We investigated macroscopic quantum tunneling (MQT) of Bi$_2$Sr$_2$CaCu$_2$O$_y$ intrinsic Josephson junctions (IJJs) with two device structures. One is a nanometer-thick small mesa structure with only two or three IJJs and the other is a stack of a few hundreds of IJJs on a narrow bridge structure. Experimental results of switching current distribution for the first switching events from zero-voltage state showed a good agreement with the conventional theory for a single Josephson junction, indicating that a crossover temperature from thermal activation to MQT regime for the former device structure was as high as that for the latter device structure. Together with the observation of multiphoton transitions between quantized energy levels in MQT regime, these results strongly suggest that the observed MQT behavior is intrinsic to a single IJJ in high-$T_c$ cuprates, independent of device structures. The switching current distribution for the second switching events from the first resistive state, which were carefully distinguished from the first switchings, was also compared between two device structures. In spite of the difference in the heat transfer environment, the second switching events for both devices were found to show a similar temperature-independent behavior up to a much higher temperature than the crossover temperature for the first switching. We argue that it cannot be explained in terms of the self-heating owing to dissipative currents after the first switching. As possible candidates, the MQT process for the second switching and the effective increase of electronic temperature due to quasiparticle injection are discussed.
We have investigated the Josephson plasma excitations in magnetic fields parallel to the $ab$-plane in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystals in a wide microwave frequency region (9.8 -- 75 GHz). It was found that there are two kind of phase-collective modes: one increases with magnetic fields in higher fields, approaching linear asymptotic dependence with $ck$, which lies well above the inherent plasma frequency $ω_p$, while the other does not show considerable field dependence. The higher linear mode is attributed to the Josephson plasma mode propagating along the reciprocal lattice v…
We observed splitting of the low-bias vortex-flow branch in a dense-Josephson-vortex state into multiple sub-branches in current-voltage characteristics of intrinsic Josephson junctions (IJJs) of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ single crystals in the long-junction limit. Each sub-branch corresponds to a plasma mode in serially coupled Josephson junctions. Splitting into low-bias linear sub-branches with a spread in the slopes and the inter-sub-branch mode-switching character are in good quantitative agreement with the prediction of the weak but finite inter-junction capacitive-coupling mod…
Dynamical nature of the Josephson vortex (JV) system in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212) has been investigated in the presence of the c-axis current with magnetic field alignments very close to the $ab$-plane. As a function of magnetic fields, the c-axis JV flux flow resistance oscillates periodically in accordance with the proposed JV triangular structure. We observe that this oscillating period becomes doubled above a certain field, indicating the structure transition from triangle to square structure. This transition field becomes lower in junctions with smaller width perpendicular to…
To study the Josephson-vortex system in the intrinsic Josephson junctions, we have measured the flow resistance as a function of magnetic field parallel to the $ab$ plane in Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+y}$ single crystals. Although it was known that the flow resistance increases smoothly with increasing field, we have found novel oscillations of vortex flow resistance in the small current regime. The period of the oscillations corresponds to the field which is needed to add ``{\it one}'' vortex quantum per ``{\it two}'' Josephson junctions. Commensurability between the lattice spacing of…
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$_{8+δ}$ si…
We have investigated macroscopic quantum tunneling in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ intrinsic Josephson junctions at millikelvin temperatures using microwave irradiation. Measurements show that the escape rate for uniformly switching stacks of N junctions is about $N^2$ times higher than that of a single junction having the same plasma frequency. We argue that this gigantic enhancement of macroscopic quantum tunneling rate in stacks is boosted by current fluctuations which occur in the series array of junctions loaded by the impedance of the environment.
In this study, we investigated the terahertz radiation from a truncated edge square mesa structure made from a superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} . Using a commercial software, the polarization characteristics were determined, and introduced, while accounting for the skin effect. The axial ratio was enhanced in the simulation by performing a parametric study on the design.
Terahertz radiation from the mesa structures of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ is detected in samples with thin electrodes $< 100$ nm. In samples with thick electrodes $\simeq$ 400 nm, neither radiations nor voltage jumps in current-voltage characteristics are detected. This suggests that the thin electrode helps excite the Josephson plasma oscillation as a result of the poor heat flow through the electrode. The shielding effect by the electrode is not essential. We consider that the local temperature rise is the origin of the synchronization of the phase kink for terahertz radiation.
