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1

Point Contact Studies of High T_{c} Superconductors

100%

Susła B., Meepagala S., Wolf E.

Acta Physica Polonica A

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1993

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vol. 84

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issue 2

315-319

EN

Point contact spectroscopy experiments were performed on both single crystals Bi_{2}Sr_{2}CaCu_{2}O_{8+y} and BiSrCaCuO/Ag sintered material using gold tips. The spectra exhibit tunneling structure, which are interpreted in terms of the energy gap structure 2Δ = 58 meV at 4.2 K. We observed the strong Andreev reflection of the Au-BiSrCaCuO/Ag boundary.

2

Non-Linear Processes in 1D Quantum Spin Ordered System under Strong Magnetic Field Pulse

100%

Borovikov V. S., Gorelik L. Y., Kulinich S. I., Popkov V. Y.

Acta Physica Polonica A

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1997

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vol. 91

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issue 3

605-608

EN

Investigation of an exactly integrable quantum model of 1D magnetic (which is equivalent to a massive fermion system) is presented. It has been shown that under certain conditions a spin system will not absorb power from the strong homogeneous magnetic field pulse.

3

Self-Induced Transparency in 1D Magnetics

100%

Borovick A., Borovikov V., Gorelik L.

Acta Physica Polonica A

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1994

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vol. 85

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issue 2

405-407

EN

The evolution of spin system with the Fermi character of the relevant excitations under the strong magnetic field pulse is presented. The nonlinear dynamic equations describing interaction of the system and external magnetic field are found. It is shown that under certain conditions the initial state of the resonantly absorbing system does not change after passing of the field pulse (similar to optical self-induced transparency in two-level molecular gas).

4

Anomalous Superconductivity and Antiferromagnetism in the U(Pt,Pd)_3 System

80%

Franse J.

Acta Physica Polonica A

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2001

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vol. 100

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issue Supplement

153-176

EN

A review is presented of the anomalous magnetic and superconducting properties of the heavy-fermion compound UPt_3 that has been a subject of extensive study during the past twenty years. The normal-state and superconducting properties of the compound were evaluated from magnetic, transport, and thermodynamic studies. In addition, neutron-diff raction and muon spin relaxation experiments were performed in the normal and superconducting states. The compound is characterized by a multiple superconducting phase diagram and by the coexistence of superconductivity and short-range antiferromagnetic interactions with quasi-static moments of the order of 10^{-2}μ_B/U-atom. Upon substituting Pt by Pd, the short-range magnetic interactions give way to long-range antiferromagnetic order with a maximal ordering temperature of 6 K for the 5 at.% Pd alloy and a magnetic moment of 0.6μ_B/U-atom. Superconductivity and long-range antiferromagnetic order are in competition resulting in a critical composition of 0.6 at.% Pd. At this concentration, non-Fermi liquid behaviour is observed.

5

Heavy Fermion Superconductor Order Parameter in High Magnetic Field

80%

Kowalewski L., Wojciechowski R., Thomas M., Nogala M.

Acta Physica Polonica A

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1994

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vol. 85

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issue 2

347-350

EN

It is shown that, independently on either the nature and the strength of pairing, the orbital effects of a high magnetic field in heavy fermion superconductor change the form of both the effective pairing and the gap function.

6

Universal Scaling of Basic Properties of the Heavy-Fermion Superconductors

80%

Karbowski J., Spałek J.

Acta Physica Polonica A

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1994

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vol. 85

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issue 2

341-345

EN

We show that the properties of the heavy-electron superconducting state induced by the interorbital kinetic exchange scale with the effective mass renormalization m*/m_{0} ~ 1/T_{K}. Explicitly, the pairing potential J̃ ~ J(m_{0}/m*)ln^{2}(m_{0}/m*), where J is the magnitude of the bare Kondo coupling; the coherence length ξ ~ T_{K}/T_{c} where T_{c} is the transition temperature, whereas the penetration depth λ ~ (m*/m_{0})^{½} so that λ/ξ >> 1. We also determine the scaling of magnetic critical fields.

7

Magnetism in UCo_{0.88}Ru_{0.12}Ge Studied by Polarized Neutrons

80%

Vališka M., Pospíšil J., Nénert G., Stunault A., Prokeš K., Sechovský V.

