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Studies in the field of superconductivity theory is one of the most bright, fruitful, and promising trends in the theoretical physics of condensed matter, since superconductivity remains to be one of the most interesting research areas in physics. In this review consider such topics of high-T c superconductivity as the structures of high-T c superc...

## Contexts in source publication

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... Figure 1, we present the plot of the critical temperatures of superconductivity over years. 8, 9 ...

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... the s-symmetry, the order parameter on both edges of the corner junction is the same, and the resulting diffraction pattern will be such as that in the case of the standard junction. But, in the case of the d-symmetry, the order parameter on the corner junction The total current is illustrated in Figure 10(c). In the zero field, the critical current turns out to be zero due to the mutual compensation of its two components. ...

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... to the pattern in Figure 10(c). Thus, by the difference of a diffraction pattern from both the standard one and that corresponding to the corner Josephson junction, we can judge about a symmetry of the order parameter. ...

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... work, 33 a similar experiment was carried out on the tunnel junction YBCO-Au-Pb. The results presented in Figure 10 testify to the d-symmetry of the order parameter in superconducting YBCO. ...

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... direct measurement of a half-quantum of the flow was realized in work. 34 The scheme of the experiment is shown in Figure 11. ...

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... G and ij are, respectively, the Green fermion and spin functions, corresponds to the contribution of two vacuum diagrams (Fig. ...

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... The results of numerical calculations are presented in Figure 15, where we can see the temperature dependence of the electron heat capacity: (1)-the curve which is an approximation of the results of computer-based calculations (crosses); (2)-the curve which describes the exponential BCS dependence. These results are in good agreement with experiments made by the group of Kapitulnik 50 at low temperatures. ...

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... is worth noting that the heat capacity jump is very sensitive to the doping. Figure 16 shows the results of recent calculations of one of the authors Ref. [45] for R as a function of the doping. It is seen that this parameter depends strongly on the doping. ...

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... It was shown in this work that d-symmetry leads to a linear dependence of C/T on the temperature, whereas the s-symmetry is related to the exponential dependence of this quantity on the temperature. The linear dependence of C/T on the temperature was observed in the experimental works 52, 54-56 for YBaCuO superconductors, The experimental results are presented in Figure 17. As was mentioned above, the problem of the determination of the symmetry of a gap in cuprate superconductors is urgent at the present time. ...

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... above, the problem of the determination of the symmetry of a gap in cuprate superconductors is urgent at the present time. Many experiments have confirmed the d-symmetry of the pairing. 33,34 In particular, we mention new experiments, 34 in which the researchers have studied the quantization of magnetic flows in a ring which includes three Fig. 16. Temperature dependence of the electron heat capacity, where (1) -the curve which is an approximation of the results of computerbased calculations (crosses); (2)-the curve which describes the exponential BCS dependence, points give the experimental data. 50 Josephson junctions. These works supporting the existence of d-pairing in ...

**Context 13**

... Figure 1, we present the plot of the critical tempera- tures of superconductivity over years. 8, 9 ...

**Context 14**

... the s-symmetry, the order parameter on both edges of the corner junction is the same, and the resulting diffraction pattern will be such as that in the case of the standard junction. But, in the case of the d-symmetry, the order parameter on the corner junction The total current is illustrated in Figure 10(c). In the zero field, the critical current turns out to be zero due to the mutual compensation of its two components. ...

**Context 15**

... to the pattern in Figure 10(c). Thus, by the difference of a diffraction pattern from both the standard one and that corresponding to the corner Josephson junction, we can judge about a symmetry of the order parameter. ...

**Context 16**

... work, 33 a similar experiment was car- ried out on the tunnel junction YBCO-Au-Pb. The results presented in Figure 10 testify to the d-symmetry of the order parameter in superconducting YBCO. ...

**Context 17**

... direct measurement of a half-quantum of the flow was realized in work. 34 The scheme of the experiment is shown in Figure 11. ...

**Context 19**

... G and ij are, respectively, the Green fermion and spin functions, corresponds to the contribution of two vac- uum diagrams (Fig. ...

**Context 21**

... The results of numerical calculations are presented in Figure 15, where we can see the temperature dependence of the electron heat capacity: (1)-the curve which is an approximation of the results of computer-based calcula- tions (crosses); (2)-the curve which describes the expo- nential BCS dependence. These results are in good agree- ment with experiments made by the group of Kapitulnik 50 at low temperatures. ...

**Context 22**

... is worth noting that the heat capacity jump is very sensitive to the doping. Figure 16 shows the results of recent cal- culations of one of the authors Ref. [45] for R as a func- tion of the doping. It is seen that this parameter depends strongly on the doping. ...

