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A. M. Dyugaev

Publications and source records attributed to A. M. Dyugaev.

14 recordsLinked to original sources
arXiv2024

A method for measuring deviation from Lambert diffuse scattering law of ultracold neutrons on material walls

Modeling the motion of ultracold neutrons (UCNs) is crucial for assessing their losses, accurately measuring their lifetime, and describing other experiments. In material traps, it is necessary to account not only for specular but also for diffuse elastic reflection of UCNs from the trap walls. Typically, the Lambert cosine law is used to describe the angular distribution of diffusely scattered neutrons. However, this law lacks a rigorous theoretical derivation and is often violated. In our work, we propose an experiment to measure the deviation of the angular distribution of UCNs during diffuse scattering from the Lambert law. This deviation can be determined by the difference in the number of neutrons exiting through the central and end windows of a long narrow UCN trap. Monte Carlo simulations corresponding to a possible experiment have been performed, demonstrating a significant effect for different trap geometries.

physics.ins-det↗
arXiv2022

On the possibility of a significant increase in the storage time of ultracold neutrons in traps coated with a liquid helium film

It is shown that rough inner walls of a trap of ultracold neutrons can be coated with a superfluid helium film much thicker than the depth of penetration of ultracold neutrons into helium. This coating should reduce the rate of loss of ultracold neutrons caused by absorption in the walls of the trap by orders of magnitude. It is demonstrated that triangular roughness is more efficient than rectangular for the reduction of the rate of loss of ultracold neutrons. Triangular roughness is more easily implemented technically and such diffraction gratings are fabricated industrially. Other methods are proposed to increase the thickness of the protective helium film.

cond-mat.other↗
arXiv2021

Helium film may greatly increase the storage time of ultracold neutrons in material traps

We propose a method to increase both the neutron storage time and the precision of its lifetime measurements by at least tenfold. The storage of ultracold neutrons (UCN) in material traps now provides the most accurate measurements of neutron lifetime and is used in many other experiments. The precision of these measurements is limited by the interaction of UCN with the trap walls. We show that covering trap walls with liquid helium may strongly decrease the UCN losses from material traps. $^4$He does not absorb neutrons at all. Superfluid He covers the trap walls as a thin film, $\sim 10$ nm thick, due to the van der Waals attraction. However, this He film on a flat wall is too thin to protect the UCN from their absorption inside a trap material. By combining the van der Waals attraction with capillary effects we show that surface roughness may increase the thickness of this film much beyond the neutron penetration depth $\sim 33$nm. Using liquid He for UCN storage requires low temperature $T<0.5$ K to avoid neutron interaction with He vapor, while the neutron losses because of the interaction with surface waves are small and can be accounted for using their linear temperature dependence.

physics.ins-det↗
arXiv2018

Inelastic neutron scattering as a confirmation of a new type of gapped surface excitations in liquid helium

We analyze the experimental data on inelastic neutron scattering by a thin ~5-atomic-layer film of liquid helium at three different temperatures: T=0.4K, 0.98K and 1.3K. These data were partially published previously, but here we present them in a better quality and at various temperatures. The neutron scattering intensity plots, in addition to the previously know dispersion of phonons and ripplons, suggest a branch of gapped surface excitations with activation energy $\sim 4.5$K and the dispersion similar to that expected for surfons - the bound quantum states of helium atoms above liquid helium surface, proposed and investigated theoretically. These data, probably, provide the first direct experimental confirmation of surfons. Before these surface excitations received only indirect experimental substantiation, based on the temperature dependence of surface tension coefficient and on their interaction with surface electrons. The existence of surfons as an additional type of surface excitations, although being debated yet, is very important for various physical properties of He surface. We also analyze previous numerical results on excitations in liquid helium and argue that surface excitations similar to surfons have been previously obtained by numerical calculations and called resonance interface states.

cond-mat.other↗
arXiv2009

Surface state atoms and their contribution to the surface tension of quantum liquids

We investigate the new type of excitations on the surface of liquid helium. These excitations, called surfons, appear because helium atoms have discrete energy level at the liquid surface, being attracted to the surface by the van der Waals force and repulsed at a hard-core interatomic distance. The concentration of the surfons increases with temperature. The surfons propagate along the surface and form a two-dimensional gas. Basing on the simple model of the surfon microscopic structure, we estimate the surfon activation energy and effective mass for both helium isotopes. We also calculate the contribution of the surfons to the temperature dependence of the surface tension. This contribution explains the great and long-standing discrepancy between theory and experiment on this temperature dependence in both helium isotopes. The achieved agreement between our theory and experiment is extremely high. The comparison with experiment allows to extract the surfon activation energy and effective mass. The values of these surfon microscopic parameters are in a reasonable agreement with the calculated from the proposed simple model of surfon structure.

cond-mat.mes-hall↗
arXiv2007

Electron mobility on a surface of dielectric media: influence of surface level atoms

