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Wyświetlanie 1-15 z 374
Tytuł:
Quantum Criticality Due to the Topological Effects in the Hubbard Model
Autorzy:
Kopeć, T. K.
Powiązania:
https://bibliotekanauki.pl/articles/2047311.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.Fg
71.10.Pm
Opis:
We argue that in a strongly correlated electron system collective instanton excitations of the phase field (dual to the charge) arise with a great degree of stability, governed by gauge flux changes by an integer multiple of 2π. By unraveling consequences of the nontrivial topology of the charge gauge U(2) group, we found that the pinning of the chemical potential and the zero-temperature divergence of charge compressibility define a novel "hidden" quantum criticality on verge of the Mott transition governed by the protectorate of stable topological numbers rather than the Landau paradigm of the symmetry breaking.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 527-536
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Topological Criticality on Brink of the Mott Transition in High-T$\text{}_{c}$ Superconductors
Autorzy:
Kopeć, T. K.
Powiązania:
https://bibliotekanauki.pl/articles/2046733.pdf
Data publikacji:
2006-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.20.Fg
71.10.Pm
Opis:
The concept of topological excitations and the related ground state degeneracy are employed to establish an effective theory of the superconducting state evolving from the Mott insulator for high-T$\text{}_{c}$ cuprates. The theory includes the effects of the relevant energy scales with the emphasis on the Coulomb interaction $U$ governed by the electromagnetic U(1) compact group. The results are obtained for the layered t-t'-t$\text{}_{⊥}$-U-J system of strongly correlated electrons relevant for cuprates. Casting the Coulomb interaction in terms of composite-fermions via the gauge flux attachment facility, we show that instanton events in the Matsubara "imaginary time", labelled by a topological winding numbers, governed by gauge flux changes by an integer multiple of 2π, are essential configurations of the phase field dual to the charge. The impact of these topological excitations is calculated for the phase diagram, which displays the "hidden" quantum critical point on verge of the Mott transition that is given by a divergence of the charge compressibility.
Źródło:
Acta Physica Polonica A; 2006, 109, 4-5; 499-506
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Superconducting Critical Temperature of Homologous Series of High-T$\text{}_{c}$ Cuprates as a Function of Number of Layers
Autorzy:
Zaleski, T. A.
Kopeć, T. K.
Powiązania:
https://bibliotekanauki.pl/articles/2038383.pdf
Data publikacji:
2004-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.72.-h
74.50.+r
Opis:
We have considered a model of n-layer high-temperature cuprates of homologous series like HgBa$\text{}_{2}$Ca$\text{}_{n-1}$Cu$\text{}_{n}$O$\text{}_{2+2n+δ}$ to determine the dependence of the critical temperature T$\text{}_{c}$(n) on the number n of Cu-O planes in an elementary cell. Focusing on the description of the high-temperature superconducting system in terms of the collective phase variables, we have studied a semi-microscopic anisotropic three-dimensional vector XY model of stacked copper-oxide layers with adjustable parameters representing microscopic in-plane and out-of-plane phase stiffnesses. The model captures the layered composition and block structure along c-axis of superconducting homologous series. Implementing the spherical closure relation we have solved the phase XY model exactly with the help of transfer matrix method for vector variables. The calculated dependence of the critical temperature T$\text{}_{c}$(n) on the block size n is monotonic with n.
Źródło:
Acta Physica Polonica A; 2004, 106, 5; 561-567
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Existence of the 60 K Plateau in the YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ Phase Diagram: the Role of Oxygen Ordering and Charge Imbalance
Autorzy:
Zaleski, T. A.
Kopeć, T. K.
Powiązania:
https://bibliotekanauki.pl/articles/2047332.pdf
Data publikacji:
2007-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.72.Bk
74.62.-c
Opis:
We propose a semi-microscopic model of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ to investigate the origin of the 60 K plateau in its phase diagram. Our model is a "phase only" approach to the high-temperature superconducting system in terms of collective variables. It is able to capture characteristic energy scales present in YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ by using adjustable parameters representing phase stiffnesses and allows for strong anisotropy within basal planes to simulate oxygen ordering. We solve the model calculated T$\text{}_{c}$ for chosen system parameters investigating the influence of oxygen ordering and doping imbalance on the shape of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ phase diagram. Our results suggest that the oxygen ordering alone does not seem to be responsible for the existence of the 60 K plateau. However, relying on experimental data unveiling that oxygen doping of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ may introduce a significant charge imbalance between CuO$\text{}_{2}$ planes and other sites, we show that simultaneously the former are underdoped, while the latter - strongly overdoped almost in the whole region of oxygen doping in which YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ is superconducting. This provides two natural counter acting factors, which possibly lead to rise the 60 K plateau with increasing oxygen doping.
