arXiv subjects

A. E. Myasnikova

Publications and source records attributed to A. E. Myasnikova.

14 recordsLinked to original sources

arXiv2024

Free energy of a two-liquid system of charge carriers in strongly coupled electron and phonon fields and common nature of three phases in hole-doped cuprates

Hole-doped cuprates demonstrate partially coexisting pseudogap, charge density wave (CDW) and superconducting phases. Recently their common nature was supposed due to similar doping dependence of their critical temperatures. In the CDW phase, a large frozen deformation of strongly ionic lattice is observed. Like for a single carrier in a highly polarizable lattice, for multiple carriers in it the choice between delocalized states of all the carriers and autolocalized states of some part of them is determined by minimum of free energy of interacting carrier and phonon fields. Applying variational approach, we calculate free energy of a two-liquid system of carriers with cuprates-like dispersion comprising liquid of autolocalized carriers (large polarons and bipolarons) and Fermi liquid of delocalized carriers. Comparing it with the free energy of pure Fermi liquid and calculating (with standard methods of Bose-liquid theory) a temperature of superfluid transition in the large-bipolaron liquid we identify areas with presence of pseudogap (caused by impact of (bi)polaron potential on delocalized quasiparticles), CDW and superconductivity in a phase diagram. They are in the same places as in hole-doped cuprates, and similarly to cuprates the shape of the calculated phase diagram is stable with respect to wide-range change of the system characteristics. Like in cuprates, the calculated temperature of the superconducting transition increases with the number of conducting planes in the unit cell, the calculated superfluid density decreases with doping at overdoping, and the bipolaron density (together with bipolaronic plasmon energy) saturates at optimal doping. The results obtained allow us to discuss ways of increasing the temperature of the superfluid transition in large-bipolaron liquid and open a possibility of studying the current-carrying state and properties of bipolaron condensate.

cond-mat.supr-con↗

arXiv2022

Tight binding approximation for bilayer graphene and nanotube structures: from commensurability to incommensurability between the layers

One- and two-dimensional bilayer systems are examples of ultra-tunable quantum materials that are considered as the basis for the new generation of electronic and photonic devices. Here we develop a general theory of the electron band structure for such commensurate and incommensurate bilayer carbon structures within the tight binding approximation. To model the band structure of commensurate twisted bilayer graphene (TBLG), we apply the classic zone folding theory. The latter leads us to the construction of TBLG Hamiltonians in the basis of shifted Bloch wave functions (SBWF), which, in contrast to the usual Bloch functions, have the wave vector q shifted by a set of vectors Q_i. The dimension of the considered Hamiltonians is equal to 4T, where the factor T is a number of vertices Q_i of the folded reciprocal space falling into the original first Brillouin zone of any of the layers. We propose and discuss a method for choosing a reduced set of SBWFs to construct effective Hamiltonians that correctly describe the low-energy spectrum of commensurate TBLG. The flattening of low-energy bands with a decrease in twist angle is discussed. As we show, this spectrum results from interactions between the lowest-energy modes of the folded dispersion curves. The effective Hamiltonians for calculating the low-energy band structure of incommensurate TBLG and double-walled carbon nanotubes (DWCNTs) are constructed in a similar way. To test the developed theory, we calculate the energies of 105 intra-tube optical transitions in 29 DWCNTs and compare them with previously published and novel experimental data. We also apply the theory to calculate the energies of recently discovered inter-tube transitions. Geometrical conditions allowing this type of transitions are discussed. We show that these transitions occur in DWCNTs which layers have close chiral angles and the same handedness.

cond-mat.mes-hall↗

arXiv2021

Topological pseudogap in highly polarizable layered systems with 2D hole-like dispersion