We calculate the contribution to the electron scattering rate from the surface level atoms (SLA), proposed in [A.M. Dyugaev, P.D. Grigoriev, JETP Lett. 78, 466 (2003)]. The inclusion of these states into account was sufficient to explain the long-standing puzzles in the temperature dependence of the surface tension of both He isotopes and to reach a very good agreement between theory and experiment. We calculate the contribution from these SLA to the surface electron scattering rate and explain some features in the temperature dependence of the surface electron mobility. This contribution is essential at low temperature $T<0.5$ when the He vapor concentration is exponentially small. For an accurate calculation of the electron mobility one also needs to consider the influence of the clamping electric field on the surface electron wave function and the temperature dependence of the He3 chemical potential.

cond-mat.mes-hall↗
arXiv2003

Lift of degeneracy of Landau levels of 2D electron gas by point-like impurities

We study the density of states of two-dimensional electron gas in magnetic field with scattering on point-like impurities that are uniformly distributed along the sample. We show that the electron-impurity interaction completely lifts the degeneracy of the Landau levels even at low impurity concentration. This statement is in contradiction with the previous results obtained in the unphysical approximation of two-dimensional impurities. There is a large region of the electron energy $ω$, counted from the Landau level, where the density of states $ρ(ω)$ is inversely proportional to $|ω|$ and proportional to the impurity concentration. Our results are applicable to different 2D electron systems as heterostructures, inversion layers and interfaces.

cond-mat.mes-hall↗
arXiv2002

Charged complexes at the surface of liquid helium

Charged clusters in liquid helium in an external electric field form a two-dimensional system below the helium surface. This 2D system undergoes a phase transition from a liquid to a Wigner crystal at rather high temperatures. Contrary to the electron Wigner crystal, the Wigner lattice of charged clusters can be detected directly.

cond-mat.stat-mech↗
arXiv2001

Nuclear ferromagnetism induced Fulde-Ferell-Larkin-Ovchinnikov state

We present a theoretical study of the influence of the nuclear ferromagnetism on superconductivity in the presence of the electron-nuclear spin interaction. It is demonstrated that in some metals, e.g. Rh, W, the BCS condensate imbedded in a matrix of ferromagneticaly ordered nuclear spins should manifest the FFLO (Fulde-Ferel-Larkin-Ovchinniov) state. We outline that the optimal experimental conditions for observation of FFLO could be achieved by creation, via adiabatic nuclear demagnetization, of the negative nuclear spin temperatures. In this case the nuclear polarization points in the opposite to the external magnetic field direction and the electromagnetic part of the nuclear spin magnetization compensates the external magnetic field, while the exchange part creates the nonhomogeneous superconducting order parameter.

cond-mat.supr-con↗
arXiv2000

On the electron scattering and dephasing by the nuclear spins

We show that scattering of the conduction electrons by nuclear spins via the hyperfine interaction may lead the upper limit on the mean free path in clean metals. Nuclear spins with s >1/2 may cause a strong dephasing in dirty limit due to the quadrupole coupling to the random potential fluctuations caused by static impurities and lattice imperfections.

cond-mat.mes-hall↗
arXiv1999

Strong coupling in the Kondo problem in the low-temperature region

The magnetic field dependence of the average spin of a localized electron coupled to conduction electrons with an antiferromagnetic exchange interaction is found for the ground state. In the magnetic field range $μH\sim 0.5 T_c$ ($T_c$ is the Kondo temperature) there is an inflection point, and in the strong magnetic field range $μH\gg T_c$, the correction to the average spin is proportional to $(T_c/μH)^2$. In zero magnetic field, the interaction with conduction electrons also leads to the splitting of doubly degenerate spin impurity states.

cond-mat.str-el↗
arXiv1997

Nuclear magnetic susceptibility of metals with magnetic impurities

We consider the contribution of magnetic impurities to the nuclear magnetic susceptibility $χ$ and to the specific heat $C$ of a metal. The impurity contribution to the magnetic susceptibility has a $1/T^2$ behaviour, and the impurity contribution to the specific heat has a $1/T$ behaviour, both in an extended region of temperatures $T$. In the case of a dirty metal the RKKY interaction of nuclear spins and impurity spins is suppressed for low temperatures and the main contribution to $C$ and $χ$ is given by their dipole-dipole interaction.

cond-mat.str-el↗
arXiv1997

Influence of magnetic impurities on the heat capacity of nuclear spins

It is found that in a wide range of temperatures and magnetic fields even a small concentration of magnetic impurities in a sample leads to a $T^{-1}$ temperature dependence of the nuclear heat capacity. This effect is related to a nuclear-spin polarization by the magnetic impurities. The parameter that controls the theory turns out not to be the impurity concentration $C_{imp}$ but instead the quantity $c_{imp} μ_e / μ_n$, where $μ_e$ and $μ_n$ are the magnetic moments of an electron and a nucleus, respectively. The ratio of $μ_e$ and $μ_n$ is of order of $10^3$.

cond-mat↗