Irina Abaloszewa - Academia.edu (original) (raw)

Papers by Irina Abaloszewa

Research paper thumbnail of Guided Vortex Motion in a Ferromagnet-Superconductor Bilayer

Research paper thumbnail of Systemic Consequences of Disorder in Magnetically Self-Organized Topological MnBi_2Te_4/(Bi_2Te_3)_n Superlattices

MnBi_2Te_4/(Bi_2Te_3)_n materials system has recently generated strong interest as a natural plat... more MnBi_2Te_4/(Bi_2Te_3)_n materials system has recently generated strong interest as a natural platform for realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic MnBi_2Te_4/(Bi_2Te_3)_n it is found that migration of Mn between MnBi_2Te_4 septuple layers (SLs) and otherwise non-magnetic Bi_2Te_3 quintuple layers (QLs) has systemic consequences - it induces ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n ≳ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional ...

Research paper thumbnail of First Order Transition of the Vortex Lattice in Disordered BI-2212 Crystals

Keywords: Using differential magneto-optical imaging, we address the question of mesoscopic inhom... more Keywords: Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Research paper thumbnail of Magnetotransport and structural properties of the Ni-doped FeTe 0.65 Se 0.35 crystals

Research paper thumbnail of M ar 2 00 4 FIRST ORDER TRANSITIONOF THEVORTEX LATTICE IN DISORDERED BI-2212 CRYSTALS

Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity i... more Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Research paper thumbnail of Se p 20 03 FIRST ORDER TRANSITIONOF THEVORTEX LATTICE IN DISORDERED BI-2212 CRYSTALS

Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity i... more Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Research paper thumbnail of Systemic Consequences of Disorder in Magnetically Self-Organized Topological MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$ Superlattices

MnBi2Te4/(Bi2Te3)n materials system has recently generated strong interest as a natural platform ... more MnBi2Te4/(Bi2Te3)n materials system has recently generated strong interest as a natural platform for realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic MnBi2Te4/(Bi2Te3)n it is found that migration of Mn between MnBi2Te4 septuple layers (SLs) and otherwise non-magnetic Bi2Te3 quintuple layers (QLs) has systemic consequences it induces ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n ≳ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional theory studies s...

Research paper thumbnail of Dynamics of the Josephson Multi-Junction Systems with Junctions Characterized by Non-Sinusoidal Current - Phase Relationship

Acta Physica Polonica A

It is shown that the inclusion of junctions characterized by non-sinusoidal current-phase relatio... more It is shown that the inclusion of junctions characterized by non-sinusoidal current-phase relationship in the systems composed of multiple Josephson junctions-results in the appearance of additional system phase states. Numerical simulations and stability considerations confirm that these phase states can be realized in practice. Moreover, spontaneous formation of the grain boundary junctions in high-Tc superconductors with non-trivial current-phase relations due to the d-wave symmetry of the order parameter is probable. Switching between the phase states of multiple grain boundary junction systems can lead to additional 1/f noise in high-T c superconductors.

Research paper thumbnail of Study of Excimer Laser Irradiation Effects on Properties of Crystalline YBaCuO Thin Films

Acta Physica Polonica A

The influence of UV laser irradiation on the physical properties of epitaxial YBa 2 Cu 3 O 7−δ th... more The influence of UV laser irradiation on the physical properties of epitaxial YBa 2 Cu 3 O 7−δ thin (< 1 µm) films fabricated by laser ablation was studied. The samples were irradiated by pulsed excimer laser beam at different incident energy densities Eir ≤ 130 mJ/cm 2 , i.e. 2-3 times below the ablation threshold of YBaCuO. The analysis of the sample cross-section using transmission electron microscope shows that such irradiation forms a disordered layer on the top of the crystalline film. Sample surface amorphization was observed also by atomic force microscope. Due to strong UV irradiation absorption in YBaCuO this surface layer acts like a protective cover for the sample interior. Only a small reduction of superconducting critical temperature T c was observed. Both transport measurements in normal state and magneto-optical studies in superconducting state indicate that between the disordered layer and the bottom non-modified part of the film there exists a wide transitional region with reduced carrier concentration.

