arXiv subjects

V. V. Dmitriev

Publications and source records attributed to V. V. Dmitriev.

At least 19 recordsLinked to original sources

arXiv2026

The effect of pressure on the splitting in $^3$He in nematic aerogel

Here, we present the results of an investigation of how the pressure affects the splitting of the superfluid transition temperature in $^3$He in anisotropic aerogel. It is well known that boundary conditions significantly influence the properties of superfluid phases in aerogel. When aerogel strands are coated with a $^4$He layer in magnetic field, new phases, such as the polar, polar-distorted A (DA), polar-distorted B (DB), and $\beta$ phases, become energetically favorable. In contrast, without this coating, the system tends to favor phases resembling the bulk A, B, and A$_1$ phases. Our earlier results showed a nonlinear dependence of the superfluid transition temperature splitting in pure $^3$He, but the range of nonlinearity did not match the theoretical predictions based on magnetic scattering effects. To further investigate this discrepancy, we performed measurements of the splitting under varying pressures for both pure $^3$He and with $^4$He coverage of the aerogel strands.

cond-mat.other↗

arXiv2025

A$_1$-A$_2$ splitting in pure $^3$He in nematic aerogel

Here, we present the results of vibrating wire experiments in pure $^3$He (without $^4$He coverage) in nematic aerogel. We investigated the dependence of splitting of the superfluid transition temperature of $^3$He in aerogel on magnetic field. In addition to our previous work, we used a wider range of magnetic fields (up to 31 kOe) and managed to detect both the "upper" and "lower" superfluid transition temperatures. The solid paramagnetic $^3$He layer on the aerogel strands activates the magnetic scattering channel. According to theory, it should result in linear splitting at high ($\ge20$ kOe) fields, while at lower fields the splitting is expected to be nonlinear. We were able to observe this nonlinearity, but we have a discrepancy with theoretical predictions regarding the range of fields where nonlinearity occurs. Possible reasons for this are discussed.

cond-mat.supr-con↗

arXiv2024

Analysis of the Third Harmonic of a Vacuum Response in a Subcritical Laser Field

We investigate a nonlinear response of the physical vacuum by the example of the third harmonic in radiation of the electron-positron-photon plasma excited by a strong time dependent electric field at the focus spot of counterpropagating laser pulses. The investigation was developed within the framework of the Bogoliubov-Born-Green-Kirkwood-Yvon kinetic theory nonperturbatively describing vacuum creation of the quasiparticle electron-positron plasma (EPP) and different channels of its interaction with the photon subsystem in the single-photon approximation that are opened in the presence of a strong semiclassical field. We investigate the radiation of EPP in the annihilation channel on the basis of the well known approximations and compare the obtained result with the semiclassical radiation of the plasma oscillations. In the high-frequency range for large adiabaticity parameter the quantum radiation dominates in comparison with the semiclassical one.

hep-ph↗

arXiv2022

Effect of Magnetic Scattering on Superfluid Transition of 3He in Nematic Aerogel

We present results of high magnetic field experiments in pure $^3$He (in the absence of $^4$He coverage) in nematic aerogel. In this case the aerogel strands are covered with few atomic layers of solid paramagnetic $^3$He, which enables the spin-exchange mechanism for $^3$He quasiparticles scattering. Our earlier NMR experiments showed that in low fields, instead of the polar phase, the A phase is expected to emerge in nematic aerogel. We use a vibrating wire resonator with the sample of aerogel attached to it and measure temperature dependencies of resonance properties of the resonator at different magnetic fields. A superfluid transition temperature of $^3$He in aerogel, obtained from the experiments, increases nonlinearly in applied magnetic field. And this increase is suppressed compared with that for bulk A$_1$ phase, which we attribute to an influence of the magnetic scattering channel, previously considered theoretically for the case of $^3$He confined in isotropic silica aerogel. However, we observe the essential quantitative mismatch with theoretical expectations.

cond-mat.supr-con↗

arXiv2022

Approximate Solutions of a Kinetic Theory for Graphene

The effective mass approximation is analysed in a nonperturbative kinetic theory approach to strong field excitations in graphene [1,2]. This problem is highly actual for the investigation of quantum radiation from graphene [3], where the collision integrals in the photon kinetic equation are rather complicated functionals of the distribution functions of the charge carriers. These functions are needed in the explicit analytical definition as solutions of the kinetic equations for the electron-hole excitations. In the present work it is shown that the suggested approach is rather effective in a certain range of parameters for the pulse of an external electromagnetic field. For example, the applicability condition of the approximation in the case of a harmonic field is $\hbar ω^2 / (\sqrt{2} e E_0 v_F) < 1$, were $v_F$ is the Fermi velocity. In the standard massive quantum electrodynamics the usability of the analogical approximation is very narrow.

