# Edward GoldobinUniversity of Tuebingen | EKU Tübingen · Physical Institute

Edward Goldobin

Prof. Dr.

## About

118

Publications

7,665

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2,898

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Introduction

physics of 0, π, 0-π, φ Josephson junctions

Education

January 2007 - January 2013

September 1993 - November 1997

## Publications

Publications (118)

By scanning with a 30-keV focused He ion beam (He-FIB) across YBa2Cu3O7 (YBCO) thin-film microbridges, we create Josephson barriers with critical current density jc adjustable by irradiation dose D. The dependence jc(D) yields an exponential decay. At 4.2K, a transition from flux-flow to Josephson behavior occurs when jc decreases below approximate...

By scanning with a 30keV focused He ion beam (He-FIB) across YBa2Cu3O7 (YBCO) thin film microbridges, we create Josephson barriers with critical current density jc adjustable by irradiation dose D. The dependence jc(D) decays exponentially. At 4.2 K, a transition from flux-flow to Josephson behavior occurs when jc decreases below ≈2MA/cm2. The Jose...

We study Nb−AlOx-Nb Josephson junctions (JJs) with a phase-discontinuity κ created by a pair of current injectors attached to one of the Nb electrodes. For κ≈π the Josephson potential energy U as a function of the average phase ψ across the JJ has the form of a 2π-periodic double-well potential. Thus, the device behaves as a φ JJ with degenerate gr...

The possibility of a fast and precise Abrikosov vortex manipulation by a focused laser beam opens the way to create laser-driven Josephson junctions. We theoretically demonstrate that a vortex pinned in the vicinity of the Josephson junction generates an arbitrary ground state phase which can be equal not only to 0 or π but to any desired φ0 value...

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 counterforce trying to stop the ratchet. Und...

We demonstrate experimentally the operation of a deterministic Josephson ratchet with tunable asymmetry. The ratchet is based on a $\varphi$ 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 rat...

We propose simple models for the current-voltage characteristics of typical Josephson ratchets. We consider the case of a ratchet working against a constant applied counter force and derive analytical expressions for the key characteristics of such a ratchet: rectification curve, stopping force, input and output powers and rectification efficiency....

We investigate experimentally the retrapping of the phase in a φ Josephson junction upon return of the junction to the zero-voltage state. Since the Josephson energy profile U0(ψ) in φ JJ is a 2π periodic double-well potential with minima at ψ=±φmod2π, the question is at which of the two minima −φ or +φ the phase will be trapped upon return from a...

Using the Usadel approach, we provide a formalism that allows us to calculate the critical current density of 21 different types of Josephson junctions (JJs) with a ferromagnetic (F) barrier and additional insulating (I) or/and normal (N) layers inserted between the F layer and superconducting (S) electrodes. In particular, we obtain that in SFS JJ...

We consider a short Josephson junction with a phase discontinuity $\kappa$
created, e.g., by a pair of tiny current injectors, at some point $x_0$ along
the length of the junction. We derive the effective current-phase relation
(CPR) for the system as a whole, i.e., reduce it to an effective point-like
junction. From the effective CPR we obtain the...

We study a 0-$\pi$ 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 $I_s(\psi)$ and
the Josephson energy $U(\psi)$, where $\psi$ is the Jose...

The 0–π transition in Superconductor-Insulator-superconductor-Ferromagnet-Superconductor (SIsFS) Josephson junctions (JJs) was investigated experimentally. As predicted by theory, an s-layer inserted into a ferromagnetic SIFS junction can enhance the critical current density up to the value of an SIS
tunnel junction. We fabricated Nb′ | AlOx | Nb |...

We used one-dimensional coupled sine-Gordon equations combined with heat
diffusion equations to numerically investigate the thermal and electromagnetic
properties of a 300$\mu$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...

We demonstrate a high-frequency generator operating at ~200GHz based on
flipping a semifluxon in a Josephson junction of moderate normalized length.
The semifluxon spontaneously appears at the $\pi$ discontinuity of the
Josephson phase artificially created by means of two tiny current injectors.
The radiation is detected by an on-chip detector (tun...