Research paper thumbnail of First Order Transition of the Vortex Lattice in Disordered BI-2212 Crystals

Magneto-Optical Imaging, 2004

Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity i... more Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Research paper thumbnail of Influence of strong microwave radiation on static properties of a small Josephson junction

Preliminary results are presented concerning static properties of a small Josephson junction unde... more Preliminary results are presented concerning static properties of a small Josephson junction under the influence of strong microwave radiation. We discuss the correspondence between a Brownian particle moving in a periodic potential and superconducting phase difference in a small Josephson junction. Next, we describe an experimental method of determining the amplitude of microwave current flowing across the junction. Typical examples of static characteristics of the junction are presented, including its dynamical resistance as a function of microwave power. We discuss also the influence of an external magnetic field on the junction dynamics and show that in this case the one-dimensional Stewart-McCumber model becomes insufficient. Comment: 6 pages, 6 figures, Revtex4

Research paper thumbnail of Laser-induced structural transitions in YBa2Cu3Oy amorphous films with nanocrystalline clusters

Physical Review B, 2000

We investigated the influence of UV (KrF, homega=5.01 eV) pulsed laser irradiation on the atomic ... more We investigated the influence of UV (KrF, homega=5.01 eV) pulsed laser irradiation on the atomic order and optical properties of amorphous YBaCuO films containing crystalline clusters of nanometer (up to 25 nm) size and characterized by high mobility of structural elements due to the lack of sharp interphase boundaries. The presence of crystalline clusters in amorphous medium leads to higher

Research paper thumbnail of Magnetic field penetration in MgB2 single crystals: Pinning and Meissner holes

Low Temperature Physics, 2014

The evolution of flux distribution in MgB 2 single crystals during their remagnetization was imag... more The evolution of flux distribution in MgB 2 single crystals during their remagnetization was imaged with magneto-optical technique. Meissner holes, formed as the areas where the annihilation of vortices and antivortices takes place, were found at the boundary between oppositely magnetized parts of the crystal. Gradient of magnetic induction in the vicinity of Meissner holes was found to be enhanced. Finger-like structures of convex shape, formed during the penetration of magnetic flux inside the crystal, were observed and explained as an effect of inhomogeneous pinning and demagnetizing field redistribution in the sample. PACS: 74.25.Ha Magnetic properties including vortex structures and related phenomena; 78.20.Ls Magneto-optical effects; 74.25.Wx Vortex pinning (includes mechanisms and flux creep).

Research paper thumbnail of Quasi-2D behaviour of HTSCs: the consequence of the small effective thickness of superconducting layers

Superconductor Science and Technology, 1996

New evidence of quasi-two-dimensional (2D) behaviour in granular bulk high-0953-2048/9/11/004/img... more New evidence of quasi-two-dimensional (2D) behaviour in granular bulk high-0953-2048/9/11/004/img7 samples is presented. Anomalously large differences between the mean-field critical temperature and the temperature of the Berezinsky - Kosterlitz - Thouless-like transition is found to be in good agreement with calculations based on the small inherent thickness of 0953-2048/9/11/004/img8 layers. Two successive mechanisms, quasiparticle and Josephson tunnelling, are used to explain the experimental data obtained on a large set of samples ranging from one unit cell to perfect single crystals. A simple phenomenological analysis based on the renormalization of 2D superfluid density of charge carriers through the thickness-restrictive mechanism of their mean free path is developed.

Research paper thumbnail of Time-dependent Ginzburg–Landau approach and its application to superconductivity*

Superconductor Science and Technology, 2003

A time dependent generalization of the Ginzburg-Landau Lagrangian is proposed. It contains two te... more A time dependent generalization of the Ginzburg-Landau Lagrangian is proposed. It contains two terms determining the time dependence and the four arbitrary scalar functions. Relevant equations, which coincide with equations following from the suitable Hamiltonian, are derived by a standard variational technique. These equations determine the energy conservation law and admit twofold time dependence which leads either to first or to second order time derivatives in Ginzburg-Landau equations. By introducing the gauge invariant potentials and choosing the gauge which differs slightly from the classical Lorentz one, the theory simplifies significantly. The results gained are discussed and compared to some earlier propositions. The presented approach, when reduced to a static one, is found to be in perfect agreement with that reported recently by the Koláček group. This indicates indirectly, that the equation with the first order time derivative seems to be more justified.

