Search results

1

Electron-Molecular Vibration Coupling in TTF-Based Donors

100%

Pokhodnia K. I.

Acta Physica Polonica A

|

1995

|

vol. 87

|

issue 4-5

815-818

EN

BEDT-TTF, BMDT-TTF and BEDO-TTF are well known thio-TTF and oxo-TTF (in the former case) derivatives on the basis of which cation-radical salts with 2D type of conductivity can be produced. In this work the comparative analysis of electron-molecular vibration coupling constants (obtained by MNDO quantum-chemical method) that describe the interaction between totally symmetric A_{g} modes and electron on HOMO level is performed.

2

Comparison of the Temperature Dependence of the Crystal Structure of LiTi_2O_4 and LiV_2O_4

63%

Moshopoulou E.

Acta Physica Polonica A

|

2008

|

vol. 113

|

issue 1

399-402

EN

The normal spinel oxide LiTi_2O_4 is an exotic superconductor with T_c=11.2 K, while the isostructural neighbouring LiV_2O_4 exhibits heavy-fermion behaviour. The origin of their physics and the role of the spinel structure on their properties are yet unsolved issues, owing mainly to the complexity of the structure, the presence of subtle disorder, and the sample dependence of the physical properties. Especially and perhaps more importantly, the enormous difference in their low-temperature properties remains an open question. This question has only been addressed theoretically but (mainly because of the above problems) there were no experimental studies that sought to understand the clearly distinct behaviour of the two systems. Here, we contribute to the understanding of such distinct low-temperature behaviour by comparing the temperature dependence of the very basic structural properties of the two systems. Upon cooling from room temperature, the lattice parameter a decreases gradually in about the same way for both systems. However, below 20 K, a clear decrease in a of LiV_2O_4 as a function of temperature contrasts strongly with the almost constant value of a of LiTi_2O_4 in the same temperature range. Therefore subtle but clearly different structural signatures are coupled with the very divergent physical properties of the two systems and suggest new directions to the theory.

3

Specific Heat of RBa_{2}Cu_{3}O_{7-x} and RBaSrCu_{3}O_{7-x} Compounds (R = Sm, Dy, Er)

63%

Tarnawski Z., Kim-Ngan N., Wang X., Duijn V., Franse J.

Acta Physica Polonica A

|

1998

|

vol. 93

|

issue 3

513-522

EN

The low-temperature specific-heat C(T) data of high-T_{c} superconductors RBa_{2}Cu_{3}O_{7-x}(R123O_{7-x}) were reviewed. A discussion of the C(T) data obtained on single-crystalline samples of Er123O_{7-x} and Sm123O_{7-x} compounds in applied magnetic fields for better evaluation of the crystal-electric-field parameters is given. The C(T) measurements of Sr-substituted compounds RBaSrCu_{3}O_{7} revealed the λ-type of peak related to the antiferromagnetic order at 1.2 K and 0.6 K respectively for Dy- and Er-compounds. The magnetic singlet ground state in these compounds is produced by weak exchange interactions of -0.05 T/μ_{B} and -0.035 T/μ_{B}, respectively. For Nd- and Sm-compounds, only a broad anomaly around 0.6 K was observed which is well fitted with a Schottky-type anomaly with an energy splitting of 1.4 K.

4

Superconducting Regions and Kondo Effect of MgB_2 Formed by Implantation of Magnesium Ions into Boron Substrate

63%

Trybuła Z., Kempiński W., Andrzejewski B., Piekara-Sady L., Kaszyński J., Trybuła M., Piekoszewski J., Stanisławski J., Barlak M., Richter E.

Acta Physica Polonica A

|

2006

|

vol. 109

|

issue 4-5

657-660

EN

The results of investigation of the polycrystalline boron implanted by magnesium and argon plasma pulse treatment are presented. The four-probe electric conductivity measurements and magnetically modulated microwave absorption showed the presence of superconducting islands below the temperature of 25 K. Below T=23 K we detected the Kondo effect, a logarithmic increase in the resistivity as the temperature is lowered, due to iron impurity.