Using the Usadel equation approach, we have calculated the critical current
density in ferromagnetic (F) Josephson junctions of different types containing
insulating (I) and normal metal (N) layers in the weak link region. Even a thin
additional N layer may change the boundary conditions at the SF or IF
interface, where S is a superconducting elect...

We consider a φ Josephson junction, which has a bistable zero-voltage state with the stationary phases ψ=±φ. In the nonzero voltage state the phase "moves" viscously along a tilted periodic double-well potential. When the tilting is reduced quasistatically, the phase is retrapped in one of the potential wells. We study the viscous phase dynamics to...

We present a combinatorial sputtering technique to fabricate alloy thin films with orthogonal gradients of thickness and stoichiometry in a planetary type sputtering system. Using this approach we prepared a library of planar Nb Josephson junctions with a magnetic compound layer made from Si and Fe on one wafer. The independent investigation of thi...

The φ Josephson junction has a doubly degenerate ground state with the Josephson phases ±φ. We demonstrate the use of such a φ Josephson junction as a memory cell (classical bit), where writing is done by applying a magnetic field and reading by applying a bias current. In the “store” state, the junction does not require any bias or magnetic field,...

We consider an infinitely long 0-π Josephson junction consisting of 0 and π regions having dif-ferent critical current densities jc,0 and jc,π. The ground state of such a junction corresponds to a spontaneosly formed asymmetric semifluxon with tails decaying on different length scales. We calculate the depinning current of such a fractional vortex...

We calculate the current-phase relation of a planar Josephson junction with a ferromagnetic weak link located on top of a thin normal metal film. Following experimental observations we assume transparent superconductor-ferromagnet interfaces. This provides the best interlayer coupling and a low suppression of the superconducting correlations penetr...

We propose to create pairs of semifluxons starting from a flat-phase state in
long, optical 0-pi-0 Josephson junctions formed with internal electronic states
of atomic Bose-Einstein condensates. In this optical system, we can dynamically
tune the length of the pi-junction, the detuning of the optical transition, or
the strength of the laser-couplin...

We study the critical current Ic dependence on applied magnetic field H for multifacet YBa2Cu3O7−δ/Au/Nb ramp-type zigzag Josephson junctions. For many experiments, one would like to apply a homogeneous field in the junction plane. However, even tiny misalignments can cause drastic deviations from homogeneity. We show this explicitly by measuring a...

For high-performance superconducting quantum devices based on Josephson
junctions (JJs) decreasing lateral sizes is of great importance. Fabrication of
sub-\mu m JJs is challenging due to non-flat surfaces with step heights of up
to several 100 nm generated during the fabrication process. We have refined a
fabrication process with significantly dec...

We demonstrate experimentally the existence of Josephson junctions having a doubly degenerate ground state with an average Josephson phase $psi=pmvarphi$. The value of $varphi$ can be chosen by design in the interval $0<varphi<pi$. The junctions used in our experiments are fabricated as 0-$pi$ Josephson junctions of moderate normalized length with...

We propose a tunable macroscopic quantum system based on two fractional
vortices. Our analysis shows that two coupled fractional vortices pinned at two
artificially created \kappa\ discontinuities of the Josephson phase in a long
Josephson junction can reach the quantum regime where coherent quantum
oscillations arise. For this purpose we map the d...

We consider a 0-$\pi$ Josephson junction consisting of asymmetric 0 and $\pi$ regions of different lengths $L_0$ and $L_\pi$ having different critical current densities $j_{c,0}$ and $j_{c,\pi}$. If both segments are rather short, the whole junction can be described by an \emph{effective} current-phase relation for the spatially averaged phase $\ps...

We investigate experimentally a deterministic underdamped Josephson vortex ratchet-a fluxon particle moving along a Josephson junction in an asymmetric periodic potential. By applying a sinusoidal driving current, one can compel the vortex to move in a certain direction, producing an average dc voltage across the junction. Being in such a rectifica...

We consider an asymmetric 0-π Josephson junction consisting of 0 and π regions of different lengths L(0) and L(π). As predicted earlier this system can be described by an effective sine-Gordon equation for the spatially averaged phase ψ so that the effective current-phase relation of this system includes a negative second harmonic ∝sin(2ψ). If its...