Research paper thumbnail of Effect of pulsed UV laser irradiation on the properties of crystalline YBa 2 Cu 3 O 7−δ thin films

Superconductor Science and Technology, 2007

ABSTRACT The influence of UV laser irradiation on the physical properties of epitaxial YBa2Cu3O7−... more ABSTRACT The influence of UV laser irradiation on the physical properties of epitaxial YBa2Cu3O7−δ (YBCO) thin (&lt;1 µm) films fabricated by laser ablation was studied. The samples were irradiated by a pulsed excimer laser beam at different incident energy densities Eir≤160 mJ cm−2, i.e. 2–3 times below the ablation threshold of YBCO. Analysis of the sample cross-section using a transmission electron microscope (TEM) has shown that such irradiation results in a disordered layer on the top of the film. Independent confirmation of the film surface amorphization was also obtained by tunnelling experiments. Strong UV absorption in YBCO prevents further spreading of the amorphous region, which can be considered as a protective layer for the sample interior. Only a small reduction of the superconducting critical temperature Tc was observed in the irradiated samples. The transport measurements in the normal state indicate that at the interface between the disordered layer and the non-modified part of the film there exists a wide transitional region with reduced carrier concentration.

Research paper thumbnail of Dynamics of Josephson multi-junction systems: stable and metastable states

Superconductor Science and Technology, 2002

We consider the dynamical behaviour of systems composed of multiple Josephson junctions, both the... more We consider the dynamical behaviour of systems composed of multiple Josephson junctions, both theoretically and experimentally, using the examples of three-junction and four-junction interferometers. Numerical simulations and stability considerations based on the Lyapunov method show that only one fundamental phase state of the interferometer is allowed. The experimental investigation of four-junction interferometers also shows no evidence of the existence of higher interferometer states.

Research paper thumbnail of The enhancement of vortex pinning in ferromagnet/superconductor bilayers

physica status solidi (c), 2005

The magnetic-domain induced vortex pinning is studied in the ferromagnet/superconductor bilayers ... more The magnetic-domain induced vortex pinning is studied in the ferromagnet/superconductor bilayers (FSB's), in which the F layers are Co/Pt multilayers with perpendicular magnetic anisotropy, and the S layers are either niobium or high temperature superconductor YBa 2 Cu 3 O 7 (YBCO). The magnetization measurements reveal the enhancement of the flux pinning in both types of FSB's during the reversal of the magnetization of the F layer, but the details of the behavior depend on the type of the S layer. In the case of niobium FSB the maximum of pinning appears when the F layer is in the final stage of the magnetic reversal process, while the FSB with YBCO shows the maximum when the F layer is saturated. The possible origins of these differences are discussed.

Research paper thumbnail of Laser irradiation effects in YBa2Cu3O7 amorphous films

Physica C: Superconductivity, 2000

The effect of laser irradiation on coupling energy of O and Cu atoms in YBa2Cu30~ thin films was ... more The effect of laser irradiation on coupling energy of O and Cu atoms in YBa2Cu30~ thin films was investigated by measuring the changes in structure, optical transmittivity and conductivity of irradiated films. Photon energies of hco = 2.44 eV, I~ = 2.15 eV (Cu vapor green laser) and hco = 5.01 eV (KrF excimer laser) were used for film irradiation. Irradiation by lower photon energies enhanced the growth of the dielectric phase by destroying the metallic clusters. With charge transfer gap Eg=l.75 eV for O 2p ~ Cu 3d transition in the insulator, the photon energy in this case is sufficient to generate a bounded exciton. By contrast, UV irradiation influences mainly the clusters with metallic conductivity.

Research paper thumbnail of Pr-ions against two-dimensional superconductivity in Y1−yPryBa2Cu3Ox

Physica C: Superconductivity, 1994

ABSTRACT The main difference of Pr from other rare-earth ions substituting Y is that only its oxy... more ABSTRACT The main difference of Pr from other rare-earth ions substituting Y is that only its oxygen environment in YBa2Cu3Ox satisfies to the condition of the formation of so-called vibron complex which release for interaction the inner 4f electrons magnetic moment of Pr ion. It can effectively interact with the neighbor 2-D CuO2 layers. Performing the analysis of current-voltage characteristics of Y1-yPryBa2Cu3Ox samples with y = 0.16, 0.32 and 0.48 the evidence of Berezinskii-Kosterlitz-Thouless transition in 2-D superconducting layers and the strong magnetic suppression of superconductivity in them by the Pr-ions is obtained.

