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We present here the results of angular-dependent magnetization measurements (both ac and dc) carried out in a weakly-pinned single crystal of a low Tc superconductor, Yb3Rh4Sn13. Both dc magnetization data (M-H) as well as the ac magnetic susceptibility plots (χ´(H)) have revealed the fingerprints of an order-disorder transition in the vortex matter for various orientations of the crystal with respect to the external magnetic field. Our findings show that the quality of the ordered Bragg glass (BG) phase in this isotropic compound depends significantly on the direction of the magnetic field with respect to the crystallographic axes; a better spatially ordered vortex configuration is obtained when the magnetic field is applied along the [110] direction than that when the magnetic field is applied along the [100] axis. The present findings in Yb3Rh4Sn13 bear resemblance with similar results reported earlier for borocarbide superconductors.

We present electro-transport studies of polycrystalline FeSe0.94 optimally doped with 6 wt % Ag. The effect of different AC current amplitudes on the superconducting transition and the pinning properties are investigated. Inverse power law dependence of the pinning energy from the applied current is detected, corresponding to a domination of collective pinning / creep of large size vortex bundles. Additionally, using a V-I dynamical (hysteresis type) characteristics, the weak links effects on the vortex dynamics were studied and particularly the temperature dependence of the critical current at close vicinity region near to Tc. There are strong implications for proximity effect (SNS type junctions) induced by Ag-addition grain periphery segregation.

We present the results of ac resistivity measurements (R(H,T)) carried out in a weakly-pinned single crystal of a low Tc superconductor, Ca3Ir4Sn13. The isofield (R(T)) and isothermal (R(H)) scans revealed the fingerprints of the quintessential peak effect phenomenon in this compound. At some temperatures (near 4 K), we also observed a step-like feature in R(H) scans across the PE region which amounts to a stepwise amorphization of the vortex matter. The present results lead us to identify precisely the location of onset of the PE in the H-T space of Ca3Ir4Sn13 which remained the major limitation in our earlier investigations, via magnetization measurements, in the same compounds. Since the magnetization data had earlier revealed the occurrence of a second magnetization peak (SMP) and the PE anomalies in unresolved manner (juxtaposed together), the identification of onset of PE in the vortex phase diagram of Ca3Ir4Sn13 was not apparently made. The new result presented here assists in the construction of a...

Vortices dynamics on two dimensional superconductor and its controlling using holes have been studied numerically. The calculation was done by solving time dependent Ginzburg-Landau equation using an explicit method. The study was done on superconductor having a mesoscopic size. The negative de Gennes boundary condition on superconductor with surrounding was used to account to see the possibly controlling or guiding the vortices motion using both holes arrangement and the boundary. The result show that the negative de Gennes extrapolation length may be used to slow done the collective vortices motion while the positive one may be to increase the speed.

We present the zero temperature molecular dynamics simulation of vortices in low Tc type-II superconductors. We observe power law variation of noise in the dynamical phase. In comparison with the ordered vortex flow region the disordered vortex flow region shows large power law correlation of noise.

The presence of barriers changes the vortex structure in superconducting Nb square in presence of a uniform applied magnetic field. The Cooper pair configurations in a mesoscopics superconducting square of Nb with a barrier are calculated within the nonlinear Ginzburg Landau equations. We predict the nucleation of multi-vortex states into the sample and a soft entry of the magnetic field inside and around into the barrier. A novel and non-conventional vortex configurations occurs at determined magnetic field.

Many phenomena of current physical interest are directly related to the difference in the healing lengths of the band condensates, such as the non-monotonic interaction between vortices, being a possible explanation for highly debated unusual vortex configurations observed in a simple ceramic MgB2. Effects due to the difference in the spatial profiles of different band condensates can be accounted for within the full microscopic numerical treatment with an enormous computational effort. These difficulties have stimulated a search for a general Ginzburg-Landau formalism with a coexistence of two band condensates with different healing lengths. In this work, we derive the free-energy functional for the extended formalism and the corresponding expression for the current density; also, using the time dependent Ginzburg-Landau theory, we calculate the vortex state in a superconducting simple ceramic exposed to a homogeneous magnetic field.

Vortex lattices in antidot arrays formed within a superconducting film constitute an interesting condensed matter system. Here, disorder induced pinning, interaction and thermal fluctuations can be tuned easily to experimentally realize a variety of interesting physical scenarios. One of the very interesting open problems in this area is the mysterious nature of vortex lattice transformations taking place in rectangular antidot arrays where a very special crossover behavior occurs as one goes from the low field to a high field regime. This is often accompanied by novel history effect. In order to explore the underlying physics is detail we fabricated rectangular antidot arrays with different aspect ratios. We present some of the preliminary results in this symposium.

