# Kooperativer Bibliotheksverbund

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• 1
Article
Language: English
In: Phys. Rev. B: Condens. Matter Mater. Phys, 31 October 2012, Vol.86(16)
Description: Using density functional theory (DFT) based calculations, we propose a family of metastable, as-yet unmade V super(5+) and Cr super(6+) double perovskite compounds with low band gaps spanning much of the visible region of the solar spectrum. Through analysis of a related set of measured optical gaps of d super(0) ABO sub(3) perovskites and A sub(2) B' BO sub(6) double perovskites, an ad hoc procedure is developed to correct DFT and many-body perturbation theory gaps, bringing them into quantitative agreement with experiment for measured compounds, and predicting that V super(5+) and Cr super(6+) double perovskites would have gaps ranging from approximately 1.1 to 2.4 eV, significantly lower than previous materials studied in this class. DFT calculations also establish that these V super(5+) and Cr super(6+) compounds are likely able to be synthesized, either in bulk form or as epitaxial thin films. These compounds would comprise a new class of semiconducting double perovskites for potential use in solar energy conversion and other optoelectronic applications.
Keywords: Catalysis (Homogeneous), Catalysis (Heterogeneous), Energy Storage (Including Batteries and Capacitors), Hydrogen and Fuel Cells, Defects, Charge Transport, Membrane, Materials and Chemistry By Design, Synthesis (Novel Materials), Synthesis (Self-Assembly), Synthesis (Scalable Processing)
ISSN: 10980121
E-ISSN: 1550235X
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• 2
Article
Language: English
In: Physical Review B, 8/2015, Vol.92(6)
Description: We study the patterns at which the current flow stabilizes in a 1D superconducting wire, for various experimentally reasonable boundary conditions, for small fixed current densities and temperatures close to $T_c$. We pay special attention to the possible existence of a stationary regime. If the contacts are superconducting, truly stationary or normal regimes do not exist, but can be approached as a limit. In the case of weak superconducting contacts, a rich phase diagram is found, with several periodic regimes that involve two phase slip centers. For some of these regimes, the density of Cooper pairs does not have mirror symmetry. If the contacts are normal, the stationary regime is possible.
Keywords: Condensed Matter - Superconductivity ; Condensed Matter - Mesoscale And Nanoscale Physics;
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 3
Article
Language: English
In: Physical Review B, 5/2011, Vol.83(17)
ISSN: 1098-0121
E-ISSN: 1550-235X
Source: American Physical Society (APS) (via CrossRef)
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• 4
Article
Language: English
In: Physical Review B, 4/2012, Vol.85(14)
Description: We evaluate the average and the standard deviation of the supercurrent in superconducting nanobridges, as functions of the temperature and the phase difference, in an equilibrium situation. We also evaluate the autocorrelation of the supercurrent as a function of the elapsed time. The behavior of supercurrent fluctuations is qualitatively different from from that of the normal current: they depend on the phase difference, have a different temperature dependence, and for appropriate range their standard deviation is independent of the probing time. We considered two radically different filaments and obtained very similar results for both. Fluctuations of the supercurrent can in principle be measured.
Keywords: Condensed Matter - Superconductivity ; Condensed Matter - Mesoscale And Nanoscale Physics ; Condensed Matter - Statistical Mechanics;
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 5
Article
Language: English
In: Physical Review B, 2/2011, Vol.83(5)
ISSN: 1098-0121
E-ISSN: 1550-235X
Source: American Physical Society (APS) (via CrossRef)
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• 6
Article
Language: English
In: Physical Review B, 6/2014, Vol.89(21)
Description: After an initial transient period, the conduction regime in a one-dimensional superconducting wire that carries a fixed current is either normal, periodic, or stationary. The phase diagram for these possibilities was studied in Phys. Rev. Lett. 99, 167003 (2007) (http://dx.doi.org/10.1103/PhysRevLett.99.167003) for particular values of the length and the material parameters. We have extended this study to arbitrary length and to a range of material parameters that includes realistic values. Variation of the length leads to scaling laws for the phase diagram. Variation of the material parameters leads to new qualitative features and new phases, including a parameter region in which all three regimes are possible.
