arXiv subjects

M. R. Trunin

Publications and source records attributed to M. R. Trunin.

16 recordsLinked to original sources

arXiv2018

Local impedance on a rough surface of a chiral $p$-wave superconductor

We develop a self-consistent approach for calculating the local impedance at a rough surface of a chiral $p$-wave superconductor. Using the quasiclassical Eilenberger-Larkin-Ovchinnikov formalism, we numerically find the pair potential, pairing functions, and the surface density of states taking into account diffusive electronic scattering at the surface. The obtained solutions are then employed for studying the local complex conductivity and surface impedance in the broad range of microwave frequencies (ranging from subgap to above-gap values). We identify anomalous features of the surface impedance caused by generation of odd-frequency superconductivity at the surface. The results are compared with experimental data for Sr$_2$RuO$_4$ and provide a microscopic explanation of the phenomenological two-fluid model suggested earlier to explain anomalous features of the microwave response in this material.

cond-mat.supr-con↗

arXiv2011

Normal state resistivity of Ba$_{1-x}$K$_x$Fe$_2$As$_2$: evidence for multiband strong-coupling behavior

We present theoretical analysis of the normal state resistivity in multiband superconductors in the framework of Eliashberg theory. The results are compared with measurements of the temperature dependence of normal state resistivity of high-purity Ba$_{0.68}$K$_{0.32}$Fe$_{2}$As$_{2}$ single crystals with the highest reported transition temperature $T_c$ = 38.5 K. The experimental data demonstrate strong deviations from the Bloch-Grüneisen behavior, namely the tendency to saturation of the resistivity at high temperatures. The observed behavior of the resistivity is explained within the two band scenario when the first band is strongly coupled and relatively clean, while the second band is weakly coupled and is characterized by much stronger impurity scattering.

cond-mat.supr-con↗

arXiv2009

Competition and coexistence of antiferromagnetism and superconductivity in RBa_2Cu_3O_{6+x} (R = Lu, Y) single crystals

We use c-axis resistivity and magnetoresistance measurements to study the interplay between antiferromagnetic (AF) and superconducting (SC) ordering in underdoped RBa_2Cu_3O_{6+x} (R = Lu, Y) single crystals. Both orders are found to emerge from an anisotropic 3D metallic state, upon which antiferromagnetism opposes superconductivity by driving the doped holes towards localization. Despite the competition, the superconductivity sets in before the AF order is completely destroyed and coexists with latter in a certain range of hole doping. We find also that strong magnetic fields affect the AF-SC interplay by both suppressing the superconductivity and stabilizing the Neel order.

cond-mat.supr-con↗

arXiv2008

Magnetic-field induced superconductor-antiferromagnet transition in lightly doped RBa_2Cu_3O_{6+x} (R = Lu, Y) crystals

The remarkable sensitivity of the c-axis resistivity and magnetoresistance in cuprates to the spin ordering is used to clarify the doping-induced transformation from an antiferromagnetic (AF) insulator to a superconducting (SC) metal in RBa_2Cu_3O_{6+x} (R = Lu, Y) single crystals. The established phase diagram demonstrates that the AF and SC regions apparently overlap: the superconductivity in RBa_2Cu_3O_{6+x}, in contrast to La_{2-x}Sr_xCuO_4, sets in before the long-range AF order is completely destroyed by hole doping. Magnetoresistance measurements of superconducting crystals with low T_c<15-20 K give a clear view of the magnetic-field induced superconductivity suppression and recovery of the long-range AF state. What still remains to be understood is whether the AF order actually persists in the SC state or just revives when the superconductivity is suppressed, and, in the former case, whether the antiferromagnetism and superconductivity reside in nanoscopically separated phases or coexist on an atomic scale.

cond-mat.supr-con↗

arXiv2006

Observation of a Transition from BCS to HTSC-like Superconductivity in Ba_{1-x}K_xBiO_3 Single Crystals

A study of temperature dependences of the upper critical field B_{c2}(T) and surface impedance Z(T)=R(T)+iX(T) in Ba_{1-x}K_xBiO_3 single crystals that have transition temperatures in the range 6 < T_c < 32 K (roughly 0.6>x>0.4) reveals a transition from BCS to unusual type of superconductivity. B_{c2}(T) curves corresponding to the crystals that have T_c>20 K have positive curvature (like in some HTSC), and those of the crystals with T_c<15 K fall on the usual Werthamer-Helfand-Hohenberg curve. R(T) and X(T) dependences of the crystals with T_c~30 K and T_c~11 K are respectively linear (like in HTSC) and exponential (BCS) in the temperature range T << T_c. The experimental results are discussed in connection with the extended saddle point model by Abrikosov.