Research paper thumbnail of Guided Vortex Motion in a Ferromagnet-Superconductor Bilayer

Research paper thumbnail of Systemic Consequences of Disorder in Magnetically Self-Organized Topological MnBi_2Te_4/(Bi_2Te_3)_n Superlattices

MnBi_2Te_4/(Bi_2Te_3)_n materials system has recently generated strong interest as a natural plat... more MnBi_2Te_4/(Bi_2Te_3)_n materials system has recently generated strong interest as a natural platform for realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic MnBi_2Te_4/(Bi_2Te_3)_n it is found that migration of Mn between MnBi_2Te_4 septuple layers (SLs) and otherwise non-magnetic Bi_2Te_3 quintuple layers (QLs) has systemic consequences - it induces ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n ≳ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional ...

Research paper thumbnail of First Order Transition of the Vortex Lattice in Disordered BI-2212 Crystals

Keywords: Using differential magneto-optical imaging, we address the question of mesoscopic inhom... more Keywords: Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Research paper thumbnail of Magnetotransport and structural properties of the Ni-doped FeTe 0.65 Se 0.35 crystals

Research paper thumbnail of M ar 2 00 4 FIRST ORDER TRANSITIONOF THEVORTEX LATTICE IN DISORDERED BI-2212 CRYSTALS

Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity i... more Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Research paper thumbnail of Se p 20 03 FIRST ORDER TRANSITIONOF THEVORTEX LATTICE IN DISORDERED BI-2212 CRYSTALS

Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity i... more Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Research paper thumbnail of Systemic Consequences of Disorder in Magnetically Self-Organized Topological MnBi$_{2}$Te$_{4}/$(Bi$_{2}$Te$_{3}$)$_{n}$ Superlattices

MnBi2Te4/(Bi2Te3)n materials system has recently generated strong interest as a natural platform ... more MnBi2Te4/(Bi2Te3)n materials system has recently generated strong interest as a natural platform for realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic MnBi2Te4/(Bi2Te3)n it is found that migration of Mn between MnBi2Te4 septuple layers (SLs) and otherwise non-magnetic Bi2Te3 quintuple layers (QLs) has systemic consequences it induces ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n ≳ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional theory studies s...

Research paper thumbnail of Dynamics of the Josephson Multi-Junction Systems with Junctions Characterized by Non-Sinusoidal Current - Phase Relationship

Acta Physica Polonica A

It is shown that the inclusion of junctions characterized by non-sinusoidal current-phase relatio... more It is shown that the inclusion of junctions characterized by non-sinusoidal current-phase relationship in the systems composed of multiple Josephson junctions-results in the appearance of additional system phase states. Numerical simulations and stability considerations confirm that these phase states can be realized in practice. Moreover, spontaneous formation of the grain boundary junctions in high-Tc superconductors with non-trivial current-phase relations due to the d-wave symmetry of the order parameter is probable. Switching between the phase states of multiple grain boundary junction systems can lead to additional 1/f noise in high-T c superconductors.

Research paper thumbnail of Study of Excimer Laser Irradiation Effects on Properties of Crystalline YBaCuO Thin Films

Acta Physica Polonica A

The influence of UV laser irradiation on the physical properties of epitaxial YBa 2 Cu 3 O 7−δ th... more The influence of UV laser irradiation on the physical properties of epitaxial YBa 2 Cu 3 O 7−δ thin (< 1 µm) films fabricated by laser ablation was studied. The samples were irradiated by pulsed excimer laser beam at different incident energy densities Eir ≤ 130 mJ/cm 2 , i.e. 2-3 times below the ablation threshold of YBaCuO. The analysis of the sample cross-section using transmission electron microscope shows that such irradiation forms a disordered layer on the top of the crystalline film. Sample surface amorphization was observed also by atomic force microscope. Due to strong UV irradiation absorption in YBaCuO this surface layer acts like a protective cover for the sample interior. Only a small reduction of superconducting critical temperature T c was observed. Both transport measurements in normal state and magneto-optical studies in superconducting state indicate that between the disordered layer and the bottom non-modified part of the film there exists a wide transitional region with reduced carrier concentration.

Research paper thumbnail of First Order Transition of the Vortex Lattice in Disordered BI-2212 Crystals

Magneto-Optical Imaging, 2004

Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity i... more Using differential magneto-optical imaging, we address the question of mesoscopic inhomogeneity in underdoped Bi2Sr2CaCu2O8 (Bi-2212) single crystals. Among other features, it is shown that an anomalous temperature dependence of the penetration field and of the first order transition (FOT) field of the vortex lattice in such crystals can be understood as arising from inhomogeneity. The effect of chemical inhomogeneity and pinning on flux penetration and the FOT is discussed.