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vol. 126

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issue 1

330-331

EN

UCoGe is an archetype of coexisting weak itinerant 5f-electron ferromagnetism (T_{C}~3 K, μ_{s}=0.03μ_{B}/f.u.) and superconductivity (T_{SC}~ 0.6 K) at ambient pressure. The Ru substitution for Co leads to an initial sharp increase of the T_{C} up to the maximum of T_{C}=8.5 K for x=0.12, increase of spontaneous magnetic moment and suppression of superconductivity. We have grown the UCo_{0.88}Ru_{0.12}Ge single crystal and studied magnetization along the principal crystallographic axes. To see the microscopic background of these findings we performed a polarized neutron diffraction experiment on D3 diffractometer in ILL. We have found that the Co and U moments are parallel in UCo_{0.88}Ru_{0.12}Ge, in contrast to the antiparallel configuration in UCoGe. This is probably the reason of the spontaneous magnetization increase with Ru doping.

8

Theory of Unconventional Superconductivity in Strongly Correlated Systems: Real Space Pairing and Statistically Consistent Mean-Field Theory - in Perspective

80%

Spałek J.

Acta Physica Polonica A

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2012

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vol. 121

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issue 4

764-784

EN

In this brief overview we discuss the principal features of real space pairing as expressed via corresponding low-energy (t-J or periodic Anderson-Kondo) effective Hamiltonian, as well as consider concrete properties of those unconventional superconductors. We also rise the basic question of statistical consistency within the so-called renormalized mean-field theory. In particular, we provide the phase diagrams encompassing the stable magnetic and superconducting states. We interpret real space pairing as correlated motion of fermion pair coupled by short-range exchange interaction of magnitude J comparable to the particle renormalized band energy ≈ tx, where x is the carrier number per site. We also discuss briefly the difference between the real-space and the paramagnon-mediated sources of superconductivity. The paper concentrates both on recent novel results obtained in our research group, as well as puts the theoretical concepts in a conceptual as well as historical perspective. No slave-bosons are required to formulate the present approach.

9

On Magnetic Impurities in Gapless Fermi Systems

80%

Borkowski L. S.

Acta Physica Polonica A

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1997

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vol. 91

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issue 2

359-362

EN

In ordinary metals, antiferromagnetic exchange between conduction electrons and a magnetic impurity leads to screening of the impurity spin below the Kondo temperature, T_{K}. In systems such as semimetals, small-gap semiconductors and unconventional superconductors, a reduction in available conduction states near the chemical potential can greatly depress T_{K}. The behavior of an Anderson impurity in a model with a power-law density of states, ρ(ε) ∝ |ε|^{r}, r>0, for |ε|<Δp, where Δp is small compared to the bandwidth, is studied using the non-crossing approximation. The transition from the Kondo singlet to the magnetic ground state can be seen in the behavior of the impurity magnetic susceptibility χ. The product Tχ saturates at a finite value at low temperature for coupling smaller than the critical one. For sufficiently large coupling Tχ → 0, as T → 0, indicating a complete screening of the impurity spin.

10

Superconductivity in Anderson Lattice Model

80%

Romano A., Noce C., Micnas R.

Acta Physica Polonica A

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1997

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vol. 91

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issue 2

381-385

EN

We study the superconducting instabilities generated by the inclusion in the Anderson lattice model of a density-density attractive potential between correlated electrons on nearest-neighbouring sites. Using a description of the normal phase based on a perturbative expansion around the atomic limit, we treat the attractive potential in the broken-symmetry Hartree-Fock scheme and analyze which of the possible symmetries of the superconducting order parameter leads to the highest possible transition temperature in the case of a two-dimensional square lattice. For values of the on-site f-repulsion large compared to the hopping amplitude, a suppression of any possible superconducting phase occurs, regardless of the symmetry of the order parameter.

Refine search results

Point Contact Studies of High T_{c} Superconductors

Non-Linear Processes in 1D Quantum Spin Ordered System under Strong Magnetic Field Pulse

Self-Induced Transparency in 1D Magnetics

Anomalous Superconductivity and Antiferromagnetism in the U(Pt,Pd)_3 System

Heavy Fermion Superconductor Order Parameter in High Magnetic Field

Universal Scaling of Basic Properties of the Heavy-Fermion Superconductors

Magnetism in UCo_{0.88}Ru_{0.12}Ge Studied by Polarized Neutrons

Theory of Unconventional Superconductivity in Strongly Correlated Systems: Real Space Pairing and Statistically Consistent Mean-Field Theory - in Perspective

On Magnetic Impurities in Gapless Fermi Systems

Superconductivity in Anderson Lattice Model