arXiv subjects

A. Buzdin

Publications and source records attributed to A. Buzdin.

45 records · Page 3Linked to original sources

arXiv2004

Influence of s-d scattering on the electron density of states in ferromagnet/superconductor bilayer

We study the dependence of the electronic density of states (DOS) on the distance from the boundary for a ferromagnet/superconductor bilayer. We calculate the electron density of states in such structure taking into account the two-band model of the ferromagnet (FM) with conducting s and localized d electrons and a simple s-wave superconductor (SC). It is demonstrated that due to the electron s-d scattering in the ferromagnetic layer in the third order of s-d scattering parameter the oscillation of the density of states has larger period and more drastic decrease in comparison with the oscillation period for the electron density of states in the zero order.

cond-mat.other↗

arXiv2003

Atomic thickness hybrid F/S/F structures

We propose an exactly solvable model to describe the properties of atomic thickness hybrid ferromagnet-superconductor-ferromagnet (F/S/F) structures. We show that the superconducting critical temperature is always higher for antiparallel orientation of the ferromagnetic moments. However at low temperature the superconducting gap occurs to be larger for parallel orientation of the ferromagnetic moments. This leads to a peculiar temperature dependence of the proximity effect in (F/S/F) structures.

cond-mat.supr-con↗

arXiv2003

Periodic alternating $0,π$-junction structures as realization of $ϕ$-Josephson junctions

We consider the properties of a periodic structure consisting of small alternating 0- and pi- Josephson junctions. We show that depending on the relation between the lengths of the individual junctions, this system can be either in the homogeneous or in the phase-modulated state. The modulated phase appears via a second order phase transition when the mismatch between the lengths of the individual junctions exceeds the critical value. The screening length diverges at the transition point. In the modulated state, the equilibrium phase difference in the structure can take any value from -pi to pi (phi-junction). The current-phase relation in this structure has very unusual shape with two maxima. As a consequence, the field dependence of the critical current in a small structure is very different from the standard Fraunhofer dependence. The Josephson vortex in a long structure carries partial magnetic flux, which is determined by the equilibrium phase.

cond-mat.supr-con↗

arXiv2002

Theoretical description of the ferromagnetic $π$-junctions near the critical temperature

The theory of ferromagnetic Pi-junction near the critical temperature is presented. It is demonstrated that in the dirty limit the modified Usadel equation adequately describes the proximity effect in ferromagnets. To provide the description of an experimentally relevant situation, oscillations of the Josephson critical current are calculated as a function of ferromagnetic layer thickness for different transparencies of the superconductor-ferromagnet interfaces.

cond-mat.supr-con↗

arXiv2002

Thermodynamic properties of ferromagnetic/superconductor/ferromagnetic nanostructures

The theoretical description of the thermodynamic properties of ferromagnetic/superconductor/ferromagnetic (F/S/F) systems of nanoscopic scale is proposed. Their superconducting characteristics strongly depend on the mutual orientation of the ferromagnetic layers. In addition, depending on the transparency of S/F interfaces, the superconducting critical temperature can exhibit four different types of dependences on the thickness of the F-layer. The obtained results permit to give some practical recommendations for the spin-valve effect experimental observation. In this spin-valve sandwich, we also expect a spontaneous transition from parallel to anti-parallel ferromagnetic moment orientation, due to the gain in the superconducting condensation energy.

cond-mat.supr-con↗

arXiv2002

New superconducting phases in field-induced organic superconductor lambda-(BETS)2FeCl4

We derive the parallel upper critical field, Hc2, as a function of the temperature T in quasi-2D organic compound lambda-(BETS)2FeCl4, accounting for the formation of the nonuniform LOFF state. To further check the 2D LOFF model we propose to study the Hc2(T) curve at low T in tilted fields, where the vortex state is described by the high Landau level functions characterized by the index n. We predict a cascade of first order transitions between vortex phases with different n, between phases with different types of the symmetry at given n and the change of the superconducting transition from the second order to the first order as FeCl4 ions are replaced partly by GaCl4 ions.

cond-mat.supr-con↗

arXiv2000

Triple approach to determination of the c-axis penetration depth in BSCCO crystals

The c-axis penetration depth $λ_c$ in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO) single crystals as a function of temperature has been determined using three high-frequency techniques, namely: (i) measurements of the ac-susceptibility at a frequency of 100 kHz for different sample alignments with respect to the ac magnetic field; (ii) measurements of the surface impedance in both superconducting and normal states of BSCCO crystals at 9.4 GHz; (iii) measurements of the surface barrier field $H_J(T)\propto 1/λ_c(T)$ at which Josephson vortices penetrate into the sample. Careful analysis of these measurements, including both numerical solution of the electrodynamic problem of the magnetic field distribution in an anisotropic plate at an arbitrary temperature and influence of defects in the sample, has allowed us to estimate $λ_c(0)\approx 50 μ$m in BSCCO crystals overdoped with oxygen ($T_c\approx 84$ K) and $λ_c(0)\approx 150 μ$m at the optimal doping level ($T_c\approx 90$ K). The results obtained by different techniques are in reasonable agreement.

cond-mat.supr-con↗

arXiv2000

Penetration of Josephson vortices and measurement of the c-axis penetration depth in $Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}$: Interplay of Josephson coupling, surface barrier and defects

The first penetration field H_{J}(T) of Josephson vortices is measured through the onset of microwave absorption in the locked state, in slightly overdoped $\rm{Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}}$ single crystals (T_{c} ~ 84 K). The magnitude of H_{J}(T) is too large to be accounted for by the first thermodynamic critical field H_{c1}(T). We discuss the possibility of a Bean-Livingston barrier, also supported by irreversible behavior upon flux exit, and the role of defects, which relates H_{J}(T) to the c-axis penetration depth $λ_{c}(T)$. The temperature dependence of the latter, determined by a cavity perturbation technique and a theoretical estimate of the defect-limited penetration field are used to deduce from H_{J}(T) the absolute value of $λ_{c}(0)=(35 \pm 15) μm$.

cond-mat.supr-con↗

arXiv2000

c-axis penetration depth in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystals measured by ac-susceptibility and cavity perturbation technique

The $c$-axis penetration depth $Δλ_c$ in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO) single crystals as a function of temperature has been determined using two techniques, namely, measurements of the ac-susceptibility at a frequency of 100 kHz and the surface impedance at 9.4 GHz. Both techniques yield an almost linear function $Δλ_c(T)\propto T$ in the temperature range T<0.5 T_c. Electrodynamic analysis of the impedance anisotropy has allowed us to estimate $λ_c(0)\approx 50 μ$m in BSCCO crystals overdoped with oxygen ($T_c\approx 84$ K) and $λ_c(0)\approx 150 μ$m at the optimal doping level ($T_c\approx 90$ K).

cond-mat.supr-con↗