Research paper thumbnail of Influence of strong microwave radiation on static properties of a small Josephson junction

Preliminary results are presented concerning static properties of a small Josephson junction unde... more Preliminary results are presented concerning static properties of a small Josephson junction under the influence of strong microwave radiation. We discuss the correspondence between a Brownian particle moving in a periodic potential and superconducting phase difference in a small Josephson junction. Next, we describe an experimental method of determining the amplitude of microwave current flowing across the junction. Typical examples of static characteristics of the junction are presented, including its dynamical resistance as a function of microwave power. We discuss also the influence of an external magnetic field on the junction dynamics and show that in this case the one-dimensional Stewart-McCumber model becomes insufficient. Comment: 6 pages, 6 figures, Revtex4

Research paper thumbnail of Laser-induced structural transitions in YBa2Cu3Oy amorphous films with nanocrystalline clusters

Physical Review B, 2000

We investigated the influence of UV (KrF, homega=5.01 eV) pulsed laser irradiation on the atomic ... more We investigated the influence of UV (KrF, homega=5.01 eV) pulsed laser irradiation on the atomic order and optical properties of amorphous YBaCuO films containing crystalline clusters of nanometer (up to 25 nm) size and characterized by high mobility of structural elements due to the lack of sharp interphase boundaries. The presence of crystalline clusters in amorphous medium leads to higher

Research paper thumbnail of Magnetic field penetration in MgB2 single crystals: Pinning and Meissner holes

Low Temperature Physics, 2014

The evolution of flux distribution in MgB 2 single crystals during their remagnetization was imag... more The evolution of flux distribution in MgB 2 single crystals during their remagnetization was imaged with magneto-optical technique. Meissner holes, formed as the areas where the annihilation of vortices and antivortices takes place, were found at the boundary between oppositely magnetized parts of the crystal. Gradient of magnetic induction in the vicinity of Meissner holes was found to be enhanced. Finger-like structures of convex shape, formed during the penetration of magnetic flux inside the crystal, were observed and explained as an effect of inhomogeneous pinning and demagnetizing field redistribution in the sample. PACS: 74.25.Ha Magnetic properties including vortex structures and related phenomena; 78.20.Ls Magneto-optical effects; 74.25.Wx Vortex pinning (includes mechanisms and flux creep).

Research paper thumbnail of Quasi-2D behaviour of HTSCs: the consequence of the small effective thickness of superconducting layers

Superconductor Science and Technology, 1996

New evidence of quasi-two-dimensional (2D) behaviour in granular bulk high-0953-2048/9/11/004/img... more New evidence of quasi-two-dimensional (2D) behaviour in granular bulk high-0953-2048/9/11/004/img7 samples is presented. Anomalously large differences between the mean-field critical temperature and the temperature of the Berezinsky - Kosterlitz - Thouless-like transition is found to be in good agreement with calculations based on the small inherent thickness of 0953-2048/9/11/004/img8 layers. Two successive mechanisms, quasiparticle and Josephson tunnelling, are used to explain the experimental data obtained on a large set of samples ranging from one unit cell to perfect single crystals. A simple phenomenological analysis based on the renormalization of 2D superfluid density of charge carriers through the thickness-restrictive mechanism of their mean free path is developed.

Research paper thumbnail of Time-dependent Ginzburg–Landau approach and its application to superconductivity*

Superconductor Science and Technology, 2003

A time dependent generalization of the Ginzburg-Landau Lagrangian is proposed. It contains two te... more A time dependent generalization of the Ginzburg-Landau Lagrangian is proposed. It contains two terms determining the time dependence and the four arbitrary scalar functions. Relevant equations, which coincide with equations following from the suitable Hamiltonian, are derived by a standard variational technique. These equations determine the energy conservation law and admit twofold time dependence which leads either to first or to second order time derivatives in Ginzburg-Landau equations. By introducing the gauge invariant potentials and choosing the gauge which differs slightly from the classical Lorentz one, the theory simplifies significantly. The results gained are discussed and compared to some earlier propositions. The presented approach, when reduced to a static one, is found to be in perfect agreement with that reported recently by the Koláček group. This indicates indirectly, that the equation with the first order time derivative seems to be more justified.