The first penetration field H_{J}(T) of Josephson vortices is measured through the onset of microwave absorption in the locked state, in slightly overdoped $\rm{Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}}$ single crystals (T_{c} ~ 84 K). The magnitude of H_{J}(T) is too large to be accounted for by the first thermodynamic critical field H_{c1}(T). We discuss the possibility of a Bean-Livingston barrier, also supported by irreversible behavior upon flux exit, and the role of defects, which relates H_{J}(T) to the c-axis penetration depth $λ_{c}(T)$. The temperature dependence of the latter, determined by a ca…
The microwave distribution inside a rectangular stack (15 $μ$m$\times$0.72 $μ$m$\times$60 nm) of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ intrinsic Josephson junctions (IJJs) was studied. The stack was microfabricated into a transmission-line geometry, with a few hundred nm thick Au layers deposited on top and bottom of the stack. The microwave distribution was monitored by measuring the anomalous suppression of the tunneling critical current of the IJJs with varied microwave power at frequencies in the W band. This technique can provide valuable information on the microwave transmission modes insi…
We report the systematic investigations of the oscillation of the Josephson vortex (JV) flow resistance in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ micro-fabricated junctions with various geometries and superconducting anisotropy parameters. As the applied magnetic field parallel to the $ab$-plane is increased, oscillation with a period corresponding to a $ϕ_0/2$ par atomic Josephson junction changes to oscillation with a doubled period. This crossover is scaled by both the junction length and the anisotropy parameter, indicating that the bulk inductive coupling that favors the triangular JV lattice is r…
Josephson plasma excitations in the high $T_c$ superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ have been investigated in a wide microwave frequency region (9.8 -- 75 GHz), in particular, in magnetic field applied parallel to the $ab$ plane of the single crystal. In sharp contrast to the case for magnetic fields parallel to the c axis or tilted from the $ab$ plane, it was found that there are two kinds of resonance modes, which are split in energy and possess two distinctly different magnetic field dependences. One always lies higher in energy than the other and has a shallow minimum at about 0.8 …
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…
Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)] prepared atomically clean Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO) Josephson junctions between identical single crystal cleaves stacked and twisted an angle $ϕ_0$ about the c axis. For each bicrystal, the ratio $J_c^J/J_c^S$ of the c-axis twist junction critical current density to that across either single crystal part is unity, independent of $ϕ_0$ and the ratio $A^J/A^S$ of junction areas. From extensive theoretical studies involving a variety of tunneling and superconducting order parameter (OP) forms, we conclude that the results provid…
We report the first measurements of the $c$-axis Josephson Plasma Resonance (JPR) in Tl$_2$Ba$_2$CaCu$_2$O$_8$ as a function of temperature with and without a $c$-axis magnetic field using terahertz time-domain spectroscopy in transmission. The JPR is sensitive to the alignment of pancake vortices along the $c$-axis, and is observed to decrease when applying a magnetic field as expected.
