# Evgeny PlekhanovKing's College London | KCL · Natural and Mathematical Science

Evgeny Plekhanov

Ph.D

## About

75

Publications

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718

Citations

Citations since 2016

Introduction

Additional affiliations

February 2012 - present

September 2004 - January 2012

## Publications

Publications (75)

The pressure-induced structural phase transitions in the lanthanide elements provide insight into changes in their electronic structures at high densities. After a series of transitions via close-packed structures, the regular trivalent lanthanides (La to Lu, excluding Ce, Eu and Yb) undergo first-order transitions to so-called collapsed phases, th...

Effective Hamiltonian of Crystal Field (EHCF) is a hybrid quantum chemical method originally developed for an accurate treatment of highly correlated d-shells in molecular complexes of transition metals. In the present work, we generalise the EHCF method to periodic systems containing transition metal atoms with isolated d-shells, either as a part...

Samarium hydrides, a group of physically viable lanthanide polyhydrides, have yet to be experimentally realized at high pressures. In this work, we combine the first-principles methods of density functional theory (DFT) with dynamical mean-field theory (DMFT) to explore the many-body correlations of samarium. We explore various stoichiometries of s...

The pressure-induced isostructural insulator-to-metal transition for SmS is characterized by the presence of an intermediate valence state at higher pressure which cannot be captured by density functional theory. As a direct outcome of including the charge and spin fluctuations incorporated in dynamical mean-field theory, we see the emergence of in...

Angle-dispersive x-ray powder diffraction experiments have been performed on praseodymium metal to a pressure of 205 GPa. Between 20 and 165 GPa only the oC4 (α-uranium) phase is observed, in agreement with previous studies. At 171(5) GPa we find a transition to a tetragonal tI2 phase which is isostructural with the high-pressure post-oC4 phase see...

Hydrogen-rich superhydrides are believed to be very promising high critical temperature (high Tc) superconductors, with experimentally observed critical temperatures near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g., LaH10 at 170 GPa and CeH9 at 150 GPa. With the motivation of discovering n...

Lanthanide hydrogen-rich materials have long been considered as one of the candidates with high-temperature superconducting properties in condensed matter physics, and have been a popular topic of research. Attempts to investigate the effects of different compositions of lanthanide hydrogen-rich materials are ongoing, with predictions and experimen...

Lanthanide hydrogen-rich materials have long been considered as one of the candidates with high-temperature superconducting properties in condensed matter physics, and have attracted great interest. Attempts to investigate the effects of different compositions of lanthanide hydrogen-rich materials are ongoing, with predictions and experimental stud...

Hydrogen-rich superhydrides are promising high-Tc superconductors, with superconductivity experimentally observed near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g., LaH10 at 170 GPa and CeH9 at 150 GPa. Superconductivity is believed to be closely related to the high vibrational modes of the...

In this paper, we show how to calculate analytical atomic forces within the self-consistent density functional theory + dynamical mean-field theory (DFT+DMFT) approach in the case when ultrasoft or norm-conserving pseudopotentials are used. We show how to treat the nonlocal projection terms arising within the pseudopotential formalism and circumven...

Hydrogen-rich superhydrides are promising high-Tc superconductors, with superconductivity experimentally observed near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g. LaH10 at 170 GPa and CeH9 at 150 GPa. Superconductivity is believed to be closely related with the high vibrational modes of th...

Pressure induced isostructural insulator to metal transition for SmS is characterised by the presence of an intermediate valence state at higher pressure which cannot be captured by the density functional theory. As a direct outcome of including the charge and spin fluctuations incorporated in dynamical mean field theory, we see the emergence of in...

Hydrogen-rich superhydrides are believed to be very promising high-T$_c$ superconductors, with experimentally observed critical temperatures near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g. LaH$_{10}$ at 170 GPa and CeH$_9$ at 150 GPa. With the motivation of discovering new hydrogen-rich h...