We present here the zero temperature dynamic structural transformation of driven vortices in low Tc type-II superconductors. In our simulation we observed anomalous kinks in the voltage current characteristics curves in a small parameter region of the phase space. The analysis of the real space configuration of the vortices reveals a structural change in this region. We also studied the pin density dependence of this anomaly.

We present the history dependence of the critical current density, jc(H,T) via the ac susceptibility measurements performed in a weakly pinned single crystal of superconducting Ca3Rh4Sn13. Our results show striking evidence for a more spatially ordered vortex states in the field-cooled mode in contrast to that expected in zero field-cooled mode well below the field limit, above which the Peak Effect could be observed for zero field-cooled vortex states.

We report the growth and characterization of single crystals of the iron chalcogenide superconductor FeCr0.02Se. It is seen to have a larger superconducting transition temperature compared to the parent material Fe1+xSe. Analysis of the critical current data suggests a δl pinning mechanism in this material.

In type-II superconductors an applied magnetic field B, between the lower and upper critical values, produces a mixed state containing Abrikosov vortices. These vortices contain a quantum of magnetic flux h/2e and consist of a core with depressed order parameter and a pattern of perpetually circulating supercurrents. When B is applied parallel to a thin film, the circulating supercurrents get squeezed by the film surfaces causing the vortex core to become unstable and explode all the way across the film when the thickness d is below the critical value of dc = 4.4ξ; here ξ is the superconducting coherence length. For temperatures above the explosion condition dc(T) > d, the applied B cannot induce single parallel vortices, however perpendicular vortices can be generated spontaneously by thermal fluctuations. We observe a transition from non-dissipative to dissipative behavior at the explosion condition and find that the dynamics of the spontaneous perpendicular vortices can be tuned by the pairbreaking eff...

We explore the physics of vortex pinning mechanism in iron arsenide superconductor SrFe1.7Co0.3As2, via magnetization based studies. In particular we try to compare the experimental results for critical current density with the theoretical pictures for fluctuation in mean free path induced (δ) pinning and the fluctuation in superconducting order parameter induced (δTc) pinning. The results points to a δl pinning scenario in SrFe1.7Co0.3As2. These results in conjunction with our earlier report on δl pinning mechanism in the iron chalcogenide superconductors FeSe1−xTex and FeCrxSe points to the generic nature of δl pinning mechanism in iron based superconductors.

We report surface superconductivity, crossover from multi-quanta vortex state to Abrikosov's Lattice and peak effect observed in a single crystal of Ca3Ir4Sn13. We present the magnetic phase diagram of Ca3Ir4Sn13. The observation of surface superconductivity at low as well as high fields differentiates the phase diagram of this compound from that of another low Tc superconductor Ca3Rh4Sn13 belonging to the same family of ternary stannides.

We explore the physics of vortex pinning mechanism in Iron chalcogenide superconductor FeSe0.5Te0.5., via magnetization based studies. In particular we try to: (i) understand the salient features of the pinning force density (Fp) within the Dew-Hughes scenario, and (ii) compare the experimental results with the theoretical pictures of fluctuation in mean free path induced (δl) pinning and the fluctuation in superconducting order parameter induced (δTc) pinning. The results points to a δl pinning scenario in FeSe0.5Te0.5.

Critical current of the superconductor is one of the important quantities determining the quality of the superconductor. Many efforts have been done to enhance this quantity including the use of holes in different form of lattices fabricated on the superconductor. In the enhancement of critical current using such holes, it is usually understood that the enhancement process is due to the commensurate effect between flux quantization with the structure of the lattice hole. However, there is another explanation that the enhancement is caused rather by the vortex-hole interaction compared to such an effect. To review this, we investigate the phenomena at superconductor having holes and slit to see the roles of those structure in increasing the pinning force responsible for the critical current enhancement. The investigation was done numerically through the calculation of vortices dynamics using time dependent Ginzburg-Landau equation on the superconductor exposed under electric current and magnetic field. To account the effect of the boundary, the holes and the slits are accompanied by de Gennes boundary condition. The result supports the explanation that the enhancement of the critical current caused by the addition of an array of hole or slit is due to the interaction of vortex and hole or slit. The result also indicates that the use of a negative de Gennes extrapolation length at the superconductor boundary enhancing the critical current higher than the use of superconductor-vacuum.