The switching dynamics of current-biased Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ intrinsic Josephson junctions (IJJs) was studied to clarify the effect of d-wave superconductivity and the stack structure on the switching properties. High quality IJJs were fabricated, and then the temperature dependence of the switching probability distribution was measured for the first and second switchings. Although the standard deviation of the distribution detected for both switchings showed similar saturation characteristics with decreasing temperature, the temperature at saturation was about 13 times higher …
Takano {\it et al.} [Phys. Rev. B {\bf 65}, 140513 (2002) and unpublished] made Josephson junctions from single crystal whiskers of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ crossed an angle $ϕ_0$ about the $c$ axis. From the mesa structures that formed at the cross-whisker interface, they inferred a critical current density $J_c(ϕ_0)$. Like the single crystal results of Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)], we show that the whisker data are unlikely to result from a predominantly d-wave order parameter. However, unlike the single crystals, these results, if correct, require the whiske…
Since the discovery of high temperature superconductivity in cuprates, Josephson junction based phase-sensitive experiments are believed and used to provide the most convincing evidence for determining the pairing symmetry. Regardless of different junction materials and geometries used, quantum tunneling involved in these experiments is essentially a nanoscale process, and thus, actual experimental results are extremely sensitive to atomic details of the junction structures. The situation has led to controversial results as to the nature of the pairing symmetry of cuprates: while in-plane junc…
We fabricated small-size stacks on the surface of Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (BSCCO-2212) single crystals with the bulk transition temperature $T_c$$\simeq$90 K, each containing a few intrinsic Josephson junctions. Below a critical temperature $T_c'$ ($\ll$ $T_c$), we have observed a weakened Josephson coupling between the CuO$_2$ superconducting double layer at the crystal surface and the adjacent one located deeper inside a stack. The quasiparticle branch in the $IV$ data of the weakened Josephson junction (WJJ) fits well to the tunneling characteristics of a d-wave superconductor($'$)/in…
We used 2D coupled sine-Gordon equations combined with 3D heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a $250 \times 70\,μ\mathrm{m}^2$ intrinsic Josephson junction stack. The 700 junctions are grouped to 20 segments; we assume that in a segment all junctions behave identically. At large input power a hot spot forms in the stack. Resonant electromagnetic modes, oscillating either along the length ((0, $n$) modes) or the width (($m$, 0) modes) of the stack or having a more complex structure, can be excited both with and without a hot spot. At…
We used one-dimensional coupled sine-Gordon equations combined with heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a $300\,μ\mathrm{m}$ long intrinsic Josephson junction stack consisting of $N = 700$ junctions. The junctions in the stack are combined to $M$ segments where we assume that inside a segment all junctions behave identically. Most simulations are for $M = 20$. For not too high bath temperatures there is the appearence of a hot spot at high bias currents. In terms of electromagnetic properties, robust standing wave patterns appear in…
As nature junction geometry of the d-wave cuprate superconductor/insulator/the mixture of s-wave and d-wave cuprate superconductor, the upmost surface junction of intrinsic Josephson junction stack fabricated on Bi$_2$Sr$_2$CaCu$_2$O$_{8+d}$ single crystals was measured and discussed. We successfully observed half-integral microwave induced steps as well as integral steps with resistively shunting technology, which shows the evidence of second order supercurrent, consistent with Tanaka's theory.
Tunneling spectra of near optimally doped, submicron Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ intrinsic Josephson junctions are presented, and examined in the region where the superconducting gap evolves into pseudogap. The spectra are analyzed using a self-energy model, proposed by Norman {\it et al.}, in which both quasiparticle scattering rate $Γ$ and pair decay rate $Γ_Δ$ are considered. The density of states derived from the model has the familiar Dynes' form with a simple replacement of $Γ$ by $γ_+$ = ($Γ$ + $Γ_Δ$)/2. The $γ_+$ parameter obtained from fitting the experimental spectra shows a roughl…
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…
The operational dc-SQUID based on intrinsic Josephson junctions in Bi$_2$Sr$_2$CaCu2O$_{8+δ}$ high-$T_c$ superconductor is fabricated and studied. The novel in-plane loop layout and the developed in-situ endpoint detection method allowed an accurate control of the number of junctions in the SQUID. A clear periodic modulation of the superconducting current as a function of magnetic flux through the SQUID loop is observed. This is an unambiguous evidence for the quantum interference phenomenon in Bi$_2$Sr$_2$CaCu2O$_{8+δ}$ single crystals.
We confirmed the existence of the collective transverse plasma modes excited by the motion of the Josephson vortex lattice in stacked intrinsic Josephson junctions of Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ by observing the multiple subbranches in the Josephson-vortex-flow current-voltage characteristics. We also observed the symptom of the microwave emission from the resonance between the Josephson vortex lattice and the collective transverse plasma modes, which provides the possibility of developing Josephson-vortex-flow electromagnetic oscillators.