Pseudogap in hole-doped cuprate superconductors is acknowledged as a possible key to understanding their ground normal state, however, existing pseudogap models have essential inconsistencies with experiments. In our approach pseudogap emerges due to impact of autolocalized carriers on stationary states of delocalized ones and topology of the 2D hole-like dispersion. Autolocalized carriers create potential which transforms Bloch quasiparticles into distributed wave packets (DWPs) with different momentums in areas with different potential. Topology of hole-like constant energy curves in 2D-conducting cuprates forbids DWPs with average momentums near antinode. Manifestation of permitted DWPs in ARPES spectra demonstrates all known pseudogap features including midpoint shift, giant broadening and Fermi momentum misalignment. Calculated doping dependence of the pseudogap width and onset temperature agrees with experiments. The obtained ground normal state of the hole-doped cuprates, in which all the doped holes are autolocalized until high doping is reached and near-antinodal electron DWPs are absent, explains Fermi surface reconstruction from small electron pocket to large hole-like Fermi surface observed in quantum oscillation measurements. Our results open a possibility of creating systems with artificial pseudogap and switchable density of states on the base of highly polarizable layered structures with 2D conductivity and hole-like dispersion.

cond-mat.supr-con↗

arXiv2017

Relaxation of strongly coupled electron and phonon fields after photoemission and high-energy part of ARPES spectra of cuprates

We consider photoemission from cuprate high-temperature superconductors taking into account joint relaxation of strongly coupled fields: a field of correlated electrons and phonon field. Such relaxation occurs in systems with predominantly long-range electron-phonon interaction at sufficiently high carrier concentration due to coexistence of autolocalized and delocalized carriers. A simple method to calculate analytically a high-energy part of the ARPES spectrum arising is proposed. The approach suggested yields all the high-energy spectral features like broad bands of Gaussian shape and vertical dispersion patterns being in good quantitative agreement with the experiments at any doping with both types of carriers. Demonstrated coexistence of autolocalized and delocalized carriers in cuprate superconductors is important for understanding their transport and magnetic properties. Presence of large-radius autolocalized carriers shown may be helpful in explanation of charge ordering in doped cuprates.

cond-mat.supr-con↗

arXiv2015

Relaxation of interstitials in spherical colloidal crystals

Spherical colloidal crystals (CCs) self-assemble on the interface between two liquids. These 2D structures unconventionally combine local hexagonal order and spherical geometry. Nowadays CCs are actively studied by altering their structures. However, the statistical analysis of such experiments results is limited by uniqueness of self-assembled structures and their short lifetime. Here we perform numerical experiments to investigate pathways of CC structure relaxation after the intrusion of interstitial. The process is simulated in the frames of overdamped molecular dynamics method. The relaxation occurs due to interaction with extended topological defects (ETDs) mandatory induced in spherical CCs by their intrinsic Gaussian curvature. Types of relaxation pathways are classified and their probabilities are estimated in the low-temperature region. To analyze the structural changes during the relaxation we use a parent phase approach allowing us to describe the global organization of spherical order. This organization is preserved by only the most typical relaxation pathway resulting in filling one of vacancies integrated inside the ETD areas. In contrast with this pathway the other ones shift the ETDs centers and can strongly reconstruct the internal structure of ETDs. Temperature dependence of the relaxation processes and the mechanism of dislocation unbinding are discussed. Common peculiarities in relaxation of spherical structures and particular fragments of planar hexagonal lattice are found.

cond-mat.soft↗

arXiv2015

On the nature of dispersion of the polaronic bands in ARPES spectra of cuprates: supplement of the Franck-Condon principle

Spin correlations are considered now as the only possible source of dispersion of the polaronic band in ARPES spectra of cuprates. However, the same dispersion is observed experimentally for broad O 2pπ band in ARPES spectra of cuprates [Phys. Rev. B 75, 075115 (2007)] although the O 2pπ states do not experience any coupling to the low-energy spin degrees of freedom. The aim of the present report is exploring dispersion of the polaronic band in ARPES spectrum in the frames of Frohlich-Pekar polaron model where this band is calculated analytically [Phys. Rev. B 77, 165136 (2008)]. We improve the method by taking into account the momentum of the recoil and obtain new analytical expression for the photoelectron rate as function of binding energy and momentum. Calculated according to it polaronic band demonstrates dispersion and broadening being in good agreement with the experiment. The dispersion is caused by the momentum of the recoil and can be used to extract the polaron effective mass from the experimental ARPES spectra. We also supplement the Franck-Condon principle by indication that if the phonon field is in a coherent state then during rapid (photo) transition the average coordinates of the phonon field harmonics do not change, but their average momentums are changed due to the recoil momentum.