Źródło:
Acta Physica Polonica A; 2007, 111, 5; 705-711
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Disturbances in a Semi-Infinite Piezoelectric Medium Coated with a Perfectly Conducting Thin Film under the Influence of Time-Dependent Flow of Heat for a Finite Interval
Autorzy:
Munshi, T. K.
Kundu, K. K.
Mahalanabis, R. K.
Powiązania:
https://bibliotekanauki.pl/articles/1930956.pdf
Data publikacji:
1994-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
77.70.+a
Opis:
An attempt was made to investigate analytically the mechanical behaviour of a semi-infinite piezoelectric medium coated with a perfectly conducting thin film under the influence of time-dependent flow of heat at the finite end. The problem involves the interaction of three fields, viz. electrical, mechanical and thermal, and the solution was obtained with the aid of operational calculus. The resultant displacement consists of a time-dependent, as well as a time-independent part and the variation of displacements exhibits an arc of a parabola.
Źródło:
Acta Physica Polonica A; 1994, 85, 3; 585-592
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Mechanical Response in an N-Electrode Piezo-Quartz Bar under Electrical and Thermal Excitations
Autorzy:
Munshi, T. K.
Kundu, K. K.
Mahalanabis, R. K.
Powiązania:
https://bibliotekanauki.pl/articles/1933453.pdf
Data publikacji:
1995-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
77.65.-j
77.70.+a
Opis:
The mechanical response in an N-electrode piezo-quartz bar where two consecutive electrodes are separated by an unelectroded region has been studied under electrical and thermal excitations. The bar is subjected to a periodic polarization gradient and a constant flow of heat. The method of operational calculus and Green's function has been used to solve the problem. For time scale ranging from 0.1 to 1.0 s the response becomes a linear function of time and is of the order of 10$\text{}^{-8}$ m.
Źródło:
Acta Physica Polonica A; 1995, 87, 6; 995-1002
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Luminescence Spectra of ZnAl$\text{}_{2}$O$\text{}_{4}$:Cr$\text{}^{3+}$ Spinel Nanopowders
Autorzy:
Luc, H. H.
Nguyen, T. K.
Nguyen, V. M.
Suchocki, A.
Kamińska, A.
Le, V. K.
Nguyen, V. H.
Luong, T. T.
Powiązania:
https://bibliotekanauki.pl/articles/2037040.pdf
Data publikacji:
2003-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.60.-b
72.80.Ga
81.05.Je
81.05.Mh
Opis:
The synthetic ZnAl$\text{}_{2}$O$\text{}_{4}$ spinels doped with Cr$\text{}^{3+}$ ions are prepared from ZnSO$\text{}_{4}$, Al$\text{}_{2}$(SO$\text{}_{4}$)$\text{}_{3}$, and Cr$\text{}_{2}$(SO$\text{}_{4}$)$\text{}_{3}$. The spinel single phase is detected from X-ray diffraction. Luminescence properties of Cr$\text{}^{3+}$ in ZnAl$\text{}_{2}$O$\text{}_{4}$ were studied by low temperature luminescence and decay measurements. Four luminescence lines at 14570, 14520, 14460, and 14330 cm$\text{}^{-1}$ were found to originate from structure distortion and the line at 14175 cm$\text{}^{-1}$ - from chromium pairs. The broad emission band at about 13540 cm$\text{}^{-1}$ is considered to arise from a new Cr$\text{}^{3+}$ center in ZnCr$\text{}_{2}$O$\text{}_{4}$.
Źródło:
Acta Physica Polonica A; 2003, 104, 6; 581-587
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Scanning Tunneling Spectroscopy Study of Surface States of 3d Metals: Chemical Identification, Magnetic Contrast and Orbital Kondo Resonance States
Autorzy:
Bischoff, M. M. J.
Fang, C. M.
de Groot, R. A.
Heijnen, G. M. M.
Katsnelson, M. I.
Kolesnychenko, O. Yu.
de Kort, R.
Lichtenstein, A. I.
Quinn, A. J.
Vasquez de Parma, A. L.
Yamada, T. K.
van Kempen, H.
Powiązania:
https://bibliotekanauki.pl/articles/2036891.pdf
Data publikacji:
2003
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.20.-r
68.37.-d
75.70.-i
Opis:
The surface states of 3d transition metals are studied by scanning tunneling microscopy and scanning tunneling spectroscopy. The results show that surface states can be used for chemical identification with high spatial resolution. The spin polarized nature of the surface states allows us to obtain magnetic contrast in scanning tunneling miroscopy imaging with near atomic resolution. For Cr(100) we found that the surface state close to the Fermi level can be explained by an orbital Kondo resonance surface state.