Research paper thumbnail of Effect of pulsed UV laser irradiation on the properties of crystalline YBa 2 Cu 3 O 7−δ thin films

Superconductor Science and Technology, 2007

ABSTRACT The influence of UV laser irradiation on the physical properties of epitaxial YBa2Cu3O7−... more ABSTRACT The influence of UV laser irradiation on the physical properties of epitaxial YBa2Cu3O7−δ (YBCO) thin (&lt;1 µm) films fabricated by laser ablation was studied. The samples were irradiated by a pulsed excimer laser beam at different incident energy densities Eir≤160 mJ cm−2, i.e. 2–3 times below the ablation threshold of YBCO. Analysis of the sample cross-section using a transmission electron microscope (TEM) has shown that such irradiation results in a disordered layer on the top of the film. Independent confirmation of the film surface amorphization was also obtained by tunnelling experiments. Strong UV absorption in YBCO prevents further spreading of the amorphous region, which can be considered as a protective layer for the sample interior. Only a small reduction of the superconducting critical temperature Tc was observed in the irradiated samples. The transport measurements in the normal state indicate that at the interface between the disordered layer and the non-modified part of the film there exists a wide transitional region with reduced carrier concentration.

Research paper thumbnail of Dynamics of Josephson multi-junction systems: stable and metastable states

Superconductor Science and Technology, 2002

We consider the dynamical behaviour of systems composed of multiple Josephson junctions, both the... more We consider the dynamical behaviour of systems composed of multiple Josephson junctions, both theoretically and experimentally, using the examples of three-junction and four-junction interferometers. Numerical simulations and stability considerations based on the Lyapunov method show that only one fundamental phase state of the interferometer is allowed. The experimental investigation of four-junction interferometers also shows no evidence of the existence of higher interferometer states.

Research paper thumbnail of The enhancement of vortex pinning in ferromagnet/superconductor bilayers

physica status solidi (c), 2005

The magnetic-domain induced vortex pinning is studied in the ferromagnet/superconductor bilayers ... more The magnetic-domain induced vortex pinning is studied in the ferromagnet/superconductor bilayers (FSB's), in which the F layers are Co/Pt multilayers with perpendicular magnetic anisotropy, and the S layers are either niobium or high temperature superconductor YBa 2 Cu 3 O 7 (YBCO). The magnetization measurements reveal the enhancement of the flux pinning in both types of FSB's during the reversal of the magnetization of the F layer, but the details of the behavior depend on the type of the S layer. In the case of niobium FSB the maximum of pinning appears when the F layer is in the final stage of the magnetic reversal process, while the FSB with YBCO shows the maximum when the F layer is saturated. The possible origins of these differences are discussed.

Research paper thumbnail of Laser irradiation effects in YBa2Cu3O7 amorphous films

Physica C: Superconductivity, 2000

The effect of laser irradiation on coupling energy of O and Cu atoms in YBa2Cu30~ thin films was ... more The effect of laser irradiation on coupling energy of O and Cu atoms in YBa2Cu30~ thin films was investigated by measuring the changes in structure, optical transmittivity and conductivity of irradiated films. Photon energies of hco = 2.44 eV, I~ = 2.15 eV (Cu vapor green laser) and hco = 5.01 eV (KrF excimer laser) were used for film irradiation. Irradiation by lower photon energies enhanced the growth of the dielectric phase by destroying the metallic clusters. With charge transfer gap Eg=l.75 eV for O 2p ~ Cu 3d transition in the insulator, the photon energy in this case is sufficient to generate a bounded exciton. By contrast, UV irradiation influences mainly the clusters with metallic conductivity.

Research paper thumbnail of Pr-ions against two-dimensional superconductivity in Y1−yPryBa2Cu3Ox

Physica C: Superconductivity, 1994

ABSTRACT The main difference of Pr from other rare-earth ions substituting Y is that only its oxy... more ABSTRACT The main difference of Pr from other rare-earth ions substituting Y is that only its oxygen environment in YBa2Cu3Ox satisfies to the condition of the formation of so-called vibron complex which release for interaction the inner 4f electrons magnetic moment of Pr ion. It can effectively interact with the neighbor 2-D CuO2 layers. Performing the analysis of current-voltage characteristics of Y1-yPryBa2Cu3Ox samples with y = 0.16, 0.32 and 0.48 the evidence of Berezinskii-Kosterlitz-Thouless transition in 2-D superconducting layers and the strong magnetic suppression of superconductivity in them by the Pr-ions is obtained.