Collective responses of Bi-2212 stacked junction to 100 GHz microwave radiation under magnetic field oriented along the c-axis

We studied a response of Bi-2212 mesa type structures to 100 GHz microwave radiation. We found that applying magnetic field of about 0.1 T across the layers enables to observe collective Shapiro step response corresponding to a synchronization of all 50 intrinsic Josephson junctions (IJJ) of the mesa. At high microwave power we observed up to 10th harmonics of the fundamental Shapiro step. Besides, we found microwave induced flux-flow step position of which is proportional to the square root of microwave power and that can exceed at high enough powers 1 THz operating frequency of IJJ oscillations.Comment: 11 pages including 5 figures, accepted for publication in JETP Letter

Electronic excitations and electron-phonon coupling in bulk graphite through Raman scattering in high magnetic fields

We use polarized magneto-Raman scattering to study purely electronic excitations and the electron-phonon coupling in bulk graphite. At a temperature of 4.2 K and in magnetic fields up to 28 T we observe $K$-point electronic excitations involving Landau bands with $\Delta |n|=0$ and with $\Delta |n|=\pm2$ that can be selected by controlling the angular momentum of the excitation laser and of the scattered light. The magneto-phonon effect involving the $E_{2g}$ optical phonon and $K$-point inter Landau bands electronic excitations with $\Delta |n|=\pm1$ is revealed and analyzed within a model taking into account the full $k_z$ dispersion. These polarization resolved results are explained in the frame of the Slonczewski-Weiss-McClure (SWM) model which directly allows to quantify the electron-hole asymmetry.Comment: 13 pages, 10 figure

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+\delta} that peaks in quasi-static magnetic fields up to 60 T. By suppressing the Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity \sigma_c (H), we find that the negative slope of \rho_c(H) above the peak is due to quasiparticle tunneling conductivity \sigma_q(H) across the CuO_2 layers below H_{c2}. At high fields (a) \sigma_q(H) grows linearly with H, and (b) \rho_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.Comment: 4p., 5 fig. (.eps), will be published in Phys. Rev. Let

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.Comment: 4 pages, 4 figure

Dynamic structure selection and instabilities of driven Josephson lattice in high-temperature superconductors

We investigate the dynamics of the Josephson vortex lattice in layered high-T$_{c}$ superconductors at high magnetic fields. Starting from coupled equations for superconducting phases and magnetic field we derive equations for the relative displacements [phase shifts] between the planar Josephson arrays in the layers. These equations reveal two families of steady-state solutions: lattices with constant phase shifts between neighboring layers, starting from zero for a rectangular configuration to $\pi$ for a triangular configuration, and double-periodic lattices. We find that the excess Josephson current is resonantly enhanced when the Josephson frequency matches the frequency of the plasma mode at the wave vector selected by the lattice structure. The regular lattices exhibit several kinds of instabilities. We find stability regions of the moving lattice in the plane lattice structure - Josephson frequency. A specific lattice structure at given velocity is selected uniquely by boundary conditions, which are determined by the reflection properties of electromagnetic waves generated by the moving lattice. With increase of velocity the moving configuration experiences several qualitative transformations. At small velocities the regular lattice is stable and the phase shift between neighboring layers smoothly decreases with increase of velocity, starting from $\pi$ for a static lattice. At the critical velocity the lattice becomes unstable. At even higher velocity a regular lattice is restored again with the phase shift smaller than $\pi/2$. With increase of velocity, the structure evolves towards a rectangular configuration.Comment: 28 pages, 12 figures, submitted to Phys. Rev.

d-like Symmetry of the Order Parameter and Intrinsic Josephson Effects in Bi2212 Cross-Whisker Junctions

An intrinsic tunnel junction was made using two Bi-2212 single crystal whiskers. The two whiskers with a cross-angle were overlaid at their c-planes and connected by annealing. The angular dependence of the critical current density along the c-axis is of the d-wave symmetry. However, the angular dependence is much stronger than that of the conventional d-wave. Furthermore, the current vs. voltage characteristics of the cross-whiskers junctions show a multiple-branch structure at any cross-angle, indicating the formation of the intrinsic Josephson junction array.Comment: 4 pages PDF fil

Aharonov-Anandan Effect Induced by Spin-Orbit Interaction and Charge-Density-Waves in Mesoscopic Rings

We study the spin-dependent geometric phase effect in mesoscopic rings of charge-density-wave(CDW) materials. When electron spin is explicitly taken into account, we show that the spin-dependent Aharonov-Casher phase can have a pronounced frustration effects on such CDW materials with appropriate electron filling. We show that this frustration has observable consequences for transport experiment. We identify a phase transition from a Peierls insulator to metal, which is induced by spin-dependent phase interference effects. Mesoscopic CDW materials and spin-dependent geometric phase effects, and their interplay, are becoming attractive opportunities for exploitation with the rapid development of modern fabrication technology.Comment: 5 pages, 6 figures, to appear in Phys.Rev.B(Aug.15, 1998

NbSe3: Effect of Uniaxial Stress on the Threshold Field and Fermiology

We have measured the effect of uniaxial stress on the threshold field ET for the motion of the upper CDW in NbSe3. ET exhibits a critical behavior, ET ~ (1 - e/ec)^g, wher e is the strain, and ec is about 2.6% and g ~ 1.2. This ecpression remains valid over more than two decades of ET, up to the highest fields of about 1.5keV/m. Neither g nor ec is very sensitive to the impurity concentraction. The CDW transition temperature Tp decreases linearly with e at a rate dTp/de = -10K/%, and it does not show any anomaly near ec. Shubnikov de-Haas measurements show that the extremal area of the Fermi surface decreases with increasing strain. The results suggest that there is an intimate relationship between pinning of the upper CDW and the Fermiology of NbSe3.Comment: 4 pages, 5 figure

Effects of an in-plane magnetic field on c-axis sum rule and superfluid density in high-TcT_{c} cuprates

In layered cuprates, the application of an in-plane magnetic field $({\bf H})$ changes the c-axis optical sum rule and superfluid density $\rho_{s}$. For pure incoherent c-axis coupling, ${\bf H}$ has no effect on either quantities but it does if an additional coherent component is present. For the coherent contribution, different characteristic variations on ${\bf H}$ and on temperature result from the constant part $(t_{\perp})$ of the hopping matrix element and from the part $(t_{\phi})$ which has zero on the diagonal of the Brillouin zone. Only the constant part $(t_{\perp})$ leads to a dependence on the direction of ${\bf H}$ as well as on its magnitude.Comment: 3 figure