Źródło:
Acta Physica Polonica A; 2003, 104, 3-4; 231-243
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Field Effect on Yb-Based Heavy Fermions near Magnetic-Nonmagnetic Transition
Autorzy:
Mito, T.
Koyama, T.
Nakagawara, K.
Ishida, T.
Ueda, K.
Kohara, T.
Matsubayashi, K.
Saiga, Y.
Powiązania:
https://bibliotekanauki.pl/articles/1534203.pdf
Data publikacji:
2010-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
75.30.Kz
75.30.Mb
78.70.Dm
Opis:
Recently magnetic field effects on f electron systems in the vicinity of a magnetic-nonmagnetic transition have attracted much interest. In order to investigate the mechanism of field induced modifications in heavy fermion systems, especially in terms of valent degrees of freedom, we have carried out the X-ray absorption spectroscopy measurement on the newly discovered heavy fermion material $YbCo_2Zn_{20}$ which exhibits extremely large specific heat at low temperatures. Our results show that the Yb valence of $YbCo_2Zn_{20}$ is very close to +3 over the whole temperature range of measurement. Besides, no significant change in the absorption spectrum was observed up to the field of 10 T. This contrasts to the previously reported strong field dependence in the resistivity, followed by an expansion of the Fermi liquid regime with increasing field. The obtained results therefore lead to the conclusion that the valent degrees of freedom play a minor role in the strong field dependence of the heavy fermion systems in this compound.
Źródło:
Acta Physica Polonica A; 2010, 118, 5; 870-872
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dibromoanthracene by Ground-State 2,5-Dimethylhexa-2,4-Diene Yielding 9-Bromoanthracene or the [4+2] Adduct
Autorzy:
Nagahara, T.
Nakayama, T.
Hamanoue, K.
Powiązania:
https://bibliotekanauki.pl/articles/1992713.pdf
Data publikacji:
1998-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
82.40.Js
82.50.Fv
Opis:
Irrespective of the dielectric constant (ε) or the hydrogen-bonding ability of a pure solvent, the lowest excited singlet state (DBA*) of 9,10-dibromoanth racene (DBA) is quenched by ground-state 2,5-dimethylhexa-2,4-diene (DMHD) giving rise to the appearance of an exciplex emission. By means of sub-picosecond and nanosecond laser photolysis as well as steady-state photolysis, however, the following solvent-dependent results are obtained; (1) in acetonitrile (ε=37.5) and acetone (ε=20.7), an exciplex (DBA-DMHD)* formed between DBA* and DMHD generates the DBA radical anion (DBA$\text{}^{•-+}$) as an intermediate for formation of 9-bromoanthracene (BA) from DBA; (2) in ethanol (ε=24.6), 2-propanol (ε=19.9), 1-octanol (ε=10.3), diethyl ether (ε=4.34), and heptane (ε=1.92), a neutral radical species (NR$\text{}^{•}$) generated by decomposition of (DBA-DMHD)* (or by a reaction of DBA* with DMHD) is an intermediate for formation of a dibenzobicyclo[2.2.2]octadiene-type compound (a [4+2] adduct); (3) both DBA$\text{}^{•-}$ and NR$\text{}^{•}$ are generated in methanol (ε=32.7) but the rate (v) of BA formation upon steady-state photolysis of DBA in the presence of 1 M DMHD decreases in the order of v(acetonitrile, ε=37.5) > v(acetone, ε=20.7) > v(methanol, ε=32.7). It thus can be concluded that the mechanism of exciplex decomposition and the reaction of DBA* with DMHD are affected by not only the dielectric constant of a pure solvent but also its hydrogen-bonding ability.
Źródło:
Acta Physica Polonica A; 1998, 94, 4; 701-713
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Formation of a Complete Electron Transfer State of 9,9-Bianthryl in a Polar Solvent
Autorzy:
Nishiyama, K.
Honda, T.
Okada, T.
Powiązania:
https://bibliotekanauki.pl/articles/1993201.pdf
Data publikacji:
1998-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
82.40.Js
82.50.Fv
0.5.40.+j
71.35.Lk
Opis:
It has been generally recognized that excited 9,9'-bianthryl in polar solvents achieves a partial charge-separation state, instead of a complete electron transfer state, even in high-polarity solvents like acetonitrile at room temperature. However, here we firstly found that 9,9'-bianthryl reaches the complete electron transfer state in a polar alkanenitrile solvent at lower temperature as elucidated by means of transient absorption and steady-state fluorescence spectroscopy. A stepwise increase in the fluorescence Stokes shift observed when temperature was reduced implies a formation of a state more polar than that dominated at the room temperature. At low temperature (165 K), the transient absorption spectra of 9,9'-bianthryl in butyronitrile gradually changed from the spectrum ascribed to the partial change-separation state toward that of the complete electron transfer state. We suggest that at low temperature, due to the increase in the solvent polarity, the energetically stabilized electron transfer state should be predominant.