In long Josephson junctions with multiple discontinuities of the Josephson
phase, fractional vortex molecules are spontaneously formed. At each
discontinuity point a fractional Josephson vortex carrying a magnetic flux
$|\Phi|<\Phi_0$, $\Phi_0\approx 2.07\times 10^{-15}$ Wb being the magnetic flux
quantum, is pinned. Each vortex has an oscillatory...

The proximity effect and the Josephson current in a
superconductor-insulator-ferromagnet-superconductor (SIFS) junction are
investigated within the framework of the quasiclassical Eilenberger equations.
This investigation allows us to compare the dirty and the clean limits, to
investigate an arbitrary impurity scattering, and to determine the
appli...

At high enough input power in stacks of Bi2Sr2CaCu2O8 intrinsic Josephson junctions a hot spot (a region heated to above the superconducting transition temperature) coexists with regions being still in the superconducting state. In the “cold” regions cavity resonances can occur, synchronizing the ac Josephson currents and giving rise to strong and...

Josephson comparator with modified dynamic behavior for improved sensitivity J. Appl. Phys. 111, 123901 (2012) Effect of thermal inhomogeneity for terahertz radiation from intrinsic Josephson junction stacks of Bi2Sr2CaCu2O8+δ Appl. Phys. Lett. 100, 242603 (2012) Two-dimensional magnetic field dependence of Josephson current and resonant current st...

In this chapter we review the basics of quantum computation and discuss promising physical systems for implementation of a qubit. The advantage of quantum computation over classical computation is shown by presenting the quantum algorithms for searching databases and factorizing numbers. In addition, quantum bits are ideal candidates for secure com...

We present the latest generation of superconductor–insulator–ferromagnet–superconductor Josephson
tunnel junctions with a step-like thickness of the ferromagnetic (F) layer. The F-layer thicknesses
d1 and
d2 in both
halves were varied to obtain different combinations of positive and negative critical current densities
jc, 1 and
jc, 2. The measured...

We have realized multifacet Josephson junctions with periodically alternating
critical current density (MJJs) using
superconductor-insulator-ferromagnet-superconductor heterostructures. We show
that anomalous features of critical current vs. applied magnetic field,
observed also for other types of MJJs, are caused by a non-uniform flux density
(par...

We propose a method to realize a phi Josephson junction by combining alternating 0 and pi parts (sub junctions) with an intrinsically nonsinusoidal current-phase relation (CPR). Conditions for the realization of the phi ground state are analyzed. It is shown that taking into account the nonsinusoidal CPR for a ``clean'' junction with a ferromagneti...

We consider a symmetric 0-$pi$ Josephson junction of length $L$, which classically can be in one of two degenerate ground states states or statea, corresponding to supercurrents circulating clockwise or counterclockwise around the 0-$pi$ boundary. When the length $L$ of the junction becomes smaller than the Josephson penetration depth $lambda_J$, t...

We present a detailed analysis of the dependence of the critical current Ic on an in-plane magnetic field B of 0, π, and 0-π superconductor-insulator-ferromagnet-superconductor Josephson junctions. Ic(B) of the 0 and the π junction closely follows a Fraunhofer pattern, indicating a homogeneous critical current density jc(x). The maximum of Ic(B) is...

We demonstrate the operation of a deterministic fluxon ratchet made of a
stack of 30 intrinsic
Bi2Sr2CaCu2O8 Josephson
junctions. The ratchet has the shape of a gear with 20 asymmetric teeth
(periods). It produces a rectified voltage of about 100μV at a 12
GHz drive frequency. The effect of coupling between intrinsic junctions,
i.e., the mode of fl...

Josephson junctions with ferromagnetic barrier can have positive or negative critical current depending on the thickness $d_F$ of the ferromagnetic layer. Accordingly, the Josephson phase in the ground state is equal to 0 (a conventional or 0 junction) or to $\pi$ ($\pi$ junction). When 0 and $\pi$ segments are joined to form a "0-$\pi$ junction",...

Within the framework of the quasiclassical Usadel equations we study the Josephson effect in superconductor-insulator-ferromagnet-superconductor (SIFS) and SIFNS (N is a normal metal) structures with a step-like transparency of the FS or NS interface. At certain parameters the step- like transparency leads to the formation of a region where the cri...

