arXiv subjects

L. N. Bulaevskii

Publications and source records attributed to L. N. Bulaevskii.

At least 37 records · Page 2Linked to original sources

arXiv2002

Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions

We compute the frequency and magnetic field dependencies of the reflectivity $R(ω)$ in layered superconductors with two alternating intrinsic Josephson junctions with different critical current densities and quasiparticle conductivities for the electric field polarized along the c-axis. The parameter $α$ describing the electronic compressibility of the layers and the charge coupling of neighboring junctions was extracted for the SmLa$_{1-x}$Sr$_{x}$CuO$_{4-δ}$ superconductor from two independent optical measurements, the fit of the loss function $L(ω)$ at zero magnetic field and the magnetic field dependence of the peak positions in $L(ω)$. The experiments are consistent with a free electron value for $α$ near the Josephson plasma frequencies.

cond-mat.supr-con↗

arXiv2002

Optical Properties of Crystals with Spatial Dispersion: Josephson Plasma Resonance in Layered Superconductors

We derive the transmission coefficient, $T(ω)$, for grazing incidence of crystals with spatial dispersion accounting for the excitation of multiple modes with different wave vectors ${\bf k}$ for a given frequency $ω$. The generalization of the Fresnel formulas contains the refraction indices of these modes as determined by the dielectric function $ε(ω,{\bf k})$. Near frequencies $ω_e$, where the group velocity vanishes, $T(ω)$ depends also on an additional parameter determined by the crystal microstructure. The transmission $T$ is significantly suppressed, if one of the excited modes is decaying into the crystal. We derive these features microscopically for the Josephson plasma resonance in layered superconductors.

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arXiv2002

Coherent Tunneling between Elementary Conducting Layers in the NbSe$_3$ Charge-Density-Wave Conductor

Characteristic features of transverse transport along the $a^*$ axis in the NbSe$_3$ charge-density-wave conductor are studied. At low temperatures, the $I$-$V$ characteristics of both layered structures and NbSe$_3$-NbSe$_3$ point contacts exhibit a strong peak of dynamic conductivity at zero bias voltage. In addition, the $I$-$V$ characteristics of layered structures exhibit a series of peaks that occur at voltages equal to multiples of the double Peierls gap. The conductivity behavior observed in the experiment resembles that reported for the interlayer tunneling in Bi-2212 high-$T_c$ superconductors. The conductivity peak at zero bias is explained using the model of almost coherent interlayer tunneling of the charge carriers that are not condensed in the charge density wave.

cond-mat.supr-con↗

arXiv2001

Evidence for LineLike Vortex Liquid Phase in Tl$_2$Ba$_2$CaCu$_2$O$_8$ Probed by the Josephson Plasma Resonance

We measured the Josephson plasma resonance (JPR) in optimally doped Tl$_2$Ba$_2$CaCu$_2$O$_{8+δ}$ thin films using terahertz time-domain spectroscopy in transmission. The temperature and magnetic field dependence of the JPR frequency shows that the c-axis correlations of pancake vortices remain intact at the transition from the vortex solid to the liquid phase. In this respect Tl$_2$Ba$_2$CaCu$_2$O$_{8+δ}$ films, withanisotropy parameter $γ\approx 150$, are similar to the less anisotropic YBa$_2$Cu$_3$O$_{7-δ}$ $(γ\approx 8)$ rather than to the most anisotropic Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystals $γ\geq 500$).

cond-mat.supr-con↗

arXiv2001

C-axis Josephson Plasma Resonance Observed in Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8}$ Superconducting Thin Films using Terahertz Time-Domain Spectroscopy

We have unambiguously observed the c-axis Josephson Plasma Resonance (JPR) in high-T$_{c}$ cuprate Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8}$ superconducting thin films employing terahertz time-domain spectroscopy in transmission as a function of temperature in zero magnetic field. These are the first measurements of the JPR temperature dependence of a high-$T_{c}$ material in transmission. With increasing temperature, the JPR shifts from 705 GHz at 10 K to $\sim$170 GHz at 98 K corresponding to a c-axis penetration depth increasing from 20.1$\pm$0.6 $μ$m to 84$\pm$9 $μ$m. The linewidth of the JPR peak increases with temperature, indicative of an increase in the quasiparticle scattering rate. We have probed the onset of the c-axis phase coherence to $\sim$0.95T$_{c}$. The JPR vanishes above T$_{c}$ as expected.

cond-mat.supr-con↗

arXiv2000

Josephson Coupling, Phase Correlations, and Josephson Plasma Resonance in Vortex Liquid Phase

