In THz wave emission from intrinsic Josephson junctions in in-plane magnetic fields, emission intensity strongly depends on the surface impedance $Z$ similarly to the case without external magnetic fields. Cavity resonance modes are stabilized for $Z \ge 3$, and the fundamental mode gives the strongest emission. As the in-plane magnetic field increases for a fixed number of junctions, dynamical phase transitions seem to occur between the $π$-phase-kink state, various incommensurate phase-kink states, and in-phase state. As $Z$ varies, a crossover of the field profile of maximum intensity takes place for $Z \approx 50$ between characteristic peaks for smaller $Z$ (typically $Z \approx 30$) and monotonic decrease for larger $Z$ (typically $Z \approx 70$). The double-peak structure reported in experiments can be explained for Z=30 by finite-size analysis with respect to number of junctions.
We theoretically propose a practical method for realizing intense terahertz (THz) emission from intrinsic Josephson junctions (IJJs) using an external heat source. An artificial inhomogeneous temperature distribution by the local heating strongly excites the Josephson plasma wave inside IJJs and enhances THz emission power. We show optimum heating conditions for achieving high power THz emission. Our result indicates that local heat control is a powerful method to realize practical solid-state THz-emitters utilizing IJJs.
We report novel non-linear phenomena in the $ab$-plane microwave impedance of $YBaCu_{2}O_{7-δ}$ single crystals. The $R_s$ vs. $H_{rf}$ data are well described by the non-linear RSJ model : $\dotϕ+\sin ϕ=i_{rf}\cos ωt$. The entire crystal behaves like a single Josephson junction. The extraordinary coherence of the data suggests an intrinsic mechanism.
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…
Theoretical and experimental studies of intrinsic Josephson junctions that naturally occur in high-Tc superconducting Bi2Sr2CaCu2O8+δ (Bi-2212) have demonstrated their potential for novel types of compact devices for the generation and sensing of electromagnetic radiation in the THz range. Here, we show that the THz-on-a-chip concept may be realized in liquid phase epitaxial-grown (LPE) thick Bi-2212 films. We have grown μm-thick Bi-2212 LPE films on MgO substrates. These films display excellent c-axis alignment and single crystal grains of about 650x150 μm2 in size. A branched current-voltage…
As possible states to characterize THz wave emission from intrinsic Josephson junctions without external fields, the McCumber-like state and $π$-phase-kink state have been proposed. In the present article it is numerically shown that both states are stationary according to the bias current $J$ and surface impedance $Z$. The McCumber-like state is stable for low $J$ and small $Z$. For higher $J$, the $π$-phase-kink state accompanied with symmetry breaking along the c axis is stable even for Z=1, though strong emission in the vicinity of cavity resonance points only takes place for larger $Z$. D…
At high enough input power in stacks of Bi_2Sr_2CaCu_2O8 intrinsic Josephson junctions a hot spot (a region heated to above the superconducting transition temperature) coexists with regions still in the superconducting state. In the ``cold'' regions cavity resonances can occur, synchronizing the ac Josephson currents and giving rise to strong coherent THz emission. We investigate the interplay of hot spots and standing electromagnetic waves by low temperature scanning laser microscopy and THz emission measurements, using stacks of various geometries. For a rectangular and a arrow-shaped struct…
Geometrical Resonance Conditions for THz Radiation from the Intrinsic Josephson Junctions in Bi2Sr2CaCu2O8+d
Institute of Materials Science, Graduate School of Pure & Applied Sciences, University of Tsukuba（筑波大学纯理学研究科物质材料科学研究所）；Department of Physics, University of Central Florida（中佛罗里达大学物理系）
We report on THz emission measurements and low temperature scanning laser imaging of Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the "cold" part of the stack, coexist. By varying the hot spot size the cavity resonance frequency and the emitted radiation can be tuned. The linewidth of radiation is much smaller than expected from the quality factor of the cavity mode excited. Thus, an additional mechanism of synchronization seems to play a role, possibly arising from nonequilibrium p…
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.
A practical method for realizing intense terahertz (THz) emission from intrinsic Josephson junctions (IJJs) by utilizing external local-heating is proposed and demonstrated theoretically. An artificial temperature distribution induced by local heating strongly excites Josephson plasma waves inside IJJs. Accordingly, the emission power of the THz wave is enhanced drastically, and it can reach the order of mW. Our result indicates that the use of local heat control is a powerful method to realize practical solid-state THz-emitters based on IJJs.