We present a standalone ΘΦ (ThetaPhi) package capable to read the results of ab initio DFT/PAW quantum‐chemical solid‐state calculations processed through various tools projecting them to the atomic basis states as an input and to perform on top of this an analysis of so derived electronic structure which includes (among other options) the possibil...

Angle-dispersive x-ray powder diffraction experiments have been performed on neodymium metal to a pressure of 302 GPa. Up to 70 GPa we observe the hP4→cF4→hR24→oI16→hP3 transition sequence reported previously. At 71(2) GPa we find a transition to a phase which has an orthorhombic structure (oF8) with eight atoms in the unit cell, space group Fddd....

In this paper, we show how to calculate analytical atomic forces within self-consistent density functional theory + dynamical mean-field theory (DFT+DMFT) approach in the case when ultrasoft or norm-conserving pseudopotentials are used. We show how to treat the non-local projection terms arising within the pseudopotential formalism and circumvent t...

The available solid-state electronic-structure codes are devoid of hot topics of physics: incommensurate magnetic, superconducting and spin-liquid electronic states/phases. The temperature dependence of the solutions of electronic problem is not accessible either. These gaps are closed by the proposed ΘΦ (ThetaPhi) package.

The available solid-state electronic-structure codes are devoid of hot topics of physics:
incommensurate magnetic, superconducting and spin-liquid electronic states/phases. The temperature dependence of the solutions of electronic problem is not accessible either. These gaps are closed by the proposed ThetaPhi package.

Simulating the incommensurate spin density waves (ISDW) states is not a simple task within the standard \emph{ab-initio} methods. Moreover, in the context of new material discovery, there is a need for fast and reliable tool capable to scan and optimize the total energy as a function of the pitch vector, thus allowing to automatize the search for n...

Simulating the incommensurate spin density waves (ISDW) states is not a simple task within the standard ab initio methods. Moreover, in the context of new material discovery, there is a need for fast and reliable tool capable to scan and optimize the total energy as a function of the pitch vector, thus allowing to automatize the search for new mate...

Angle-dispersive x-ray powder diffraction experiments have been performed on yttrium metal up to 183 GPa. We find that the recently discovered oF 16 structure observed in the high-Z trivalent lanthanides is also adopted by yttrium above 106 GPa, pressures where it has a superconducting temperature of ∼20 K. We have also refined both tetragonal and...

We propose the ΘΦ package which addresses two of the most important extensions of the essentially single-particle mean-field paradigm of the computational solid state physics: the admission of the Bardeen–Cooper–Schrieffer electronic ground state and allowance of the magnetically ordered states with an arbitrary superstructure (pitch) wave vector....

The conducting states, recently discovered at the surface of two special class of insulators—topological insulators and topological crystalline insulators—are distinguished by their insensitivity to local and nonmagnetic surface defects at a level of disorder, sufficiently small to be described within the perturbation theory. However, the behavior...

Using synchrotron x-ray diffraction, we show that the long-accepted monoclinic structure of the “collapsed” high-pressure phases reported in seven lanthanide elements [Nd, Tb, Gd, Dy, Ho, Er, and (probably) Tm] is incorrect. In Tb, Gd, Dy, Ho, Er, and Tm we show that the collapsed phases have a 16-atom orthorhombic structure (oF16) not previously s...

Dynamical mean-field theory (DMFT) is one of the most widely-used methods to treat accurately electron correlation effects in ab-initio real material calculations. Many modern large-scale implementations of DMFT in electronic structure codes involve solving a quantum impurity model with a continuous-time quantum Monte Carlo (CT-QMC) solver [Rubtsov...

In condensed matter, a tremendous effort has been generated to realise Kondo lattices both experimentally and theoretically. The pursuit of independent magnetic moments, via charge localization, is paramount for applications in nanotechnology. Particularly, systems with simultaneous charge/spin degrees of freedom can manifest both Kondo spin quench...

We propose the $\Theta\Phi$ (Theta-Phi) package which address two of the most important extensions of the essentially single-particle mean-field paradigm of the computational solid state physics: the admission of the Bardeen-Cooper-Schrieffer electronic ground state and allowance of the magnetically ordered states with an arbitrary superstructure (...