Josephson plasma resonance has been introduced recently as a powerful tool to probe interlayer Josephson coupling in different regions of the vortex phase diagram in layered superconductors. In the liquid phase, the high temperature expansion with respect to the Josephson coupling connects the Josephson plasma frequency with the phase correlation function. This function, in turn, is directly related to the pair distribution function of the liquid. We develop a recipe to extract the phase and density correlation functions from the dependencies of the plasma resonance frequency $ω_p({\bf B})$ and the $c$ axis conductivity $σ_c({\bf B}) $ on the {\it ab}-component of the magnetic field at fixed {\it c} -component. Using Langevin dynamic simulations of two-dimensional vortex arrays we calculate density and phase correlation functions at different temperatures. Calculated phase correlations describe very well the experimental angular dependence of the plasma resonance field. We also demonstrate that in the case of weak damping in the liquid phase, broadening of the JPR line is caused mainly by random Josephson coupling arising from the density fluctuations of pancake vortices. In this case the JPR line has a universal shape, which is determined only by parameters of the superconductors and temperature.

cond-mat.supr-con↗

arXiv2000

Ferromagnetic Film on a Superconducting Substrate

We study the equilibrium domain structure and magnetic flux around a ferromagnetic (FM) film with perpendicular magnetization M_0 on a superconducting (SC) substrate. At 4πM_0 > 1. Here λ_L is the London penetration length. For 4πM_0 > H_{c1} and l_{N} in excess of about 35 λ_{L}, the domains are connected by SC vortices. We argue that pinning of vortices by magnetic domains in FM/SC multilayers can provide high critical currents.

cond-mat.supr-con↗

arXiv2000

Quasiparticle and Cooper Pair Tunneling in the Vortex State of Bi-2212

From measurements of the c-axis I-V characteristics of intrinsic Josephson junctions in Bi_2Sr_2CaCu_2O_{8+delta} (Bi-2212) mesas we obtain the field dependence (H || c) of the quasiparticle (QP) conductivity, sigma_q(H,T), and of the Josephson critical current density, J_c(H,T). The quasiparticle conductivity sigma_q(H) increases sharply with H and reaches a plateau at 0.05 T <H< 0.3 T. We explain such behavior by the dual effect of supercurrents around vortices. First, they enhance the QP DOS, leading to an increase of sigma_q with H at low H and, second, they enhance the scattering rate for specular tunneling as pancakes become disordered along the c-axis at higher H, leading to a plateau at moderate H.

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arXiv2000

Interlayer Tunneling of Quasiparticles and Cooper Pairs in Bi-2212 Single Crystal Whiskers

The interlayer tunneling has been studied on high quality Bi-2212 stacks of micron to the submicron lateral size. We found that low temperature and low voltage tunneling I-V characteristics can be self-consistently described by Fermi-liquid model for a d-wave superconductor with a significant contribution from coherent interlayer tunneling. The gap and pseudogap interplay with variation of temperature and magnetic field has been extracted from the I-V characteristics. We consider also the role of charging effects for submicron stacks.

cond-mat.supr-con↗

arXiv2000

Josephson coupling and plasma resonance in vortex crystal

We investigate the magnetic field dependence of the plasma resonance frequency in vortex crystal state. We find that low magnetic field induces a small correction to the plasma frequency proportional to the field. The slope of this linear field dependence is directly related to the average distance between the pancake vortices in the neighboring layers, the wandering length. This length is determined by both Josephson and magnetic couplings between layers. At higher fields the plasma frequency is suppressed collectively and is determined by elastic energy of the vortex lattice. Analyzing experimental data, we find that (i) the wandering length becomes comparable with the London penetration depth near T_{c}, (ii) at small melting fields (< 20G) the wandering length does not change noticeably at the melting transition demonstrating existence of the line liquid phase in this field range, and (iii) the self consistent theory of pancake fluctuations describes very well the field dependence of the Josephson plasma resonance frequency up to the melting point.

cond-mat.supr-con↗

arXiv1999

Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors

We consider the magnetic field dependence of the plasma resonance frequency in pristine and in irradiated Bi$_2$Sr$_2$CaCu$_2$O$_8$ crystals near $T_c$. At low magnetic fields we relate linear in field corrections to the plasma frequency to the average distance between the pancake vortices in the neighboring layers (wandering length). We calculate the wandering length in the case of thermal wiggling of vortex lines, taking into account both Josephson and magnetic interlayer coupling of pancakes. Analyzing experimental data, we found that (i) the wandering length becomes comparable with the London penetration depth near T$_{c}$ and (ii) at small melting fields ($< 20$ G) the wandering length does not change much at the melting transition. This shows existence of the line liquid phase in this field range. We also found that pinning by columnar defects affects weakly the field dependence of the plasma resonance frequency near $T_c$.