cond-mat.mes-hall↗

arXiv2021

Superfluid $β$ phase in liquid $^3$He

We report the first observation of superfluid $β$ phase of $^3$He. This phase is realized in $^3$He in nematic aerogel in presence of high magnetic field right below the superfluid transition temperature. We use a vibrating aerogel resonator to detect the transition to the $β$ phase and measure the region of existence of this phase.

cond-mat.other↗

arXiv2020

Oscillating nematic aerogel in superfluid 3He

We present experiments on nematic aerogel oscillating in superfluid $^3$He. This aerogel consists of nearly parallel mullite strands and is attached to a vibrating wire moving along the direction of the strands. Previous nuclear magnetic resonance experiments in $^3$He confined in similar aerogel sample have shown that the superfluid transition of $^3$He in aerogel occurs into the polar phase and the transition temperature ($T_{ca}$) is only slightly suppressed with respect to the superfluid transition temperature of bulk $^3$He. In present experiments we observed a change in resonant properties of the vibrating wire at $T=T_{ca}$ and found that below $T_{ca}$ an additional resonance mode is excited which is coupled to the main resonance.

cond-mat.other↗

arXiv2020

Superfluid $^3$He in Planar Aerogel

We report results of experiments with liquid $^3$He confined in a high porosity anisotropic nanostructure which we call planar aerogel. This aerogel consists of nanofibers (with diameters $\sim10$ nm) which are randomly oriented in the plane normal to the specific axis. We used two samples of planar aerogel prepared using different techniques. We have found that on cooling from the normal phase of $^3$He the superfluid transition in both samples occurs into an equal spin pairing superfluid phase. NMR properties of this phase qualitatively agree with the properties of the superfluid A phase in the anisotropic Larkin-Imry-Ma state. We have observed differences between results obtained in the presence and absence of solid paramagnetic $^3$He on the aerogel strands. We propose that these differences may be due, at least in part, to a magnetic scattering channel which appears in the presence of solid paramagnetic $^3$He.

cond-mat.supr-con↗

arXiv2020

Spin diffusion in liquid $^3$He confined in planar aerogel

We report the results of theoretical and experimental investigation of spin diffusion in the normal phase of liquid $^3$He confined in planar aerogel: a material consisting of nanostrands which are almost parallel to a specific plane and randomly oriented in this plane. Using spin echo technique we measure the spin diffusion coefficients in the directions perpendicular and parallel to the plane. We see good agreement between the experiment and the theory.

cond-mat.other↗

arXiv2020

Kinetic description of vacuum $e^+ e^-$ production in strong electric fields of arbitrary polarization

We present a detailed analysis of the self-consistent system of kinetic equations (KEs) describing electron-positron pair production from vacuum under the action of a spatially homogeneous time-dependent electric field of arbitrary polarization. The physical significance of all the basic functions of the kinetic theory is ascertained. It is demonstrated that the total system of the KEs consists of two coupled quasiparticle and spin subsystems with their integrals of motion. A projection method is proposed in order to obtain the KE system in two particular cases: linearly polarized external electric field and (2+1)-dimensional description of quasiparticles in graphene. We also address the energy conservation law taking into account the internal plasma field and describe an alternative rigorous derivation of the KE system.

hep-ph↗

arXiv2019

Superfluid 3He in squeezed nematic aerogel

We present results of nuclear magnetic resonance (NMR) experiments in superfluid 3He in two samples of nematic aerogel consisting of nearly parallel mullite strands. The samples were cut from the same piece of the aerogel, but one of them was squeezed by 30% in the direction transverse to the strands. In both samples the superfluid transition of 3He occurred into the polar phase, where no qualitative difference between NMR properties of 3He in these samples was found. The difference, however, has appeared on further cooling, after the transition to the polar-distorted A phase (PdA phase) with the orbital part of the order parameter in the 2D Larkin-Imry-Ma (LIM) state. In the squeezed sample the 2D LIM state is anisotropic that results in changes in the NMR, which can be used as an additional marker of the PdA phase and have allowed us to measure the value of the anisotropy.

