Search results for "Ballistic"

HEAT FLUX IN SUPERFLUID TRANSITION AND IN TURBULENT HELIUM COUNTERFLOW

External ballistic of volcanic explosions

1983

In order to determine the kinetic energy of an explosion it is necessary to know the initial velocities of ejected fragments. Calculations of initial velocities made earlier with few exceptions did not take into account the resistance of the air and therefore, greatly underestimated the initial velocities, and consequently the energy of the explosions. A solution of the inverse problem of ballistics which takes into account air resistance makes it possible to find precise values of initial velocities of ejection, determined from the distance of ejected fragments and their ballistic coefficients. The method makes it possible to determine the kinetic energy of explosions for eruptions which w…

Domain-wall induced large magnetoresistance effects at zero applied field in ballistic nanocontacts

2013

We determine magnetoresistance effects in stable and clean Permalloy nanocontacts of variable cross section, fabricated by UHV deposition and in situ electromigration. To ascertain the magnetoresistance (MR) effects originating from a magnetic domain wall, we measure the resistance values with and without such a wall at zero applied field. In the ballistic transport regime, the MR ratio reaches up to 50% and exhibits a previously unobserved sign change. Our results can be reproduced by recent atomistic calculations for different atomic configurations of the nanocontact, highlighting the importance of the detailed atomic arrangement for the MR effect. DOI: 10.1103/PhysRevLett.110.067203

Dependence of Exciton Mobility on Structure in Single-Walled Carbon Nanotubes

2010

Optically generated excitons in semiconducting single-walled carbon nanotubes (SWCNTs) display substantial diffusional mobility. This property allows excitons to encounter ∼104 carbon atoms during their lifetime and accounts for their efficient deactivation by sparse quenching sites. We report here experimental determinations of the mobilities of optically generated excitons in 10 different (n,m) species of semiconducting SWCNTs. Exciton diffusional ranges were deduced from measurements of stepwise photoluminescence quenching in selected individual SWCNTs coated with sodium deoxycholate surfactant and immobilized in agarose gel. A refined data analysis method deduced mean exciton ranges fro…

Exploring the graphene edges with coherent electron focusing

2010

We study theoretically the coherent electron focusing in graphene nanoribbons. Using semiclassical and numerical tight binding calculations we show that perfect armchair edges give rise to equidistant peaks in the focusing spectrum. In the case of zigzag edges at low magnetic fields one can also observe focusing peaks but with increasing magnetic field a more complex interference structure emerges in the spectrum. This difference in the spectra can be observed even if the zigzag edge undergoes structural reconstruction. Therefore transverse electron focusing can help in the identification and characterisation of the edge structure of graphene samples.

Ballistic transport through quantum point contacts of multi-orbital oxides

2020

Linear and non-linear transport properties through an atomic-size point contact based on oxides two-dimensional electron gas is examined using the tight-binding method and the $\mathbf{k\cdot p}$ approach. The ballistic transport is analyzed in contacts realized at the (001) interface between band insulators $LaAlO_3$ and $SrTiO_3$ by using the Landauer-B\"uttiker method for many sub-bands derived from three Ti 3d orbitals ($d_{yz}$, $d_{zx}$ and $d_{xy}$) in the presence of an out-of-plane magnetic field. We focus especially on the role played by the atomic spin-orbit coupling and the inversion symmetry breaking term pointing out three transport regimes: the first, at low energies, involvi…

Persistent spin and charge currents and magnification effects in open ring conductors subject toRashba coupling

2007

We analyze the effect of Rashba spin-orbit coupling and of a local tunnel barrier on the persistent spin and charge currents in a one-dimensional conducting Aharonov-Bohm (AB) ring symmetrically coupled to two leads. First, as an important consequence of the spin-splitting, it is found that a persistent spin current can be induced which is not simply proportional to the charge current. Second, a magnification effect of the persistent spin current is shown when one tunes the Fermi energy near the Fano-type antiresonances of the total transmission coefficient governed by the tunnel barrier strength. As an unambiguous signature of spin-orbit coupling we also show the possibility to produce a p…

Optimizing the operating temperature of a transition edge sensor

2006

We discuss the theory for optimizing the operating temperature of a voltage biased superconducting transition edge sensor (TES) in terms of energy resolution and speed, considering only internal detector noise sources. The noise processes included in the modeling are the unavoidable Johnson and phonon noise. The phonon noise is calculated for the case of ballistic transport. If other external and excess internal noise sources are not dominant, an optimal operating temperature can be found to minimize the energy resolution. The detector slows down by approximately a factor of two at the optimal energy resolution point.

Ballistic phonon transport in dielectric membranes

2006

We have calculated the ballistic phononic heat transport in dielectric membranes as a function of radiator temperature and membrane thickness. The phonon modes of such membranes are known as Lamb-modes from elasticity theory. The striking result is that, for a fixed temperature, the radiated power first decreases with decreasing membrane thickness, but then develops a minimum when the transition to two dimensionality is reached. Further decrease of the membrane thickness in the 2D limit leads to increasing radiated power.

Quantum Coherence Effects in One-Dimensional Chains with Inelastic Scattering

1991

To describe the ballistic transport in a 1 D chain Landauer [1] has calculated the resistance R of a series of elastic scatterers from their transmission coefficient T $$R = \frac{h}{{{e^2}}}\frac{{1 - T}}{T}$$ (1) This relation implies complete quantum coherence between incident and all backscattered waves. Dephasing due to irreversible processes has been introduced into this model by Buttiker [2] who added inelastic scatterers coupled to an external heat bath to the chain. In this way it is possible to describe also certain dissipative aspects of electron transport. However, his approach does not allow to study the gradual transition from coherent to incoherent transport with increasing s…