arXiv subjects

A. Z. Msezane

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

At least 37 records · Page 2Linked to original sources

arXiv2018

New state of matter: heavy-fermion systems, quantum spin liquids, quasicrystals, cold gases, and high temperature superconductors

We report on a new state of matter manifested by strongly correlated Fermi systems including various heavy-fermion (HF) metals, two-dimensional quantum liquids such as $\rm ^3He$ films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion-condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their thermodynamic, transport, and relaxation properties. That is, the quantum physics of different HF compounds is found to be universal, emerging irrespective of the individual details of their symmetries, interactions, and microscopic structure. This observed universal behavior reveals the existence of a new state of matter manifest in HF compounds. We propose a simple, realistic model to study the appearance of flat bands in two-dimensional ensembles of ultracold fermionic atoms, interacting with coherent resonant light. It is shown that signatures of these flat bands may be found in peculiarities in their thermodynamic and spectroscopic properties. We also show that the FCQPT, in generating flat bands and altering Fermi surface topology, is an essential progenitor of the exotic behavior of the overdoped high-temperature superconductors represented by $\rm La_{2-x}Sr_xCuO_4$, whose superconductivity differs from that predicted by the classical Bardeen-Cooper-Schrieffer theory. The theoretical results presented are in good agreement with recent experimental observations, closing the colossal gap between these empirical findings and Bardeen-Cooper-Schrieffer-like theories.

cond-mat.str-el↗

arXiv2018

Flat bands and the physics of strongly correlated Fermi systems

Some materials can have the dispersionless parts in their electronic spectra. These parts are usually called flat bands and generate the corps of unusual physical properties of such materials. These flat bands are induced by the condensation of fermionic quasiparticles, being very similar to the Bose condensation. The difference is that fermions to condense, the Fermi surface should change its topology, leading to violation of time-reversal (T) and particle-hole (C) symmetries. Thus, the famous Landau theory of Fermi liquids does not work for the systems with fermion condensate (FC) so that several experimentally observable anomalies have not been explained so far. Here we use FC approach to explain recent observations of the asymmetric tunneling conductivity in heavy-fermion compounds and graphene and its restoration in magnetic fields, as well as the violation of Leggett theorem, recently observed experimentally in overdoped cuprates, and recent observation of the challenging universal scaling connecting linear-$T$-dependent resistivity to the superconducting superfluid density.

cond-mat.str-el↗

arXiv2017

The influence of topological phase transition on the superfluid density of overdoped copper oxides

We show that a topological quantum phase transition, generating flat bands and altering Fermi surface topology, is a primary reason for the exotic behavior of the overdoped high-temperature superconductors represented by $\rm La_{2-x}Sr_xCuO_4$, whose superconductivity features differ from what is described by the classical Bardeen-Cooper-Schrieffer theory [J.I. Bozović, X. He, J. Wu, and A. T. Bollinger, Nature 536, 309 (2016)]. We demonstrate that 1) at temperature $T=0$, the superfluid density $n_s$ turns out to be considerably smaller than the total electron density; 2) the critical temperature $T_c$ is controlled by $n_s$ rather than by doping, and is a linear function of the $n_s$; 3) at $T>T_c$ the resistivity $ρ(T)$ varies linearly with temperature, $ρ(T)\propto αT$, where $α$ diminishes with $T_c\to 0$, while in the normal overdoped (non superconducting) region with $T_c=0$, the resistivity becomes $ρ(T)\propto T^2$. The theoretical results presented are in good agreement with recent experimental observations, closing the colossal gap between these empirical findings and Bardeen-Cooper-Schrieffer-like theories.

cond-mat.supr-con↗

arXiv2017

Simple method for determining binding energies of fullerene negative ions

A robust potential wherein is embedded the crucial core polarization interaction is used in the Regge Pole methodology to calculate low energy electron elastic scattering total cross section (TCS) for the C60 fullerene in the electron impact energy range 0.02 through 10.0 eV. The energy position of the characteristic dramatically sharp resonance appearing at the second Ramsauer Townsend (RT) minimum of the TCS representing stable C60 fullerene negative ion formation agrees excellently with the measured electron affinity (EA) of C60 [Huang et al 2014 J. Chem. Phys. 140 224315]. The benchmarked potential and the Regge-pole method are then used to calculate electron elastic scattering TCSs for selected fullerenes, from C54 through C240. The TCSs are found to be characterized generally by RT minima, shape resonances (SRs) and dramatically sharp resonances representing long lived ground state fullerene negative ion formation. For the TCSs of C70, C76, C78, and C84 the agreement between the energy positions of the very sharp resonances, corresponding to the binding energies (BEs) of the resultant fullerene negative ions, and the measured EAs is outstanding. Additionally, we extract the BEs of the resultant fullerene negative ions from our calculated TCSs of the C86, C90 and C92 fullerenes with estimated EAs larger than 3.0 eV by the experiment [Boltalina et al, 1993 Rapid Commun. Mass Spectrom. 7 1009] as well as of other fullerenes, including C180 and C240. Most of the TCSs presented in this paper are the first and only. Our novel approach is general and should be applicable to other fullerenes as well and complex heavy atoms, such as the lanthanide atoms. We conclude with a remark on the catalytic properties of the fullerenes through their negative ions.

