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| 2. |
- Adnane, Bouchaib, et al.
(author)
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Origin of photoresponse at 8-14 μm in stacks of self-assembled SiGe/Si quantum dots
- 2009
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X.
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Journal article (other academic/artistic)abstract
- A normal incidence photodetector operating at 8-14 μm is demonstrated using p-type δ-doped SiGe dot multilayer structures grown by molecular beam epitaxy on Si(001) substrates. Based on the experimental results of photoluminescence and photoluminescence excitation spectroscopies together with numerical analysis, the origin of the measured photocurrent was attributed to intersubband optical transitions between the heavy hole and light hole states of the valence band of the self-assembled SiGe dots and subsequent lateral transport of photo-excited carriers in the conduction channels formed by Ge wetting layers.
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| 3. |
- Babaev, Egor, et al.
(author)
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Comment on "Ginzburg-Landau theory of two-band superconductors : Absence of type-1.5 superconductivity"
- 2012
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:1, s. 016501-
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Journal article (other academic/artistic)abstract
- The recent paper by V. G. Kogan and J. Schmalian [Phys. Rev. B 83, 054515 (2011)] argues that the widely used two-component Ginzburg-Landau (GL) models are not correct, and further concludes that in the regime which is described by a GL theory there could be no disparity in the coherence lengths of two superconducting components. This would in particular imply that [in contrast to U(1) x U(1) superconductors] there could be no "type-1.5" superconducting regime in U(1) multiband systems for any finite interband coupling strength. We point out that these claims are incorrect and based on an erroneous scheme of reduction of a two-component GL theory.
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| 4. |
- Refson, Keith, et al.
(author)
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Comment on "First-principles study of the influence of (110)-oriented strain on the ferroelectric properties of rutile TiO2"
- 2013
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In: Physical Review B. Condensed Matter and Materials Physics. - New York : American Physical Society. - 1098-0121 .- 1550-235X. ; 88:13, s. 136101-
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Journal article (other academic/artistic)abstract
- In a recent Brief Report, Grunebohm et al. [Phys. Rev. B 84, 132105 (2011)] report that they fail to reproduce the A(2u) ferroelectric instability of TiO2 in the rutile structure calculated with density functional theory within the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) by Montanari et al. [Chem. Phys. Lett. 364, 528 (2002)]. We demonstrate that this disagreement arises from an erroneous treatment of Ti 3s and 3p semicore electrons as core in their calculations. Fortuitously the effect of the frozen-semicore pseudopotential cancels the phonon instability of the PBE exchange correlation, and the combination yields phonon frequencies similar to the local density approximation harmonic values. Grunebohm et al. also attempted and failed to reproduce the soft acoustic phonon mode instability under (110) strain reported by Mitev et al. [Phys. Rev. B 81, 134303 (2010)]. For this mode the combination of PBE-GGA and frozen semicore yields a small imaginary frequency of 9.8i. The failure of Grunebohm et al. to find this mode probably arose from numerical limitations of the geometry optimization approach in the presence of a shallow double well potential; the optimization method is not suitable for locating such instabilities.
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| 5. |
- Wessely, Ola, et al.
(author)
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Dynamical core-hole screening in the x-ray absorption spectra of hydrogenated carbon nanotubes and graphene
- 2007
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:16, s. 161402-
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Journal article (other academic/artistic)abstract
- We have calculated the electronic structure and the x-ray absorption (XA) spectrum of a hydrogenated single graphite plane, in order to simulate recent experimental results on hydrogenated single wall carbon nanotubes (SWCNT) as well as hydrogenated graphene. We find that the presence of H induces a substantial component of sp3 bonding and as a result the and * components to the electronic structure vanish. We have calculated a theoretical x-ray absorption spectrum using a multiband version of the Mahan-Nozières–De Dominicis theory. By making a fitting of the XA signal of C atoms that have H attached to them and C atoms without H in the vicinity we obtain a good representation of the experimental data and we can draw the conclusion that in the experiments [A. Nikitin et al., Phys. Rev. Lett. 95, 225507 (2005)] some 35–50 % H have been absorbed in the SWCNT.
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