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Wyszukujesz frazę "74.70.Wz" wg kryterium: Temat

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    Wyświetlanie 1-10 z 10
    Tytuł:
    Effect of van Hove Singularity on T$\text{}_{c}$ in Rb doped C$\text{}_{60}$
    Autorzy:
    Agrawal, B. K.
    Agrawal, S.
    Yadav, P. S.
    Srivastava, P.
    Srivastava, R.
    Singh, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2035748.pdf
    Data publikacji:
    2003-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.25.Jb
    74.62.Fj
    74.70.Wz
    Opis:
    In the present study we investigate the role of van Hove singularity on the optimization of T$\text{}_{c}$ in Rb doped fullerenes C$\text{}_{60}$ Rb$\text{}_{3}$. A first principles self-consistent full potential linear muffin-tin orbital method using density functional theory in local density approximation was employed. The doped Rb atoms are of two types occupying the tetrahedral and interstitial positions in the fcc lattice. The added Rb atoms fill the t$\text{}_{1u}$ band of the undoped fullerenes C$\text{}_{60}$ up to half which makes C$\text{}_{60}$Rb$\text{}_{3}$ conducting. Saddle points leading to van Hove singularities are observed in the neighbourhood of the symmetry point L. The shifting of the van Hove singularity with the volume of the lattice is investigated. We observe a saddle point just at the Fermi level for a lattice constant of 14.435Å. The highest value of T$\text{}_{c}$ should thus be observed at the above lattice constant. This result is in excellent agreement with the observed high value of T$\text{}_{c}$ measured in C$\text{}_{60}$Rb$\text{}_{3}$ for a lattice constant of 14.435Å.
    Źródło:
    Acta Physica Polonica A; 2003, 103, 5; 477-482
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    EPR and MMMA Study of C$\text{}_{60}$ upon K-Doping
    Autorzy:
    Kempiński, W.
    Stankowski, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933662.pdf
    Data publikacji:
    1995-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Wz
    76.30.-v
    Opis:
    EPR and ΜΜMΑ studies of C$\text{}_{60}$ upon K-doping have been performed. Two different and well separated EPR narrow lines were detected for C$\text{}_{60}^{1-}$ and C at temperatures below 100 K. Time dependent changes in the intensities of both and C$\text{}_{60}^{3-}$ lines were observed when the system undergoes an eutectoid transformation. The evolution of superconductivity with two T$\text{}_{c}$ related to different valences (v) of C$\text{}_{60}^{v}$ ion radicals have been found.
    Źródło:
    Acta Physica Polonica A; 1995, 88, 3; 549-552
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superconductivity of Carbon Materials - Unstable Phases
    Autorzy:
    Kempiński, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/2038391.pdf
    Data publikacji:
    2004-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    76.30.-v
    74.70.Wz
    Opis:
    Different intercalated carbon systems: K$\text{}_{x}$C$\text{}_{60}$, Rb$\text{}_{x}$C$\text{}_{60}$ as well as highly oriented pyrolytic graphite + potassium with unstable structural and superconducting behavior were investigated with the EPR and magnetically modulated microwave absorption techniques. Three characteristic, well-separated EPR signals were observed for A$\text{}_{x}$C$\text{}_{60}$ (A = K or Rb) systems at the early stages of doping process. We ascribed these signals to C$\text{}_{60}^{+}$, C$\text{}_{60}^{1-}$, and C$\text{}_{60}^{3-}$ radicals. Evolution of the EPR spectrum characterizes different phases of K$\text{}_{x}$C$\text{}_{60}$ system including superconducting one. Two superconducting phases with T$\text{}_{c}^{(1)}$=(21±0.5) K (unstable) and T$\text{}_{c}^{(2)}$=(18.5±0.5) K (final, stable) were distinctly separated for K$\text{}_{x}$C$\text{}_{60}$ system. For C$\text{}_{60}$ intercalated by rubidium a similar evolution of EPR spectrum is observed. Prior to well-defined superconducting Rb$\text{}_{3}$C$\text{}_{60}$ phase was created, strong instabilities of the magnetically modulated microwave absorption signal were observed at the narrow part of the doping process. For potassium intercalated highly oriented pyrolytic graphite, EPR oscillations below 100 K were observed as well as Josephson hysteresis loops were registered at 5 K.
