Josephson Vortex States Research Articles

Multidimensional Josephson vortices in spin-orbit-coupled Bose-Einstein condensates: Snake instability and decay through vortex dipoles

We analyze the dynamics of Josephson vortex states in two-component Bose-Einstein condensates with Rashba-Dresselhaus spin-orbit coupling by using the Gross-Pitaevskii equation. In 1D, both in homogeneous and harmonically trapped systems, we report on stationary states containing doubly charged, static Josephson vortices. In multidimensional systems, we find stable Josephson vortices in a regime of parameters typical of current experiments with $^{87}$Rb atoms. In addition, we discuss the instability regime of Josephson vortices in disk-shaped condensates, where the snake instability operates and vortex dipoles emerge. We study the rich dynamics that they exhibit in different regimes of the spin-orbit coupled condensate depending on the orientation of the Josephson vortices.

21aPS-51 Bi2212固有ジョセフソン接合における高磁場でのジョセフソン磁束状態(領域8ポスターセッション(低温),領域8,強相関系:高温超伝導,強相関f電子系など)

21aPS-51 Bi2212固有ジョセフソン接合における高磁場でのジョセフソン磁束状態(領域8ポスターセッション(低温),領域8,強相関系:高温超伝導,強相関f電子系など)

Collective Josephson vortex dynamics in a finite number of stacked intrinsic Josephson junctions

We report the experimental confirmation of the collective transverse plasma modes excited by the Josephson vortex lattice in stacks of intrinsic Josephson junctions in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ single crystals. The excitation was confirmed by analyzing the temperature ($T$) and magnetic field ($H$) dependencies of the multiple sub-branches in the Josephson-vortex-flow region of the current-voltage characteristics of the system. In the near-static Josephson vortex state for a low tunneling bias current, pronounced magnetoresistance oscillations were observed, which represented a triangular-lattice vortex configuration along the c axis. In the dynamic vortex state in a sufficiently high magnetic field and for a high bias current, splitting of a single Josephson vortex-flow branch into multiple sub-branches was observed. Detailed examination of the sub-branches for varying $H$ field reveals that sub-branches represent the different modes of the Josephson-vortex lattice along the c axis, with varied configuration from a triangular to a rectangular lattices. These multiple sub-branches merge to a single curve at a characteristic temperature, above which no dynamical structural transitions of the Josephson vortex lattice is expected.

Abrikosov-to-Josephson vortex lattice crossover in heavy fermion CeCoIn5

We present torque magnetization measurements on the quasi-2D heavy fermion superconductor CeCoIn5 at temperatures down to 20 mK and magnetic fields up to 18 T. At orientations with the magnetic field perpendicular to the conducting planes, a prominent vortex lattice peak effect is present at around 0.5H c2. The peak effect gradually disappears upon rotating the field into the plane parallel orientation. We interpret the absence of the peak effect for the plane parallel case as a transformation of the Abrikosov lattice into a Josephson vortex state, favored by the Pauli paramagnetic limit in CeCoIn5 together with the unusually large condensation energy. Additionally, we do not observe flux avalanches as found in organic superconductors and suggest that the complete absence of vortex activity in the plane parallel field orientation is crucial for the formation of Fulde–Ferrell–Larkin–Ovchinnikov superconductivity in CeCoIn5.

Josephson-vortex states at higher magnetic fields in Bi2Sr2CaCu2O8+y

Josephson-vortex (JV) states in Bi2Sr2CaCu2O8+y (Bi-2212) have been studied by measuring the flow resistance of JVs and I–V characteristics with a current along the c-axis and a magnetic field parallel to the superconducting layers. In the flow resistance, periodic oscillations have been found as a function of the parallel field. As this phenomenon is related to the formation of a triangular lattice of JVs as the ground state, the 3D-ordered state of JVs can be determined in the magnetic phase diagram. With increasing the doping level of Bi-2212, the 3D-ordered phase is shifted towards a higher magnetic field and a higher temperature, which is well explained by the theoretical analyses. Above the 3D-ordered phase, JV state has been studied with I–V characteristic measurements, in which the voltage shows a distinct change in the exponent of the power-law dependence to the current between two phases. This suggests that the 3D-ordered phase changes to the disordered phase along the c-axis.

