arXiv subjects

M. Daumens

Publications and source records attributed to M. Daumens.

4 recordsLinked to original sources

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↗

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↗