    Źródło:
    Acta Physica Polonica A; 2004, 106, 5; 627-636
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    On Stability of Frustrated Quantum Magnetic States in Fullerenes
    Autorzy:
    Koper, A.
    Mucha, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1964713.pdf
    Data publikacji:
    1997-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Wz
    61.46.+w
    71.10.-w
    71.27.+a
    75.10.Jm
    02.50.Ng
    02.70.Lq
    Opis:
    Gutzwiller variational ground states |Φ$\text{}^{G}$⟩ of π electrons, described by single-band half-filling Hubbard model, were determined for the molecules C$\text{}_{60}$ and C$\text{}_{70}$ and their energies and magnetic properties investigated. To construct these states two types of trial functions were used: generalized spin-density wave |Φ$\text{}_{SD}$⟩ and tight-binding wave |Φ$\text{}_{ΤΒ}$⟩. Our results evidently show that the Gutzwiller state |Φ$\text{}_{TΒ}^{G}$⟩ determined by means of function |Φ$\text{}_{ΤΒ}$⟩ has lower energy than the other investigated variational states |Φ$\text{}_{SD}^{G}$⟩. Mean values of the operators in the Gutzwiller states were calculated using Monte Carlo method.
    Źródło:
    Acta Physica Polonica A; 1997, 92, 2; 395-398
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superconducting density of states in B-doped diamond
    Autorzy:
    Onufriienko, O.
    Samuely, T.
    Zhang, G.
    Vanacken, J.
    Xu, Zheng
    May, P.
    Szabó, P.
    Moshchalkov, V.
    Samuely, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1052993.pdf
    Data publikacji:
    2017-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Wz
    74.62.En
    74.55.+v
    Opis:
    In the presented work, we investigated the superconducting boron doped diamond polycrystalline film prepared by chemical vapor deposition by means of scanning tunneling microscopy/spectroscopy. Differential conductance spectra measured at various temperatures were used to obtain the values of superconducting critical temperature and energy gap. Comparing various theoretical models fitted to the differential conductance spectra measured at 0.5 K suggests weak pair breaking. However, this cannot account for the high 2Δ/(k_{B}T_{C}) ratio, which therefore indicates strong coupling.
    Źródło:
    Acta Physica Polonica A; 2017, 131, 4; 1033-1035
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Alkali Intercalated C$\text{}_{60}$: NMR and Magnetic Susceptibility Studies
    Autorzy:
    Rachdi, F.
    Goze, C.
    Reichenbach, J.
    Lukyanchuk, J.
    Kirova, N.
    Zimmer, G.
    Mehring, M.
    Molinié, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933392.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    76.60.-k
    74.70.Wz
    Opis:
    We report on $\text{}^{13}$C NMR measurements on potassium intercalated C$\text{}_{60}$ compounds. By using high resolution NMR technique we were able to characterize the different thermodynamically stable phases. The effects of the intercalation on the molecular dynamics as well as on the electronic properties will be discussed. We also performed the magnetic susceptibility measurements on Rb$\text{}_{4}$C$\text{}_{60}$ compound, which reveal the activation temperature behavior with the activation energy about 1200 K. By comparison with the NMR and ESR data of the same sample we conclude that the additional electrons are localized on the C$\text{}_{60}$ molecule and form the spin singlet ground state.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 861-867
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Free Radicals in K and Rb Admixtured Fullerene C$\text{}_{60}$
    Autorzy:
    Stankowski, J.
    Kempiński, W.
    Byszewski, P.
    Trybuła, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1929831.pdf
    Data publikacji:
    1993-12
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    76.30.Rn
    74.70.Wz
    Opis:
    Molecules of C$\text{}_{60}$ form Van der Waals type crystals. The observations reported here concern EPR investigations of such C$\text{}_{60}$ samples with only a slight amount of Rb or K. Detected defects are (C$\text{}_{60}$)$\text{}^{+}$ or (C$\text{}_{60}$)$\text{}^{y-}$ ion-radicals. A hole (h) or trapped electron (t) are localized on one fullerene ball. In the case of potassium fullerites C$\text{}_{60}$:K the line shape of EPR signal was of the Dysonian form which is characteristic of conducting electrons in metal. The EPR lines of holes (C$\text{}_{60}$)$\text{}^{+}$ are characterized by g$\text{}_{h}$ ≥ g$\text{}_{0}$ whereas for electrons g$\text{}_{t}$ is below the value g$\text{}_{0}$ = 2.0023 characteristic of a free electron (g$\text{}_{t}$ ≤ g$\text{}_{0}$). The EPR linewidth 2ΔB$\text{}_{1s}^{h}$ of the (C$\text{}_{60}$)$\text{}^{+}$ weakly increased with decreasing temperature whereas the EPR linewidth attributed to the electron 2ΔB$\text{}^{t}$$\text{}_{1s}$ significantly decreases with decreasing temperature. The C$\text{}_{60}$:K sample reached superconducting phase below T$\text{}_{c}$ = 11 K which is significantly less than T$\text{}_{c}$ = 16.5 K observed for K$\text{}_{x}$C$\text{}_{60}$ where 2 ≤ x ≤ 4.
