Unconventional Current-phase Relation Research Articles

Effect of unconventional current-phase relation of Josephson junction on escape rate in ac SQUID

The escape rate of S→R switching (from superconducting S state to unstable resistive R state) in an ac SQUID on Josephson junction with unconventional current-phase relation was investigated. We used two types of current-phase relations with additional terms to the first harmonic sinϕ: a case of the second harmonic sin2ϕ and a case of the fractional term sin(ϕ/2). It was shown that escape rate can exhibit qualitative features in the case of junctions with unconventional current-phase relations.

Effect of Unconventional Current-Phase Relation of Josephson Junction on Escape Rate in Ac Squid

Effect of Unconventional Current-Phase Relation of Josephson Junction on Escape Rate in Ac Squid

Return current of dc SQUID based on tunnel Josephson junctions with unconventional current-phase relation

We carried out the analysis of the return current of dc SQUID based on tunnel Josephson junction with unconventional current-phase relation. We analyzed two cases of current-phase relation with additional terms to the first harmonic sin φ: a case of the second harmonic sin 2φ and the case of the fractional term sin (φ/2). It is shown that the changing of the return current of dc SQUID on junctions with unconventional current-phase relation is determined by the amplitude of the second term in current-phase relation, geometrical inductance, and external magnetic field.

CURRENT-VOLTAGE CHARACTERISTIC OF JOSEPHSON JUNCTION WITH FRACTIONAL TERM IN CURRENT-PHASE RELATION

In this study, we carried out the analysis of the influence of unconventional current-phase relation of Josephson junction with additional fractional term sin\phi/2 to first harmonic sin\phion current-voltage characteristics. The current-voltage characteristic of the junction was calculated for the different amplitudes of fractional term m and McCumber parameter . It was shown increasing the amplitude of fractional terms leads to increasing in the hysretesis on the current-voltage characteristics.

INFLUENCE OF UNCONVENTIONAL CURRENT-PHASE RELATION ON CHAOTIC DYNAMICS OF JOSEPHSON JUNCTIONS

In this paper, we study the influence of unconventional current-phase relation (CPR) of Josephson junction on chaotic dynamics. The influence of the second term of CPR on an externally shunted Josephson junction with nonzero inductance has been studied. Using the circuit model, the time-dependent simulations are carried out for a variety of control parameters. It is shown that the presence of the second term on CPR leads to a change in the boundary of the chaotic region in the bifurcation diagram.

Critical current of dc SQUID on Josephson junctions with unconventional current-phase relation

Here we present calculations of the critical current of dc SQUID based on Josephson junction with un-conventional current-phase relation. We analyzed two cases of current-phase relation of junction: with anhar-monic and Majorana term. It is shown that the changing of the critical current in the case of the small geo-metrical inductance of dc SQUID based on Josephson junctions with unconventional current-phase relation is determined by the amplitude of the second term in current-phase relation, the geometrical inductance of dc SQUID and external magnetic field. In the case of the high inductance of dc SQUID unconventional terms can be ignored.

Influence of Unconventional Current-Phase Relation on Return Current of Tunnel Josephson Junctions

In this study, we carried out the analysis of the return current of Josephson junction with unconventional current-phase relation. We analyzed two types of current-phase relation with additional terms to first harmonic sinφ: the case of second harmonic sin2φ and the case of fractional term $$ \sin \frac{\varphi }{2} $$ . Numerical methods were employed for the calculations of return current by considering the different amplitudes of the second term in unconventional current-phase relation. It is shown that there is an opposite relation between the return current of Josephson junction with unconventional current-phase relation and the amplitude value of the second term. It can be stated that the return current of Josephson junction can be decreased by increasing the amplitude of the second term.

Influence of unconventional current-phase relation of Josephson junction on the escape rate in macroscopic quantum tunneling regime

In this study, we carried out the analysis of the quantum fluctuations on Josephson junction (JJ) dynamics with unconventional current-phase relation (CPR). We analyzed two case CPR: anharmonic term case and the case of Majorana term. The expression was obtained for the escape rate in macroscopic tunneling regime. It is shown that the changing of the escape rate JJ with unconventional CPR is determined by the renormalized critical current of JJ.

Effects of Thermal Fluctuations on Dynamics of Josephson Junction with Unconventional Current-Phase Relation

In this study, we carried out the analysis of the thermal fluctuations on Josephson junction (JJ) dynamics with unconventional current-phase relation (CPR). We analyzed two cases of CPR: the anharmonic term case and the case of Majorana term. An expression was obtained for the delay time and the critical current fluctuations in the case of linear growth of current via junction in two limits: low and high growth rate. The dynamical properties of JJ with unconventional CPR are determined by the renormalized critical current of JJ.

Quantum pumping in deformable quantum dots

The charge current pumped adiabatically through a deformable quantum dot is studied within the Green's function approach. Differently from the non-deformable case, the current shows an undefined parity with respect to the pumping phase \phi. The unconventional current-phase relation, analyzed in the weak pumping regime, is due to a dynamical phase shift \phi_D caused by the elastic deformations of the central region (classical phonons). The role of the quality factor Q of the oscillator, the effects induced by a mechanical resonance and the implications for current experiments on molecular systems are also discussed.