**Context 23**

... It was shown in this work that d-symmetry leads to a linear dependence of C/T on the temperature, whereas the s-symmetry is related to the exponential dependence of this quantity on the temperature. The linear dependence of C/T on the temperature was observed in the experimental works 52, 54-56 for YBaCuO superconductors, The experimental results are presented in Figure 17. As was mentioned above, the problem of the determination of the symmetry of a gap in cuprate superconductors is urgent at the present time. ...

**Context 24**

... above, the problem of the determination of the symmetry of a gap in cuprate superconductors is urgent at the present time. Many experiments have confirmed the d-symmetry of the pairing. 33,34 In particular, we mention new experi- ments, 34 in which the researchers have studied the quan- tization of magnetic flows in a ring which includes three Fig. 16. Temperature dependence of the electron heat capacity, where (1) -the curve which is an approximation of the results of computer- based calculations (crosses); (2)-the curve which describes the expo- nential BCS dependence, points give the experimental data. 50 Josephson junctions. These works supporting the existence of d-pairing in ...

## Citations

... Although numerous 2D phononmediated superconductors have recently been predicted from first-principles calculations, the highest predicted intrinsic T c stayed around 20 K 17-24 (19 K for B 2 C monolayer 21 , 10.3 K for B 2 O monolayer 17 , and 19-25 K for borophenes 22 , to name a few). Though in some cases T c has been enhanced by means of the chemical doping, intercalation, strain, and/or substrate proximity effects 17,23,[25][26][27][28][29][30][31][32] , it is essential to discover intrinsic 2D superconductors that exhibit high-T c without any doping or tuning of external parameters (here high-T c does not refer to unconventional superconductivity as in case of cuprates or iron-based superconductors 33 ). ...

A two-dimensional material – Mg 2 B 4 C 2 , belonging to the family of the conventional superconductor MgB 2 , is theoretically predicted to exhibit superconductivity with critical temperature T c estimated in the 47–48 K range (predicted using the McMillian-Allen-Dynes formula) without any tuning of external parameters such as doping, strain, or substrate-induced effects. The origin of such a high intrinsic T c is ascribed to the presence of strong electron-phonon coupling and large density of states at the Fermi level. This system is obtained after replacing the chemically active boron-boron surface layers in a MgB 2 slab by chemically inactive boron-carbon layers. Hence, the surfaces of this material are inert. Our calculations confirm the stability of 2D Mg 2 B 4 C 2 . We also find that the key features of this material remain essentially unchanged when its thickness is increased by modestly increasing the number of inner MgB 2 layers.

... Since, huge attention has been afforded not only by physicists, but also chemists and materials scientists around the world to study of this new unique class of functional materials. Nowadays, in addition to the above pointed binary compounds [13][14][15][16][17][18][19] The development of magnetizm inTIs is also "hot topic" in few recent years [35][36][37][38][39][40]. Stated above binary and ternary compounds also serve as a good matrix for design of new materials with desired properties. ...

The goal of this review is to briefly introduce the chemistry of the topological insulators (TIs) based on thallium chalcogenides. Numerous phase diagrams of ternary Tl-B V-X (B V – Sb, Bi; X – Se, Te) systems having TlB V X 2 type compounds which exhibit spin polarized topological surface state is evaluated and compiled. Published data on the phase equilibria in the quaternary Tl-Sb-Bi-X and Tl-BV-X-X / systems are also reviewed and it has been revealed that their quasiternary Tl 2 X-Sb 2 X 3-Bi 2 X 3 and reciprocal 3Tl 2 X+B V 2 X / 3 ↔3Tl 2 X / +B V 2 X 3 subsystems form a wide range of solid solutions based on compounds TlB V X 2 and B V 2 X 3 , whose both confirmed as potential 3D TIs materials. All phase diagrams of respective systems offer profound possibilities for growth their large single crystals from melt.

The compound Sn2-xAgxSr2Ca2Cu3O10+& were successfully prepared by the solid state reaction and Nano technique at different concentrations (x = 0.2, 0.4, 0.6, 0.8). The samples were then subjected to Nano technique, and samples were annealed in (850 C⁰). The morphology were also observed by Atomic force microscopy (AFM) in three dimensions, the best value of Nano is 62.09 nm at x = 0.6. We used the solid-state reaction method and then nanotechnology in different proportions of X and then we performed the annealing process of the models at a temperature of 850 C⁰ for the purpose of obtaining a regular installation and we conducted Nanos copy tests using an atomic force microscope and we got a lower bug after nanostructures 62.09 with the electrical measurements were examined using a difference measuring it the voltage with current are under low temperatures and resistance is obtained at the nanometer 62. 09. The best result is. 142.5 K.