From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature $T_c$ superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$, the local surface temperature $T({\bm r})$ was directly measured during simultaneous sub-THz emission from the $N\sim10^3$ intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents $I$ and low bath temperatures $T_{\rm bath}\lesssim~35$ K, the center of a large elliptical hot spot with $T({\bm r})> T_c$ jumps dramatically with little current-voltage characteristic changes. The hot spot doesn't alter the ubiqui…
The Josephson Plasma Resonance is used to study the c-axis supercurrent in the superconducting state of underdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ with varying degrees of controlled point-like disorder, introduced by high-energy electron irradiation. As disorder is increased, the Josephson Plasma frequency decreases proportionally to the critical temperature. The temperature dependence of the plasma frequency does not depend on the irradiation dose, and is in quantitative agreement with a model for quantum fluctuations of the superconducting phase in the CuO$_{2}$ layers.
We have observed the zero-crossing steps in a surface junction of a mesa structure micro-fabricated on the surface of a Bi-2212 single crystal. With the application of microwave of frequencies 76 and 94 GHz, the current-voltage characteristics show clear voltage steps satisfying the ac Josephson relation. Increasing the microwave power, the heights of the steps show the Bessel-function behavior up to step number n=4. We confirm that the intrinsic surface junction meets the criterion for the observation of zero-crossing steps.
We perform a detailed comparison of magnetotunneling in conventional low-$T_c$ Nb/AlAlOx/Nb junctions with that in slightly overdoped Bi$_{2-y}$Pb$_y$Sr$_2$CaCu$_2$O$_{8+δ}$ [Bi(Pb)-2212] intrinsic Josephson junctions and with microscopic calculations. It is found that both types of junctions behave in a qualitatively similar way. Both magnetic field and temperature suppress superconductivity in the state-conserving manner. This leads to the characteristic sign-change of tunneling magnetoresistance from the negative at the sub-gap to the positive at the sum-gap bias. We derived theoretically a…
The experimental evidence of the breakpoint on the current-voltage characteristics (IVCs) of the stacks of intrinsic Josephson junctions (IJJs) is presented. The influence of the capacitive coupling on the IVCs of Bi$_2$Sr$_2$CaCu$_2$O$_y$ IJJs has been investigated. At 4.2 K, clear breakpoint region is observed on the branches in the IVCs. It is found that the hysteresis observed on the IVC is suppressed due to the coupling compared with that expected from the McCumber parameter. Measurements agree well with the results obtained by the theoretical model.
Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} (Bi-2212) are a promising source of coherent continuous-wave terahertz radiation. It is thought that at electrical bias conditions under which THz-emission occurs hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power. Here we perform an imaging study of the temperature distribution at the surface of BSCCO stacks utilizing the temperature-dependent 612nm fluorescence line of Eu^{3+} …
I propose a new mechanism of intense high-frequency electromagnetic wave generation by spatially uniform stacked Josephson junctions at zero magnetic field. The ac-Josephson effect converts the dc-bias voltage into ac-supercurrent, however, in the absence of spatial variation of Josephson phase difference, does not provide dc-to-ac power conversion, needed for emission of electromagnetic waves. Here I demonstrate that at geometrical resonance conditions, the spatial homogeneity of phase can be spontaneously broken by appearance of breathers (bound fluxon-antifluxon pairs), facilitating effecti…
Using a novel technique of measuring direct rf power dissipation, the temperature and magnetic field dependence of rf absorption in superconducting single crystals of Bi_2Sr_2CaCu_2O_8 is studied. An unexpected, larger than normal state, dissipation is observed below Tc, which exhibits peaks at magnetic field dependent temperatures. An explanation is provided for this observation in terms of the energy required to decouple the intrinsic Josephson junctions in the crystals.