Electron phase microscopy based on the Aharonov-Bohm (AB) effect principle has been used to illuminate fundamental phenomena concerning magnetism and superconductivity by visualizing quantitative magnetic lines of force. This paper deals with confirmation experiments on the AB effect, the magnetization process of tiny magnetic heads for perpendicular recording, and vortex behaviors in high-Tc superconductors.

In ordinary single component Ginzburg‐Landau theory, the interface between type I and type II behaviour coincides with the interface between long range vortex attraction and repulsion. We will argue that the situation in two component Ginzburg‐Landau theory is more complex, allowing for a regime where vortices are thermodynamically stable and repel at short range, but attract at long range. This phenomenon has recently been observed in MgB2, and is called type 1.5 superconductivity.

Created at nano‐Kelvin temperatures, rotating Bose gases present an opportunity to study striking phenomena in a regime which is completely unattainable in the condensed matter analogue of 4He. In this theoretical paper we discuss what happens at and beyond the limits of current experiments. Vortex lattices, as expected by analogy with helium and superconductivity, have been observed, but we demonstrate that the dynamics are unconventional. At faster rotation we demonstrate links to fractional quantum Hall effect physics and predict completely uncondensed but correlated ground states. In the mesoscopic regime we predict tunnelling as the route to vortex nucleation.

Magnetic measurements on MgB2 superconductors doped with various concentration (0 < x < 0.6%) of Al2O3 nano‐particles (∼20 nm) have been performed in the temperature range 4–40K and in a magnetic field of strength up to 9 Tesla. A significant increase in the irreversibility field (Hirr), critical current density (Jc) and remanent magnetization (MR) have been obtained with increasing the concentration of the Al2O3 nano‐particle. At low field we have observed large vortex instabilities (known as vortex‐avalanche) associated with all doped samples characterized with high critical current density. Vortex avalanche effect is reduced with increasing temperature vanishing near 20K. The results are discussed in terms of local‐vortex instabilities caused by doping of Al2O3 nano‐particles.

Two‐dimensional temperature dependent vortex dynamics has been studied by Monte‐Carlo method. At low temperatures far below TC, well known phase transition from glassy state to vortex liquid state known as melting has been obtained. Assuming the possible future existence of real high temperature superconductivity, the simulations extended to the range of room temperature. There, vortex state has shown a possible second phase transition analogous to gas state where vortices behave totally independent of each other. Since mobility of vortices means dissipation, this poses a real challenge for future applications of room temperature superconductivity.

Achieving high critical currents in YBa2Cu3O7 (YBCO) films on metallic polycrystalline substrates (coated conductors) is an essential step to make coated conductors a technological reality. Therefore it is extremely important to identify the vortex pinning centers responsible for the high critical current density (Jc), to find ways to further improve the vortex pinning in these superconducting films. We present a comparative study of the angular and field dependences of Jc for two successful approaches used to improve vortex pinning, one that introduces correlated defects and another one that increases the random pinning contribution. The correlated defects are obtained by the introduction of BaZrO3 nano‐particles into the superconducting film matrix, which in turn induce c‐axis correlated defects. The enhanced random pinning contribution is achieved by mixing different rare earth. The presence of additional correlated defects results in a slower Jc field decay together with a Jc enhancement around the c‐...

The vortex behavior of superconducting finite‐sized Pb networks with 2×2‐, 3×3‐, 5×5‐, and 10×10‐hole‐arrays have been investigated in a small DC magnetic field. The Pb networks have been fabricated by electron beam lithography of photoresist layer and a lift‐off process after depositing Pb film on the resist patterns. The magnetization measurements of the Pb networks by a SQUID magnetometer reveal the matching effect in the magnetization curve. Vortex image observations are also carried out by a SQUID microscope to compare with the theoretical predictions.

A method is presented that allows to compute from Maxwell‐London theory the static and dynamic electromagnetic properties of thin flat superconducting films of any shape, also for SQUIDs, with and without vortices.

We observed hysteretic voltage‐current (VI) curves in superconducting tantalum thin films at zero magnetic field (B=0) at temperatures (T) below a characteristic temperature T*. This is in contrast to the Kosterlitz‐Thouless (KT) theory which expects continuous and reversible VI’s. We interpret that the hysteresis arises from the critical dynamics of self‐generated magnetic vortices, and map the area in B‐T plane where the VI’s are hysteretic.