cond-mat.supr-con↗

arXiv2014

Slightly broken icosahedral symmetry advances Thomson problem

To advance Thomson problem we generalize physical principles suggested by Caspar and Klug (CK) to model icosahedral capsids. Proposed simplest distortions of the CK spherical arrangements yield new-type trial structures very close to the lowest energy ones. In the region 600<N<1000, where N is the number of particles in the structure, we found 40 new spherical crystals with the lowest ever seen energies and curvature-induced topological defects being not the well-known elongated scars but flatten pentagons. These crystals have N values prohibited in the CK model and demonstrate a new way to combine the local hexagonal order and spherical geometry.

cond-mat.soft↗

arXiv2014

Vibrational heat capacity of carbon nanotubes in low and ultra-low temperature regions

We develop a continuous theory of low-frequency dynamics for single-walled carbon nanotubes (SWCNTs) weakly interacting with the environment. In the frame of the approach proposed we obtain temperature dependence of SWCNTs specific heat in the low (T<40 K) and ultra-low (T<2.5 K) temperature ranges. We take into account the main term in the coupling between SWCNT and the environment that slightly increases the frequencies of those SWCNT modes, which possess predominantly radial polarization. The coupling drastically decreases the density of phonon states in the lowest frequencies region. The theoretically predicted fall of the specific heat in the interval T<2.5 K properly explains available experimental data in contrast to the preceding approaches. The theory proposed can be the basis for studies of low-temperature heat capacity and phonon dynamics of many other single-walled and multi-walled tubular structures (boron nitride, transition metal dichalcogenides) which have emerged in the past decade.

cond-mat.mes-hall↗

arXiv2014

Distribution function of charge carriers in electron-phonon systems with spontaneously broken translational symmetry and 'vertical dispersion' in ARPES spectra of cuprates

We show that spontaneous breaking of the translational symmetry (SBTS) of strongly interacting electron and phonon fields acknowledged in lightly doped cuprates to interpret broad bands in their ARPES and optical conductivity spectra influences the carrier distribution function as charge carrier momentum is no longer certain. We develop appropriate distribution and use it to calculate the carrier concentration in different states in essentially doped systems with SBTS. This allows studying doping and temperature evolution of ARPES spectra of such systems. We reveal that at increasing both temperature or doping polarons concede dominance to bipolarons that results in a shift of the broad band maximum to higher binding energy as it occurs in ARPES spectra of cuprates. At further doping delocalized carriers appear and coexist with bipolarons. We show that intimate property of systems with SBTS is partition of the momentum space between autolocalized and delocalized carriers caused by Pauli exclusion rule. We demonstrate that in ARPES spectra such partition manifests itself as `vertical dispersion` or waterfalls universally observed in all the cuprates at essential doping and in undoped parent compounds. Thus, studying the carriers distribution in systems where electron-phonon interaction breaks the translation symmetry leads simultaneously to both types of waterfalls observed in significantly doped and undoped cuprates. The article also represents the methods developed to calculate the band in ARPES spectrum caused by bipolaron photodissociation and the bipolaron binding energy and radius using coherent states for the phonon field characterization.

cond-mat.supr-con↗

arXiv2014

Extended topological defects as sources and outlets of dislocations in spherical hexagonal crystals

Extended topological defects (ETDs) arising in spherical hexagonal crystals due to their curvature are considered. These prevalent defects carry a unit total topological charge and are surrounded by scalene pentagonal boundaries. Topological peculiarities of reactions between ETDs and dislocations are considered. Similarly to boundaries of the usual planar crystalline order the ETDs emit and absorb the dislocations without preservation of their dislocational charge. Dislocations located inside the ETD area lose it and the enforced ETD decay can proceed in different ways without conservation of the total Burgers vector of the dislocations emitted.

cond-mat.mtrl-sci↗

arXiv2013

Transfer of planar orders onto a sphere: formation and properties of complex topological defects