5

Electronic Properties of High-Temperature Superconductor DyBa_{2}Cu_{3}O_{7} from Critical Fields and Specific Heat Studies

63%

Kołodziejczyk A., Kozłowski A., Chmist J., Zalecki R., Ściężor T., Tarnawski Z., Woch W.

Acta Physica Polonica A

|

1993

|

vol. 84

|

issue 1

127-138

EN

The lower and upper critical fields, as well as the specific heat were measured as a function of temperature for good quality DyBa_{2}Cu_{3}O_{7} high-temperature superconductor in the vicinity of superconducting transition temperature T_{c} = 91.2 K. The number of superconducting and normal state electronic quantities were determined basing on the Ginzburg-Landau-Abrikosov-Gorkov theory. It is argued that on the basis of this BCS-like theory one can describe the superconducting properties and, in combination with some information on the electronic structure, also the magnetic properties of high-temperature superconductors.

6

On the Surfacegrived State of Cleaved YBa_{2}Cu_{3}O_{7-δ} Single Crystals

63%

Harm S., Mante G., Manzke R., Fink J., Skibowski M.

Acta Physica Polonica A

|

1992

|

vol. 82

|

issue 2

349-354

EN

Angle-resolved photoemission experiments on the cleaved surface of YBa_{2}Cu_{3}O_{7-δ} single crystals revealed an intrinsic surface-derived electronic state around the X and Y point of the Brillouin zone with 0.92 eV binding energy. A surface electronic structure different to the bulk can be of basic importance for the surface superconductivity of this high-T_{c} cuprate. Here we briefly review recent experimental results and present new hydrogen adsorption experiments, demonstrating the surface character of the 0.92 eV state.

7

The Critical Behaviour of Pyroelectric-Type Superconductors

63%

Krzyżanowski I.

Acta Physica Polonica A

|

1991

|

vol. 80

|

issue 1

81-98

EN

The quasiclassical, Eilenberger-type equations are applied to description of rotating P-wave pyroelectric-type superconductor in the presence of magnetic field H and superflow υ. In analogy to type-II superconductors the possibility of vortex solution is discussed. We determine the symmetry of eigensolutions and the upper critical velocity Ω_{c2}. We discuss the paramagnetic critical behaviour of the system depending on the strength of spin-orbit interaction.

8

Formation of Superconducting Regions of MgB_2 by Implantation of Boron Ions into Magnesium Substrate

63%

Trybuła Z., Kempiński W., Andrzejewski B., Piekara-Sady L., Kaszyński J., Piekoszewski J., Werner Z., Richter E., Prokert F., Stanisławski J., Barlak M.

Acta Physica Polonica A

|

2005

|

vol. 108

|

issue 1

165-170

EN

The results of investigation of the MgB_2 inter-metallic compound with the use of boron ions implantation and plasma pulse treatment are presented. The samples were characterized by: four-probe electric conductivity measurements, magnetically modulated microwave absorption, and magnetic measurements. For hydrogen and argon pulsed plasma treatment the samples with T_c ranging from 10 K to 32 K were obtained. The superconducting phase does not form a continuous layer since the resistivity does not fall down to zero. Apparently, separate islands of superconducting phase are connected through metallic Mg paths. All samples are still below the percolation threshold.

9

XANES Experiments for High-Temperature Superconductors

63%

Kołodziejczyk A.

Acta Physica Polonica A

|

1992

|

vol. 82

|

issue 2

273-281

EN

The paper presents the results of XANES (X-ray Absorption Near Edge Structure) experiments, of the high-temperature superconductors of Y-Ba-Cu-O-type carried out at the Cu L_{II,III}- and O K_{I}-edges using synchrotron radiation and the KMC double monochromator and SX-700 grading monochromator beamlines of BESSY/Berlin synchrotron storage ring. The aim of the paper is to show that the XANES studies are well suited for characterization of the local electronic structure of the high-temperature superconductors.

10

Synthesis and Characterization of the Superconductor Mo_3Sb_7

63%

Tran V., Bukowski Z.

