We investigate the Josephson transport properties in a Josephson junction consisting of a conventional $s$-wave superconductor coupled to a multi-orbital noncentrosymmetric superconductor marked by an orbitally driven inversion asymmetry and isotropic interorbital spin-triplet pairing. Contrary to the canonical single band noncentrosymmetric superconductor, we demonstrate that the local interorbital spin-triplet pairing is tied to the occurrence of sign-changing spin-singlet pair amplitude on different bands with $d$-wave symmetry. Such multi-band $d^{\pm}$-wave state is a unique superconducting configuration that drives unexpected Josephson effects with 0-$π$ transitions displaying a high degree of electronic control. Remarkably, we find that the phase state of a noncentrosymmetric/$s$-wave Josephson junction can be toggled between 0 and $π$ in multiple ways through a variation of electron filling, strength of the spin-orbital coupling, amplitude of the inversion asymmetry interaction, and junction transparency. These results highlight an intrinsic orbital and electrical tunability of the Josephson response and provide unique paths to unveil the nature of unconventional multiorbital superconductivity as well as inspire innovative designs of Josephson quantum devices.
We discuss the Josephson current between two noncentrosymmetric superconductors. The coexistence of superconducting order parameters between spin-singlet $Δ_{\text{S}}$ and helical p-wave spin-triplet $Δ_{\text{T}}$ enriches a variety of low-temperature behavior of Josephson current depending on their relative amplitudes. We will show that characteristic behaviors of the Josephson current for $Δ_{\text{S}} > Δ_{\text{T}}$ are clearly different from those for $Δ_{\text{S}} < Δ_{\text{T}}$. The topologically protected zero-energy surface bound states are responsible for the clear difference. We …
We show that the two-band nature of noncentrosymmetric superconductors leads naturally to an anomalous Josephson current appearing at zero phase difference in a clean noncentrosymmetric superconductor/ferromagnet/noncentrosymmetric superconductor junction. The two-band nature provides two sets of Andreev bound states which carry two supercurrents with different amplitudes. When the magnetization direction of the ferromagnet is suitably chosen, two supercurrents experience opposite phase shifts from the conventional sinusoidal current-phase relation. Then the total Josephson current results in …
In two-dimensional electron systems with broken inversion and time-reversal symmetries, a Josephson junction reveals an anomalous response: the supercurrent is nonzero even at zero phase difference between two superconductors. We consider details of this peculiar phenomenon in the planar double-barrier configurations of hybrid circuits, where the noncentrosymmetric normal region is described in terms of the paradigmatic Rashba model of spin-orbit coupling. We analyze this anomalous Josephson effect by means of both the Ginzburg-Landau formalism and the microscopic Green's functions approach in…
We consider transport through a Josephson junction consisting of a conventional s-wave superconductor coupled via a double quantum dot to a noncentrosymmetric superconductor with both, singlet and triplet pairing. We calculate the Andreev bound state energies and the associated Josephson current. We demonstrate that the current-phase relation is a sensitive probe of the singlet-triplet ratio in the noncentrosymmetric superconductor. In particular, in the presence of an inhomogeneous magnetic field the system exhibits a $φ$-junction behavior.
We study the Josephson effect in a clean noncentrosymmetric superconductor/half-metal/noncentrosymmetric superconductor junction, which is grown on the surface of a three-dimensional Topological Insulator (TI) in the ballistic limit. We find the signature of anomalous Andreev Bound States (ABS) and band splitting for a spin-active barrier whose barrier magnetic moment is misaligned with the bulk moment. The chiral Majorana mode and 4$π$ periodic ABS are found to exist on the surface of TI for parallel orientation of the moments in the normal incidence condition. But for anti-parallel misalignm…
Majorana corner modes appearing in two-dimensional second-order topological superconductors have great potential applications for fault-tolerant topological quantum computations. We demonstrate that in the presence of an in-plane magentic field two-dimensional ($s+p$)-wave superconductors host Majorana corner modes, whose location can be manipulated by the direction of the magnetic field. In addition, we discuss the effects of edge imperfections on the Majorana corner modes. We describe how different edge shapes and edge disorder affect the number and controllability of the Majorana corner mod…
We report on the microwave characterization of a novel one-dimensional Josephson metamaterial composed of a chain of asymmetric superconducting quantum interference devices (SQUIDs) with nearest-neighbor coupling through common Josephson junctions. This metamaterial demonstrates a strong Kerr nonlinearity, with a Kerr constant tunable over a wide range, from positive to negative values, by a magnetic flux threading the SQUIDs. The experimental results are in good agreement with the theory of nonlinear effects in Josephson chains. The metamaterial is very promising as an active medium for Josep…
We present a mechanism for emission of electromagnetic terahertz waves by simulation. High $T_{c}$ superconductors form naturally stacked Josephson junctions. When an external current and a magnetic field are applied to the sample, fluxon flow induces voltage. The voltage creates oscillating current through the Josephson effect and the current excites the Josephson plasma. The sample works as a cavity, and the input energy is stored in a form of standing wave of the Josephson plasma. A part of the energy is emitted as terahertz waves.
