arXiv subjects

I. Skachko

Publications and source records attributed to I. Skachko.

4 recordsLinked to original sources

arXiv2026

The motion of tracer particles in turbulent superfluid $^4$He down to the zero-temperature limit

An injection system for polymer particles, with diameters ranging from 1 to 6 $\mu$m, has been developed for visualizing flows in superfluid $^4$He at temperatures down to 0.14 K. Using an ultrasound transducer, bursts of particles were launched into a sample of superfluid and allowed to descend under gravity. The particles were imaged using their fluorescence in the presence of a sheet of laser light. We report on the statistical behavior of particles during their descent, including descriptions of a mixture of smooth and erratic trajectories, indicative of the interactions with thermal excitations and quantized vortex lines. Temperature-dependent velocity distributions were measured and analyzed, yielding Gaussian distributions with power law tails persisting into the zero temperature limit. When sampled over increasing length scales, these distributions bifurcated into exponential for the smallest particles and bimodal Gaussian for the largest. We also report observations of long-lived suspensions of small particles at temperatures near 1 K, which appear to be associated with the trapping of large numbers of particles in a turbulent vortex tangle. A method was developed for identifying and quantifying the numbers of particles bound to vortex lines, allowing for a description of the temporal dynamics of their population by an analytical model.

cond-mat.other↗

arXiv2026

Apparatus to visualize flows in superfluid $^4$He below 1 K

We describe a versatile apparatus for optical observations of experimental processes at temperatures down to 0.1 K. The cooling is achieved by a wet cryostat with a dilution refrigerator on a vibrationally-isolated platform, capable of continuous rotation at angular velocity of up to 3 rad/s. The illumination light beam from lasers on a non-rotating optical table at room temperature is introduced via an optical fiber. The images are transferred to the intensified camera at room temperature through a coherent bundle of $10^5$ optical fibers giving a spatial resolution of $\sim 30 \mu$m, depending on the magnification used. The adjustment of the position of the illumination light, as well as of the focusing of the camera on the object under investigation, can be controlled remotely with the help of piezoelectric positioners. The apparatus was used for visualization of particles dispersed in superfluid helium at temperatures down to 0.14 K. In one version of experiment, fluorescent light from clouds of excimer molecules He$_2^*$, generated in liquid helium by electron impact from electrons injected by sharp field-emission tips, was recorded and analyzed. In another, fluorescent particles of diameters between 1 $\mu$m and 6 $\mu$m were initially loaded onto the horizontal surface of a piezoelectric crystal of LiNbO$_3$ and then injected into liquid helium by short bursts of high-amplitude oscillations at the crystal's resonant frequency 1 MHz. The particle trajectories were filmed at a frame rate of up to 990 fps and analyzed.

cond-mat.other↗

arXiv2009

Fractional Quantum Hall Effect in Suspended Graphene: Transport Coefficients and Electron Interaction Strength

Strongly correlated electron liquids which occur in quantizing magnetic fields reveal a cornucopia of fascinating quantum phenomena such as fractionally charged quasiparticles, anyonic statistics, topological order, and many others. Probing these effects in GaAs-based systems, where electron interactions are relatively weak, requires sub-kelvin temperatures and record-high electron mobilities, rendering some of the most interesting states too fragile and difficult to access. This prompted a quest for new high-mobility systems with stronger electron interactions. Recently, fractional-quantized Hall effect was observed in suspended graphene (SG), a free-standing monolayer of carbon, where it was found to persist up to T=10 K. The best results in those experiments were obtained on micron-size flakes, on which only two-terminal transport measurements could be performed. Here we pose and solve the problem of extracting transport coefficients of a fractional quantum Hall state from the two-terminal conductance. We develop a method, based on the conformal invariance of two-dimensional magnetotransport, and illustrate its use by analyzing the measurements on SG. From the temperature dependence of longitudinal conductivity, extracted from the measured two-terminal conductance, we estimate the energy gap of quasiparticle excitations in the fractional-quantized nu=1/3 state. The gap is found to be significantly larger than in GaAs-based structures, signaling much stronger electron interactions in suspended graphene. Our approach provides a new tool for the studies of quantum transport in suspended graphene and other nanoscale systems.

cond-mat.mes-hall↗

arXiv2009

Integer and Fractional Quantum Hall Effect in Two-Terminal Measurements on Suspended Graphene

We report the observation of the quantized Hall effect in suspended graphene probed with a two-terminal lead geometry. The failure of earlier Hall-bar measurements is discussed and attributed to the placement of voltage probes in mesoscopic samples. New quantized states are found at integer Landau level fillings outside the sequence 2,6,10.., as well as at a fractional filling ν=1/3. Their presence is revealed by plateaus in the two-terminal conductance which appear in magnetic fields as low as 2 Tesla at low temperatures and persist up to 20 Kelvin in 12 Tesla. The excitation gaps, extracted from the data with the help of a theoretical model, are found to be significantly larger than in GaAs based electron systems.

cond-mat.mes-hall↗