Acta Physica Polonica A

|

2008

|

vol. 114

|

issue 1

67-74

EN

We synthesized a polycrystalline sample of the superconductor Mo_3Sb_7 and characterized its basic properties by measurements of magnetization, electrical resistivity and specific heat. The measurements establish a superconducting phase transition at T_c=2.25 (0.05) K. In applied magnetic fields, the magnetization and resistivity show the behavior of type-II superconductor. From the specific heat measurement, the electronic specific heat coefficient,γ, specific heat jump at T_c, ΔC(T_c)/γT_c, and the Debye temperature Θ_D, are evaluated to be 34.5 mJ/(mol K^2), 1.56 and 283 K, respectively. From analysis of the specific heat data we suggest that this compound belongs to an intermediate strong coupling regime in the BCS context. The observed enhancement in theγ-value suggests a substantial contribution of Mo-4d-electrons to the density of states. Our experimental data do not support interpretation of superconductivity in Mo_3Sb_7 in terms of neither unconventional superconductivity or spin fluctuations proposed previously.

11

Superconductivity of MgB_2 Layers Prepared on Silicon Substrate by Implantation of Magnesium Ions into Boron Substrate

63%

Trybuła Z., Kempiński W., Łoś S., Kaszyńska K., Trybuła M., Piekoszewski J., Werner Z., Barlak M.

|

issue 2

323-325

EN

The results of investigation of the MgB_2 layers prepared on silicon substrate by implantation of Mg ions into boron substrate are presented. After implantation the annealing processes were carried out at temperatures 673 K, 773 K, and 873 K in a furnace in an atmosphere of flowing Ar-4%H_2 gas mixture. The samples were characterized by: four-probe electric conductivity measurements and magnetically modulated microwave absorption. Our results showed that due to silicon substrate the diffusion of implanted Mg ions into boron materials should be limited, and the superconducting phase forms a continuous MgB_2 layer and the resistivity for all samples fall down to zero below T_{c}. The transition temperature T_{c} becomes higher with increasing annealing temperature: T_{c}=18 K (for annealing at T_{A}=673 K), T_{c}=20 K (for annealing at T_{A}=773 K), and T_{c}=27 K (for annealing at T_{A}=873 K).

12

Ion Implantation and Transient Melting: A New Approach to Formation of Superconducting MgB_2 Phases

63%

Piekoszewski J., Kempiński W., Stankowski J., Prokert F., Richter E., Stanisławski J., Werner Z., Szymczyk W.

Acta Physica Polonica A

|

2004

|

vol. 106

|

issue 6

861-868

EN

An attempt to synthesize superconducting MgB_2 inter-metallic compound from the liquid state is presented. The process consists of two steps. In the first one, boron ions are implanted into a magnesium substrate. In the second one, the near-surface region of such system is melted by short, intense hydrogen plasma pulses without necessity of annealing in Mg vapor. A magnetically modulated microwave absorption method was used to detect superconducting regions in the obtained MgB_2 layer. Percolation between nano-regions (islands) of MgB_2 has not been observed. However, a superconducting state of the insulated islands has been experimentally proven with transition temperatures T_C as high as 31 K.

13

The Evolution of Superconducting Phase MgB_x

63%

Łoś S., Kempiński W., Piekara-Sady L., Andrzejewski B., Jurga W., Kaszyńska K., Piekoszewski J., Werner Z., Barlak M.

Acta Physica Polonica A

|

2008

|

vol. 114

|

issue 1

179-184

EN

Thin layers of MgB_x were studied in order to define evolution of superconducting phase after Mg ions implantation into boron substrate. Three fluencies of energies 140, 80, and 40 keV were used to establish proper stoichiometry to synthesize homogeneous MgB_2 film. Additionally, the annealing processes were carried out at temperatures 400, 500, and 600°C in a furnace in an atmosphere of flowing Ar-4%H_2 gas mixture. The quality of the superconducting material was examined by magnetically modulated microwave absorption, and magnetic and resistivity measurements. The results showed that T_c becomes higher with increasing annealing temperature. However, the fraction of superconducting phase decreases, due to partial evaporation of Mg ions and their deeper migration into boron substrate.