The conducting states, recently discovered at the surface of two special class of insulators -- topological insulators and topological crystalline insulators - are distinguished by their sensitivity to local and non-magnetic surface defects. For the latter, the behavior of the surface states is in particular dependent on macroscopic imperfections,...

Dynamical mean-field theory (DMFT) is one of the most widely-used methods to treat accurately electron correlation effects in ab-initio real material calculations. Many modern large-scale implementations of DMFT in electronic structure codes involve solving a quantum impurity model with a Continuous-Time Quantum Monte Carlo (CT-QMC) solver. The mai...

Spin is a quantum degree of freedom with no classical analogue. The quenching and un-quenching of the spin angular momentum is a fascinating topic of study in condensed matter. The other interesting phenomenon in condensed matter is the localization of charge through Coulomb correlations. Systems with simultaneous charge and spin degrees of freedom...

We present the implementation of dynamical mean-field theory (DMFT) in the CASTEP ab initio code. We explain in detail the theoretical framework for DFT+DMFT and we demonstrate our implementation for three strongly-correlated systems with f-shell electrons: γ-cerium, cerium sesquioxide Ce2O3, and samarium telluride SmTe by using a Hubbard I solver....

The delicate interplay of electronic charge, spin, and orbital degrees of freedom is in the heart of many novel phenomena across the transition metal oxide family. Here, by combining high-resolution angle-resolved photoemission spectroscopy and first principles calculations (with and without spin-orbit coupling), the electronic structure of the rut...

We present the implementation of Dynamical Mean-Field Theory (DMFT) in the CASTEP ab-initio code. We explain in detail the theoretical framework for DFT+DMFT and we benchmark our implementation on two strongly-correlated systems with $f$-shell electrons: $\gamma$-cerium and cerium sesquioxide Ce$_{2}$O$_{3}$ by using a Hubbard I solver. We find ver...

High temperature superconductivity has been found in many kinds of compounds built from planes of Cu and O, separated by spacer layers. Understanding why critical temperatures are so high has been the subject of numerous investigations and extensive controversy. To realize high temperature superconductivity, parent compounds are either hole-doped,...

This chapter combines two complementary parts. In the first part, we discuss (largely qualitatively) the relations between the resonance valence bond (RVB) and tight-binding/linear combination of atomic orbitals (LCAO) pictures of the electronic structure using the archetypal example: the π-system of benzene. The second more formal part is devoted...

By combining high-resolution angle resolved photoemission spectroscopy and first principles calculations, we explored the detailed electronic structure of IrO$_2$, a material exhibiting large spin Hall resistivity which makes it particularly suitable as a spin detector. We discuss the role of spin-orbit coupling in the formation of critical bands r...

Within the crucial issue of the electric field control of magnetism, the use of antiferromagnets (AFMs) coupled to ferroelectrics is much less explored than the ferromagnets counterpart, although the first choice might lead to better performances and larger stability with respect to external perturbations (such as magnetic fields). Here, we explore...

Interfacial magnetoelectric coupling for electrically altering the magnetization of ferromagnetic electrodes is a viable path to achieve the electrical writing of the magnetic information in spintronic devices. Exploiting the piezoelectric behavior of a ferroelectric material (FE) in contact with a ferromagnetic (FM) thin film, the electric control...

By addressing the interplay between substitutional disorder and spin-orbit-coupling in chalcogenide alloys, we predict a strong robustness of spectral features at the Fermi energy. Indeed, supplementing our state of the art first-principles calculations with modeling analysis, we show that the disorder self-energy is vanishingly small close to the...

Spin-orbit coupling is increasingly seen as a rich source of novel phenomena,
as shown by the recent excitement around topological insulators and Rashba
effects. We here show that the addition of ferroelectric degrees of freedom to
a semiconductor featuring topologically-non-trivial properties, such as SnTe,
merges the intriguing field of spin-orbi...