The dependence of microwave impedance of a dc-biased Josephson Fluxonic Diode (JFD) under application of both dc magnetic field and rf excitation is calculated with a variety of conditions. For finite length of a JFD excited by a very low microwave excitation below its plasma frequency, applied dc magnetic field increases the rate of Vortex and Anti-Vortex (VAV) pair generation which fine-tunes the microwave resistance up to several factors more than its zero field microwave resistance (R0). Under this circumstance, adding a dc bias for moving VAVs causes oscillation-like features in microwave…
This paper reports a practical method of generating circularly polarized terahertz (THz) waves from intrinsic Josephson junctions (IJJs) and controlling their polarization states by external local heating. We theoretically find that a mesa-structure IJJ whose geometry is almost square can emit circularly polarized THz waves by local heating of the mesa. Moreover, we demonstrate that the polarization states of the THz waves change dramatically with the local heating position. Our results indicate that the use of local heating can provide a high level of controllability of the THz emissions and …
Systematic modulation of superconducting gap dynamics in YBCO|BNT|YBCO Josephson Junctions through THz field interaction and BNT ferroelectric barrier
Chiang Mai University（清迈大学）；Universität Stuttgart（斯图加特大学）；University of Zambia（赞比亚大学）；Khon Kaen University（孔敬大学）；Institute of Nanomaterials Research and Innovation for Energy (IN-RIE), Research Network of NANOTEC- KKU (RNN)（纳米材料研究与能源创新研究所（IN-RIE），NANOTEC-孔敬大学研究网络（RNN））；University of Macau（澳门大学）；Macau University of Science and Technology（澳门科技大学）
Cuprate superconductor Bi2Sr2CaCu2O8+δ (BSCCO) has been a promising candidate of a coherent, continuous, and compact THz light source owing to its intrinsic Josephson junction inside the crystal structure. In this paper, we utilized BSCCO cross-whisker junctions to produce THz emitter device using the whisker crystals which can be easily obtained compared with single crystals. As a result, we have successfully observed the emission from the cross-whisker intrinsic Josephson junction, with frequency of ~0.7 THz. Our findings might enlarge the applicability of BSCCO superconductors for the THz e…
We propose a mechanism of coherent emission from driven vortices in stacked intrinsic Josephson junctions. In contrast to super-radiance, which occurs only for highly ordered vortex lattices, we predict resonant radiation emission from weakly correlated vortex arrays. Our analytical results for the THz wave intensity, resonance frequencies, and the dependence of THz emission power on dissipation are in good agreement with the ones obtained by recent simulations.
We have observed a dissipative phase diffusion branch in arrays of hysteretic high-Tc intrinsic Josephson junctions. By comparing the data with a thermal activation model we extract the impedance seen by the junction in which phase diffusion is occurring. At the plasma frequency this junction is isolated from its environment and it sees its own large (~ kilo Ohm) impedance. Our results suggest that stacks of Josephson junctions may be used for isolation purposes in the development of a solid state quantum computer.