We have fabricated and measured a high-Q Josephson junction resonator with a tunable resonance frequency. A dc magnetic flux allows the resonance frequency to be changed by over 10 %. Weak coupling to the environment allows a quality factor of $\thicksim$7000 when on average less than one photon is stored in the resonator. At large photon numbers, the nonlinearity of the Josephson junction creates two stable oscillation states. This resonator can be used as a tool for investigating the quality of Josephson junctions in qubits below the single photon limit, and can be used as a microwave qubit …
We consider a 0-$π$ Josephson junction consisting of asymmetric 0 and $π$ regions of different lengths $L_0$ and $L_π$ having different critical current densities $j_{c,0}$ and $j_{c,π}$. If both segments are rather short, the whole junction can be described by an \emph{effective} current-phase relation for the spatially averaged phase $ψ$, which includes the usual term $\propto\sin(ψ)$, a \emph{negative} second harmonic term $\propto\sin(2ψ)$ as well as the unusual term $\propto H \cosψ$ tunable by magnetic field $H$. Thus one obtains an electronically tunable current-phase relation. At H=0 t…
The diode effect is fundamental to electronic devices and is widely used in rectifiers and AC-DC converters. At low temperatures, however, conventional semiconductor diodes possess a high resistivity, which yields energy loss and heating during operation. The superconducting diode effect (SDE), which relies on broken inversion symmetry in a superconductor may mitigate this obstacle: in one direction a zero-resistance supercurrent can flow through the diode, but for the opposite direction of current flow, the device enters the normal state with ohmic resistance. The application of a magnetic fi…
Magic-angle twisted bilayer graphene (MATBG) has recently emerged as a highly tunable two-dimensional (2D) material platform exhibiting a wide range of phases, such as metal, insulator, and superconductor states. Local electrostatic control over these phases may enable the creation of versatile quantum devices that were previously not achievable in other single material platforms. Here, we exploit the electrical tunability of MATBG to engineer Josephson junctions and tunneling transistors all within one material, defined solely by electrostatic gates. Our multi-gated device geometry offers com…
We consider an asymmetric 0-pi Josephson junction consisting of 0 and pi regions of different lengths L_0 and L_pi. As predicted earlier this system can be described by an effective sine-Gordon equation for the spatially averaged phase psi so that the effective current-phase relation of this system includes a \emph{negative} second harmonic ~sin(2 psi). If its amplitude is large enough, the ground state of the junction is doubly degenerate psi=\pmvarphi, where varphi depends on the amplitudes of the first and second harmonics. We study the behavior of such a junction in an applied magnetic fie…
We demonstrate unusual features of phase dynamics, IV-characteristics and magnetization dynamics of the $φ_0$ Josephson junction at small values of spin-orbit interaction, ratio of Josephson to magnetic energy and Gilbert damping. In particular, an anomalous shift of the ferromagnetic resonance frequency with an increase of Gilbert damping is found. The ferromagnetic resonance curves show the Duffing oscillator behaviour, reflecting the nonlinear nature of Landau-Lifshitz-Gilbert (LLG) equation. Based on the numerical analysis of each term in LLG equation we obtained an approximated equation d…
We propose tunable superconducting split-ring resonators (SRRs) employing nonlinear Josephson inductance. A fraction of SRR is replaced by Nb-AlOx-Nb Josephson tunnel junctions connected in parallel and forming a superconducting quantum interference device (SQUID), whose inductance is sensitive to the external dc magnetic field. Due to the lumped nature of the Josephson inductance, the SRR can be made very compact and its resonance frequency can be tuned by applying magnetic field. We present the model, results of extensive EM-simulation and experimental data for the SRR weakly coupled to a tr…
We study a 0-$π$ dc superconducting quantum interference device (SQUID) with asymmetric inductances and critical currents of the two Josephson junctions (JJs). By considering such a dc SQUID as a black box with two terminals, we calculate its effective current-phase relation $I_s(ψ)$ and the Josephson energy $U(ψ)$, where $ψ$ is the Josephson phase across the terminals. We show that there is a domain of parameters where the black box has the properties of a $φ$ JJ with degenerate ground state phases $ψ=\pmφ$. The $φ$ domain is rather large, so one can easily construct a $φ$ JJ experimentally. …
With a combination of simple analytical arguments and extensive numerical simulations, we theoretically propose a Josephson junction with $n+1$ superconductors where the current-phase relation can be toggled in situ between a $\sin(δφ)$ and $\sin(δφ/n)$ shape using an applied magnetic field. Focusing in particular on the case $n=2$, we show that by using realistic system parameters such as unequal interface transparencies, the $\sin(δφ/2)$-shaped solution retains its $2π$-periodicity due to discontinuities at $δφ= \pm π$. Moreover, we demonstrate that as one toggles between the $\sin(δφ)$- and…
We propose a controlled Josephson spin current across the junction of two non-centrosymmetric superconductors like CePt_3Si. The Josephson spin current arises due to direction dependent tunneling matrix element and different momentum dependent phases of the triplet components of the gap function. Its modulation with the angle ξbetween the noncentrosymmetric axes of two superconductors is proportional to \sin ξ. This particular dependence on ξmay find application of the proposed set-up in making a Josephson spin switch.