We re-examined the angular dependence of the radiation from the intrinsic Josephson junctions in rectangular mesas of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$, in order to determine if the cavity mode part of the radiation arises from waves across the width $w$ or along the length $\ell$ of the mesas, associated with ``hot spots'' [Wang {\it et al.}, Phys. Rev. Lett. {\bf 105}, 057002 (2010)]. We derived analytic forms for the angular dependence expected in both cases for a general cavity mode in which the width of the mesa corresponds to an integer multiple of one-half the wavelength of the radiation. A…
We investigate the collective phase dynamics in conventional long Josephson junction (LJJ) stacks and in layered superconductors, exhibiting intrinsic LJJ behaviors. Using a theoretical model which accounts for both the magnetic induction effect and the breakdown of local charge neutrality (i.e., charging effect), we show that the collective motion of Josephson vortices, including the dispersion of Josephson plasma mode and the Swihart-type velocity, in an intrinsic LJJ stack such as Bi$_2$Sr$_2$CaCu$_2$O$_{8+y}$ (BSCCO) is significantly modified from those in a conventional LJJ stack. In BSCC…
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 trian…
We report tunneling spectra of near optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ intrinsic Josephson junctions with area of 0.09 $μ$m$^2$, which avoid some fundamental difficulties in the previous tunneling experiments and allow a stable temperature-dependent measurement. A d-wave Eliashberg analysis shows that the spectrum at 4.2 K can be well fitted by considering electron couplings to a bosonic magnetic resonance mode and a broad high-energy continuum. Above $T_c$, the spectra show a clear pseudogap that persists up to 230 K, and a crossover can be seen indicating two different pseudogap p…
In order to enhance the radiation power in terahertz band based on the intrinsic Josephson junctions of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystal, we investigate a long cylindrical sample embedded in a dielectric material. Tuning the dielectric constant, the radiation power has a maximum which is achieved when it equals the dissipation caused by Josephson plasma. This yields the optimal dielectric constant of wrapping material in terms of the properties of BSCCO single crystal. The maximal radiation power is found proportional to the product of the typical superconducting current squared an…
Coupling of Klein-Andreev Resonant States in Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$-graphene-Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ Devices
College of Nanoscale Science and Engineering, SUNY Polytechnic Institute（纽约州立大学波利技术学院纳米科学与工程）；College of Nanotechnology, Science, and Engineering, University at Albany, SUNY（纽约州立大学奥尔巴尼分校纳米技术科学与工程学院）；Department of Applied Physics, Aalto University（阿尔托大学应用物理系）；Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory（布鲁克海文国家实验室凝聚态物理与材料科学部）；Department of Physics and Astronomy, Stony Brook University（石溪大学物理与天文学系）
We present a study of the first and second switches (SWs) with nearly identical switching current $I_{\rm SW}$ in Bi$_2$Sr$_2$Ca$_{0.85}$Y$_{0.15}$Cu$_2$O$_y$ intrinsic Josephson junctions (IJJs). In contrast to early studies where a large difference between $I_{\rm SW}^{\rm 1st}$ and $I_{\rm SW}^{\rm 2nd}$ was observed, a crossover temperature $T_{\rm cr}$ to the quantum phase escapes for the 2nd SW is strongly reduced $(\sim$2.8~K) and agrees with that for the 1st SW. This confirms that the anomalous enhancement of $T_{\rm cr}^{\rm 2nd}$, commonly observed in the IJJs with $I_{\rm SW}^{\rm 1…
Anomalously high and sharp peaks in the conductance of intrinsic Josephson junctions in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ (Bi2212) mesas have been universally interpreted as superconducting energy gaps, but here we show they are a result of heating. This interpretation follows from a direct comparison to the equilibrium gap, $\mathit Δ$, measured in break junctions on similar Bi2212 crystals. As the dissipated power increases with a greater number of junctions in the mesa, the conductance peak abruptly sharpens and its voltage decreases to well below 2$\mathit Δ$. This sharpening, found in o…
Tunneling spectroscopy measurements are reported on optimally-doped and overdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ single crystals. A novel point contact method is used to obtain superconductor-insulator-normal metal (SIN) and SIS break junctions as well as intrinsic Josephson junctions (IJJ) from nanoscale crystals. Three junction types are obtained on the same crystal to compare the quasiparticle peaks and higher bias dip/hump structures which have also been found in other surface probes such as scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy. However, our IJ…
