Search results for "Hall Effect"
showing 10 items of 702 documents
Incommensurate phases of a bosonic two-leg ladder under a flux
2016
A boson two--leg ladder in the presence of a synthetic magnetic flux is investigated by means of bosonization techniques and Density Matrix Renormalization Group (DMRG). We follow the quantum phase transition from the commensurate Meissner to the incommensurate vortex phase with increasing flux at different fillings. When the applied flux is $\rho \pi$ and close to it, where $\rho$ is the filling per rung, we find a second incommensuration in the vortex state that affects physical observables such as the momentum distribution, the rung-rung correlation function and the spin-spin and charge-charge static structure factors.
Phase transitions and quantum effects in adsorbed monolayers
1996
Phase transitions in absorbed (two-dimensional) fluids and in absorbed layers of linear molecules are studied with a combination of path integral Monte Carlo (PIMC), Gibbs ensemble Monte Carlo (GEMC), and finite size scaling techniques. For a classical (nonadditive) hard-disk fluid the “critical” nonadditivities, where the entropy-driven phase separations set in, are presented. For a fluid with internal quantum states the gas-liquid coexistence region, tricritical, and triple points can be determined, and a comparison with density functional (DFT) results shows good agreement for the freezing densities. LinearN 2 molecules adsorbed on graphite (in the √3 × √3 structure) show a transition fr…
Multidimensional quantum walks: Diabolical points, optical wave-like propagation, and multipartite entanglement
2013
Quantum walks (QWs) are important for quantum information science, but are becoming also interesting for other fields of research as this simple quantum diffusion model finds analogues in diverse physical systems, optical ones in particular. The experimental capabilities regarding QWs have remarkably increased along recent years and several aspects of QWs are now open to experimental research, multidimensional QWs in particular [1].
Exciton recombination dynamics inInAs∕InPself-assembled quantum wires
2005
In this work we investigate the exciton recombination dynamics in InAs/ InP semiconductor self-assembled quantum wires, by means of continuous wave and time resolved photoluminescence. The continuous wave photoluminescence results seem to indicate that the temperature quenching of the emission band seems to be more probably due to unipolar thermal escape of electrons towards the InP barrier. On the other hand, the analysis of time resolved photoluminescence reveals that the temperature dependence of the radiative and nonradiative recombination times is mainly determined by the dynamics of excitons localized by disorder shigh energy tail of the PL bandd and strongly localized slow energy tai…
Low-pressure synthesis and Bridgman growth of Hg1−xMnxTe
1999
To reduce Hg high pressure related to the high-temperature synthesis reaction between the components in elemental form, Hg 1-x Mn x Te bulk crystals were produced by a two-step procedure including (I) the alloy synthesis using HgTe crystals grown by the cold travelling heater method and elemental Mn and Te to complete the desired composition, followed by (II) the Bridgman growth. The growth was carried out at temperature in the range of 700-850°C and rate of 1 mm/h. The Hg 1-x Mn x Te crystals have been characterised by X-ray diffractometry, energy dispersive X-ray analysis, Fourier transformed infrared spectroscopy and Hall effect techniques. Although the distribution coefficient of Mn was…
Phonon Cooling of Nanomechanical Beams with Tunnel Junctions
2009
We demonstrate electronic cooling of 1D phonon modes in suspended nanowires for the first time, using normal-metal-insulator-superconductor (N-I-S) tunnel junctions. Simultaneous cooling of both electrons and phonons to a common temperature was achieved. In comparison with nonsuspended devices, better cooling performance is achieved in the whole operating range of bath temperatures between 0.1-0.7 K. The observed low-temperature thermal transport characteristics are consistent with scattering of ballistic phonons at the nanowire-bulk contact as being the mechanism limiting thermal transport. At the lowest bath temperature of the experiment approximately 100 mK, both phonons and electrons in…
Raman study of strain in GaN/AlN quantum dot multilayered structures
2005
Raman spectroscopy has been used to investigate self-assembled stacks of GaN/AlN quantum dots with increasing number of periods. The E2H phonon modes associated to GaN and AlN are clearly resolved with visible excitation, and their energies allow the simultaneous monitoring of the dot and barrier strain states. The compression of the quantum dots is evidenced by a shift of the E2H phonon mode of circa 29 cm–1 to higher energies with respect to its relaxed value. The strain of the AlN spacer is found to be correlated to that of the dot, with an increase in its tensile component for the samples with fewer periods and a partial relaxation for samples over 50 periods. Additionally, resonant eff…
Raman Spectroscopy and Low-Temperature Transport Measurements of Individual Single-Walled Carbon Nanotubes with Varying Thickness
2009
We have investigated two metallic and one semiconducting individual single-walled carbon nanotubes (SWNT) and one bundle of two semiconducting nanotubes with a diameter range 1.1−2.9 nm with Raman spectroscopy and low-temperature electric transport measurements. With these two methods, we obtain mutually independent measurements on the basic properties of a specific nanotube. In particular, we obtain data on metallic and semiconducting properties. Evidence of a small band gap for one metallic tube was obtained. For the semiconducting SWNTs with diameters of 2.7−2.9 nm, a special resonance condition was observed which causes an anomalous intensity ratio for the two components of the G-band. …
Solvatochromism Unravels the Emission Mechanism of Carbon Nanodots
2016
High quantum yield, photoluminescence tunability, and sensitivity to the environment are hallmarks that make carbon nanodots interesting for fundamental research and applications. Yet, the underlying electronic transitions behind their bright photoluminescence are strongly debated. Despite carbon-dot interactions with their environment should provide valuable insight into the emitting transitions, they have hardly been studied. Here, we investigate these interactions in a wide range of solvents to elucidate the nature of the electronic transitions. We find remarkable and systematic dependence of the emission energy and kinetics on the characteristics of the solvent, with strong response of …
Huge Quantum Symmetry Effect in the O + O2 Exchange Reaction.
2015
We report extensive, full quantum-mechanical calculations for the (16)O + (16)O(16)O → (16)O(16)O + (16)O collisions, for both inelastic and atom exchange processes, using a time-independent method based on hyperspherical coordinates. The rates obtained in the present study are much larger than the previously reported ones for this system. The discrepancy is attributed to a huge symmetry effect that was missing in the studies so far. This effect differs from the well-known isotope effect. Importance of this quantum effect is further confirmed by comparison with results for the (16)O + (18)O(18)O → (16)O(18)O + (18)O, exchange reaction.