Superconducting materials with noncentrosymmetric lattices lacking space inversion symmetry exhibit a variety of interesting parity-breaking phenomena, including the magneto-electric effect, spin-polarized currents, helical states, and the unusual Josephson effect. We demonstrate, within a Ginzburg-Landau framework describing noncentrosymmetric superconductors with $O$ point group symmetry, that vortices can exhibit an inversion of the magnetic field at a certain distance from the vortex core. In stark contrast to conventional superconducting vortices, the magnetic-field reversal in the parity…
We demonstrate experimentally the operation of a deterministic Josephson ratchet with tunable asymmetry. The ratchet is based on a $φ$ Josephson junction with a ferromagnetic barrier operating in the underdamped regime. The system is probed also under the action of an additional dc current, which acts as a counter force trying to stop the ratchet. Under these conditions the ratchet works against the counter force, thus producing a non-zero output power. Finally, we estimate the efficiency of the $φ$ Josephson junction ratchet.
Josephson tunnel junctions are proposed as efficient phase-tunable thermal rectifiers. The latter exploit the strong temperature dependence of the superconducting density of states and phase-dependence of heat currents flowing through Josephson junctions to operate. Remarkably, large heat rectification coefficients up to 800% can potentially be achieved using conventional materials and standard fabrication methods. In addition, these devices allow for the in-situ fine tuning of the thermal rectification magnitude and direction.
We report on experiments with superconducting metamaterials containing Josephson junctions. In these structures, split-ring resonators used in conventional metamaterials are replaced by superconducting loops that are interrupted by Josephson junctions, so called rf-SQUIDs. Like the split-ring resonators, these elements can be seen as LC-resonators that couple to the magnetic field. The advantage of superconducting thin-film metamaterials is that, due to the tunable intrinsic inductance of the Josephson junction, the resonance frequency of the rf-SQUID can be changed by applying an external dc …
We report the discovery of superconductivity in a series of noncentrosymmetric compounds La$_4$$TX$ ($T$ = Ru, Rh, Ir; $X$ = Al, In), which have a cubic crystal structure with space group $F\bar{4}3m$. La$_4$RuAl, La$_4$RhAl, La$_4$IrAl, La$_4$RuIn and La$_4$IrIn exhibit bulk superconducting transitions with critical temperatures $T_c$ of 1.77 K, 3.05 K, 1.54 K, 0.58 K and 0.93 K, respectively. The specific heat of the La$_4$$T$Al compounds are consistent with an $s$-wave model with a fully open superconducting gap. In all cases, the upper critical fields are well described by the Werthamer-He…
Stochastic switching-current distribution in a graphene-based Josephson junction exhibits a crossover from the classical to quantum regime, revealing the macroscopic quantum tunneling (MQT) of a Josephson phase particle at low temperatures. Microwave spectroscopy measurements indicate a multi-photon absorption process occurring via discrete energy levels in washboard potential well. The crossover temperature for MQT and the quantized level spacing are controlled with the gate voltage, implying its potential application to gate-tunable superconducting quantum bits.
An improved tunable coupling element for building networks of coupled rf-SQUID flux qubits has been experimentally demonstrated. This new form of coupler, based upon the compound Josephson junction rf-SQUID, provides a sign and magnitude tunable mutual inductance between qubits with minimal nonlinear crosstalk from the coupler tuning parameter into the qubits. Quantitative agreement is shown between an effective one-dimensional model of the coupler's potential and measurements of the coupler persistent current and susceptibility.