Observation of Josephson-vortex-flow submodes in Bi 2Sr 2CaCu 2O 8+ x intrinsic Josephson junctions

Stacked intrinsic Josephson junctions form in highly anisotropic high- T c superconductors such as Bi 2Sr 2CaCu 2O 8+ x . Josephson-vortex dynamics in such systems attracts much research interests, both academic and application points of view. In a dense Josephson-vortex state (in the range of 4–5 T external magnetic field applied in parallel with the junction planes) of Bi 2Sr 2CaCu 2O 8+ x stacked intrinsic Josephson junctions vortex-flow motion is in resonance with the collective plasma oscillation modes. With increasing magnetic fields beyond ∼2 T hysteretic quasiparticle branches keep shrinking, while the collective Josephson-vortex-flow branches start appearing and become clearer. The Josephson-vortex-flow branches split into multiple sub-branches corresponding to the number of coupled junctions in the stack. The low-bias characteristics of the Josephson-vortex-flow sub-branches fit well to the inductive-capacitive hybrid coupling model.

Josephson vortex state across the phase diagram ofLa2−xSrxCuO4: A magneto-optics study

We present a detailed doping dependent study of the Josephson vortex state in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ using infrared spectroscopy. A magnetic field as high as $17\phantom{\rule{0.3em}{0ex}}\text{tesla}$, applied along the $\mathrm{Cu}{\mathrm{O}}_{2}$ planes, is found to suppress the Josephson plasmon in all measured samples. We find the strongest suppression in samples with dopings close to $x=1∕8$ and attribute this effect to the spontaneous formation of in-plane charge inhomogenities at this doping level. Several theoretical models of the Josephson vortex state are applied to explain the observed effects.

Josephson vortex states in Bi 2Sr 2CaCu 2O 8+ δ obtained from vortex flow resistance measurements

We found the periodic oscillations in Josephson-vortex-flow resistance with the current perpendicular to the Cu–O layers of Bi 2Sr 2CaCu 2O 8+ δ . As the flow resistance is closely related to the configurations of the Josephson vortices, we have observed clear boundaries between the triangular-lattice phase and others. It is strongly suggested that the flow resistance measurements open the window to investigate magnetic phase diagram of Josephson vortices in strongly anisotropic high T c superconductors.

Shapiro step response in the vortex state of Bi2Sr2CaCu2O8+$delta;

We report the first observation of Shapiro step effect in the Josephson vortex state of Bi 2 Sr 2 CaCu 2 O 8+ δ in high magnetic field (H⩾1 T ) . We observed phase locking between external microwave radiation and Josephson oscillation in whole stack of N intrinsic Josephson junctions at fields tilted with respect to the c -axis. Steps were observed in Josephson flux-flow (JFF) on the I – V characteristic at voltage V st = pNhν /2 e , with p integer, ν =45– 142 GHz . The amplitude of both Shapiro steps and Josephson critical current increase sharply with tilting angle and then decrease. We attribute this behavior to the interaction between Josephson and pancake vortices.

Josephson vortex flow and pinning probed by c-axis transport measurements

Measurements on current–voltage (I–V) characteristics along the c-axis of Bi2Sr2CaCu2O8+δ single crystals have been performed as functions of temperature and magnetic field closely parallel to the ab-plane in order to investigate dynamics of the Josephson vortex (JV) system. Two JV states, one in which JVs are pinned and the other in which JVs are flowing parallel to the ab-plane, were found in I–V characteristics. The threshold current between the pinned and the flowing states shows a peak effect slightly below Tc. This phenomenon cannot be explained with random pinning of JVs.

Josephson Vortex States in Intermediate Fields

Motivated by recent resistance data in high T c superconductors under magnetic fields parallel to the CuO layers, we address two key issues on the Josephson–vortex phase diagram, an appearance of structural transitions on the observed first order transition (FOT) curve in intermediate fields and of a lower critical point of the FOT line. The structural transitions reflected on the thermal transition curve in YBCO are identified based on our mean field calculation, and it is argued that a lower critical point more easily occurs in the present B ⊥ c case compared with that in B ∥ c case.

Josephson plasma resonance in Josephson vortex states

Josephson plasma resonance of under-doped Bi 2Sr 2CaCu 2O 8+ δ single crystals in magnetic fields parallel to the ab-plane has been studied at microwave frequencies ν between 10 and 52 GHz. Two resonance lines are discovered with distinctly different characters as functions of different physical parameters such as magnetic fields, microwave frequencies, temperatures, etc. Those two resonances behave entirely differently from the ones for H∥c and are attributed to the mixed resonance plasma modes with collective motion of the Josephson vortices.