topological insulators possess $rm (d - 1)$-dimensional boundaries that, unlike those of conventional topological insulators, do not conduct via gapless states but instead are themselves topological insulators. Precisely, an $rm n^{rm th}$-order topological insulator in $rm m$ dimensions hosts $rm d_{c} = (m - n)$-dimensional boundary modes $rm (n leq m)$. For instance, a three-dimensional second (third) order topological insulator hosts gapless modes on the hinges (corners), characterized by $rm d_{c} = 1 (0)$. Similarly, a second order topological insulator in two dimensions only has gapless corner states ($rm d_{c} = 0$) localized at the boundary. These higher order phases are protected by various crystalline symmetries. Moreover, in presence of proximity induced superconductivity and appropriate symmetry breaking perturbations, the above mentioned bulk-boundary correspondence can be extended to higher order topological superconductors hosting Majorana hinge or corner modes. Such higher-order systems constitute a distinctive new family of topological phases of matter which has been experimentally observed in acoustic systems, multilayer $rm WTe_{2}$ and $rm Bi_{4}Br_{4}$ chains. In this general article, the basic phenomenology of higher order topological insulators and higher order topological superconductors are presented along with some of their experimental realization.
We consider the non-equilibrium zero frequency noise generated by a temperature gradient applied on a device composed of two normal leads separated by a quantum dot. We recall the derivation of the scattering theory for non-equilibrium noise for a general situation where both a bias voltage and a temperature gradient can coexist and put it in a historical perspective. We provide a microscopic derivation of zero frequency noise through a quantum dot based on a tight binding Hamiltonian, which constitutes a generalization of the pioneering work of Caroli et al. for the current obtained in the context of the Keldysh formalism. For a single level quantum dot, the obtained transmission coefficient entering the scattering formula for the non-equilibrium noise corresponds to a Breit-Wigner resonance. We compute the delta-$T$ noise as a function of the dot level position, and of the dot level width, in the Breit-Wigner case, for two relevant situations which were considered recently in two separate experiments. In the regime where the two reservoir temperatures are comparable, our gradient expansion shows that the delta-$T$ noise is dominated by its quadratic contribution, and is minimal close to resonance. In the opposite regime where one reservoir is much colder, the gradient expansion fails and we find the noise to be typically linear in temperature before saturating. In both situations, we conclude with a short discussion of the case where both a voltage bias and a temperature gradient are present, in order to address the potential competition with thermoelectric effects.
We have investigated the cross-over from Zener tunneling of single charge carriers to avalanche type of bunched electron transport in a suspended graphene Corbino disk in the zeroth Landau level. At low bias, we find a tunneling current that follows the gyrotropic Zener tunneling behavior. At larger bias, we find avalanche type of transport that sets in at a smaller current the larger the magnetic field is. The low-frequency noise indicates strong bunching of the electrons in the avalanches. On the basis of the measured low-frequency switching noise power, we deduce the characteristic switching rates of the avalanche sequence. The simultaneous microwave shot noise measurement also reveals intrinsic correlations within the avalanche pulses and indicate decrease of correlations with increasing bias.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