General topological principles how to transfer the planar orders onto a sphere are considered. Formation of extended topological defects (ETDs), which have a reconstructed inner structure surrounded by perfect initial order, is discussed. Topological charge of the ETD can be determined from the shape of a characteristic polygon bounding the defect. Relation between the total topological charge of all defects in the spherical structure and the type of initial planar order is found. It is also demonstrated that in the spherical hexagonal crystal a dislocation located in the ETD area is actually absorbed by it, because the order outside the defect doesn't display existence of dislocation in any way. For the case of singly connected spherical hexagonal order arising from mutual repulsion of N particles (N < 1000) only triangulation of the order inside the ETD regions recovers the linear scars which represent a narrow parts of wider ETD areas.

cond-mat.soft↗

arXiv2007

Correlation of optical conductivity and ARPES spectra of strong-coupling large polarons and its display in cuprates

Common approach is used to calculate band due to strong-coupling large polaron (SCLP) photodissociation in ARPES and in optical conductivity (OC) spectra. It is based on using the coherent-states representation for the phonon field in SCLP. The calculated positions of both band maximums are universal functions of one parameter - the SCLP binding energy Ep: ARPES band maximum lies at binding energy about 3.2Ep; the OC band maximum is at the photon energy about 4.2Ep. The half-widths of the bands are mainly determined by Ep and slightly depend on Frohlich electron-phonon coupling constant: for its value 6-8 the ARPES band half-width is 1.7-1.3Ep and the OC band half-width is 2.8-2.2Ep. Using these results one can predict approximate position of ARPES band maximum and half-width from the maximum of mid-IR OC band and vice versa. Comparison of the results with experiments leads to a conclusion that underdoped cuprates contain SCLPs with Ep=0.1-0.2 eV that is in good conformity with the medium parameters in cuprates. The values of the polaron binding energy determined from experimental ARPES and OC spectra of the same material are in good conformity too: the difference between them is within 10 percent.

cond-mat.supr-con↗

arXiv2007

Band in ARPES caused by photodissociation of Landau-Pekar polarons

We consider decay of phonon condensate into phonons at photodissociation of the strong coupling large polaron (SCLP), when the charge carrier becomes free. Expression to calculate the band in ARPES caused by photodissociation of SCLP is obtained. The band in ARPES caused by photodissociation of strong-coupling large-radius polarons is a broad band with the shape determined by Poisson distribution. It can be structured or unstructured depending on the phonon dispersion since a distance between neighbouring lines comprising the band is the phonon energy. Half-width of the band is in the interval 1.3 - 1.7Ep, depending on the phonon energy. The band maximum is situated approximately at the electron energy Ephot-W-3.2Ep (where Ephot is the photon energy, W is work function), and its position does not depend on the electron wave vector direction.

cond-mat.supr-con↗

arXiv2007

Phonon condensate in Landau-Pekar polarons and optical absorption due to their photoionization

Quantum-field theory methods are applied to consider the state of the polarization field in a strongly-coupled large polaron (SCLP) and after its photodissociation. It is demonstrated that in the adiabatic approximation the polarization field in such a polaron coincides with the classical polarization field considered in Landau-Pekar theory up to small quantum fluctuations. However the state of this field after the polaron photodissociation is in principle different from that obtained in theories of Pekar and Emin. This results from the fact that as it is shown below the polarization field in a SCLP is a spatially inhomogeneous phonon condensate. If the charge carrier is removed from the SCLP on its photodissociation the phonon condensate decays into phonons. As any Bose-condensate, the phonon condensate is a superposition of states with different number of quanta where summands are phased up to small quantum fluctuations. Therefore decay of the phonon condensate at the SCLP photodissociation results in an essentially wider band in the absorption spectrum than that predicted by theories with classical consideration of the polarization: the position of maximum is 4.2Ep and the half-width 2.5Ep (3 Ep and Ep in Emin theory, respectively), where Ep is the polaron binding energy. The calculated band is in good conformity with mid-IR band in the optical conductivity spectra of complex oxides. The predicted ratio (approximately 4) of the maximum position of the band caused by the SCLP photoionization to the frequency of maximum of the band caused by phototransitions into polaron excited states calculated by other group is also in good conformity with experiments.

cond-mat.supr-con↗