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arXiv1999

High-Field Quasiparticle Tunneling in Bi_2Sr_2CaCu_2O_8+delta: Negative Magnetoresistance in the Superconducting State

We report on the c-axis resistivity rho_c(H) in Bi_2Sr_2CaCu_2O_{8+δ} that peaks in quasi-static magnetic fields up to 60 T. By suppressing the Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity σ_c (H), we find that the negative slope of ρ_c(H) above the peak is due to quasiparticle tunneling conductivity σ_q(H) across the CuO_2 layers below H_{c2}. At high fields (a) σ_q(H) grows linearly with H, and (b) ρ_c(T) tends to saturate (sigma_c \neq 0) as T->0, consistent with the scattering at the nodes of the d-gap. A superlinear sigma_q(H) marks the normal state above T_c.

cond-mat.supr-con↗

arXiv1999

Interlayer Quasiparticle Transport in the Vortex State of Josephson Coupled Superconductors

We calculate the dependence of the interlayer quasiparticle conductivity, $σ_q$, in a Josephson coupled d-wave superconductor on the magnetic field B||c and the temperature T. We consider a clean superconductor with resonant impurity scattering and a dominant coherent interlayer tunneling. When pancake vortices in adjacent layers are weakly correlated at low T the conductivity increases sharply with B before reaching an extended region of slow linear growth, while at high T it initially decreases and then reaches the same linear regime. For correlated pancakes $σ_q$ increases much more strongly with the applied field.

cond-mat.supr-con↗

arXiv1999

Fluctuation broadening of plasma resonance line in the vortex liquid state of layered superconductors

The Josephson plasma resonance (JPR) provides a sensitive probe of vortex states in layered superconductors. We demonstrate that in the case of weak damping in the liquid phase, broadening of the JPR line is caused mainly by random Josephson coupling arising from the density fluctuations of pancake vortices. In this case the JPR line has the universal shape, which is determined only by parameters of the superconductors and temperature. This mechanism gives a natural explanation for the experimentally observed asymmetric lineshape. The tail at high frequencies arises due to mixing of the propagating plasma modes by random Josephson coupling, while the tail at small frequencies is caused by the localized plasma modes originating from a rare fluctuation suppression of the Josephson coupling in large areas.

cond-mat.supr-con↗

arXiv1999

The effect of an in-plane magnetic field on the interlayer transport of quasiparticles in layered superconductors

We consider the quasiparticle c-axis conductivity in highly anisotropic layered compounds in the presence of the magnetic field parallel to the layers. We show that at low temperatures the quasiparticle interlayer conductivity depends strongly on the orientation of the in-plane magnetic field if the excitation gap has nodes on the Fermi surface. Thus measurements of the angle-dependent c-axis (out-of-plane) magnetoresistance, as a function of the orientation of the magnetic field in the layers, provide information on the momentum dependence of the superconducting gap (or pseudogap) on the Fermi surface. Clean and highly anisotropic layered superconductors seem to be the best candidates for probing the existence and location of the nodes on the Fermi surface.

cond-mat.supr-con↗

arXiv1999

Interlayer Transport of Quasiparticles and Cooper pairs in Bi2Sr2CaCu2O8+y Superconductors

We study the c-axis transport of stacked, intrinsic junctions in Bi2Sr2CaCu2O8+y single crystals, fabricated by the double-sided ion beam processing technique from single crystal whiskers. Measurements of the I-V characteristics of these samples allow us to obtain the temperature and voltage dependence of the quasiparticle c-axis conductivity in the superconducting state, the Josephson critical current, and the superconducting gap. We show that the BCS d-wave model in the clean limit for resonant impurity scattering with a significant contribution from coherent interlayer tunneling, describes satisfactorily the low temperature and low energy c-axis transport of both quasiparticles and Cooper pairs.

cond-mat.supr-con↗

arXiv1999

Angular Dependence of C-Axis Magnetoresistance in Bi-2212 Single Crystals With Columnar Defects

We measured the angular dependence of the c-axis magnetoresistance rho_c(B) of Bi-2212 irradiated with heavy ions. At temperatures near 68 K the scaling of rho_c(B) with the c-axis magnetic field component B_perp is broken and the in-plane field, B_parallel, affects rho_c. At this temperature, at a specific field B_cr \approx B_Phi/2, magnetoresistance becomes independent of field orientation. This crossing point allows us to estimate the correlation length L of pancake positions along the c axis. We find L/s is about 100 at B=B_cr, where s is the interlayer spacing. This provides evidence of strong enhancement of pancake alignment in the vortex liquid in crystals with columnar defects.

cond-mat.supr-con↗

arXiv1999

Structure of vortex liquid phase in irradiated BSCCO(2212) crystals

The c-axis resistivity in irradiated and in pristine BSCCO(2212) crystals is measured as a function of the in-plane magnetic field component at fixed out-of-plane component B_\perp in the vortex liquid phase at T=67 K. From this data we extract the dependence of the phase difference correlation length inside layers on B_\perp and estimate the average length of pieces of vortex lines confined inside columnar defects as a function of the filling factor f=B_\perp / B_ϕ. The maximum length, about 15 interlayer distances, is reached near f=0.35.

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