Search results for "Materials Science | Hot Paper"
showing 10 items of 1457 documents
Local Control and v-Representability of Correlated Quantum Dynamics
2012
We present a local control scheme to construct the external potential v that, for a given initial state, produces a prescribed time-dependent density in an interacting quantum many-body system. The numerical method is efficient and stable even for large and rapid density variations irrespective of the initial state and the interactions. The method can at the same time be used to answer fundamental v-representability questions in density-functional theory. In particular, in the absence of interactions, it allows us to construct the exact time-dependent Kohn-Sham potential for arbitrary initial states. We illustrate the method in a correlated one-dimensional two-electron system with different…
A novel picture for charge transport interpretation in epitaxial manganite thin films
2013
Transport characterizations of epitaxial La0.7Sr0.3MnO3 thin films in the thickness range 5-40 nm and 25-410 K temperature interval have been accurately collected. We show that taking into account polaronic effects allows to achieve the best ever fitting of the transport curves in the whole temperature range. The Current Carriers Density Collapse picture accurately accounts for the properties variation across the metal-insulator-transition. The electron-phonon coupling parameter estimations are in a good agreement with theoretical predictions. The results promote a clear and straightforward quantitative description of the manganite films involved in charge transport device applications.
Observation of the Anomalous Hall Effect in a Collinear Antiferromagnet
2020
Time-reversal symmetry breaking is the basic physics concept underpinning many magnetic topological phenomena such as the anomalous Hall effect (AHE) and its quantized variant. The AHE has been primarily accompanied by a ferromagnetic dipole moment, which hinders the topological quantum states and limits data density in memory devices, or by a delicate noncollinear magnetic order with strong spin decoherence, both limiting their applicability. A potential breakthrough is the recent theoretical prediction of the AHE arising from collinear antiferromagnetism in an anisotropic crystal environment. This new mechanism does not require magnetic dipolar or noncollinear fields. However, it has not …
Ferroelectric thin film properties with account of metallic electrodes and depolarization field influence
2004
Within the framework of the phenomenological Ginzburg-Landau theory influence of metallic electrodes on the properties of thin ferroelectric films is considered. The contribution of the metallic electrodes with different screening length of carriers is included in functional of free energy. The influence of conventional metallic electrodes on the depolarization field and the film properties was shown to be practically the same as for superconductive ones.
The nature of an enhanced ferroelectric phase transition temperature in perovskite-based solid solutions
2004
We explain the phenomena of ferroelectric phase transition temperature $T_c$ enhancement beyond the end members in perovskite solid solutions like BiMeO$_3$-PbTiO$_3$ (Me=Sc, In, etc.) is related to nonlinear and spatial correlation effects. The explanation is based on the calculation of $T_c$ in the framework of our random field theory with additional account for nonlinear effects in the above substances. We show that the maximum of $T_c$ for certain PbTiO$_3$ content takes place when coefficient of nonlinearity is positive, the value of this coefficient is found from best fit between theory and experiment. This nonlinearity coefficient is the only adjustable parameter of the theory. We sh…
Inter- and intra-layer excitons in MoS$_2$/WS$_2$ and MoSe$_2$/WSe$_2$ heterobilayers
2018
Accurately described excitonic properties of transition metal dichalcogenide heterobilayers (HBLs) are crucial to comprehend the optical response and the charge carrier dynamics of them. Excitons in multilayer systems posses inter or intralayer character whose spectral positions depend on their binding energy and the band alignment of the constituent single-layers. In this study, we report the electronic structure and the absorption spectra of MoS$_2$/WS$_2$ and MoSe$_2$/WSe$_2$ HBLs from first-principles calculations. We explore the spectral positions, binding energies and the origins of inter and intralayer excitons and compare our results with experimental observations. The absorption sp…
Correlation in the transition metal based Heusler compounds Co$_2$MnSi and Co$_2$FeSi
2006
Half-metallic ferromagnets like the full Heusler compounds with formula X$_2$YZ are supposed to show an integer value of the spin magnetic moment. Calculations reveal in certain cases of X = Co based compounds non-integer values, in contrast to experiments. In order to explain deviations of the magnetic moment calculated for such compounds, the dependency of the electronic structure on the lattice parameter was studied theoretically. In local density approximation (LDA), the minimum total energy of Co$_2$FeSi is found for the experimental lattice parameter, but the calculated magnetic moment is about 12% too low. Half-metallic ferromagnetism and a magnetic moment equal to the experimental v…
Quantum paraelectric behavior of pyrochlore PMN
2007
Pb_1.83Mg_0.29Nb_1.71O_6.39 (PMN) crystallizing in a cubic pyrochlore structure exhibits, as the first dielectrics with pyrochlore structure, typical feature of quantum paraelectrics - its permittivity continuously increases on cooling and levels off below ~ 30K, without any signature of a structural phase transition. Broad-band dielectric spectra do not show any dielectric dispersion in the real part of permittivity up to 8.8 GHz. THz and infrared spectra reveal a soft polar optic mode which is responsible for the temperature dependence of the permittivity. The leveling-off of the permittivity at low temperatures obeys the Barrett formula and the fitted vibrational zero-point energy 1/(2*k…
Depolarization field in thin ferroelectric films with account of semiconductor electrodes
2004
Within the framework of the phenomenological Ginzburg-Landau theory influence of semiconductor electrodes on the properties of thin ferroelectric films is considered. The contribution of the semiconductor electrodes with different Debye screening length of carriers is included in functional of free energy. The influence of highly doped semiconductor electrodes on the depolarization field and the film properties was shown to be great.
Fast scanning nitrogen-vacancy magnetometry by spectrum demodulation
2023
We demonstrate a spectrum demodulation technique allowing for rapid imaging in scanning nitrogen-vacancy center magnetometry. Our method relies on a periodic excitation of the electron spin resonance by wide-band frequency sweeps at a kilohertz rate combined with a phase-locked detection of the photoluminescence signal. The technique is robust against changes in spectrum shape and photoluminescence intensity, and is readily extended by a frequency feedback to enable real-time tracking of the spin resonance. Fast scanning magnetometry is especially useful for samples where the signal dynamic range is large, of order millitesla, such as for ferromagnets or ferrimagnets. We demonstrate our met…