arXiv subjects

A. A. Zhukov

Publications and source records attributed to A. A. Zhukov.

44 records · Page 3Linked to original sources

arXiv2003

Suppression of 2D superconductivity by the magnetic field: quantum corrections vs superconductor-insulator transition

Magnetotransport of superconducting Nd_{2-x}Ce_xCuO_{4+y} (NdCeCuO) films is studied in the temperature interval 0.3-30 K. The microscopic theory of the quantum corrections to conductivity, both in the Cooper and in the diffusion channels, qualitatively describes the main features of the experiment including the negative magnetoresistance in the high field limit. Comparison with the model of the field-induced superconductor-insulator transition (SIT) is included and a crossover between these two theoretical approaches is discussed.

cond-mat.str-el↗

arXiv2002

Lock-in to commensurate states induced by a periodic array of nanoscale anti-dots in Nb superconductor

We study the interactions of the vortex lattice with a periodic square array of holes in a superconducting Nb film. Using high resolution magnetic field measurements of electrical losses, extremely narrow states with a magnetic field width reaching 1% of the matching field value are found at the commensurate points. They are accompanied by pronounced harmonic generation in response to ac modulation of the magnetic field or current. We relate these sharp anomalies to a locked commensurate state of the Mott insulator type.

cond-mat.supr-con↗

arXiv2001

Microwave Power, DC Magnetic Field, Frequency and Temperature Dependence of the Surface Resistance of MgB2

The microwave power, dc magnetic field, frequency and temperature dependence of the surface resistance of MgB2 films and powder samples were studied. Sample quality is relatively easy to identify by a number of characteristics, the most clear being the breakdown in the omega squared law for poor quality samples. Analysis of the experimental data suggests the most attractive procedure for high quality film growth for technical applications.

cond-mat.supr-con↗

arXiv2001

Temperature dependence of the microwave surface impedance measured on different kinds of MgB$_2$ samples

In this paper we present the results of measurements of the microwave surface impedance of a powder sample and two films of MgB$_2$. One film has $T_c=30$ K and is not textured, the other is partially c-axis orientated with $T_c=38$ K. These samples show different types of temperature dependence of the field penetration depth: linear for the powder sample, exponential with $Δ/kT_c<1.76$ (film with $T_c=30$ K) and strong coupling behaviour with $Δ/kT_c\sim 2.25$ (film with $T_c=38$ K). The results are well described in terms of an anisotropic gap model or presence of a slightly deficient MgB$_2$ phase. The data set for all samples - taken as a whole cannot be fitted into a two gap scenario.

cond-mat.supr-con↗

arXiv2001

Microwave Surface Resistance in MgB2

Measurements of the temperature dependence of the surface resistance at 3 GHz of 100 micron size grains of MgB_2 separated powder are presented and discussed. The microwave surface resistance data is compared to experimental results of Nb, Bi_2Sr_2CaCu_2O_{8+δ} (BSCCO) and theoretical predictions of s-wave weak coupling electron-phonon theory (BCS).

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↗