The effect of a magnetic field component parallel to the superconducting layers on longitudinal Josephson plasma oscillations in the layered high temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ is shown to depend on the thermodynamic state of the underlying vortex lattice. Whereas the parallel magnetic field component depresses the Josephson Plasma Resonance (JPR) frequency in the vortex solid phase, it may enhance it in the vortex liquid. There is a close correlation between the behavior of microwave absorption near the JPR frequency and the effectiveness of pancake vortex pinning, w…
Mutually synchronized macroscopic Josephson oscillations demonstrated by polarization analysis of superconducting terahertz emitters
University of Tsukuba（筑波大学）；Kyoto University（京都大学）；ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎高等师范学院，PSL大学，法国国家科学研究中心，索邦大学，巴黎大学）
We calculate the critical current density $J^J_c$ for c-axis Josephson tunneling between identical high temperature superconductors twisted an angle $ϕ_0$ about the c-axis. We model the tunneling matrix element squared as a Gaussian in the change of wavevector q parallel to the junction, $<|t({\bf q})|^2>\propto\exp(-{\bf q}^2a^2/2π^2σ^2)$. The $J^J_c(ϕ_0)/J^J_c(0)$ obtained for the s- and extended-s-wave order parameters (OP's) are consistent with the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ data of Li {\it et al.}, but only for strongly incoherent tunneling, $σ^2\ge0.25$. A $d_{x^2-y^2}$-wave OP is alw…
We calculate exactly the Josephson current for $c$-axis coherent tunneling between two layered superconductors, each with internal coherent tight-binding intra- and interlayer quasiparticle dispersions. Our results also apply when one or both of the superconductors is a bulk material, and include the usually neglected effects of surface states. For weak tunneling, our results reduce to our previous results derived using the tunneling Hamiltonian. Our results are also correct for strong tunneling. However, the $c$-axis tunneling results of Tanaka and Kashiwaya are shown to be incorrect in any l…
We studied response of the Josephson vortex lattice in layered superconductors to the high-frequency c-axis electric field. We found a simple relation connecting the dynamic dielectric constant with the perturbation of the superconducting phase, induced by oscillating electric field. Numerically solving equations for the oscillating phases, we computed the frequency dependences of the loss function at different magnetic fields, including regions of both dilute and dense Josephson vortex lattices. The overall behavior is mainly determined by the c-axis and in-plane dissipation parameters, which…
A comparative study of the magnetic properties of shunted and unshunted two-dimensional Josephson junction arrays (2D-JJA) is presented. Using a single-plaquette approximation of the 2D-JJA model, we were able to successfully fit all our experimental data (for the temperature, AC and DC field dependencies of susceptibility) and demonstrate that the dynamic reentrance of AC susceptibility is directly linked to the value of the Stewart-McCumber parameter β_C. Based on extensive numerical simulations, a phase diagram β_C vs β_L is plotted which demarcates the border between the reentrant and non-…
The point contact tunneling technique is used to examine quasiparticle and Josephson currents in overdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ (Bi-2212) single crystals with bulk T$_{c}$ values near 62 K. High quality superconductor-insulator-normal metal (SIN) tunnel junctions are formed between Bi-2212 crystals and a Au tip, which display well-resolved quasiparticle gap features including sharp conductance peaks. Reproducible superconductor- insulator-superconductor (SIS) tunnel junctions are also obtained between two pieces of the Bi-2212 crystals, resulting in simultaneous quasiparticle an…
The peculiarities of the phase dynamics of stacks of coupled Josephson junctions with topologically trivial and nontrivial barriers have been investigated numerically and their comparative analysis is carried out. The effect of coupling and dissipation parameters on the parametric resonance in the breakpoint region is shown. It is found that the dependence of the breakpoint voltage on the dissipation parameter demonstrates a minimum due to the changing of frequency of longitudinal plasma wave. We have shown that in case of the stack with nontrivial barriers the observed minimum shifts along th…
We study macroscopic quantum tunneling (MQT) in c-axis twist Josephson junctions made of high-T_c superconductors in order to clarify the influence of the anisotropic order parameter symmetry (OPS) on MQT. The dependence of the MQT rate on the twist angle $γ$ about the c-axis is calculated by using the functional integral and the bounce method. Due to the d-wave OPS, the $γ$ dependence of standard deviation of the switching current distribution and the crossover temperature from thermal activation to MQT are found to be given by $\cos2γ$ and $\sqrt{\cos2γ}$, respectively. We also show that a d…
