Search results for "Point contact"
showing 10 items of 16 documents
Charge control in laterally coupled double quantum dots
2011
4 figuras, 4 páginas.-- PACS number(s): 78.67.Hc, 73.21.La, 78.55.Cr
Detector's quantum backaction effects on a mesoscopic conductor and fluctuation-dissipation relation
2016
When measuring quantum mechanical properties of charge transport in mesoscopic conductors, backaction effects occur. We consider a measurement setup with an elementary quantum circuit, composed of an inductance and a capacitor, as detector of the current flowing in a nearby quantum point contact. A quantum Langevin equation for the detector variable including backaction effects is derived. Differences with the quantum Langevin equation obtained in linear response are pointed out. In this last case, a relation between fluctuations and dissipation is obtained, provided that an effective temperature of the quantum point contact is defined.
Pfaffian and fragmented states atν=52in quantum Hall droplets
2008
When a gas of electrons is confined to two dimensions, application of a strong magnetic field may lead to startling phenomena such as emergence of electron pairing. According to a theory this manifests itself as appearance of the fractional quantum Hall effect with a quantized conductivity at an unusual half-integer v=5/2 Landau level filling. Here we show that similar electron pairing may occur in quantum dots where the gas of electrons is trapped by external electric potentials into small quantum Hall droplets. However, we also find theoretical and experimental evidence that, depending on the shape of the external potential, the paired electron state can break down, which leads to a fragm…
Single Photon Emission from Site-Controlled InAs Quantum Dots Grown on GaAs(001) Patterned Substrates
2009
5 páginas, 5 figuras.
Electronic and magnetic structure of artificial atoms
1999
The concept of shell structure has been found useful in the description of semiconductor quantum dots, which today can be made so small that they contain less than 20 electrons. We review the experimental discovery of magic numbers and spin alignment following Hund’s rules in the addition spectra of vertical quantum dots, and show that these results compare well to model calculations within spin density functional theory. We further discuss the occurrence of spin density waves in quantum dots and quantum wires. For deformable two-dimensional quantum dots (for example, jellium clusters on surfaces), we study the interplay between Hund’s rules and Jahn–Teller deformations and investigate the …
Reversed polarized emission in highly strained a-plane GaN/AlN multiple quantum wells
2010
The polarization of the emission from a set of highly strained $a$-plane GaN/AlN multiple quantum wells of varying well widths has been studied. A single photoluminescence peak is observed that shifts to higher energies as the quantum well thickness decreases due to quantum confinement. The emitted light is linearly polarized. For the thinnest samples the preferential polarization direction is perpendicular to the wurtzite $c$ axis with a degree of polarization that decreases with increasing well width. However, for the thickest well the preferred polarization direction is parallel to the $c$ axis. Raman scattering, x-ray diffraction, and transmission electron microscopy studies have been p…
Single scatterings in single artificial atoms: Quantum coherence and entanglement
2003
We employ the quantum-jump approach to study single scatterings in single semiconductor quantum dots. Two prototypical situations are investigated. First, we analyze two-photon emissions from the cascade biexciton decay of a dot where the single-exciton states exhibit a fine-structure splitting. We show that this splitting results for appropriately chosen polarization filters in an oscillatory behavior of two-photon correlations, and carefully examine the proper theoretical description of the underlying scattering processes. Secondly, we analyze the decay of a single-electron charged exciton in a quantum dot embedded in a field effect structure. We show how the quantum properties of the cha…
On the half-metallicity of Co2FeSi Heusler alloy: Point-contact Andreev reflection spectroscopy andab initiostudy
2013
Co2FeSi, a Heusler alloy with the highest magnetic moment per unit cell and the highest Curie temperature, has largely been described theoretically as a half-metal. This conclusion, however, disagrees with point contact Andreev reflection (PCAR) spectroscopy measurements, which give much lower values of spin polarization, P. Here, we present the spin polarization measurements of Co2FeSi by the PCAR technique, along with a thorough computational exploration, within the DFT and a GGA+U approach, of the Coulomb exchange U parameters for Co and Fe atoms, taking into account spin-orbit coupling. We find that the orbital contribution (mo) to the total magnetic moment (mT) is significant, since it…
Effect of quantized conductivity on the anomalous photon emission radiated from atomic-size point contacts
2019
We observe anomalous visible to near-infrared electromagnetic radiation emitted from electrically driven atomic-size point contacts. We show that the number of photons released strongly depends on the quantized conductance steps of the contact. Counter-intuitively, the light intensity features an exponential decay dependence with the injected electrical power. We propose an analytical model for the light emission considering an out-of-equilibrium electron distribution. We treat photon emission as bremsstrahlung process resulting from hot electrons colliding with the metal boundary and a find qualitative accord with the experimental data.
Tuning the exciton luminescence in an acoustically depleted two-dimensional electron gas
2007
Standing-wave piezoelectric fields can be used to vary spatially and temporally charge conditions in $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ quantum wells (QWs), offering a versatile tool to control the two-dimensional electron gas (2DEG) density in the well. A $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ piezoelectric resonator imparts a MHz-frequency oscillating piezoelectric field with a controllable ratio of the in-plane and the vertical field components to a 2DEG placed in close proximity to the plate surface. This allows us to dynamically tune the charge state in the plane of the QW and to influence the photoluminescence spectra. It is found that spatially distributed r…