In order to carefully address the interplay between substitutional disorder
and spin-orbit-coupling in IV-VI alloys, we propose a novel theoretical
approach that integrates the reliability of plane-wave based density-functional
theory beyond the local-density approximation with the Coherent Potential
Approximation. By applying the proposed method t...

Interfacial magnetoelectric coupling is a viable path to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO3 system, only tiny changes of the interfacial Fe magnetic moment upon reversal of the BaTiO3 dielectric polarization have been predicted so far. Here, by using X-ray magnetic circular dichr...

We present the exact solution, obtained by means of the Transfer Matrix (TM) method, of the 1D Hubbard model with nearest-neighbor (NN) and next-nearest-neighbor (NNN) Coulomb interactions in the atomic limit (t = 0). The competition among the interactions (U, V
1, and V
2) generates a plethora of T = 0 phases in the whole range of fillings. U, V
1...

Within the Composite Operator Method (COM), we report the solution of the
Emery model (also known as p-d or three band model), which is relevant for the
cuprate high-Tc superconduc- tors. We also discuss the relevance of the
often-neglected direct oxygen-oxygen hopping for a more accurate, sometimes
unique, description of this class of materials. T...

In this paper we present for the first time the exact solution in the
narrow-band limit of the 1D extended Hubbard model with nearest-neighbour
spin-spin interactions described by an exchange constant J. An external
magnetic field h is also taken into account. This result has been obtained in
the framework of the Green's functions formalism, using...

In this paper we study a generalization of the 1D Hubbard model by
considering density-density and Ising-type spin-spin nearest neighbor (NN)
interactions, parameterized by $V$ and $J$, respectively. We present the T=0
phase diagram for both ferro ($J>0$) and anti-ferro ($J<0$) coupling obtained
in the narrow-band limit by means of an extension to...

We study the two-dimensional p-d model by means of a four-pole approximation within the Composite Operator Method framework. Many results of numerical simulations have been correctly reproduced by considering as basic composite field a four-component spinor field, including the p field, the two Hubbard operators for the d field, and a composite ope...

In this paper we study a generalization of the Hubbard model by considering spin-spin interactions described by the exchange constant J. An external magnetic field h is also taken into account. In the narrowband limit and for the 1D case, we present the exact solution obtained in the framework of the Green’s function formalism, using the Composite...

The two-dimensional p–d model has been solved within the Composite Operator Method (COM) in an original four-pole approximation where the basic four-component composite field contains both the standard electronic fields p and d, the latter split into two Hubbard operators, and a composite operator describing the coupling between the p electrons and...

The two-dimensional Hubbard model in the superconducting d-wave phase has been solved within the Composite Operator Method (COM) in the two-pole approximation [1]. The unknowns of the theory have been computed exploiting the operatorial relations, dictated by the Pauli principle, existing between the composite operators belonging to the basis. Such...

We study the two-dimensional three-band Hubbard model by means of a four-pole approximation within the Composite Operator Method framework. The model has been solved by considering as basic composite field a four-component spinor field, which includes the p field, the two Hubbard operators for the d field, and a composite operator describing the p...

The two-dimensional Hubbard model has been studied within the Composite Operator Method (COM) [1] starting from a basis made of the two Hubbard composite fields in the Nambu representation and computing the residual self-energy in the non-crossing approximation (NCA) [2]. The charge-charge, spin-spin and pair-pair susceptibilities, involved in the...

By using Density Matrix Renormalization Group (DMRG) technique we study the
phase diagram of 1D extended anisotropic Heisenberg model with ferromagnetic
nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. We
analyze the static correlation functions for the spin operators both in- and
out-of-plane and classify the zero-tempera...

The orbital degrees of freedom are of vital importance in explanation of various phenomena. Among them is the orbital-selective Mott transition (OSMT), which is thought to occur in several materials as Ca$_{2-x}$Sr$_x$RuO$_4$ and La$_{n+1}$Ni${_n}$O$_{3n+1}$. OSMT is usually studied in the infinite-dimension limit, and for the time being, it is not...