Keywords: Phases ; Phase Diagrams ; Scaling Laws ; Electric Wire ; Electric Current ; Condensed Matter ; Superconductivity ; Dynamics ; Condensed Matter Physics (General) (So) ; Solid-State Physics (Ah);
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 7
Article
Language: English
In: Physical Review B, 6/2015, Vol.91(21)
Keywords: Physics;
ISSN: 1098-0121
E-ISSN: 1550-235X
Source: American Physical Society (APS) (via CrossRef)
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• 8
Article
Language: English
In: Physical Review B, 2/2015, Vol.91(5)
Description: A Landau-theoretical approach is utilized to model the magnetic field induced reversal of the antiferromagnetic order parameter in thin films of magnetoelectric antiferromagnets. A key ingredient of this peculiar switching phenomenon is the presence of a robust spin polarized state at the surface of the antiferromagnetic films. Surface or boundary magnetization is symmetry allowed in magnetoelectric antiferromagnets and experimentally established for chromia thin films. It couples rigidly to the antiferromagnetic order parameter and its Zeeman energy creates a pathway to switch the antiferromagnet via magnetic field application. In the framework of a minimalist Landau free energy expansion, the temperature dependence of the switching field and the field dependence of the transition width are derived. Least-squares fits to magnetometry data of (0001) textured chromia thin films strongly support this model of the magnetic reversal mechanism.
Keywords: Magnetic Fields ; Switching ; Antiferromagnetism ; Boundaries ; Least Squares Method ; Order Parameters ; Condensed Matter ; Thin Films ; Chromium Oxides ; Condensed Matter Physics (General) (So) ; Solid-State Physics (Ah);
ISSN: 1098-0121
E-ISSN: 1550-235X
Source: American Physical Society (APS) (via CrossRef)
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• 9
Article
Language: English
In: Physical Review B, 01 August 2015, Vol.92(7)
Description: We perform full-potential screened-hybrid density-functional theory (DFT) calculations to compare the thermodynamic stability of neutral and charged states of the surface oxygen vacancy at the rutile TiO$_2$(110) surface. Solid-state (QM/MM) embedded-cluster calculations are employed to account for the strong TiO$_2$ polarization response to the charged defect states. Similar to the situation for the bulk O vacancy, the +2 charge state $V_{\rm O}^{2+}$ is found to be energetically by far most stable. Only for Fermi-level positions very close to the conduction band, small polarons may at best be trapped by the charged vacancy. The large decrease of the $V_{\rm O}^{2+}$ formation energy with decreasing Fermi-level position indicates strongly enhanced surface O vacancy concentrations for $p$-doped samples.
Keywords: Physics
ISSN: 1098-0121
E-ISSN: 1550-235X
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• 10
Article
Language: English
In: Physical Review B, 12/2011, Vol.84(21)
Description: Starting from the Ginzburg-Landau energy functional, we discuss how the presence of two order parameters and the coupling between them influence a superconducting ring in the fluctuative regime. Our method is exact, but requires numerical implementation. We also study approximations for which some analytic expressions can be obtained, and check their ranges of validity. We provide estimates for the temperature ranges where fluctuations are important, calculate the persistent current in magnesium diboride rings as a function of temperature and enclosed flux, and point out its additional dependence on the cross-section area of the ring. We find temperature regions in which fluctuations enhance the persistent currents and regions where they inhibit the persistent current. The presence of two order parameters that can fluctuate independently always leads to larger averages of the order parameters at Tc, but only for appropriate parameters this yields larger persistent current. In cases of very different material parameters for the two coupled condensates, the persistent current is inhibited.
Keywords: Condensed Matter - Superconductivity ; Condensed Matter - Mesoscale And Nanoscale Physics ; Condensed Matter - Statistical Mechanics;
ISSN: 1098-0121
E-ISSN: 1550-235X
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