arXiv subjects

A. Z. Msezane

Publications and source records attributed to A. Z. Msezane.

67 records · Page 4Linked to original sources

arXiv2006

Phase Diagram of Heavy Fermion Metal CeCoIn5

We present a comprehensive analysis of the low temperature experimental H-T phase diagram of CeCoIn5. The main universal features of the diagram can be explained within the Fermi-liquid theory provided that quasiparticles form so called fermion-condensate state. We show that in this case the fluctuations accompanying an ordinary quantum critical point are strongly suppressed and cannot destroy the quasiparticles. Analyzing the phase diagram and giving predictions, we demonstrate that the electronic system of CeCoIn5 provides a unique opportunity to study the relationship between quasiparticles properties and non-Fermi liquid behavior.

cond-mat.str-el↗

arXiv2006

Soft X-ray emission lines of Fe XV in solar flare observations and the Chandra spectrum of Capella

Recent calculations of atomic data for Fe XV have been used to generate theoretical line ratios involving n = 3-4 transitions in the soft X-ray spectral region (52-83 A), for a wide range of electron temperatures and densities applicable to solar and stellar coronal plasmas. A comparison of these with solar flare observations from a rocket-borne spectrograph (XSST) reveals generally good agreement between theory and experiment. In particular, the 82.76 A emission line in the XSST spectrum is identified, for the first time to our knowledge in an astrophysical source. Most of the Fe XV transitions which are blended have had the species responsible clearly identified, although there remain a few instances where this has not been possible. The line ratio calculations are also compared with a co-added spectrum of Capella obtained with the Chandra satellite, which is probably the highest signal-to-noise observation achieved for a stellar source in the 25-175 A soft X-ray region. Good agreement is found between theory and experiment, indicating that the Fe XV lines are reliably detected in Chandra spectra, and hence may be employed as diagnostics to determine the temperature and/or density of the emitting plasma. However the line blending in the Chandra data is such that individual emission lines are difficult to measure accurately, and fluxes may only be reliably determined via detailed profile fitting of the observations. The co-added Capella spectrum is made available to hopefully encourage further exploration of the soft X-ray region in astronomical sources.

astro-ph↗

arXiv2005

On the modification of the photoionization of subvalent subshells in endohedral noble gas atoms

It is demonstrated that outer and inner electron shells, including that formed by collectivized electrons of the fullerene C60, affects dramatically the cross section of the subvalent ns-subshells of the noble gas endohedral atoms A@C60. The calculations are performed within the framework of a very simple, so-called "orange skin", model that makes it possible, in spite of its simplicity, to take into account the modification of the ns-subshell due to its interaction with inner and outer atomic shells, as well as with the collectivized electrons of the C60. As a concrete example, we consider the Xe 5s electrons completely collectivized by the powerful action of the Xe close and remote multi-electron neighboring shells.

physics.atom-ph↗

arXiv2005

Universal Cause of High-Tc Superconductivity and Anomalous Behavior of Heavy Fermion Metals

Unusual properties of strongly correlated liquid observed in the high-$T_c$ superconductors and heavy-fermion (HF) metals are determined by quantum phase transitions taking place at their critical points. Therefore, direct experimental studies of these transitions and critical points are of crucial importance for understanding the physics of high-$T_c$ superconductors and HF metals. In case of high-$T_c$ superconductors such direct experimental studies are absent since at low temperatures corresponding critical points are occupied by the superconductivity. Recent experimental data on the behavior of HF metals illuminate both the nature of these critical points and the nature of the phase transitions. We show that it is of crucial importance to simultaneously carry out studies of both the high-$T_c$ superconductivity and the anomalous behavior of HF metals. Our general consideration suggests that FCQPT and the emergence of novel quasiparticles near and behind FCQPT are distinctive features of strongly correlated substances such as the high-$T_c$ superconductors and HF metals. We show that the main properties and universal behavior of the high-$T_c$ superconductors and HF metals can be understood within the framework of presented here theory based on FCQPT. A large number of the experimental evidences in favor of the existence of FCQPT in high-$T_c$ superconductors and HF metals is presented.

cond-mat.str-el↗

arXiv2005

Quasiparticles and order parameter near quantum phase transition in heavy fermion metals

It is shown that the Landau paradigm based upon both the quasiparticle concept and the notion of the order parameter is valid and can be used to explain the anomalous behavior of the heavy fermion metals near quantum critical points. The understanding of this phenomenon has been problematic largely because of the absence of theoretical guidance. Exploiting this paradigm and the fermion condensation quantum phase transition, we investigate the anomalous behavior of the heavy electron liquid near its critical point at different temperatures and applied magnetic fields. We show that this anomalous behavior is universal and can be used to capture the essential aspects of recent experiments on heavy-fermion metals at low temperatures.

cond-mat.str-el↗

arXiv2004

On the relation between the Hartree-Fock and Kohn-Sham approaches

We show that the Hartree-Fock (HF) results cannot be reproduced within the framework of Kohn-Sham (KS) theory because the single-particle densities of finite systems obtained within the HF calculations are not $v$-representable, i.e., do not correspond to any ground state of a $N$ non-interacting electron systems in a local external potential. For this reason, the KS theory, which finds a minimum on a different subset of all densities, can overestimate the ground state energy, as compared to the HF result. The discrepancy between the two approaches provides no grounds to assume that either the KS theory or the density functional theory suffers from internal contradictions.

cond-mat.other↗

arXiv2004

"Superluminal" tunnelling, quantum measurements and the speed of information transfer