We present a lumped-element Josephson parametric amplifier designed to operate with strong coupling to the environment. In this regime, we observe broadband frequency dependent amplification with multi-peaked gain profiles. We account for this behaviour using the "pumpistor" model which allows for frequency dependent variation of the external impedance. Using this understanding, we demonstrate control over gain profiles through changes in the environment impedance at a given frequency. With strong coupling to a suitable external impedance we observe a significant increase in dynamic range, and…
We report the efficient coupling of a $50\,Ω$ microwave circuit to a high impedance conductor. We use an impedance transformer consisting of a $λ/4$ co-planar resonator whose inner conductor contains an array of superconducting quantum interference devices (SQUIDs), providing the resonator with a large and tunable lineic inductance $\mathcal{L}\sim 80 μ_0$, resulting in a large characteristic impedance $Z_C\sim 1\,\mathrm{k}Ω$. The impedance matching efficiency is characterized by measuring the shot noise power emitted by a dc biased high resistance tunnel junction connected to the resonator. …
The recent growing interest in terahertz (THz) and sub-THz science and technology is due to its many important applications in physics, astronomy, chemistry, biology, and medicine. We review the problem of linear and non-linear THz and sub-THz Josephson plasma waves in layered superconductors and their excitations produced by moving Josephson vortices. We start by discussing the coupled sine-Gordon equations for the gauge-invariant phase difference of the order parameter in the junctions, taking into account the effect of breaking the charge neutrality, and deriving the spectrum of Josephson p…
The most developed integrated receivers for THz radiation nowadays are based on Josephson junction SIS devices. In this kind of devices, the highest receivable frequency is determined by the energy gap of the superconducting electrodes and limited to approximately 700 GHz in case of Nb/AlOx/Nb multilayers. We have developed a technology for NbN/AlN/NbN Josephson junctions on sapphire substrates which allow operation at frequencies above 1 THz. The trilayers are deposited in-situ in a 3-chamber DC-magnetron sputtering system at temperatures as high as 775 °C. Each layer is reactively sputtered …
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…
By patterning mesoscopic crystals of Bi2Sr2CaCu2O8 (BSCCO) into electromagnetic resonators the oscillations of a large number of intrinsic Josephson junctions can be synchronized into a macroscopic coherent state accompanied by the emission of strong continuous wave THz-radiation. The temperature dependence of the emission is governed by the interplay of self-heating in the resonator and by re-trapping of intrinsic Josephson junctions which can yield a strongly nonmonotonic temperature dependence of the emission power. Furthermore, proper shaping of the resonators yields THzsources with voltag…
The dynamics of fluxons in long Josephson junctions is a well-known example of soliton physics and allows for studying highly nonlinear relativistic electrodynamics on a microscopic scale. Such fluxons are supercurrent vortices that can be accelerated by a bias current up to the Swihart velocity, which is the characteristic velocity of electromagnetic waves in the junction. We experimentally demonstrate slowing down relativistic fluxons in Josephson junctions whose bulk superconducting electrodes are replaced by thin films of a high kinetic inductance superconductor. Here, the amount of magnet…
The non-linear dependence on applied $ac$ field ($b_ω$) or current ($% i_ω$) of the microwave (ac) impedance $R_ω+iX_ω$ of both short and long Josephson junctions is calculated under a variety of excitation conditions. The dependence on the junction width is studied, for both field symmetric (current anti-symmetric) and field anti-symmetric (current symmetric) excitation configurations.The resistance shows step-like features every time a fluxon (soliton) enters the junction, with a corresponding phase slip seen in the reactance. For finite widths the interference of fluxons leads to some inter…
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.
We report on measurements of the linewidth Δf of THz radiation emitted from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated receiver for detection. Previous resolution limited measurements indicated that Δf may be below 1 GHz - much smaller than expected from a purely cavity-induced synchronization. While at low bias we found Δf to be not smaller than ? 500 MHz, at high bias, where a hotspot coexists with regions which are still superconducting, Δf turned out to be as narrow as 23 MHz. We attribute this to the hotspot acting as a synchronizing element. Δf decreases with incr…
The Hamiltonian operator for an unbiased array of Josephson junctions with gate voltages is constructed when only Cooper pair tunnelling and charging effects are taken into account. The supercurrent through the system and the pumped current induced by changing the gate voltages periodically are discussed with an emphasis on the inaccuracies in the Cooper pair pumping. Renormalisation of the Hamiltonian operator is used in order to reliably parametrise the effects due to inhomogeneity in the array and non-ideal gating sequences. The relatively simple model yields an explicit, testable predictio…
Evidence for a Dual-Source Mechanism of THz Radiation from Rectangular Mesas of Single Crystalline \bm{$\mathrm{Bi_2Sr_2CaCu_2O_{8+δ}}$} Intrinsic Josephson Junctions
Graduate School of Pure & Applied Sciences, University of Tsukuba（筑波大学理工学群）；Department of Physics, University of Central Florida（中佛罗里达大学物理系）
We analyze the influence of noise on magnetic properties of a su- perconducting loop which contains three Josephson junctions. This circuit is a classical analog of a persistent current (flux) qubit. A loop supercurrent induced by external magnetic field in the presence of thermal fluctuations is calculated. In order to get connection with experiment we calculate the impedance of the low-frequency tank cir- cuit which is inductively coupled with a loop of interest. We compare obtained results with the results in quantum mode - when the three junction loop exhibits quantum tunneling of the magn…
The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from …
We propose how to control the THz radiation generated by fast moving Josephson vortices in spatially modulated (either along the c-axis or the ab-plane) samples of Bi-2212 and related superconducting compounds. We show that the JVs moving in a subset of weaker junctions can generate out-of-ab-plane and outside-the-cone Cherenkov radiation. The ab-plane modulation of superconducting properties (achieved, for instance, by ion irradiation lithography) can result in transition radiation within certain frequency windows, i.e., allowing the design of tunable THz emitters and THz photonic crystals.