Certain significant fallacies are involved in discussions of the high-Tc mechanism unsolved for over 30 years in cuprate superconductors. These fallacies are explored with the aim of unravelling this mechanism. Moreover, using polarised electronic Raman scattering in inhomogeneous underdoped cuprate superconductors, the intrinsic nonlinear Raman spectrum is obtained by subtracting the pseudogap characteristic of a nonlinear from the linear Raman spectrum measured in the B2g mode of the node area below the critical temperature. The intrinsic nonlinear behaviour implies the existence of the nodal superconducting gap denying dx2-y2-wave pairing symmetry. An origin of the nodal superconducting gap is discussed.

Certain significant fallacies are involved in discussions of the high-[Formula: see text] mechanism unsolved for over 30 years in cuprate superconductors. These fallacies are explored with the aim of unraveling this mechanism. Moreover, using polarized electronic Raman scattering in inhomogeneous underdoped cuprate superconductors, the intrinsic nonlinear Raman spectrum is obtained by subtracting the pseudogap characteristic of a nonlinear from the linear Raman spectrum measured in the [Formula: see text] mode of the node area below the critical temperature. The intrinsic nonlinear behavior implies the existence of the nodal superconducting gap denying [Formula: see text]-wave pairing symmetry. An origin of the nodal superconducting gap is discussed.

We predict high Tc superconductivity in the doped channel of a field effect transistor; where the electron-phonon interaction is due to the Jahn-Teller effect. An analytic expression of the electron-phonon interaction constant is derived; and the McMillan formula is used to estimate the transition temperature in semiconductors with different Debye temperatures. Experiments are also suggested.

We deal with thermodynamic features of organic conductors and superconductors where itinerant π-electrons/holes released from organic molecules are playing essential roles for electronic properties. Since they are low-dimensional electronic systems with relatively soft lattice framework, they show variety of phenomena related to electron correlations and electron–lattice coupling. The drastic changes of conductive and magnetic properties owing to quantum features of π-electrons can be induced by external perturbations such as magnetic/electric field, pressure, etc. It is especially emphasized that the possible mechanism and relation with other phenomena of the superconductivity in π-electrons system remains to be one of the interesting research areas in fundamental condensed matter science. In this review paper, we consider several topics of organic conductors and superconductors from the standpoints of thermodynamic experiments, data analyses and theories performed up to now. Starting from the overall picture of the electronic states in charge transfer complexes, thermodynamic properties of the quasi-one-dimensional systems, quasi-two-dimensional systems and π–d interacting systems are reviewed. The thermodynamic parameters of the superconductive compounds in them are compared and discussed. The relations with crystal structures, electronic states, phase diagram and other experiments are also discussed in comparison with these thermodynamic properties. The possible pairing symmetries in organic superconductors and some models are mentioned in the last part. This review deals with a wide scope of theoretical and experimental topics in superconductivity in molecule-based conductive systems.

Organic superconductors with κ-type structure are most frequently identified as nodal gap superconductors from the experimental observation of a power-law behavior in the low-temperature thermodynamic properties such as specific heat capacity. We perform series of theoretical calculations of specific heat capacity of three typical organic complexes with different transition temperatures by using Bogolyubov–de Gennes equations. The good agreement between the experimental data and the calculations demonstrates that the d-wave pairing is certainly realized in these superconductors.

Recent femtosecond pump-probe experiments on Mott insulators reveal charge recombination, which is in picosecond range, i.e., much faster than in clean bandgap semiconductors although excitation gaps in Mott insulators are even larger. The charge response in photo-excited insulators can be generally divided in femtosecond transient relaxation of charge excitations, which are holons and doublons, and a second slower, but still very fast, holon–doublon (HD) recombination. We present a theory of the recombination rate of the excited HD pairs, based on the two-dimensional (2D) model relevant for cuprates, which shows that such fast processes can be explained even quantitatively with the multi-magnon emission. We show that the condition for the exponential decay as observed in the experiment is the existence of the exciton, i.e., the bound HD pair. Its recombination rate is exponentially dependent on the charge gap and on the magnon energy, while the ultrafast process can be traced back to strong charge-spin coupling. We comment also fast recombination times in the one-dimensional (1D) Mott insulators, as e.g., organic salts. The recombination rate in the latter cases can be explained with the stronger coupling with phonon excitations.

The recently discovered charge order is an intrinsic and universal property of cuprate superconductors, however, its microscopic origin remains debated. Here we review briefly the theoretical work about the nature of charge order in cuprate superconductors. In particular, we show that the electron self-energy obliterates the electron Fermi surface around the antinodal region, leaving behind disconnected Fermi arcs located around the nodal region. The charge-order state on the other hand is driven by the Fermi-arc instability, with a characteristic wavevector corresponding to the hot spots of the Fermi arcs rather than the antinodal nesting vector. Since the pseudogap emanates from the electron self-energy, the Fermi arc, charge order, and pseudogap in cuprate superconductors are intimately related each other.