We exploit the analogy between tunnelling across a potential barrier and Aharonov's weak measurements to resolve the long standing paradox between the impossibility to exceed the speed of light and the seemingly 'superluminal' behaviur of the tunnelling particle in the barrier. We demonstrate that 'superluminality' occurs when the value of the duration $τ$ spent in the barrier is uncertain, whereas when $τ$ is known accurately, no 'superluminal' behaviur is observed. In all cases only subluminal durations contribute to the transmission, which precludes faster-than-light information transfer, as shown by a recent experiment.

quant-ph↗

arXiv2003

Density Functional Theory versus the Hartree Fock Method: Comparative Assessment

We compare two different approaches to investigations of many-electron systems. The first is the Hartree-Fock (HF) method and the second is the Density Functional Theory (DFT). Overview of the main features and peculiar properties of the HF method are presented. A way to realize the HF method within the Kohn-Sham (KS) approach of the DFT is discussed. We show that this is impossible without including a specific correlation energy, which is defined by the difference between the sum of the kinetic and exchange energies of a system considered within KS and HF, respectively. It is the nonlocal exchange potential entering the HF equations that generates this correlation energy. We show that the total correlation energy of a finite electron system, which has to include this correlation energy, cannot be obtained from considerations of uniform electron systems. The single-particle excitation spectrum of many-electron systems is related to the eigenvalues of the corresponding KS equations. We demonstrate that this spectrum does not coincide in general with the eigenvalues of KS or HF equations.

cond-mat.mtrl-sci↗

arXiv2003

New Approach to Density Functional Theory and Description of Spectra of Finite Electron Systems

The self consistent version of the density functional theory is presented, which allows to calculate the ground state and dynamic properties of finite multi-electron systems. An exact functional equation for the effective interaction, from which one can construct the action functional, density functional, the response functions, and excitation spectra of the considered systems, is outlined. In the context of the density functional theory we consider the single particle excitation spectra of electron systems and relate the single particle spectrum to the eigenvalues of the corresponding Kohn-Sham equations. We find that the single particle spectrum coincides neither with the eigenvalues of the Kohn-Sham equations nor with those of the Hartree-Fock equations.

cond-mat.mtrl-sci↗

arXiv2003

Two Types of the Effective Mass Divergence and the Grüneisen Ratio in Heavy Fermion Metals

The behavior of the specific heat $c_p$, effective mass $M^*$, and the thermal expansion coefficient $α$ of a Fermi system located near the fermion condensation quantum phase transition (FCQPT) is considered. We observe the first type behavior if the system is close to FCQPT: the specific heat $c_p\propto \sqrt{T}$, $M^*\propto1/\sqrt{T}$, while the thermal expansion coefficient $α\propto \sqrt{T}$. Thus, the Grüneisen ratio ${\rm Γ}(T)=α/c_p$ does not diverges. At the transition region, where the system passes over from the non-Fermi liquid to the Landau Fermi liquid, the ratio diverges as ${\rm Γ}(T)\propto 1/\sqrt{T}$. When the system becomes the Landau Fermi liquid, ${\rm Γ}(T,r)\propto 1/r$, with $r$ being a distance from the quantum critical point. Provided the system has undergone FCQPT, the second type takes place: the specific heat behaves as $c_p\propto \sqrt{T}$, $M^*\propto 1/T$, and $α=a+bT$ with $a,b$ being constants. Again, the Grüneisen ratio diverges as ${\rm Γ}(T)\propto 1/\sqrt{T}$.

cond-mat.str-el↗

arXiv2003

From the Bose-Einstein to Fermion Condensation

The appearance of the fermion condensation, which can be compared to the Bose-Einstein condensation, in different liquids is considered, its properties are discussed, and a large number of experimental evidences in favor of the existence of the fermion condensate is presented.

cond-mat.supr-con↗

arXiv2003

Correlation structure in nondipole photoionization

The nondipole parameters that characterize the angular disribution of the photoelectrons from the 3d subshell of Cs are found to be altered qualitatively by the inclusion of correlation in the form of interchannel coupling between the $3d_{3/2}$ and $3d_{5/2}$ photoionization channels. A prominent characteristic maximum is predicted only in the parameters for $3d_{5/2}$ photoionization, while the effect for $3d_{3/2}$ is rather weak. The results are obtained within the framework of the Generalized Random Phase Approximation with Exchange (GRPAE), which in addition to the RPAE effects takes into account the rearrangement of all atomic electrons due to the creation of a 3d vacancy.

physics.atom-ph↗

arXiv2001

Trapped Atomic Fermi Gases

A many-body system of fermion atoms with a model interaction characterized by the scattering length $a$ is considered. We treat both $a$ and the density as parameters assuming that the system can be created artificially in a trap. If $a$ is negative the system becomes strongly correlated at densities $ρ\sim |a|^{-3}$, provided the scattering length is the dominant parameter of the problem. It means that we consider $|a|$ to be much bigger than the radius of the interaction or any other relevant parameter of the system. The density $ρ_{c1}$ at which the compressibility vanishes is defined by $ρ_{c1}\sim |a|^{-3}$. Thus, a system composed of fermion atoms with the scattering length $a\to -\infty$ is completely unstable at low densities, inevitably collapsing until the repulsive core stops the density growth. As a result, any Fermi system possesses the equilibrium density and energy if the bare particle-particle interaction is sufficiently strong to make $a$ negative and to be the dominant parameter. This behavior can be realized in a trap. Our results show that a low density neutron matter can have the equilibrium density.

cond-mat.stat-mech↗