YBCO SQUIDs with unconventional current phase relation

We have studied the dynamics of YBa2Cu3O7−δ (YBCO) dc sperconducting quantum interference devices (SQUIDs) characterized by an unconventional Josephson current phase relation (CPR). We have focused on SQUID configurations with Josephson junctions where the lobe of the order parameter in one electrode is facing a node in the other electrode. This order parameter arrangement should enhance the appearance of a sin(2φ) term in the CPR. The response of the critical current of the dc SQUID, under the effect of an external magnetic field, has been measured in temperature, down to 20mK. Our experimental data have been compared with numerical simulations of the SQUIDs dynamics by considering a CPR of a single junction of the form I(φ)=IIsin(φ)−IIIsin(2φ) where II and III are, respectively, the first and second harmonic component. In our devices the values of the sin(2φ) term are such that the fundamental state of the SQUID is naturally double degenerate. This is of great relevance for applications of d-wave SQUIDs in quantum information processing.

Superconducting Quantum Interference Filters Consisting of Josephson Junctions With Unconventional Current-Phase Relation

Superconducting quantum interference filters (SQIFs) are parallel or serial Josephson junction arrays with a unique DC voltage output around vanishing magnetic field B = 0. Certain features of the voltage output also depend on the current-phase relation of the individual junctions in the array. Taking into account the first two harmonics I/sub c1/ and I/sub c2/ of the supercurrent we investigate the DC voltage output of the array. In particular we describe a characteristic magnetic field asymmetry of the voltage output. Applications of the theory include the design of SQIFs with novel flux to voltage transfer functions using high-T/sub c/ superconductors on bi- or tri-crystal substrates.

Macroscopic Quantum Tunneling ind-WaveYBa2Cu3O7−δJosephson Junctions

The escape rate from the zero voltage state in a superconducting Josephson junction (JJ) is determined by the temperature, but it saturates at low temperature due to macroscopic quantum tunneling (MQT). Complications due to d-wave symmetry in a high temperature superconductor, like low energy quasiparticles and an unconventional current-phase relation, may influence the escape rate. We report, for the first time to our knowledge, the observation of MQT in a YBa(2)Cu(3)O(7-delta) grain boundary biepitaxial JJ. This proves that dissipation can be significantly reduced by a proper junction configuration, which is of significance for quantum coherence.

Structurally asymmetric d.c. SQUID?s in the presence of coupling energy inhomogeneity of the junctions studied by means of the reduced two-junction interferometer model

The effects of structural asymmetries and of inhomogeneities in the junction parameters on the electrodynamic response of conventional d.c. SQUID’s are studied both analytically and numerically. By a first-order perturbative expansion with respect to the parameter β and to the deviation parameters describing structural asymmetry and inhomogeneity, we write the reduced dynamical equation for the average superconducting phase difference of a conventional d.c. SQUID. As in homogeneous and symmetric SQUID’s, the resulting dynamical equation is seen to be similar to that of a single junction with an unconventional current-phase relation characterized by a second harmonic contribution; in addition, a cosine term appears as a consequence of superconducting coupling inhomogeneity. By means of the reduced dynamical equation, the I-V characteristics in the presence of an external rf field and the critical current of the device are studied in the absence of noise.

Effective non-sinusoidal current-phase dependence in conventional d.c. SQUIDs

We show, by a first-order perturbative expansion with respect to the parameter β, that the dimensionality of the dynamical equations for the superconducting phase differences of a structurally symmetric conventional d.c. SQUID can be reduced from two to one. Taking completely into account the electromagnetic coupling of the two junctions, the resulting dynamical equation is seen to be similar to that of a single junction with an unconventional current-phase relation characterized by a second harmonic contribution. Effects of this unconventional term on the I– V characteristics of d.c. SQUIDs in the presence of an external rf field are presented.

Dynamical effects of an unconventional current-phase relation in YBCO dc SQUIDs.

The predominant d-wave pairing symmetry in high-temperature superconductors allows for a variety of current-phase relations in Josephson junctions, which is to a certain degree fabrication controlled. In this Letter, we report on direct experimental observations of the effects of a nonsinusoidal current-phase dependence in YBCO dc SQUIDs, which agree with the theoretical description of the system.

Peculiarities of radio frequency YBa2Cu3O7−x superconducting quantum interference device response with a finite amplitude of the second harmonic in the current-phase relationship

The signal properties of radio frequency (rf) (SQUIDs) based on YBa2Cu3O7−x symmetrical 30° and asymmetrical 45° grain-boundary Josephson junctions have been experimentally investigated. Both amplitude as well as phase detection have been used to read out the SQUID output signal. Comparison of the SQUID output signals to each other is given. It is shown that peculiarities of the rf SQUID response of SQUIDs with a 45° grain-boundary Josephson junction are consistent with an unconventional current-phase relation (CPR) of the Josephson junction, namely, the CPR contains a finite amplitude of the second harmonic.