A magnetic two dimensional organic conductor λ‐(BETS)2FeCl4 has a superconducting phase only under high magnetic fields between 18T and 42 T. This field induced superconductivity is qualitatively understood by Jaccarino‐Peter effect, and an inhomogeneous superconducting phase, the so‐called FFLO phase, whose order parameter oscillates in space, is expected to be stabilized. Under high magnetic fields parallel to the conducting layers, characteristic features in the interlayer resistance are observed, suggesting that the Josephson vortices are strongly pinned at some fields. The results are explained in terms of a commensurability effect between the vortex lattice and the oscillating order parameter.

Within the framework of the nonlinear Ginzburg-Landau theory, we calculated the full phase diagram for a superconducting disk with radius R = 4 (T = 0) and we studied the behavior of the penetration and expulsion fields as a function of temperature for multivortex and giant vortex states.

We have measured the I–V characteristics in a mesoscopic Al square at low temperatures. The resistance at sufficiently low current is zero in magnetic field H < 250 G for T = 900 mK. At H < 250 G, the current Ic above which a finite voltage appears periodically has minima with increasing magnetic field. These minima are ascribed to the transitions between different vortex states in the sample. The resistance V/I exceeds the normal state value RN at |I|< Ic for H < 250 G. The experimental results suggest that the field dependence of Ic as well as the resistance larger than RN is attributed to the dynamics of the vortices in the superconducting Al square.

The dynamic of moving vortex matter is considered in the framework of the time dependent Ginzburg ‐ Landau equation beyond linear response. Both disorder and thermal fluctuations are included using the Martin‐Siggia‐Rose formalism within the lowest Landau level approximation. We determine the critical current as function of magnetic field and temperature. The surface in the J‐B‐T space defined by the function separates between the dissipative moving vortex matter regime (qualitatively appearing as either the vortex creep and flux flow) and dissipation less current state in which vortices are pinned creating an amorphous vortex “glass”. Both the thermal depinning and the depinning by a driving force are taken into account. The static irreversibility line is compared to experiments and is consistent with the one obtained in the replica approach. The non‐Ohmic I–V curve (in the depinned phase) is obtained and resistivity compared with experiments in layered superconductors and thin films.

It is argued that only a single spontaneous long-range order, namely the phase coherence exists in the Abrikosov state, and the prediction of the crystalline long-range order of vortex lattice does not correspond to the facts., 2 pages, 0 figures, will be published in the Proceedings of the 24th International Conference on Low Temperature Physics

The paring sysmmetry of the triplet superconductor Sr2RuO4 is still controversial. Recently, the scanning tunneling microscopy measurement has been done on the quasi‐particle structure in Sr2RuO4. They obtained the local density of states around a single vortex. Using the Bogoliubov‐de Gennes equation in the differential form off‐wave (Δ± (k) = Δd (kx ± ky) cos (ckz)) superconductivity that has the horizontal nodes, we investigate the quasi‐particle structure. As compared with the p‐wave pairing, the local density of states of f‐wave paring at the vortex core is much similar to the experimental data.

In this work we discuss the limits of the standard analysis dealing with material defects as potential wells for flux quanta in type II superconductors. Such description, based on the thermodynamic free energy, is appropriate for quasi‐static processes only, and its validity should be tested against dynamic conditions for vortices driven by a constant bias above the critical current. We briefly discuss the non equilibrium phenomena that occur during the entry and the exit of vortices from defects, comparing the characteristic times of the vortex motion with the non equilibrium characteristic time scales. Specifically, in BCS superconductors the Cooper pair recombination processes determine phonon emission and corresponding energy losses. For this reason, we underline that non equilibrium processes doubt the validity of the treatment of defects as potential wells, especially well above the critical current when vortices are driven at higher speed.

We develop a unifying approach bridging between the spin and vortex glasses, based, on one hand, on the application of the replica method to Ginzburg‐Landau description of the system in terms of the superconductor order parameter near Tc and, on the other hand, on the notion of the extreme value statistics that govern the distribution of the energy barriers controlling the glassy slow dynamics of the vortices. Focusing on the vortex systems not very far from the upper critical Field we demonstrate that the glassy behavior is associated with the continuous replica symmetry breaking, which is the inherent feature of the long range spin glasses. We apply our results to the description of vortex phase diagram and find the vortex glass transition line, which appears different and well separated from both the melting line and from the so‐called second peak lines.