14

The Measurement of YBa_2Cu_3O_{7-δ} Single Crystals Using the Atomic/Magnetic Force Microscopy

51%

Kamiński M., Wróblewski M., Susła B.

Acta Physica Polonica A

|

2008

|

vol. 114

|

issue 1

91-97

EN

In this paper the experimental investigations of the YBa_2Cu_3O_{7-δ} single crystal, using atomic force microscopy and magnetic force microscopy, are presented. The atomic force microscopy was used to identify oxidized and unoxidized YBa_2Cu_3O_{7-δ} crystal. The YBa_2Cu_3O_{7-δ} single oxidized crystal was examined for magnetic properties by means of magnetic force microscopy. The research was carried out at a room temperature and in the air atmosphere without external magnetic field.

15

XPS Investigation of Y_{1-x}Dy_xNi_2B_2C Superconductors

51%

Winiarski A., Winiarska A., Drzazga Z.

Acta Physica Polonica A

|

2008

|

vol. 114

|

issue 1

243-246

EN

The analysis of the valence band photoemission spectra of Y_{1-x}Dy_xNi_2B_2C (0≤x≤1) is presented. The valence bands are mainly plotted for Ni 3d, Y 4d and Dy 4f contributions, according to theoretical predictions. The valence bands of Y_{1-x}Dy_xNi_2B_2C compounds markedly change shape with the x parameter, especially in the binding energy region from 3 eV to 14 eV. For large content of Dy (above 55%) the valence band is predominant by Dy 4f states whereas Ni 3d states govern the valence band of yttrium rich compounds. Changing in domination of valence sub-band correlates with plot of superconducting transition temperature T_c with Dy concentration.

16

Superconducting Instability Temperature of a Non-Centrosymmetric System

51%

Grzybowska D., Harań G.

Acta Physica Polonica A

|

2016

|

vol. 130

|

issue 2

604-606

EN

We discuss a direct effect of the energy band splitting due to the antisymmetric spin-orbit coupling on the superconducting phase transition. Employing the square lattice tight-binding model we show a significant contribution of the spin-split energy band to the pair-breaking effect in the weak- and intermediate-coupling non-centrosymmetric superconductors. We establish a general tendency of the spin-orbit coupling to suppress the critical temperature of the spin singlet and triplet states. For the weak-coupling systems we report a possible development of sharp maxima of the critical temperature for the band fillings which support the spin-orbit coupling induced Fermi surface singularities of the density of states. We note that the initial suppression of the most stable triplet state becomes comparable to the suppression of other triplet states in the intermediate-coupling regime of superconductivity.

17

Microwave Absorption Study on (Bi,Pb)-Sr-Ca-Cu-O Granular Superconductors

51%

Jurga W., Piekara-Sady L., Gazda M.

Acta Physica Polonica A

|

2008

|

vol. 114

|

issue 1

253-256

EN

(Bi,Pb)-Sr-Ca-Cu-O is considered as a system of 2201, 2212 and 2223 superconductors embedded in the insulating matrix. The size of the grains depends on the time of recrystallization. These types of ceramics exhibit a two-step transition to superconducting state. Because electrical properties depend among other on the Josephson coupling between grains, the magnetically modulated microwave absorption study was undertaken. Magnetically modulated microwave absorption signal was observed to arise just as temperature had been lowered below T₁. The shape of this signal was studied to recognize the second temperature T₂. Some strong oscillations appear on magnetically modulated microwave absorption at lower temperatures, which might be related to local percolation breakdown in superconducting network.

18

Chemical Potential Evidence for Phase Transitions in Magnetic and Superconducting Compounds and Alloys

51%

Matlak M., Pietruszka M.

Acta Physica Polonica A

|

2000

|

vol. 97

|

issue 1

253-256

EN

We announce that all phase transitions (induced by temperature or concentration) including structural ones and transitions between metastable or "exotic" states can be detected by the chemical potential critical behaviour, as well as, from the average occupation numbers of the electronic system (critical electron redistribution).