Źródło:
Acta Physica Polonica A; 1998, 94, 5-6; 847-856
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Studies of Magnetoresistance in GaAs:Te Crystals with Structural Disorder at Doping Limit
Autorzy:
Tarkowski, T.
Słupiński, T.
Karpierz, K.
Powiązania:
https://bibliotekanauki.pl/articles/2048144.pdf
Data publikacji:
2011-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.72.-y
61.72.uj
72.20.My
Opis:
Transverse magnetoresistance was studied in monocrystalline GaAs:Te doped above the equilibrium doping limit and annealed to partially deactivate donor impurities. It is shown that in a sample with partial deactivation of Te impurities, which exhibits structural fluctuations in microscale, both strong positive and some negative magnetoresistances arise, which are difficult to understand within the relaxation time approximation in degenerated homogeneous semiconductor. It is discussed that a consideration of the role of spatial fluctuations (in carrier concentration, conductivity, etc.), e.g. as proposed by Herring, allows for an understanding of positive component of magnetoresistance observed in the sample with a distinct microscopic structural disorder. With the aim to better understand the transport in GaAs:Te, a model material doped above the doping limit, we discuss both positive and negative components of measured magnetoresistance.
Źródło:
Acta Physica Polonica A; 2011, 119, 5; 726-728
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical and Experimental Analysis of Photonic Crystal Fiber Selectively Infiltrated with Silicon Oil
Autorzy:
Mileńko, K.
Rutkowska, K.
Woliński, T.
Powiązania:
https://bibliotekanauki.pl/articles/1399409.pdf
Data publikacji:
2013-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
42.81.-i
42.70.Qs
42.81.Pa
Opis:
In this paper we demonstrate the numerical and experimental investigation of the photonic crystal fiber selectively infiltrated with polymer material, that is a silicon oil DC-704. The results are compared with those obtained for fully infiltrated fiber. The influence of the infiltration on light propagation properties, as well as on temperature sensitivity of the fiber are also presented. The infiltration causes the formation of photonic bandgap effect, and in the case of full infiltration the bandgaps shift equal to 50 nm is observed due to the change in external temperature in the range of about 40C (i.e. from 24 to 61°C).
Źródło:
Acta Physica Polonica A; 2013, 124, 3; 589-591
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Dependence of the Proton Conductivity on Concentration for Networks with Different Symmetry of Molecules
Autorzy:
Masłowski, T.
Dudek, K.
Powiązania:
https://bibliotekanauki.pl/articles/1032489.pdf
Data publikacji:
2017-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
66.30.Dn
66.30.jp
82.20.Wt
Opis:
The one-dimensional numerical model of the proton conductivity in anhydrous solids is used to obtain the conductivity for different values of proton concentration. The model is constructed as a chain of rods or triangles, depending on the symmetry of molecules, linked by hydrogen bonds. An evolution of such system governed by the Grotthuss mechanism is described by means of the kinetic Monte Carlo method. It is shown that in the case of a system with molecules represented by triangles, a decrease in the conductivity corresponds to a significantly broader range of concentrations than is the case for a system constructed by means of rods. This result may prove to be of a potential importance in the case of possible electronic applications. Moreover, for the discussed systems, a strong dependence on the defect formation energies is demonstrated.
Źródło:
Acta Physica Polonica A; 2017, 132, 1; 129-131
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Structural Alterations in Mechanically Activated Malachite
Autorzy:
Tunç, T.
Yıldız, K.
Powiązania:
https://bibliotekanauki.pl/articles/1207506.pdf
Data publikacji:
2014-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.20.Wk
61.43.Gt
91.60.Ed
Opis:
Malachite, a copper carbonate hydroxide mineral with the formula $Cu_2CO_3(OH)_2$ was mechanically activated for different durations in a planetary mill and analyzed by means of scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and particle size analysis to investigate the structural alterations in malachite structure. The results showed that decrease in intensity of the X-ray diffraction peaks and some alterations in carbonate and hydroxyl units of malachite occurred with increase in mechanical activation duration.
Źródło:
Acta Physica Polonica A; 2014, 125, 2; 177-179
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 374

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