Ryo Nakamura

Systematic study of Josephson plasma resonance in Bi2Sr2CaCu2O8+δ with columnar defects

Abstract We have examined microscopic vortex states in single-crystalline Bi2Sr2CaCu2O8+δ with various doses of columnar defects by Josephson plasma resonance measurements. The global angular dependence of the resonance field was found to obey an anisotropic 3D scaling law with a temperature-dependent anisotropy parameter γeff. The anisotropy parameter γeff drastically changes at the threshold temperature T ∗ , which is independent of the irradiation dose. This gives a unified and quantitative description of interlayer coupling in the vortex liquid state.

TEMPERATURE DEPENDENCE OF JOSEPHSON PLASMA MODES IN Bi2Sr2CaCu2O8+δ NEAR Tc

A strong temperature dependent phenomenon of the Josephson plasma resonance mode has been found in high-Tc superconductor Bi2Sr2CaCu2O8+δ in a microwave frequency region between 9 and 50 GHz. The longitudinal plasma frequency sharply decreases and disappears just below Tc. The extrapolated plasma energy is estimated to be ℏωp(0)=2.59× 10-4eV. Since the plasma frequency, ωp, is determined by the Anderson-Higgs–Kibble mechanism and it is expected to be temperature independent, this phenomenon can not be accounted for by the conventional underst and ing of the plasma mode in superconductors. Experimental results are discussed in terms of the two fluid model, in which the intrinsic Josephson nature of the coupling restricting the tunneling probability of quasiparticles between layers is considered to be as a dumping mechanism of the quasiparticles in this system.

Josephson plasma resonance in solid and glass phases of Bi2Sr2CaCu2O8+δ

Abstract Vortex matter phases and phase transitions are investigated by means of Josephson plasma resonance in under-doped Bi 2 Sr 2 CaCu 2 O 8+ δ single crystals in a microwave frequency range between 19 and 70 GHz. Accompanied by the vortex lattice melting transition, a jump of the interlayer phase coherence extracted from the field dependence of the plasma frequency was observed. In the solid phase, the interlayer coherence little depends on field at a temperature region well below T c while it gradually decreases as field increases toward the melting line up to just below T c . As a result, the magnitude of the jump decreases with increasing temperature and is gradually lost in the vicinity of T c . This indicates that the vortex lines formed in the vortex solid phase are thermally meandering and the phase transition becomes weak especially just below T c .

Josephson plasma mode in fields parallel to layers of Bi2Sr2CaCu2O8+δ

Abstract Josephson plasma resonance measurements under magnetic fields parallel to the CuO 2 layers as functions of magnetic field, temperature, and microwave frequency have been performed in Bi 2 Sr 2 CaCu 2 O 8+δ single crystals with doping range being from optimal to under-doped side. The feature of the resonance is quite unique and cannot be explained by the conventional understandings of the Josephson plasma for H ‖ c , that requires a new theory including coupling effect between Josephson vortex lattice and Josephson plasma.

Josephson plasma resonance in Bi2Sr2CaCu2O8+δ in vortex liquid and solid states

Abstract Both vortex liquid and solid states of high-temperature superconductor Bi2Sr2CaCu2O8+δ have been studied by means of Josephson plasma resonance (JPR). It is found that although the JPR frequency changes at the first-order vortex lattice melting transition (VLMT), TM, by 20–30% at low temperatures, it crosses TM almost continuously at high temperatures near Tc. Such a nearly continuous change from liquid to solid state strongly implies that the phase transition is so weak that the disappearance of the superconducting phase correlations is nearly continuous. This situation may be realized by considering the strong 2D superconducting fluctuations, resulting in the strong softening of the proper plasma mode in the solid phase.

In-plane Field Contribution for Josephson Plasma Mode in Under-doped Bi 2 Sr 2 CaCu 2 O 8+δ

Josephson plasma resonance (JPR) experiments under magnetic fields parallel to CUO2 layers have been performed in Bi2Sr2CaCu2O8+δ single crystals with doping range being from optimal to under-doped side. The results are found to be quite unique and cannot be accounted for the conventional notion of JPR for H // c, the systematic measurements as functions of the doping, applied microwave frequency, and magnetic field suggest that the new JPR mode can be excited with strong coupling to the Josephson vortex lattice.

Temperature dependence of Josephson plasma modes in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} near {Tc}

A strong temperature dependent phenomenon of the Josephson plasma resonance mode has been found in high-{Tc} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} in a microwave frequency region between 9 and 50 GHz. The longitudinal plasma frequency sharply decreases and disappears just below {Tc}. The extrapolated plasma energy is estimated to be {bar h}{omega}{sub p}(0) = 2.59 x 10{sup {minus}4} eV. Since the plasma frequency, {omega}{sub p}, is determined by the Anderson-Higgs-Kibble mechanism and it is expected to be temperature independent, this phenomenon can not be accounted for by the conventional understanding of the plasma mode in superconductors. Experimental results are discussed in terms of the two fluid model, in which the intrinsic Josephson nature of the coupling restricting the tunneling probability of quasiparticles between layers is considered to be as a dumping mechanism of the quasi-particles in this system.

A Systematic Study of Vortex States by Means of Josephson Plasma Resonance

Josephson plasma resonance has been studied in magnetic field orientation being nearly parallel to the ab plane in samples with wide range of doping levels in two experimental ways: field and temperature sweep. The characteristic features of the resonance depend on doping levels, which control anisotropy of the sample. In under-doped samples, the experimental results show a clearly separated two regions of the resonance, which strongly suggests two distinct phases existing in the case of parallel magnetic field.

Josephson plasma resonance in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} under parallel magnetic field

Josephson plasma resonance in under-doped Bi2Sr2CaCu2O8+δsingle crystals has been observed when magnetic field is applied parallel to the ab plane and its vicinity. The resonance mode splits into two branches at higher and lower temperature regions, and a definite gap appears in the temperature region between them. As the magnetic field is tilted from the ab plane, these branches come closer and finally merge to a single mode. This leads to a general interpretation that the resonance mode observed in a parallel field may be due to continuous extension of the c axis plasma mode. However, splitting of the mode as well as the peculiar temperature dependence of the resonance field, the line shape, and its intensity strongly imply that these behaviors may originate from the inherent resonance modes in parallel field. In particular, the high temperature mode fields goes even higher in temperature beyond the zero field resonance as the field increases, suggesting that a new explanation may be required for the case of parallel magnetic field.

Temperature Dependence of Collective Josephson Plasma Modes in Bi2Sr2CaCu2O8+δ

Three plasma excitation modes, the longitudinal (Erf//c) and the transverse (Hrf//c) Josephson plasma excitation modes as well as the surface impedance mode (Hrf //ab), have been measured in single crystalline Bi2Sr2CaCu208+δ in the vicinity of Tc at 35.6 GHz. We found that both Josephson plasma modes show a sharp softening phenomenon as temperature approach to Tc without significant broadening of the line width and without losing their intensities, and disappear above Tc, whereas the surface impedance behaves in a conventional manner.