The scattering through a Josephson junction interrupting a superconducting line is revisited including power leakage. We discuss also how to make tunable and broadband resonant mirrors by concatenating junctions. As an application, we show how to construct cavities using these mirrors, thus connecting two research fields: JJ quantum metamaterials and coupled cavity arrays. We finish by discussing the first non-linear corrections to the scattering and their measurable effects.
We study new types of Josephson junctions composed of helical $p$-wave superconductors with $k_{x}\hat{x}\pm k_{y}\hat{y}$ and $k_{y}\hat{x}\pm k_{x}\hat{y}$-pairing symmetries using quasiclassical Green's functions with the generalized Riccati parametrization. The junctions can host rich ground states: $π$ phase, $0+π$ phase, $φ_{0}$ phase and $φ$ phase. The phase transition can be tuned by rotating the magnetization in the ferromagnetic interface. We present the phase diagrams in the parameter space formed by the orientation of the magnetization or by the magnitude of the interfacial potenti…
We study microwave properties of a superconducting tunable coplanar waveguide (CPW). Pairs of Josephson junctions are forming superconducting quantum interference devices (SQUIDs), which shunt the central conductor of the CPW. The Josephson inductance of the SQUIDs is varied in the range of 0.08-0.5 nH by applying an external dc magnetic field. The central conductor of the CPW contains Josephson junctions connected in series that provide extra inductances; the magnetic field controlling the SQUIDs is weak enough not to influence the inductance of the chain of the single junctions. The circuit …
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.
We investigate the coupling between ferromagnet and superconducting phase dynamics in superconductor-ferromagnet-superconductor Josephson junction. The current-voltage characteristics of the junction demonstrate a pattern of subharmonic current steps which forms a devil's staircase structure. We show that a width of the steps becomes maximal at ferromagnetic resonance. Moreover, we demonstrate that the structure of the steps and their widths can be tuned by changing the frequency of the external magnetic field, ratio of Josephson to magnetic energy, Gilbert damping and the junction size.
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.
In noncentrosymmetric metals, the spin degeneracy of the electronic bands is lifted by spin-orbit coupling. We consider general symmetry properties of the pairing function Delta(k) in noncentrosymmetric superconductors with spin-orbit coupling (NSC), including CePt3Si, UIr and Cd2Re2O7. We find that Delta(k) = chi(k) t(k), where chi(k) is an even function which transforms according to the irreducible representations of the crystallographic point group and t(k) is a model dependent phase factor. We consider tunnelling between a NSC and a conventional superconductor. It is found that, in terms o…
A quantum-mechanical model for the interaction of Josephson vortices (fluxons) embedded in superconducting transmission line is presented. The vortices interact through emission and absorption of linear waves (electromagnetic cavity modes). We show that in a classical regime this peculiar type of interaction is determined by the product of instantaneous velocities of fluxons. In a quantum regime, this property provides tunable coupling between vortices which can be used for entanglement of vortex qubits. The physical mechanism of the vortex interaction is similar to that proposed for qubits ba…
We demonstrate a low-dissipation dielectric metamaterial with tunable properties based on the Josephson effect. Superconducting wires loaded with regularly spaced Josephson junctions ($I_c \approx 0.25$ $μ$A) spanning a K-band waveguide and aligned with the microwave electric fields create a superconducting dielectric metamaterial. Applied dc current tunes the cutoff frequency and effective permittivity of this unique electric metamaterial. The results are in agreement with an analytical model for microwave transmission through the artificial dielectric medium.