We investigate the dynamics of a resistively shunted Josephson junction. We compute the Josephson frequency and the generalized impedances for a variety of the parameters, particularly with relevance to predicting the measurable effects of zero-temperature current noise in the resistor.
We have theoretically demonstrated the emission of circularly-polarized terahertz (THz) waves from intrinsic Josephson junctions (IJJs) which is locally heated by an external heat source such as the laser irradiation. We focus on a mesa-structured IJJ whose geometry is slightly deviate from a square and find that the local heating make it possible to emit circularly-polarized THz waves. In this mesa, the inhomogeneity of critical current density induced by the local heating excites the electromagnetic cavity modes TM (1,0) and TM (0,1), whose polarizations are orthogonal to each other. The mix…
The dependence of sheet impedance of a Josephson junction array on the applied magnetic field is investigated in the regime when vortex diffusion between array plaquettes is effectively frozen due to low enough temperature. The field dependent contribution to sheet inductance is found to be proportional to f*ln(1/f), where f<<1 is the magnitude of the field expressed in terms of flux quanta per plaquette.
We predict the existence of surface waves in layered superconductors in the THz frequency range, below the Josephson plasma frequency $ω_J$. This wave propagates along the vacuum-superconductor interface and dampens in both transverse directions out of the surface (i.e., towards the superconductor and towards the vacuum). This is the first prediction of propagating surface waves in any superconductor. These predicted surface Josephson plasma waves are important for different phenomena, including the complete suppression of the specular reflection from a sample (Wood's anomalies) and a huge enh…
The form of the fluctuation-dissipation theorem for a resistively shunted Josephson juction array is derived with the help of the method which explicitely takes into acoount screening effects. This result is used to express the flux noise power spectrum in terms of frequency dependent sheet impedance of the array. The relation between noise amplitude and parameters of the detection coil is analysed for the simplest case of a single-loop coil.
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…
We discuss how complex-oxide heterostructures that include high-Tc superconducting cuprates can be used to realize an array of sub-millimeter cavities that support Josephson plasmon polaritons. These cavities have several attractive features for new types of light matter interaction studies and we show that they promote "ultrastrong" coupling between THz frequency radiation and Josephson plasmons. Cavity electrodynamics of Josephson plasmons allows to manipulate the superconducting order-parameter phase coherence. As an example, we discuss how it could be used to cool superconducting phase flu…
We show that a moving Josephson vortex in spatially modulated layered superconductors generates out-of-plane THz radiation. Remarkably, the magnetic and in-plane electric fields radiated are of the same order, which is very unusual for any good-conducting medium. Therefore, the out-of-plane radiation can be emitted to the vacuum without the standard impedance mismatch problem. Thus, the proposed design can be more efficient for tunable THz emitters than previous proposals, for radiation only propagating along the ab-plane.
Terahertz imaging system with on-chip superconducting Josephson plasma emitters for nondestructive testing
National Institute of Advanced Industrial Science and Technology (AIST)（产业技术综合研究所）；James Watt School of Engineering, University of Glasgow（格拉斯哥大学詹姆斯·瓦特工程学院）；Faculty of Pure and Applied Sciences, University of Tsukuba（筑波大学理工学群）
The hallmark of superconductivity is the rigidity of the quantum-mechanical phase of electrons, responsible for superfluid behavior and Meissner effect. The strength of the phase stiffness is set by the Josephson coupling, which is strongly anisotropic in layered superconducting cuprates. So far, THz light pulses have been efficiently used to achieve non-linear control of the out-of-plane Josephson plasma mode, whose frequency scale lies in the THz range. However, the high-energy in-plane plasma mode has been assumed to be insensitive to THz pumping. Here, we show that THz driving of both low-…
The dynamical vortex response of a two-dimensional array of the resistively shunted Josephson junctions in a perpendicular magnetic field is inferred from simulations. It is found that, as the magnetic field is increased at a fixed temperature, the response crosses over from normal to anomalous, and that this crossover can be characterized by a single dimensionless parameter. It is described how this crossover should be reflected in measurements of the complex impedance for Josephson junction arrays and superconducting films.