cond-mat.other↗

arXiv2018

NMR shifts in $^3$He in aerogel induced by demagnetizing fields

Magnetic materials generate demagnetizing field that depends on geometry of the sample and results in a shift of magnetic resonance frequency. This phenomenon should occur in porous nanostructures as well, e.g., in globally anisotropic aerogels. Here we report results of nuclear magnetic resonance (NMR) experiments with liquid $^3$He confined in anisotropic aerogels with different types of anisotropy (nematic and planar aerogels). Strands of aerogels in pure $^3$He are covered by a few atomic layers of paramagnetic solid $^3$He which magnetization follows the Curie-Weiss law. We have found that in our samples the NMR shift in solid $^3$He is clearly seen at ultralow temperatures and depends on value and orientation of the magnetic field. The obtained results are well described by a model of a system of non-interacting paramagnetic cylinders. The shift is proportional to the magnetization of solid $^3$He and may complicate NMR experiments with superfluid $^3$He in aerogel.

cond-mat.other↗

arXiv2018

Half-quantum vortices and walls bounded by strings in the polar-distorted phases of topological superfluid $^3$He

Symmetries of the physical world have guided formulation of fundamental laws, including relativistic quantum field theory and understanding of possible states of matter. Topological defects (TDs) often control the universal behavior of macroscopic quantum systems, while topology and broken symmetries determine allowed TDs. Taking advantage of the symmetry-breaking patterns in the phase diagram of nanoconfined superfluid $^3$He, we show that half-quantum vortices (HQVs) -- linear topological defects carrying half quantum of circulation -- survive transitions from the polar phase to other superfluid phases with polar distortion. In the polar-distorted A phase, HQV cores in 2D systems should harbor non-Abelian Majorana modes. In the polar-distorted B phase, HQVs form composite defects -- walls bounded by strings hypothesized decades ago in cosmology. Our experiments establish the superfluid phases of $^3$He in nanostructured confinement as a promising topological media for further investigations ranging from topological quantum computing to cosmology and grand unification scenarios.

cond-mat.other↗

arXiv2017

Bose-Einstein condensation of magnons and spin superfluidity in the polar phase of $^3$He

The polar phase of $^3$He, which is topological spin-triplet superfluid with the Dirac nodal line in the spectrum of Bogolubov quasiparticles, has been recently stabilized in a nanoconfined geometry. We pump magnetic excitations (magnons) into the sample of polar phase and observe how they form a Bose-Einstein condensate, revealed by coherent precession of the magnetization of the sample. Spin superfluidity, which supports this coherence, is associated with the spontaneous breaking of U(1) symmetry by the phase of precession. We observe the corresponding Nambu-Goldstone boson and measure its mass emerging when applied rf field violates the U(1) symmetry explicitly. We suggest that the magnon BEC in the polar phase is a powerful probe for topological objects such as vortices and solitons and topological nodes in the fermionic spectrum.

cond-mat.other↗

arXiv2017

Influence of Magnetic Scattering on Superfluidity of 3He in Nematic Aerogel

We report results of experiments with superfluid 3He confined in aerogels with parallel strands which lead to anisotropic scattering of 3He quasiparticles. We vary boundary conditions for the scattering by covering the strands by different numbers of atomic 4He layers and observe that the superfluid phase diagram and the nature of superfluid phases strongly depend on the coverage. We assume that the main reason of these phenomena is a magnetic channel of the scattering which becomes important at low coverages. Our results show that the magnetic channel also may be important in other Fermi systems with the triplet pairing.

cond-mat.supr-con↗

arXiv2016

Observation of half-quantum vortices in topological superfluid 3He

One of the most sought-after objects in topological quantum matter systems is a vortex carrying half a quantum of circulation. They were originally predicted to exist in superfluid 3He-A, but have never been resolved there. Here we report an observation of half-quantum vortices (HQVs) in the polar phase of superfluid 3He. The vortices are created with rotation or by the Kibble-Zurek mechanism and identified based on their nuclear magnetic resonance signature. This discovery provides a pathway for studies of unpaired Majorana modes bound to the HQV cores in the polar-distorted A phase.

cond-mat.other↗

arXiv2016

Interaction of two magnetic resonance modes in polar phase of superfluid 3He

We report results of low frequency nuclear magnetic resonance (NMR) experiments in the superfluid polar phase of 3He which is stabilized by a new type of "nematic" aerogel - nafen. We have found that an interaction between transverse and longitudinal NMR modes may essentially influence the spin dynamics. Theoretical formulas for NMR resonant frequencies are derived and applied for interpretation of the experimental results.

cond-mat.other↗

arXiv2015

Polar phase of superfluid 3He in anisotropic aerogel

We report the observation of a new superfluid phase of 3He -- polar phase. This phase appears in 3He confined in a new type of aerogel with nearly parallel arrangement of strands which play a role of ordered impurities. Our observations qualitatively agree with theoretical predictions and suggest that in other systems with unconventional Cooper pairing (e.g. in unconventional superconductors) similar phenomena may be found in presence of anisotropic impurities.

cond-mat.supr-con↗