It is widely accepted that the low-energy physics in edge-sharing cuprate
materials has one-dimensional (1D) character. The relevant model to study such
systems is believed to be the 1D extended Heisenberg model with ferromagnetic
nearest-neighbor (NN) interaction and antiferromagnetic next-nearest-neighbor
one. Thus far, however, theoretical studi...

For the 1D spin-1/2 Heisenberg model with ferromagnetic nearest-neighbor interaction and antiferromagnetic next-nearest neighbor one we present the phase diagram at T = 0 as obtained by DMRG analysis. The interplay of interactions generates two massless and two massive phases in the range of parameters considered. We discuss the properties of the c...

By means of the Density Matrix Renormalization Group technique, we have studied the region where XXZ-like behavior is most
likely to emerge within the phase diagram of the F-AF anisotropic extended (J-J’) Heisenberg chain. We have analyzed, in great
detail, the equal-time two-spin correlation functions, both in- and out-of- plane, as functions of t...

By using density matrix renormalization group technique we study the 1D extended anisotropic Heisenberg model. We find that starting from the ferromagnetic phase, the system undergoes two quantum phase transitions induced by frustration. By increasing the next-nearest-neighbor interaction, the ground state of the system changes smoothly from a comp...

We present a study of the entanglement properties of the F-AF zig-zag Heisenberg chain done by means of the Density Matrix Renormalization Group method. In particular, we have selected the concurrence as measure of entanglement and checked its capability to signal the presence of quantum phase transitions within the previously found ergodicity phas...

We present a concise, but systematic, review of the ergodicity issue in strongly correlated systems. After giving a brief historical overview, we analyze the issue within the Green's function formalism by means of the equations of motion approach. By means of this analysis, we are able to individuate the primary source of non-ergodic dynamics for a...

We present the results of exact diagonalization calculations of the isolated and isothermal on-site static susceptibilities in the anisotropic extended Heisenberg model on a linear chain with periodic boundary conditions. Based on the ergodicity considerations we conclude that the isothermal susceptibility will diverge as $T\to 0$ both in finite cl...

By using Density Matrix Renormalization Group (DMRG) technique we study the 1D extended anisotropic Heisenberg model. We find that starting from the ferromagnetic phase, the system undergoes two quantum phase transitions (QPTs) induced by frustration. By increasing the next-nearest-neighbor (NNN) interaction, the ground state of the system changes...

We present a study of entanglement in the case of the 1D extended anisotropic Heisenberg model. We investigate two quantum phase transitions (QPTs) within the previously found ergodicity phase diagram [E. Plekhanov, A. Avella, and F. Mancini Phys. Rev. B \textbf{74}, 115120 (2006)]. Our calculations are done by means of the numerically exact Lanczo...

The two-dimensional Hubbard model is studied within the composite operator method (COM) with the electronic self-energy computed in the self-consistent Born approximation (SCBA). The COM describes interacting electrons in terms of the composite elementary excitations appearing in the system owing to the strong correlations; the residual interaction...

The issue of ergodicity is often underestimated. The presence of zero-frequency excitations in bosonic Green's functions determine the appearance of zero-frequency momentum-dependent quantities in correlation functions. The implicit dependence of matrix elements make such quantities also relevant in the computation of susceptibilities. Consequently...

We define a suitable quantity $Z_c$ that measures the pairing strength of two electrons added to the ground state wave function by means of the anomalous part of the one-particle Green's function. $Z_c$ discriminates between systems described by one-electron states, like ordinary metals and band insulators, for which $Z_c=0$, and systems where the...

В работе изучается начальная стадия конденсации - нуклеация на основе квантовохимических расчетов структуры и энергетических характеристик малых молекулярных кластеров. Результаты расчетов структуры и энергетики малых кластеров позволили получить асимптотические выражения для произведения главных моментов инерции, энергии диссоциации и характеристи...

We study, through the variational Monte Carlo technique, an extended Hubbard model away from half filled band density which contains two competing nearest-neighbor interactions: a superexchange J favoring d-wave superconductivity and a repulsion V opposing it. We find that the on-site repulsion U effectively enhances the strength of J while suppres...