We describe an experimental distinction between giant vortex and multivortex states in mesoscopic superconducting disks by using two methods: the multiple-small-tunnel-junction method and the temperature dependence of vortex expulsion fields. The experimental results are in good agreement with the theoretical simulations based on the non-linear Ginzburg-Landau theory.

The critical state of the superconducting layered structures consisting of isolated superconducting plates is investigated. The critical current density, pinning force, the distribution of the local magnetic field, and the current in the structures are found via numerical solution of the Ginzburg‐Landau equations. The external magnetic field and the transport current are directed along plates perpendicularly to each other. The vortices are believed to be absent in the plates. A method for analyzing the critical state of superconducting layered structures in a parallel magnetic field based on simple transformation of the current distribution in a zero external magnetic field is found.

The vortex phase diagram of high‐Tc superconductors in the field parallel to the c‐axis have been already extensively explored. It has been commonly observed that pinning effects are quite weak at high temperatures and high fields in high quality single crystals. Such weak pinning phases, like the vortex liquid and the Bragg glass, are good candidate to study the influence of additional artificial pinning arrays on vortex phases, because the original quenched disorders do not work well as effective pinning centers in these phases. We have introduced several types of hole arrays in Bi2Sr2CaCu2O8+y single‐crystal thin film using a focused ion beam. To preserve the quality of the crystals we have made film samples from bulk crystals by the cleaving. In samples with triangular and square pinning arrays of 1μm lattice spacing, the flow resistance of pancake vortices exhibit a matching effect at multiples of the matching fields. This matching effect occurs in the vortex liquid phase. It is difficult to explain these results by the idea of the normal vortex liquid because of the lack of in‐plane symmetries. There is a possibility that the in‐plane order is induced in the vortex liquid by the introduction of the periodic pinning arrays.

We present the mode locking (ML) phenomenon of vortex matter observed in a layered superconductor of 2H‐NbSe2 pure single crystal. On application of ac current on top of dc current, clear ML resonance appears in differential conductance voltage curves, indicating the presence of elastic modes excited collectively over driven vortices. On increasing magnetic field, the ML voltage shows square root dependence on field, consistent with the ML condition for vortex matter.

A theory of the macroturbulent instability in the system containing vortices of opposite directions (vortices and antivortices) in hard superconductors is proposed. The origin of the instablity is connected with the anisotropy of the current capability in the sample plane. The anisotropy results in the appearance of tangential discontinuity of the hydrodynamic velocity of vortex and antivortex motion near the front of magnetization reversal. The examination is performed on the basis of the anisotropic power‐law current‐voltage characteristics. The instability is shown to be observed even at relatively weak anisotropy. The physical nature of the macroturbulent instability in the vortex matter in YBCO superconductors is verified by means of magnetooptic study of the instability in a single crystal prepared specially for this purpose. The instability develops near those sample edges where the oppositely directed flow of vortices and antivortices, guided by twin boundaries, is characterized by the discontinui...

Time‐resolved, optical pump‐probe measurements on a thin Nb0.5Ti0.5N film in applied magnetic fields were performed at the National Synchrotron Light Source, Brookhaven National Laboratory. Despite the presence of normal cores from vortices in the films, we find that the relaxation time of photoexcited quasiparticles does not decrease with magnetic field as one might expect. The change in the far‐infrared transmittance due to the applied magnetic field is also discussed.

We have studied the temperature dependencies of the complex sheet conductance of 1-3 unit cell (UC) thick YBa2Cu3O7-x films sandwiched between semiconducting Pr0.6Y0.4Ba2Cu3O7-x layers at high frequencies. Experiments have been carried out in a frequency range between: 2 - 30 MHz with one-spiral coil technique, 100 MHz - 1 GHz frequency range with a new technique using the spiral coil cavity and at 30 GHz by aid of a resonant cavity technique. The real and imaginary parts of the mutual-inductance between a coil and a film were measured and converted to complex conductivity by aid of the inversion procedure. We have found a quadratic temperature dependence of the kinetic inductance, L_k^-1(T), at low temperatures independent of frequency, with a break in slope at T^dc_BKT, the maximum of real part of conductance and a large shift of the break temperature and the maximum position to higher temperatures with increasing frequency. We obtain from these data the universal ratio T^dc_BKT/L_k^-1(T^dc_BKT) = 25, 25, and 17 nHK for 1-, 2- and 3UC films, respectively in close agreement with theoretical prediction of 12 nHK for vortex-antivortex unbinding transition. The activated temperature dependence of the vortex diffusion constant was observed and discussed in the framework of vortex-antivortex pair pinning. PACS numbers: 74.80.Dm, 74.25.Nf, 74.72.Bk, 74.76.Bz, Comment: PDF file, 10 pages, 6 figures, to be published in J. Low Temp. Phys.; Proc. of NATO ARW: VORTEX 2004

