Main scientific results

1. Physics of superfluidity

- Detection of a new collective mode in HeII in narrow channels under partial drag of the normal component.

- Energy spectrum reconstruction in superfluid 3 He- 4 He mixtures by systematic measurements of the normal component density and detection of a new feature - end point of the Fermi branch of the spectrum.

- Proposition and practical realization of a NMR method to study phase diagrams of liquid 3 He- 4 He mixtures.

- Identification of the main dissipative processes in superfluid 3He in 4He mixtures in the waves of the first, second and fourth sounds.  

- Discovery of the process of roton production by phonons as well as establishing its role in the superfluid helium kinetic processes.

- Pioneering investigations of kinetics of the phonon impurity system of superfluid mixtures and discovery of a new two-step relaxation process.

- Detection of new features of superfluid He II transfer along the film in a alternating electric field.

- Detection of anomalous dispersion of the phonon spectrum of superfluid 3 e- 4 He mixtures and its relation to kinetic processes.

- Observation of long-lived metastable superfluid liquid and elucidation of the nucleation mechanisms under the separation of superfluid solutions.

- Investigations of nucleation and layering kinetics of superfluid mixtures, observation of metastable long-living superfluid liquid and elucidation of nucleation mechanisms.

- Detection of anomalous transfer along a superfluid helium film at the solid hydrogen surface.

- Detection of mutual transformation of the first and second sounds at the solid-superfluid helium boundary.

- Detection of convective instability in stratified superfluid solutions 3 4 under heating from below.

- Identification of relaxation mechanisms of temperature and concentration in superfluid solutions 3 4 at temperature lower than 0.5 K.

- Detection of mechano-electrical effect in superfluid helium (appearance of the electric response) in the presence of a temperature gradient.

  - Observation of arising the turbulent flows and identification of dissipative processes in superfluid mixtures of helium isotopes.

- Finding the resonance excitation of rotons by UHF microwave electromagnetic waves in superfluid helium.

  - Monitoring the evolution of collective modes in superfluid helium, filling a highly porous aerogel.

- Identification of the relaxation processes in phonon-phonon He II system.  

  2. Physics of quantum crystals

- Discovery of quantum diffusion of 3He impurities in solid 3 He- 4 He mixtures.

- Detection of a large difference between the 3He diffusion coefficients in coexisting bcc and hcp phases of solid helium.

- Finding of a important role of dislocations in thermal conductivity of solid 4 He and 3 He- 4 He mixtures.

- Detection of the effect of impuriton self-localization in hcp helium crystals at low temperatures and their delocalization due to impuriton-phonon interaction under rising temperature.

- Detection of correlation between the rates of phase layering and quantum diffusion of impuritons in solid 3 He- 4 He mixtures.

- Detection of a nonmonotonic temperature dependence of the decay rate of weak solid 3 He- 4 He mixtures.

- Observation of an anomalously fast mass transfer during dissolution of solid 3 He clusters in a layered mixtures of He isotopes.

- Observation of a fast diffusion process in solid 3 He- 4 He mixtures in the vicinity of the bcc-hcp transition.

- Detection of anomalous features in the temperature dependence of spin-lattice relaxation in the concentrated phase of a layered solid 3 He- 4 He mixtures.

- Proof of homogeneous nucleation during layering of solid 3 He- 4 He mixtures.

- Observation of the Andreev-Pushkarov nanoclusters consisting of 4 He atoms around quasi-equilibrium vacancies.

- Detection of giant asymmetry of the processes of decay and homogenization in solution of quantum crystals.

- First observation of NMR multi-echo signal in decayed solid solution 3 4 .

- Detection of correlation effects in a susbsystem of excitations due to large-scaled fluctuations of concentration in solid 3 4 solutions.

- Detection of anomalous behavior of temperature and pressure of 4 in triple points BCC HCP liquid.

- Finding the liquid-like inclusions in quenched hcp samples of 3He - 4He.  

- Evidence of homogeneous nucleation during bcc - hcp transition in 4He. The study of conditions for homo-and heterogeneous nucleation.  

- Detection of a disordered (glass) phase in solid 4He in supersolid region.  

- Determination of mass diffusion coefficients under the decay of solid solutions of helium isotopes in the whole range of 3He concentrations.  

 3. Physics of low-dimensional charged systems at liquid helium surface

- Elucidation of the character of the interaction between 3 He impurities and charged particles through measurement of the ion mobility in superfluid He and 3 He- 4 He mixtures.

- Detection of electron-riplon interaction in a two-dimensional electron system over liquid helium.

- Construction of a liquid-electron crystal phase diagram at ultralow temperatures.

- btaining the first information about the conductivity and resonance properties of the electron crystal over liquid helium in nonlinear regimes.

- Detection of new modes of coupled electron-riplon oscillations in a Wigner crystal on the helium surface.

- Complex data on the lifetime of ground-state surface electrons under approaching the crystallization point.

- Detection of a new optical mode of edge magnetic plasma oscillations in a two-dimensional electron crystal.

- Realization of a quasi-one-dimensional electron system over liquid helium and investigation of its transport properties.

- Detection of the effect of restricted geometry on collective and kinetic phenomena in multi-level two-dimensional and one-dimensional surface electron systems over bulk helium and a helium film.

- Construction of an electromagnetic radiation generator and a high-sensitivity detector using the electrons localized over the superfluid helium surface.

- Construction of an IR bolometer based on spectroscopic transitions of surface electrons over liquid helium.

- Detection of the localization-delocalization transition in the electron layer over a superfluid helium film.

- Observation of weak localization in a quasi-one-dimensional electron system over liquid helium.

- Detection of anomalous transport of electrons in quasi-one-dimensional channels over superfluid helium.

- Study of the influence of screening effects in Coulomb interaction on plasma mode spectrum in electron system localized over helium film.

- Detection of autolocalized state of the surface electrons in dense helium gas.

- Observation of anomalous conductivity of electrons in quasi-one-dimensional conducting channels over liquid helium in the presence of an inhomogeneous potential along the channel.

- Establishing a dependence of the nonlinear conductivity of electron system over liquid helium in the electron-ripplon scattering conditions.

- Detection of non-equilibrium phase transitions in two-dimensional electron crystal over liquid helium, stimulated by electrical fields.

4. Equipment and techniques of ultralow temperature experiments

1. Development and construction of new refrigerators for physical investigations at ultralow temperatures:

- a continuous-operation dilution refrigerator with sorption pumping to 10 mK;

- a nuclear copper demagnetization refrigerator for measurements down to 0.7 mK;

- a powerful dilution refrigerator with a hybrid circulation system for the 5 mK level;

- a dilution refrigerator with condensation sorption pumping and low temperature circulation cycle down to 10 mK.

2. Development of original devices for low temperature physical experiments:

- a thermomechanical thermal switch with superconducting liquid;

- a miniature cryogenic pneumatic superfluid helium-tight valve;

- a helium cryostat without nitrogen cooling;

- a vibration protection system for a refrigerator;

- detachable conic thermal contacts for low temperatures.

3. New methodical developments:

- a technique of growing high-quality crystals from superfluid helium;

- an osmotic method of varying superfluid mixture concentration in the process of experiment;

- a technique of improving quality of two-phase solid 3 He- 4 He mixture crystals by thermocycling in the region of phase layering;

- a technique of measuring ultralow diffusion coefficients in solid 3 He- 4 He solutions using an impulse magnetic field gradient;

- a technique of direct measurement of self-diffusion coefficients in solid helium using a moving porous membrane.