Higher harmonics in the Josephson effect

In the low temperature regime where macroscopic flux tunneling allows a SQUID magnetometer to follow the stable thermodynamic free energy without hysteretic dissipation, it is possible to exhibit macroscopic quantum behaviour via higher Josephson harmonic oscillations in the thermal response. A simple theory is presented here; the experimental data will appear elsewhere.     

Spin-asymmetric Josephson effect

We propose that with ultracold Fermi gases one can realize a spin-asymmetric Josephson effect in which the two spin components of a Cooper pair are driven asymmetrically--corresponding to driving a Josephson junction of two superconductors with different voltages V(↑) and V(↓) for spin up and down electrons, respectively. We predict that the spin up and down components oscillate at the same frequency but with different amplitudes. Furthermore our results reveal that the standard interpretation of the Josephson supercurrent in terms of coherent bosonic pair tunneling is insufficient. We provide an intuitive interpretation of the Josephson supercurrent as interference in Rabi oscillations of pairs and single particles, the latter causing the asymmetry.     

Mesoscopic Josephson effect

In the classical Josephson effect the phase difference across the junction is well defined, and the supercurrent is reduced only weakly by phase diffusion. For mesoscopic junctions with small capacitance the phase undergoes large quantum fluctuations, and the current is also decreased by Coulomb blockade effects. We discuss the behavior of the current–voltage characteristics in a large range of parameters comprising the phase diffusion regime with coherent Josephson current as well as the supercurrent peak due to incoherent Cooper pair tunneling in the Coulomb blockade regime.     

Josephson effect in fulde-ferrell-larkin-ovchinnikov superconductors

Because of the difference in the momenta of the superconducting order parameters, the Josephson current in a Josephson junction between a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor and a conventional BCS superconductor is suppressed. We show that the Josephson current may be recovered by applying a magnetic field in the junction. The field strength and direction at which the supercurrent recovery occurs depend upon the momentum and structure of the order parameter in the FFLO state. Thus the Josephson effect provides an unambiguous way to detect the existence of an FFLO state, and to measure the momentum of the order parameter.     

Josephson effect in nuclear reactions

The transfer of Cooper pairs during the scattering of two superfluid nuclei just below the Coulomb barrier is discussed on a phenomenological and a microscopic level. This transfer is analogous to the Josephson current between two superconductors. Candidates for the observation of such an effect are heavy ions with a small difference in mass number. Numerical estimates are presented.     

Josephson effect in ferromagnetic superconductors

The DC Josephson effect in ferromagnetic superconductors is theoretically studied in the presence of external magnetic fields. In addition to the usual term for the Josephson tunneling current, a new term expressing the pair tunneling current induced by the magnetization appears. The amplitude and period of the Fraunhofer pattern of the maximum Josephson current drastically diminish near the phase transition temperature for the magnetization bound around the junction.     

Josephson effect throughout the BCS-BEC crossover

We study the stationary Josephson effect for neutral fermions across the BCS-BEC (Bose-Einstein condensate) crossover, by solving numerically the Bogoliubov-de Gennes equations at zero temperature. The Josephson current is found to be considerably enhanced for all barriers at about unitarity. For vanishing barrier, the Josephson critical current approaches the Landau limiting value which, depending on the coupling, is determined by either pair-breaking or sound-mode excitations. In the coupling range from the BCS limit to unitarity, a procedure is proposed to extract the pairing gap from the Landau limiting current.     

Spatial AC Josephson effect

Investigating the current threshold in the mixed state of superconductors basing on the Ginzburg-Landau theory, we find that the threshold is determined by a mechanism analogous to the Josephson effect. An experimental evidence of this phenomenon is presented.     

Josephson effect in coherent roton aggregates

A localized microwave electromagnetic field in liquid helium behaves as a laser of rotons: it produces a coherent roton aggregate. We show that the whispering gallery mode of the dielectric resonator excites multiple coherent aggregates simultaneously and predict a Josephson effect between them. The superfluid velocity around the resonator acts as a “voltage across the weak link” in superconducting Josephson junctions. Josephson frequency-velocity relation agrees with existing experimental data.     

Novel Josephson effect in triplet-superconductor-ferromagnet-triplet-superconductor junctions

We predict a novel type of Josephson effect to occur in triplet-superconductor-ferromagnet-triplet-superconductor Josephson junctions. We show that the Josephson current, IJ, exhibits a rich dependence on the relative orientation between the ferromagnetic moment and the d vectors of the superconductors. This dependence can be used to build several types of Josephson current switches. Moreover, we predict an unconventional sign change of IJ with increasing temperature.     

Magnetic-thermoelectric effect in Josephson SNS junction

A response of the Josephson SNS junction to a heat flow and to an electric current has been studied with the same junction. A non-monotonous dependence of a critical heat flow on the magnetic field B_e is discovered. This dependence is found to be completely identical with the measured function I_c(B_e).     

现场激光能量计量技术的研究

由于激光能量计传感器的灵敏度与温度条件有关，在温差较大时，有的传感器灵敏度偏差可达到16%，因而在靶场、野外现场温度条件下，现有的激光能量计无法进行准确测试。为了解决这一问题，研制了一种新型的现场激光能量计。在现有激光能量计的基础上，通过选择相对透明、吸收层相对较厚(毫米量级)、热敏面不易损伤的激光吸收材料，对激光能量计内置温度传感器及数字处理电路进行了重新设计，满足了不同温度条件下现场能量测量的需求。     

Resistance metrology based on the quantum Hall effect

The Quantum Hall effect (QHE), a macroscopic effect of solid state physics, provides a universal representation of the unit of resistance which depends on the elementary charge e and the Planck constant h only. If implemented according to specific technical guidelines, the quantum resistance standard can be reproduced with a relative uncertainty below one part in 10⁹. Calibrations of wire resistors in terms of the QHE can be carried out with similarly low uncertainties by using resistance bridges equipped with cryogenic current comparators, the performance of which relies on the magnetic flux sensitivity of superconducting quantum interference devices (SQUID). Using a special connection technique, the fundamental properties of the QHE allow the fabrication of arrays combining a large number of single Hall bars connected in series or in parallel and which demonstrate quantum accuracy. Similar to the case of voltage metrology with Josephson array voltage standards, an improvement of resistance metrology is expected from the availability of quantum Hall array resistance standards (QHARS). The QHE Wheatstone bridge, which is another application of the same connection technique, opens the way to new universality tests of the QHE with a relative uncertainty below one part in 10¹¹. At frequencies in the kilohertz range, the recent progress in the application of coaxial bridges to the QHE allows metrologists to operate a quantum resistance standard with alternating current reaching an accuracy of some parts in 10⁸. Finally, the discovery of the QHE in graphene opens new horizons for the resistance metrology.     

AC Josephson effect in the long voltage-biased SINIS junction

Theory of non-stationary coherent effects is developed for superconductor-normal-superconductor (SNS) structures with relatively strong normal scattering on S/N interfaces (interface resistance is large compared to intrinsic resistance of N metal). Analytical expressions are found for the time-dependent anomalous Green’s functions induced in the N region under the fixed-voltage-bias. The amplitude of the current oscillations is determined in non-equilibrium conditions. Non-stationary correction to the distribution function is calculated in high-temperature limit and found to be slowly decreasing with the temperature, leading to the dominance of the second-harmonic term in the Josephson current, I _s (t) ∝ sin(4eVt) at high temperatures and low voltage. The article is published in the original.     

A scattering model of the DC Josephson effect

We introduce the idea of phase shift into the scattering model of the Josephson effect by Orlowski.