A. M. Tskhovrebov

Self-consistent spatially inhomogeneous state in HTSC Ba1-x KxBiO3 single crystals

A spatially inhomogeneous state in HTSC Ba1-xKxBiO3 single crystals (Tc ≈ 30 K, x = 0.4) has been studied at T < Ť ≈ 17 K, where Ť is the temperature of separation into superconducting and dielectric phases. This separation has earlier been detected in Ba1-xKxBiO3 polycrystals. In the single crystals, the main results are obtained from hysteretic magnetization reversal curves, whereas the character of separation in the polycrystals is clearly visible from I–V curves. The results obtained support the theoretical model of HTSC separation proposed in [1].

The anomalous magnetic properties of high-TC Ba–K–Bi–O in superconducting state

Abstract The magnetic response of HTSC Ba–K–Bi–O single crystals in superconducting state was investigated with the help of a small Hall detector. The magnetic moment of the sample was measured as a function of the magnetic field up to 650 Oe and as a function of temperature while heating in the external magnetic field. Distinct paramagnetic response (PMR) was observed. In contrast to the other works where “paramagnetic Meissner effect” was noted these experiments were carried out on zero field cooled samples and the paramagnetic response was exhibited both at very low (

The dc-current destruction of superconducting state and hysteresis effects in Ba−K−Bi−O

The dc-current destruction of superconducting state in Ba−K−Bi−O was registered simultaneously both by measuring V–I characteristic and magnetic susceptibility χ. The experiments were carried out on the polycrystall samples in the temperature interval 1.5–4.2 K. The hysteresis of both characteristics was observed, the temperature dependencies of hysteresis value of V–I and c-I being quiet opposite. The nonmonotonic temperature dependence of I has been found. The observed effects can be explained in the framework of the model, according to which the special nonhomogeneous state can arise—the space structure of the alternate superconducting and insulating regions with Josephson tunnelling between the former.

Two-channel scheme for dark matter particle detection based on a low-temperature magnetic calorimeter

Problems of dark matter (DM) particle detection are briefly reviewed. An original two-channel scheme for direct detection of cosmic DM particles is proposed. This scheme is based on a superlow-temperature calorimeter which includes a nuclear spin system whose magnetic response is measured by a quantum interferometer (SQUID). Low threshold and the capability for efficiently suppressing the recoil-electron background are the most important advantages of the proposed scheme. They make it possible to detect DM particles in the range of extremely low recoil energies and carry out direct DM search with high sensitivity.

Observation of latent coherent effects in randomized systems

Coherent interference effects of the following three types are experimentally discovered in disordered (randomized) systems: (i) Josephson behavior of the HTSC polycrystal BaKBiO in the phase-separated state; (ii) oscillations of bismuth film resistance, which are periodic in “direct” magnetic field; and (iii) mesoscopic oscillations of the resistance in the course of film growth. In the first case, the method for detecting the “latent” nonstationary Josephson effect is substantiated by the frequency modulation method for microwave radiation, while in the other two cases, simple models are proposed to explain the nature of coherent oscillations of the resistance. The analogy between the observed oscillations and the Josephson effect in randomized systems is discussed.

H–T phase diagram of high-Tc Ba–K–Bi–O

Abstract The magnetic behavior of Ba–K–Bi–O single crystals below T c was investigated. The magnetic moment hysteresis loops were examined with the help of a small Hall detector. The complex analysis of the data on the temperature dependencies of the residual magnetic moment and H c1 , obtained from the magnetic experiments, and the resistive superconducting transition curves give rise to the following picture: at T c =30 K the transition to the continuous superconducting phase takes place, while at T * =17 K one more transition happens––to the spatially inhomogeneous superconductor–insulator state, that also could be destroyed either by temperature or by magnetic field.

On the possibility of detecting low-energy scalar and pseudo-scalar bosons

The properties of the conversion of “cold” extra-light scalar or pseudo-scalar bosons weakly interacting with material media to photons with energies of 0.001–1.0 meV are analyzed. Various possible experimental schemes including closed resonant cells at low temperatures and highly sensitive receivers of radio-frequency photons are presented. The existence of such elementary particles is predicted in various expansion versions of the “standard model”. Their direct or indirect detection would make it possible to clarify the nature of the “dark matter” phenomenon.

Ordinary SQUID interferometers and superfluid helium matter wave interferometers: The role of quantum fluctuations

When comparing the operation of a superfluid helium matter wave quantum interferometer (He SQUID) with that of an ordinary direct-current quantum interferometer (dc SQUID), we estimate their resolution limitation that correspond to quantum fluctuations. An alternative mode of operation of the interferometer as a unified macroquantum system is considered.

The resolution limit of the detector on the base of the magnetic adiabatic calorimeter operating in the region of the ferromagnetic transition

The energy resolution of the detector on the base of the magnetic adiabatic calorimeter (MAC) operating in the region of the ferromagnetic transition has been estimated on the basis of the Ginzburg-Landau theory. It is assumed that the MAC is set into operating position at low temperature by the adiabatic demagnetisation method. The magnetic response caused by the energy release at a particle entering is detected by SQUID. The estimation of the system sensibility demonstrates the feasibility of the application of the MAC as a weak interacting particles detector.

The new method of frequency modulated microwave field to observe Josephson behavior of the weak links system

Abstract The method of frequency modulation of microwave radiation to observe Josephson behavior of multicircuit weak links system is suggested. The possibilities of the method are theoretically analyzed for the case of the system consisting of many Josephson contacts with random parameters. The technique was sampled on the example of polycrystalline high-T c Ba 0.6 K 0.4 BiO 3 .