cond-mat.supr-con↗

arXiv2005

Microwave Response of V3Si Single Crystals: Evidence for Two-Gap Superconductivity

The investigation of the temperature dependences of microwave surface impedance and complex conductivity of V3Si single crystals with different stoichiometry allowed to observe a number of peculiarities which are in remarkable contradiction with single-gap Bardeen-Cooper-Schrieffer theory. At the same time, they can be well described by two-band model of superconductivity, thus strongly evidencing the existence of two distinct energy gaps with zero-temperature values Delta1~1.8Tc and Delta2~0.95Tc in V3Si.

cond-mat.supr-con↗

arXiv2003

Pseudogap in the microwave response of YBa_2Cu_3O_{7-x}

The in-plane and out-of-plane surface impedance and microwave conductivity components of one and the same YBa_2Cu_3O_{7-x} (0.07\le x\le 0.47) single crystal are determined in the wide ranges of temperature T and carrier concentration p in CuO_2 planes. The following features of the superfluid density n_s(T,p)\proptoλ_{ab}^{-2}(T,p) are observed at T<Tc/2 and 0.078\le p\le 0.16: (i) n_s(0,p) depends linearly on p, (ii) the derivative |dn_s(T,p)/dT|_{T\to 0} depends on p slightly in the optimally and moderately doped regions (0.10<p\le 0.16); however, it rapidly increases with p further lowering and (iii) the latter finding is accompanied by the linear low-temperature dependence Δn_s(T)\propto(-T) changing to Δn_s(T)\propto(-\sqrt{T}). For optimum oxygen content the temperature dependence of the normalized imaginary part of the c-axis conductivity λ_c^2(0)/λ_c^2(T) is found to be strikingly similar to that of λ_{ab}^2(0)/λ_{ab}^2(T) and becomes more convex with p lowering. λ_c^{-2}(0,p) values are roughly proportional to the normal state conductivities σ_c(T_c,p) along the c-axis. All these properties can be treated in the framework of d-density wave order of pseudogap.

cond-mat.supr-con↗

arXiv2003

Superfluid density in the underdoped YBa_2Cu_3O_{7-x}: Evidence for d-density wave order of pseudogap

The investigation of the penetration depth λ_{ab}(T,p) in YBa_2Cu_3O_{7-x} crystals allowed to observe the following features of the superfluid density n_s(T,p)\propto λ_{ab}^{-2}(T,p) as a function of temperature T<Tc/2 and carrier concentration 0.078\le p\le 0.16 in CuO_2 planes: (i) n_s(0,p) depends linearly on p, (ii) the derivative |dn_s(T,p)/dT|_{T\to 0} depends on p slightly in the optimally and moderately doped regions (0.10<p\le 0.16); however, it rapidly increases with p further lowering and (iii) the latter finding is accompanied by the linear low-temperature dependence [-Δn_s(T)]\propto T changing to [-Δn_s(T)]\propto \sqrt{T}. All these peculiarities can be treated in the framework of d-density wave scenario of electronic processes in underdoped high-Tc materials.

cond-mat.supr-con↗

arXiv2003

Anisotropy of microwave conductivity of YBaCuO in superconducting and normal states: Crossover 3D-2D

Imaginary part of the microwave conductivity σ''(T T_c) along (σ_{ab}'' and ρ_{ab}) and perpendicular to (σ_c'' and ρ_c) cuprate ab-planes of YBa_2Cu_3O_{7-x} crystal were measured in the temperature range 5\leq T \leq 200 K, having varied the oxygen doping level x in the crystal from 0.07 to 0.47. The superconducting state was found to have the dependences σ_{ab}''(T)/σ_{ab}''(0) and σ_c''(T)/σ_c''(0) coincide in the optimally doped (x=0.07) crystal. With the increase of x the dependences σ_c''(T)/σ_c''(0) have smaller slope at T 0.07) takes place. This is proved by both estimating minimum metallic c-conductivity and maximum tunneling c-conductivity and quantitatively comparing the measured dependences ρ_c(T) with the ones calculated in the polaron model of quasiparticles' c-transport.