We consider a fractional Josephson vortex in an infinitely long 0-kappa Josephson junction. A uniform bias current applied to the junction exerts a Lorentz force acting on a vortex. When the bias current becomes equal to the critical (or depinning) current, the Lorentz force tears away an integer fluxon and the junction switches to the resistive st...

Low-temperature scanning electron microscopy (LTSEM) has been used to image the supercurrent distribution in ramp-type Josephson junctions between Nb and either the electron-doped cuprate Nd_{2-x}Ce_{x}CuO_{4-y} or the hole-doped cuprate YBa_{2}Cu_{3}O_{7}. For zigzag-shaped devices in the short junction limit the critical current is strongly suppr...

We present experimental studies of high quality underdamped 0, pi, and 0-pi ferromagnetic Josephson tunnel junctions of intermediate length L (lambda_J < L < 5 lambda_J, where lambda_J is the Josephson penetration depth). The junctions are fabricated as Nb/Al_2O_3/Cu_40Ni_60/Nb Superconductor-Insulator-Ferromagnet-Superconductor heterostructures. U...

We consider a fractional Josephson vortex in a long 0-kappa Josephson junction. A uniformly applied bias current exerts a Lorentz force on the vortex. If the bias current exceeds the critical current, an integer fluxon is torn off the kappa-vortex and the junction switches to the voltage state. In the presence of thermal fluctuations the escape pro...

Josephson junctions with a phase drop of pi in the ground state allow us to create vortices of supercurrent carrying only half of the magnetic flux quantum Phi0 approximately 2.07 x 10(-15) Wb. Such semifluxons have twofold degenerate ground states denoted upward arrow (with flux +Phi0/2 and supercurrent circulating clockwise) and downward arrow (w...

We consider a symmetric 0-pi Josephson junction of length $L$, which
classically can be in one of two degenerate ground states up or down,
corresponding to supercurrents circulating clockwise or counterclockwise
around the 0-pi boundary. When the length $L$ of the junction becomes
smaller than the Josephson penetration depth $\lambda_J$, the system...

We summarize our results on Josephson heterostructures Nb/Au/YBa2Cu3Ox that combine conventional (S) and oxide high-Tc superconductors with a dominant d-wave symmetry of the superconducting order parameter (D). The heterostructures were fabricated on (001) and (1 1 20) YBa2Cu3Ox films grown by pulsed laser deposition. The structural and surface stu...

We present experimental studies of static and dynamic properties of 0, pi and 0-pi superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson junctions of small and intermediate length. In the underdamped limit these junctions exhibit a rich dynamical behavior such as resonant steps on the current-voltage characteristics. Varying the expe...

The Josephson effect in a superconductor-insulator-ferromagnet-superconductor structure with a stepwise change in the transparency
of the superconductor/ferromagnet interface has been investigated within the formalism of the Usadel equations. It is shown
that, at a certain thickness of the ferromagnet layer, this feature leads to the formation of a...

Josephson junctions and junction arrays are well studied devices in superconductivity. With external magnetic fields one can modulate the phase in a long junction and create traveling, solitonic waves of magnetic flux, called fluxons. Today, it is also possible to device two different types of junctions: depending on the sign of the critical curren...

Within the framework of the Usadel equations, the Josephson effect in a superconductor-insulator-ferromagnet-superconductor
(SIFS) structure with a spatially heterogeneous transparency of the SF interface has been studied. It is shown that, at a
certain thickness of the F layer, a stepwise variation of the transparency leads to the formation of a r...

Several recent experiments revealed a change of the sign of the first harmonic in the current-phase relation of Josephson junctions (JJs) based on, e.g., d-wave superconductors or JJs with ferromagnetic barrier. In this situation, the role of the second harmonic can become dominant; in this case, it determines the scenario of a 0-π transition. We d...

We present a study on low-Tc superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson junctions. SIFS junctions have gained considerable interest
in recent years because they show a number of interesting properties for future classical and quantum computing devices. We
optimized the fabrication process of these junctions to achieve a ho...