19

Magnetic Properties of Milled and Thermal Relaxed YBa_{2} (Cu_{1-x}Fe_{x})_{3}O_{y}

51%

Timko M., Kováč J., Sargánková I., Zentková M., Mihalik M., Maťaš S., Čiasnohová A.

Acta Physica Polonica A

|

1997

|

vol. 91

|

issue 2

355-358

EN

The influence of the mechanical milling and subsequent thermal relaxation on magnetic and superconducting behaviour of YBa_{2}(Cu_{1-x}Fe _{x})_{3}O_{y} system has been studied. Two methods of heat treatment were used: Set I - slow cooling from 980°C in flowing O_{2} and Set II - reducing at 770°C in flowing Ar_{2} followed by reoxidation in flowing O_{2} below 400°C. The transition to superconductivity, diamagnetic response, critical current density and the effective magnetic moment in the normal state have been estimated. Our measurements indicate that the reducing atmosphere preparation is less detrimental on superconducting properties. The results are discussed in terms of occupancy Cu sites by Fe and redistribution of oxygen atoms.

20

First Principles Calculation of ε-Phase of Solid Oxygen

51%

Kamaruddin K., Abedin A., Zabidi N., Yahya M., Taib M., Rosli A.

Acta Physica Polonica A

|

2016

|

vol. 129

|

issue 4

468-471

EN

The electronic structures of ε-phase of solid oxygen (O₂)₄ are studied within the framework of density-functional theory. The intriguing molecule has been known to have magnetic properties at room temperature by applying pressure. Nevertheless, until now there was no evidence of band structure studied in the antiferromagnetic behaviour of (O₂)₄. We report a comparison study for spin and non-spin polarization orbital which suggests that this ferromagnetic configuration of (O₂)₄ could not be seen experimentally, and antiferromagnetic configuration of (O₂)₄ was seen at higher pressure of about 10 GPa. The antiferromagnetic state transforms into the superconducting state as the sample temperature decreases. The results can serve as a useful approximation in studying general features of the electronic structure. The (O₂)₄ clusters are reported in the Raman study, having significant absorption at 1516 cm¯¹ below infrared region.

Refine search results

Electron-Molecular Vibration Coupling in TTF-Based Donors

Comparison of the Temperature Dependence of the Crystal Structure of LiTi_2O_4 and LiV_2O_4

Specific Heat of RBa_{2}Cu_{3}O_{7-x} and RBaSrCu_{3}O_{7-x} Compounds (R = Sm, Dy, Er)

Superconducting Regions and Kondo Effect of MgB_2 Formed by Implantation of Magnesium Ions into Boron Substrate

Electronic Properties of High-Temperature Superconductor DyBa_{2}Cu_{3}O_{7} from Critical Fields and Specific Heat Studies

On the Surfacegrived State of Cleaved YBa_{2}Cu_{3}O_{7-δ} Single Crystals

The Critical Behaviour of Pyroelectric-Type Superconductors

Formation of Superconducting Regions of MgB_2 by Implantation of Boron Ions into Magnesium Substrate

XANES Experiments for High-Temperature Superconductors

Synthesis and Characterization of the Superconductor Mo_3Sb_7

Superconductivity of MgB_2 Layers Prepared on Silicon Substrate by Implantation of Magnesium Ions into Boron Substrate

Ion Implantation and Transient Melting: A New Approach to Formation of Superconducting MgB_2 Phases

The Evolution of Superconducting Phase MgB_x

The Measurement of YBa_2Cu_3O_{7-δ} Single Crystals Using the Atomic/Magnetic Force Microscopy

XPS Investigation of Y_{1-x}Dy_xNi_2B_2C Superconductors

Superconducting Instability Temperature of a Non-Centrosymmetric System

Microwave Absorption Study on (Bi,Pb)-Sr-Ca-Cu-O Granular Superconductors

Chemical Potential Evidence for Phase Transitions in Magnetic and Superconducting Compounds and Alloys

Magnetic Properties of Milled and Thermal Relaxed YBa_{2} (Cu_{1-x}Fe_{x})_{3}O_{y}

First Principles Calculation of ε-Phase of Solid Oxygen