cond-mat.supr-con↗

arXiv2003

Microwave surface impedance anisotropy of YBa$_2$Cu$_3$O$_x$ single crystals with different oxygen content

The linear microwave response of ultra high-quality YBa$_2$Cu$_3$O$_x$ single crystals grown in BaZrO$_3$ crucibles is measured at 9.4 GHz in rf magnetic fields parallel and perpendicular to the $ab$-plane in the temperature range 5$\leq T\leq 200$ K. Having found the analytic solution for the magnetic field distribution on the sample surface we determine both the surface impedance $Z_{ab}=R_{ab}+iX_{ab}$ in the $ab$-plane and $Z_c=R_c+iX_c$ along c-axis of the crystals. For the first time the evolution of the $Z_{ab}(T)$ and $Z_c(T)$ dependences on the same sample and in a wide range of oxygen content is obtained. For $x=6.95$ (optimum oxygen content) the temperature dependence of the imaginary part $σ_{c}''(T)/σ_{c}''(0)$ of the c-axis conductivity is found to be strikingly similar to that of $σ_{ab}''(T)/σ_{ab}''(0)$ and becomes more convex with $x$ lowering.

cond-mat.supr-con↗

arXiv2003

Surface impedance anisotropy of YBa$_2$Cu$_3$O$_{6.95}$ single crystals: electrodynamic basis of the measurements

An electrodynamic technique is developed for determining the components of surface impedance and complex conductivity tensors of HTSC single crystals on the basis of measured quantities of a quality factor and a resonator frequency shift. A simple formula is obtained for a geometrical factor of a crystal in the form of a plate with dimensions $b\gg a>c$ in a microwave magnetic field ${\bf H_ω}\perp ab$. To obtain the c-axis complex conductivity from measurements at ${\bf H_ω}\parallel ab$ we propose a procedure which takes account of sample size effects. With the aid of the technique involved temperature dependences of all impedance and conductivity tensors components of YBa$_2$Cu$_3$O$_{6.95}$ single crystal, grown in BaZrO$_3$ crucible, are determined at a frequency of $f=9.4$ GHz in its normal and superconducting states. All of them proved to be linear at $T<T_c/2$, and their extrapolation to zero temperature gives the values of residual surface resistance $R_{ab}(0)\approx 40$ $μΩ$ and $R_c(0)\approx 0.8$ m$Ω$ and magnetic field penetration depth $λ_{ab}(0)\approx 150$ nm and $λ_c(0)\approx 1.55$ $μ$m.

cond-mat.supr-con↗

arXiv2002

Characteristic features of the temperature dependence of the surface impedance in polycrystalline MgB$_2$ samples

The real $R_s(T)$ and imaginary $X_s(T)$ parts of the surface impedance $Z_s(T)=R_s(T)+iX_s(T)$ in polycrystalline MgB$_2$ samples of different density with the critical temperature $T_c\approx 38$ K are measured at the frequency of 9.4 GHz and in the temperature range $5\le T<200$ K. The normal skin-effect condition $R_s(T)=X_s(T)$ at $T\ge T_c$ holds only for the samples of the highest density with roughness sizes not more than 0.1 $μ$m. For such samples extrapolation $T\to 0$ of the linear at $T<T_c/2$ temperature dependences $λ_L(T)=X_s(T)/ωμ_0$ and $R_s(T)$ results in values of the London penetration depth $λ_L(0)\approx 600$ Åand residual surface resistance $R_{res}\approx 0.8$ m$Ω$. In the entire temperature range the dependences $R_s(T)$ and $X_s(T)$ are well described by the modified two-fluid model.

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↗

arXiv1999

Phenomenological description of the microwave surface impedance and complex conductivity of high-$T_c$ single crystals

Measurements of the microwave surface impedance $Z_s(T)=R_s(T)+iX_s(T)$ and of the complex conductivity $σ_s(T)$ of high-quality, high-$T_c$ single crystals of YBCO, BSCCO, TBCCO, and TBCO are analyzed. Experimental data of $Z_s(T)$ and $σ_s(T)$ are compared with calculations based on a modified two-fluid model which includes temperature-dependent quasiparticle scattering and a unique temperature variation of the density of superconducting carriers. We elucidate agreement as well as disagreement of our analysis with the salient features of the experimental data. Existing microscopic models are reviewed which are based on unconventional symmetry types of the order parameter and on novel mechanisms of quasiparticle relaxation.

cond-mat.supr-con↗