Josephson vortex (JV) states in Bi2Sr2CaCu2O8+y (Bi‐2212) have been studied by measuring the flow resistivity of JV’s and I‐V characteristics with a current along the c‐axis. In the flow resistivity, periodic oscillations have been found as a function of the parallel magnetic field to the superconducting layers. As this phenomenon is related to the formation of a triangular lattice of JV’s as the ground state, the 3D‐ordered state (triangular lattice phase) of JV’s could be determined. With changing the doping level of Bi‐2212, the BD‐ordered phase is shifted towards a higher magnetic field and a higher temperature, which is well explained from the theoretical analyses. Above the 3D‐ordered phase, vortex state has been studied with I‐V characteristic measurements, in which the voltage shows a distinct change in the exponent of the power‐law dependence to the current between two phases. This suggests that the 3D‐ordered phase changes to the disordered phase along the c‐axis.

Solving the nonlinear Ginzburg‐Landau equations self‐consistently, we investigate the influence of a triangular surface defect (i.e. a pacman shaped sample) on the vortex transitions in mesoscopic superconducting disks. Depending on the size of the defect, vortices may enter/leave one by one or in pairs.

Through experiments in cuprate superconductors, the vortex state just below the first order transition (FOT1), corresponding to the melting line in clean limit, often has no positional order, and the presence of a lower critical point (LCP) of this FOT line is found at least in YBCO. We have performed a Monte Carlo simulation of the layered Ginzburg‐Landau model within the lowest Landau level (LLL), by including a low density of columnar (line) defects parallel to the applied magnetic field. We have found another first order transition (FOT2) curve lying at lower temperatures, presumably corresponding to the Bragg‐Bose glass to the Bose glass melting, and the absence of FOT1, i.e., the presence of a LCP, in lower fields. These findings are consistent with the predictions in a previous theory.

Superconductors containing mesoscopic artificially‐engineered defects are orders of magnitude more resistant to the detrimental effect of the magnetic field. Here we present scanning tunnelling microscopy study of the vortex lattice configurations in a mesoscopic single crystal superconductor — normal metal heterostructure. We observe co‐existence of a strongly interacting multiquanta vortex lattice and interstitial Abrikosov vortices that form a composite magnetic flux distribution which undergoes a series of transitions between different topological configuration states. The vortex configuration states are strongly dependent on the nanoscale architecture of the superconductor and applied magnetic field. Scanning tunnelling spectroscopy images show the evolution of vortex topological states when the number of flux quanta per unit cell changes.

We present two‐dimensional computer simulation results of magnetic vortex systems driven by Lorentz force in type‐II superconductors having the Corbino disk geometry. Langevin dynamics simulations of a point vortex model demonstrate that (1) at low injected currents in the superconductor the vortices rotate as a rigid solid having the linear velocity profile as a function of r with r the distance from the disk center, (2) at large currents the vortices move free as a liquid having the inversely linear velocity profile, and (3) at moderate currents the complicated plastic flow of the vortices appears.

Spectral noise power measurements are reported in a bulk YBa2Cu3O7−δ superconductor at 4.2 K to investigate the flux vortex avalanche processes originated from thermomagnetic instabilities in an applied magnetic field up to 600 mT and in feeding current close to the critical value. 1/fγ behavior is shown at frequencies below 10 Hz, γ values range from 0.7 to 1.7. A sharp peak is observed in applied field and from these results we have obtained a cutoff frequency around 20 Hz for Lorentzian shape knee from which we estimate a mean number of 500 vortices and a mean velocity of about 20 cm/s for the average avalanche.

We present the measurements of the fluctuating component of the flux(vortex)‐flow voltage δV(t) about the average in the low‐temperature(T) vortex‐liquid phase of amorphous MoxSi1−x films. For the thick film δV(t) and broad‐band noise originating from the vortex motion is clearly visible in the quantum‐vortex‐liquid phase, where the amplitude of δV(t) is pronounced and the distribution of δV(t) is anomalously asymmetric, implying the unstational vortex motion. For the thin film the similar unusual vortex motion is observed in nearly the same reduced‐T regime. Physical origin responsible for the phenomena is discussed.