Search results for "scale [mass]"
showing 10 items of 997 documents
Heat transfer across a vacuum gap induced by piezoelectrically mediated acoustic phonon tunneling
2023
In contradictin to the common concept that acoustic phonons can only travel inside a material medium, they can in fact "tunnel" across a vacuum gap with the help of piezoelectricity, transmitting a significantly stronger heat flux than that of blackbody radiation. Here, we present a theoretical formulation for the heat flux of such piezoelectrically mediated heat transfer, applicable to any anisotropic piezoelectric crystals with an arbitrary orientation. A few numerical results are demonstrated and compared to heat transfer driven by other close-range mechanisms, including near-field radiative heat transfer and other acoustic phonon tunneling mechanisms. We find that piezoelectrically medi…
Mechanical effects in quantum dots in magnetic and electric fields
2001
The mechanical effects in finite two-dimensional electron systems (quantum dots or droplets) in a strong perpendicular magnetic field are studied. It is shown that, due to asymmetry of the cyclotron dynamics, an additional in-plane electric field causes a ground state transition accompanied by a change in the average total angular momentum of the system, unless the lateral confining potential is exactly parabolic. A precise mechanical experiment is proposed in which a macroscopic angular momentum of a dense matrix of quantum dots could be measured and used to detect and estimate anharmonicity of the confinement.
Coexistence of weak and strong coupling with a quantum dot in a photonic molecule
2018
We study the emission from a molecular photonic cavity formed by two proximal photonic crystal defect cavities containing a small number (<3) of In(Ga)As quantum dots. Under strong excitation we observe photoluminescence from the bonding and antibonding modes in excellent agreement with expectations from numerical simulations. Power dependent measurements reveal an unexpected peak, emerging at an energy between the bonding and antibonding modes of the molecule. Temperature dependent measurements show that this unexpected feature is photonic in origin. Time-resolved measurements show the emergent peak exhibits a lifetime $��_M=0.75 \, \pm 0.1 \, ns $, similar to both bonding and antibondi…
Noise in refrigerating tunnel junctions and in microbolometers
2000
Microrefrigerators based on normal metal-insulator-superconductor (NIS) junctions represent a very attractive alternative to cool the microbolometers and calorimeters for astrophysical observations in space-borne experiments. The performance in such measurements requires a good knowledge of the noise sources in the detectors. In this paper we present detailed calculations of the thermal fluctuations and of the noise equivalent power due to the heat transfer through the NIS junctions or due to the thermal contact between different subsystems of the detector. The influence of the background radiation will also be evaluated. Analytical approximations, valid at low temperatures, are given.
First-principles many-body calculations of electronic conduction in thiol- and amine-linked molecules
2011
The electronic conductance of a benzene molecule connected to gold electrodes via thiol, thiolate, and amino anchoring groups is calculated using nonequilibrium Green functions in combination with the fully selfconsistent GW approximation. The calculated conductance of benzenedithiol and benzenediamine is five times lower than predicted by standard density functional theory (DFT) in very good agreement with experiments. In contrast, the widely studied benzenedithiolate structure is found to have a significantly higher conductance due to the unsaturated sulfur bonds. These findings suggest that more complex gold/thiolate structures where the thiolate anchors are chemically passivated by Au a…
Electronic and optical trends in carbon nanotubes under pure bending
2010
The high aspect ratio of carbon nanotubes makes them prone to bending. To know how bending affects the tubes is therefore crucial for tube identification and for electrical component design. Very few studies, however, have investigated tubes under small bending well below the buckling limit, because of technical problems due to broken translational symmetry. In this Letter a cost-effective and exact modeling of singe-walled nanotubes under such small bending is enabled by revised periodic boundary conditions, combined with density-functional tight-binding. The resulting, bending-induced changes in electronic and optical properties fall in clear chirality-dependent trend families. While the …
Antiferromagnet-mediated interlayer exchange: hybridization versus proximity effect
2023
We investigate the interlayer coupling between two thin ferromagnetic (F) films mediated by an antiferromagnetic (AF) spacer in F*/AF/F trilayers and show how it transitions between different regimes on changing the AF thickness. Employing layer-selective Kerr magnetometry and ferromagnetic-resonance techniques in a complementary manner enables us to distinguish between three functionally distinct regimes of such ferromagnetic interlayer coupling. The F layers are found to be individually and independently exchange-biased for thick FeMn spacers - the first regime of no interlayer F-F* coupling. F-F* coupling appears on decreasing the FeMn thickness below 9 nm. In this second regime found in…
Proposal for a dual spin filter based on [VO(C$_3$S$_4$O)$_2$]$^{2-}$
2017
Polynuclear magnetic molecules often present dense transmission spectra with many overlapping conduction spin channels. Single-metal complexes display a sparser density of states, which in the presence of a fixed external magnetic field makes them interesting candidates for spin filtering. Here we perform a DFT study of a family of bis- and tris-dithiolate vanadium complexes sandwiched between Au(111) electrodes and demonstrate that [VO(C$_3$S$_4$O)$_2$]$^{2-}$ can behave as a dual spin filter. This means that an external stimulus can switch between the selective transmission of spin-up and spin-down carriers. By using an electrostatic gate as external stimulus we show that the onset for th…
Photoluminescence at the ground state level anticrossing of the nitrogen-vacancy center in diamond
2020
The nitrogen-vacancy center (NV center) in diamond at magnetic fields corresponding to the ground state level anticrossing (GSLAC) region gives rise to rich photoluminescence (PL) signals due to the vanishing energy gap between the electron spin states, which enables to have an effect on the NV center's luminescence for a broad variety of environmental couplings. In this article we report on the GSLAC photoluminescence signature of NV ensembles in different spin environments at various external fields. We investigate the effects of transverse electric and magnetic fields, P1 centers, NV centers, and the $^{13}$C nuclear spins, each of which gives rise to a unique PL signature at the GSLAC. …
Zero-frequency chiral magnonic edge states protected by non-equilibrium topology
2023
Topological bosonic excitations must, in contrast to their fermionic counterparts, appear at finite energies. This is a key challenge for magnons, as it prevents straightforward excitation and detection of topologically-protected magnonic edge states and their use in magnonic devices. In this work, we show that in a non-equilibrium state, in which the magnetization is pointing against the external magnetic field, the topologically-protected chiral edge states in a magnon Chern insulator can be lowered to zero frequency, making them directly accessible by existing experimental techniques. We discuss the spin-transfer torque required to stabilize this non-equilibrium state, and show explicitl…