    Źródło:
    Acta Physica Polonica A; 1993, 84, 6; 1117-1123
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Thermodynamic Properties of the Superconducting State in the $K_{3}C_{60}$ Fulleride
    Autorzy:
    Szczęśniak, R.
    Barasiński, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1585095.pdf
    Data publikacji:
    2009-12
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.Fg
    74.70.Wz
    Opis:
    In the framework of the Eliashberg formalism, we have calculated the thermodynamic properties of the superconducting state in $K_{3}C_{60}$ (the critical temperature $T_C$ = 19.50 K). We have obtained the following results: (i) The critical value of the Coulomb pseudopotential is equal to 0.387. (ii) The values of the ratios $R_1$ ≡ 2Δp(0)/$k_{B}T_C$ and $R_2$ ≡ $ΔC(T_C)//C^{N}(T_C)$ are bigger than in the BCS model; $R_1$ = 4.01 and $R_2$ = 1.58. (iii) The electron effective mass $m_{e}^\ast$ reaches the highest value for $T = T_C$; [$m_{e}^\ast]_\text{max}$ = 2.86 $m_{e}$, where $m_{e}$ is the bare electron mass. Additionally, we have given the analytical expressions for $T_C$, Δ(T), $R_1$ and $R_2$.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 6; 1053-1058
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Dielectric Study of Pressure Induced fcc-sc Phase Transition in Fullerene C$\text{}_{60}$
    Autorzy:
    Trybuła, Z.
    Krupski, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2014286.pdf
    Data publikacji:
    2000-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Wz
    62.50.+p
    64.70.-p
    77.22.Ch
    Opis:
    Phase transition in polycrystalline fullerene C$\text{}_{60}$ from fcc phase to a simple cubic phase sc induced by hydrostatic pressure up to 0.5GPa was studied by dielectric method. Pressure coefficient dT$\text{}_{c}$/dp=144±8 K/GPa was determined. This value is consistent with pressure coefficients obtained with other experimental techniques.
    Źródło:
    Acta Physica Polonica A; 2000, 98, 4; 389-392
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Phonon Drag and Carrier Diffusion Contributions in Thermoelectric Power of $M_3C_{60}$ (M = K, Rb) Fullerides
    Autorzy:
    Varshney, D.
    Singh, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1400154.pdf
    Data publikacji:
    2013-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Wz
    74.25.fg
    74.25.Kc
    Opis:
    The thermoelectric power (S) of $M_3C_{60}$ (M = K, Rb) alkali intercalated fullerides is theoretically investigated by considering the Mott expression within parabolic band approximation to reveal the electron diffusive thermoelectric power $(S_{c}^{diff})$. We follow the Fermi energy as electron parameter and $S_{c}^{diff}$ discerned linear temperature dependence. S infers a change in slope above transition temperature and becomes almost linear above 70 K for $M_3C_{60}$ alkali intercalated fullerides. As a next step, the phonon drag thermoelectric power $(S_{ph}^\text{drag})$ is computed within relaxation time approximation when thermoelectric power is limited by scattering of phonons from defects, grain boundaries, phonons and electrons as carriers. It is noticed that the $S_{ph}^\text{drag}$ of $K_3C_{60}$ is anomalous and it is an artifact of strong phonon-electron and -phonon scattering mechanism. The thermoelectric power within relaxation time approximation has been taken into account ignoring a possible energy dependence of the scattering rates. Behaviour of S(T) is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions in $M_3C_{60}$ (M = K, Rb) alkali intercalated fullerides.
    Źródło:
    Acta Physica Polonica A; 2013, 123, 4; 752-760
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-10 z 10

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