We investigate the response of a stack of intrinsic Josephson junctions (IJJs) to terahertz (THz) electromagnetic (EM) irradiation. A significant amplification of the EM wave can be achieved by the IJJs stack when the incident frequency equals to one of the cavity frequencies. The irradiation excites pi phase kinks in the junctions, which stimulate the cavity resonance when the bias voltage is tuned. A large amount of dc energy is then pumped into the Josephson plasma oscillation, and the incident wave gets amplified. From the profound current step in IV characteristics induced at the cavity r…
Impedance matching and heat management are important factors influencing performance of THz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. Two types of devices are considered, containing either a conventional large single crystal, or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of…
We present a quantitative analysis of an escape rate for switching from the superconducting state to a resistive one in series arrays of globally coupled Josephson junctions. A global coupling is provided by an external shunting impedance. Such an impedance can strongly suppress both the crossover temperature from the thermal fluctuation to quantum regimes, and the macroscopic quantum tunneling (MQT) in short Josephson junction series arrays. However, in large series arrays we obtain an enhancement of the crossover temperature, and a giant increase of the MQT escape rate. The effect is explain…
We theoretically investigate the temperature-to-phase conversion (TPC) process occurring in dc superconducting quantum interferometers based on superconductor--normal metal--superconductor (SNS) mesoscopic Josephson junctions. In particular, we predict the temperature-driven rearrangement of the phase gradients in the interferometer under the fixed constraints of fluxoid quantization and supercurrent conservation. This allows sizeable phase variations across the junctions for suitable structure parameters and temperatures. We show that the TPC can be a basis for sensitive single-photon sensors…
We report on an experimental and theoretical study of the high-frequency mixing properties of ion-irradiated YBa2Cu3O7 Josephson junctions embedded in THz antennas. We investigated the influence of the local oscillator power and frequency on the device performances. The experimental data are compared with theoretical predictions of the general three-port model for mixers, in which the junction is described by the resistively shunted junction model. A good agreement is obtained for the conversion efficiency in different frequency ranges, spanning above and below the characteristic frequencies f…
We show that the non-local polarization response in a multimode circuit-QED setup, devised from a Cooper pair box coupled to a long chain of Josephson junctions, provides an alternative route to access the elusive Kondo screening cloud. For moderate circuit impedance, we compute analytically the universal lineshape for the decay of the charge susceptibility along the circuit, that relates to spatial entanglement between the qubit and its electromagnetic environment. At large circuit impedance, we numerically find further spatial correlations that are specific to a true many-body state.
We show that Infrared radiation impinging onto a 1-d array of grooves drilled in the superconductor electrode of a long overlap junction can improve matching between fluxon oscillations at THz frequencies and a spoof plasmon of comparable wavelength. This example proves that metamaterials can be very helpful in integrating superconductive and subwavelength optical circuits with optimized matching bridging the gap between infrared and microwave radiation.
Nonreciprocal microwave transmission through a long Josephson junction in the flux-flow regime is studied analytically and numerically within the framework of the perturbed sine-Gordon model. We demonstrate that the maximum attenuation of the transmitted power occurs when the direction of the flux flow is opposite to the direction of the microwave propagation. This attenuation is nonreciprocal with respect to the flux-flow direction and can be enhanced by increasing the system length and proper impedance matching of the junction ends to external transmission line.
Bloch oscillations predicted to occur in current-biased single Josephson junctions have eluded direct observation up to now. Here, we demonstrate similar Bloch oscillations in a slightly richer Josephson circuit, the quantronium. The quantronium is a Bloch transistor with two small junctions in series, defining an island, in parallel with a larger junction. In the ground state, the microwave impedance of the device is modulated periodically with the charge on the gate capacitor coupled to the transistor island. When a current flows across this capacitor, the impedance modulation occurs at the …
Recently, it has been shown that large stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2O8 emit synchronous THz radiation, the synchronization presumably triggered by a cavity resonance. To investigate this effect we use Low Temperature Scanning Laser Microscopy to image electric field distributions. Apart from verifying the appearance of cavity modes at low bias we find that, in a high input power regime, standing-wave patterns are created through interactions with a hot spot, possibly pointing to a new mode of generating synchronized radiation in intrinsic Josephson junction stacks.