We theoretically study the Josephson current in a superconductor/quantum anomalous Hall insulator/superconductor junction by using the lattice Green function technique. When an in-plane external Zeeman field is applied to the quantum anomalous Hall insulator, the Josephson current $J$ flows without a phase difference across the junction $θ$. The phase shift $φ$ appealing in the current-phase relationship $J\propto \sin(θ-φ$) is proportional to the amplitude of Zeeman fields and depends on the direction of Zeeman fields. A phenomenological analysis of the Andreev reflection processes explains t…
Atomtronics has the potential for engineering new types of functional devices, such as Josephson junctions (JJs). Previous studies have mainly focused on JJs whose ground states have 0 or $π$ superconducting phase difference across the junctions, while arbitrarily tunable phase JJs may have important applications in superconducting electronics and quantum computation. Here we show that a phase tunable JJ can be implemented in a spin-orbit coupled cold atomic gas with the magnetic tunneling barrier generated by a spin-dependent focused laser beam. We consider the JJ confined in either a linear …
We propose a heat valve based on the interplay between thermal transport and proximity-induced exchange splitting in Josephson tunnel junctions. We demonstrate that the junction heat conductance strongly depends on the relative alignment of the exchange fields induced in the superconductors. Colossal magneto-heat resistance ratios as large as 10^7% are predicted to occur under proper temperature and phase conditions, as well as suitable ferromagnet-superconductor combinations. Moreover, the quantum phase tailoring, intrinsic to the Josephson coupling, offers an additional degree of freedom for…
Combining the Josephson effect with magnetism, or spin dependence in general, creates novel physical phenomena. The spin-asymmetric Josephson effect is a predicted phenomenon where a spin-dependent potential applied across a Josephson junction induces a spin-polarized Josephson current. Here, we propose an approach to observe the spin-asymmetric Josephson effect with spin-dependent superlattices, realizable, e.g., in ultracold atomic gases. We show that observing this effect is feasible by studying numerically the quantum dynamics of the system in one dimension. Furthermore, we show that the e…
We report experiments on micron-scale normal metal loop connected by superconducting wires, where the sample geometry enables full modulation of the thermal activation barrier with applied magnetic flux, resembling a symmetric quantum interference device. We find that except a constant factor of five, the modulation of the barrier can be well fitted by the Ambegaokar-Halperin model for a resistively shunted junction, extended here to a proximity junction with flux-tunable coupling energy estimated using quasiclassical theory. This observation sheds light on the understanding of effect of therm…
Single flux quantum (SFQ) circuits form a natural neuromorphic technology with SFQ pulses and superconducting transmission lines simulating action potentials and axons, respectively. Here we present a new component, magnetic Josephson junctions, that have a tunablility and re-configurability that was lacking from previous SFQ neuromorphic circuits. The nanoscale magnetic structure acts as a tunable synaptic constituent that modifies the junction critical current. These circuits can operate near the thermal limit where stochastic firing of the neurons is an essential component of the technology…
We consider a finite-size topological Josephson junction formed at the edge of a two-dimensional topological insulator in proximity to conventional superconductors and study the impact of Cooper pair symmetries on the electron transport. We find that, due to the finite junction size, electron transport is highly tunable by the superconducting phase difference $ϕ$ across the junction. At zero frequency and $ϕ=π$, the setup exhibits vanishing local Andreev reflection and perfect normal transmission due to the interplay of finite junction size and formation of topological Andreev bound states in …
We investigate one-dimensional Josephson junction arrays with generalized unit cells as a circuit approach to engineer microwave band gaps. An array described by a lattice with a basis can be designed to have a gap in the electromagnetic spectrum, in full analogy to electronic band gaps in diatomic or many-atomic crystals. We derive the dependence of this gap on the array parameters in the linear regime, and suggest experimentally feasible designs to bring the gap below the single junction plasma frequency. The gap can be tuned in a wide frequency range by applying external flux, and it persis…
We report low temperature, microwave transmission measurements on a new switchable and tunable class of nonlinear metamaterials. A wireless two dimensional array of Josephson junctions (JJ) is probed as a metamaterial where each plaquette in the array is considered as a meta-atom. In the presence of microwaves, this compact metamaterial of 30,000 connected meta-atoms synchronizes the flow of Cooper pairs to yield a single robust resonant signal with a quality factor of 2800 at the lowest temperature for our measurements. The transmission signal is switched on and off and its amplitude and freq…
Broadly Tunable Sub-terahertz Emission from Internal Branches of the Current-voltage Characteristics of Superconducting Bi2Sr2CaCu2O8+d Single Crystals
Dissipation is ubiquitous in quantum systems, and its interplay with fluctuations is critical to maintaining quantum coherence. We experimentally investigate the dissipation dynamics in single-walled carbon nanotubes coupled to superconductors. The voltage-current characteristics display gate-tunable hysteresis, with sizes that perfectly correlate with the normal state resistance RN, indicating the junction undergoes a periodic modulation between underdamped and overdamped regimes. Surprisingly, when a device's Fermi-level is tuned through a local conductance minimum, we observe a gate-control…
We study the coherence of flux-tunable Josephson junction resonators made with two different fabrication processes. In the first process, devices are made using a single step of evaporation in which the resonator and the junctions of the SQUID are made at the same time. In the second process, devices are made with an identical geometry, but in which the resonators are made from a MoRe superconding layer to which an the junctions are added later in a second step. To characterize the coherence of the two types of SQUID cavities, we observe and analyze the quality factor of their resonances as a …
