Fiske steps studied by flux-flow resistance oscillation in a narrow stack ofBi2Sr2CaCu2O8

Abstract

We have experimentally investigated the fluxon dynamics in a narrow Bi2Sr2CaCu2O 8+d stack with junction length L ∼1.8 µm. As an evidence of high-frequency excitation by a collective cavity mode, under an (in-plane) external magnetic field, the current-voltage characteristics show prominent Fiske steps with the corresponding resonance frequencies of 75-305 GHz. Further study of flux-flow resistance oscillation with various c-axis currents clarifies the correlation with Fiske steps by distinguishing two different regions i.e., static flux-flow region at low bias current level and dynamic Fiske step region at high bias current level. PACS numbers: 72.30.+q, 74.25.Qt, 85.25.Cp In stacked Bi 2 Sr 2 CaCu 2 O 8+d (BSCCO) intrinsic Josephson junctions (IJJs), the mutual interaction between junctions is expected since the superconducting layers, with the layer thickness d = 0.3 nm, are much thinner than the London penetration depth λ L = 170 nm 1 . Under the applied magnetic field parallel to the layers, Josephson vortices in a stack form lattice configurations that depend on a constant phase shift between neighboring layers, ranging from 0 for the rectangular lattice to π for the triangular lattice (see Fig. 1 (a))2,3,4 . Under the appropriate conditions, the fluxon lattice will excite the two-dimensional cavity modes in N stacked junctions, leading to the emission of electromagnetic wave with characteristic frequency f nm ≈ mc n /2L (c n is the phase velocity of electromagnetic wave, L is the junction length, m (=1, 2, 3,. . . ) denotes L-direction mode, and n (=1, 2, 3,. . . N ) denotes the stacking direction mode)5 . The c n is given bywith the Josephson penetration depth λ J , the coupling parameter S, the junction number N and the Josephson plasma frequency ω pl 1,2,5 . Among the N different modes along the stacking direction, the mode with the lowest velocity c N is usually stimulated by a triangular vortex lattice; while for the mode with the highest velocity c 1 , a rectangular lattice is favorable 6,7 . Being driven by a c-axis bias current, the moving fluxon lattice generates flux-flow resistance (FFR) in the junctions. Recent experimental 8,9,10 and numerical 11,12 studies show that the motion of traveling fluxon lattice in the layers is reflected into the periodic oscillation of FFR under the low bias current by considering the dynamical matching between the vortex lattice and the sample edges. The H 0 /2-period oscillation of FFR is interpreted as a result of the formation of triangular lattice in a longjunction stack, where H 0 is the field for adding one flux quantum per one junction (H 0 ≡ Φ 0 /Ls, Φ 0 being the flux quantum and s the layer periodicity along the c−axis i.e. 1.5 nm) 8,11 . Recent studies indicate that when the junction size is reduced down to a few µm and approaches the short-junction stack limit (L < λ J ), the oscillation period becomes predominantly H 0 rather than H 0 /2 due to the deformation of the Josephson vortex lattice by strong interaction with junction edges 9,10 . The res...

Radiation from Flux Flow in Josephson Junction Structures

“…Very pronounced Fiske steps have been observed recently by Kim et al [23] We also estimated that the lattice with random parameters κ n gives incoherent radiation with approximately the same power and the conversion coefficient as triangular lattice.…”

“…The first indication of the intrinsic Josephson effect was observation of switching of individual junctions to the resistive state in the I-V characteristics [14]. After that many Josephson effects have been found in these systems including the Fraunhofer patterns in the dependence of the critical current on the dc magnetic field applied parallel to the layers [15], Josephson plasma resonance [16] strongly affected by pancake vortices in the presence of the magnetic field applied perpendicular to the layers [17,18], Shapiro steps in the I-V characteristics induced by external microwave radiation [19,20], and Fiske resonances [21,22,23] One can anticipate much smaller variations of intrinsic-junction parameters in comparison with the artificially-fabricated junction arrays. In addition, the intrinsic junctions are much closer to each other and one can anticipate much stronger coupling between them.…”

Coexisting multiple dynamic states generated by magnetic field in Bi 2 Sr 2 CaCu 2 O 8+δ stacked Josephson junctions

“…In this high-field region, JVs configurations in the static state are well understood and are known to be in a triangular lattice [2,3,4,5]. Despite much interest, however, dynamic state of JVs is far less understood although various aspects of dynamical properties are proposed including the possible lattice structures [6,7,8], interaction between JVs and electromagnetic excitations [9,10,11,12], and coherent characters of the JV motion [13] over the whole junctions in a stack.Key elements governing the dynamics of JVs are well reflected in the tunneling current-voltage (I-V) characteristics, which reveal the relation between the driving force acting on JVs in a junction by the bias current and the responsive JVs motion that induces a voltage drop across the junctions. For instance, JV viscosity is determined by the in-and out-of-plane quasiparticle dissipation that is extracted from the tunneling JV-flow resistance [14,15].…”

“…In this high-field region, JVs configurations in the static state are well understood and are known to be in a triangular lattice [2,3,4,5]. Despite much interest, however, dynamic state of JVs is far less understood although various aspects of dynamical properties are proposed including the possible lattice structures [6,7,8], interaction between JVs and electromagnetic excitations [9,10,11,12], and coherent characters of the JV motion [13] over the whole junctions in a stack.…”

“…Oscillatory tunneling magnetoresistance is also used to confirm the coherently moving JV lattice and the influence of the edge barrier potential on * Corresponding author: hjlee@postech.ac.kr the JV motion [16,17,18]. Interaction between JVs and electromagnetic excitations is another interesting subject of JV dynamics where the resonance with cavity modes appears as Fiske steps [12,19]. Moreover, resonance between collectively moving JVs and plasma mode excitations in naturally stacked JJs has been studied extensively [9,10,11] where multiple subbranches in the I-V characteristics have been claimed to be an experimental evidence for the resonance [8].…”