physics.atm-clus↗

arXiv2016

Strongly correlated Fermi systems as a new state of matter

The aim of this review paper is to expose a new state of matter exhibited by strongly correlated Fermi systems represented by various heavy-fermion (HF) metals, two-dimensional liquids like $\rm ^3He$, compounds with quantum spin liquids, quasicrystals, and systems with one-dimensional quantum spin liquid. We name these various systems HF compounds, since they exhibit the behavior typical of HF metals. In HF compounds at zero temperature the unique phase transition, dubbed throughout as the fermion condensation quantum phase transition (FCQPT) can occur; this FCQPT creates flat bands which in turn lead to the specific state, known as the fermion condensate. Unlimited increase of the effective mass of quasiparticles signifies FCQPT; these quasiparticles determine the thermodynamic, transport and relaxation properties of HF compounds. Our discussion of numerous salient experimental data within the framework of FCQPT resolves the mystery of the new state of matter. Thus, FCQPT and the fermion condensation can be considered as the universal reason for the non-Fermi liquid behavior observed in various HF compounds. We show analytically and using arguments based completely on the experimental grounds that these systems exhibit universal scaling behavior of their thermodynamic, transport and relaxation properties. Therefore, the quantum physics of different HF compounds is universal, and emerges regardless of the microscopic structure of the compounds. This uniform behavior allows us to view it as the main characteristic of a new state of matter exhibited by HF compounds.

cond-mat.str-el↗

arXiv2016

Comment on "Correlated impurities and intrinsic spin liquid physics in the kagome material Herbertsmithite" (T. H. Han et al., Phys. Rev. B 94, 060409(R) (2016))

Recently Han et al. have provided an analysis of the observed behavior of $\rm ZnCu_{3}(OH)_6Cl_2$ Herbertsmithite based on a separation of the contributions to its thermodynamic properties due to impurities from those due to the kagome lattice. The authors developed an impurity model to account for the experimental data and claimed that it is compatible with the presence of a small spin gap in the kagome layers. We argue that the model they advocate is problematic, conflicting with the intrinsic properties of $\rm ZnCu_{3}(OH)_6Cl_2$ as observed and explained in recent experimental and theoretical investigations. We show that the existence of the gap in the kagome layers is not in itself of a vital importance, for it does not govern the thermodynamic and transport properties of $\rm ZnCu_3(OH)_6Cl_2$. Measurements of heat transport in magnetic fields could clarify the quantum-critical features of spin-liquid physics of $\rm ZnCu_{3}(OH)_6Cl_2$.

cond-mat.str-el↗

arXiv2016

Negative ion formation in lanthanide atoms: Many-body effects

Investigations of low-energy electron-scattering of the lanthanide atoms Eu, Nd, Tb, Tm demonstrate that electron-correlation effects and core polarization are the dominant fundamental many-body effects responsible for the formation of metastable states of negative ions. Ramsauer Townsend minima, shape resonances and binding energies of the resultant anions are identified and extracted from the elastic total cross sections calculated using the complex angular momentum method. The large discrepancy between the recently measured electron affinity of 0.116 and the previously measured value of 1.053 eV for Eu is resolved. Also, the previously measured electron affinities for Nd, Tb and Tm are reconciled and new values are extracted from the calculated total cross sections. The large electron affinities found here for these atoms, should be useful in negative ion nanocatalysis, including methane conversion to methanol without CO2 emission, with significant environmental impact.. The powerful complex angular momentum method which requires only a few poles, yields reliable binding energies for the metastable states of negative ions with no a priori knowledge of experimental or other theoretical data and should be applicable to other complex systems for the fundamental understanding of their interactions.

physics.atom-ph↗

arXiv2016

Topological basis for understanding the behavior of the heavy-fermion metal $\rm {β-YbAlB_4}$ under application of magnetic field and pressure

Informative recent measurements on the heavy-fermion metal $\rm β-YbAlB_4$ performed with applied magnetic field and pressure as control parameters are analyzed with the goal of establishing a sound theoretical explanation for the inferred scaling laws and non-Fermi-liquid (NFL) behavior, which demonstrate some unexpected features. Most notably, the robustness of the NFL behavior of the thermodynamic properties and of the anomalous $T^{3/2}$ temperature dependence of the electrical resistivity under applied pressure $P$ in zero magnetic field $B$ is at variance with the fragility of the NFL phase under application of a field. We show that a consistent topological basis for this combination of observations, as well as the empirical scaling laws, may be found within fermion-condensation theory in the emergence and destruction of a flat band, and explain that the paramagnetic NFL phase takes place without magnetic criticality, thus not from quantum critical fluctuations. Schematic $T-B$ and $T-P$ phase diagrams are presented to illuminate this scenario.

cond-mat.str-el↗

arXiv2016

Electronic Quantum Confinement in Cylindrical Potential Well

The effects of quantum confinement on the momentum distribution of electrons confined within a cylindrical potential well have been analyzed. The motivation is to understand specific features of the momentum distribution of electrons when the electron behavior is completely controlled by the parameters of a non-isotropic potential cavity. It is shown that studying the solutions of the wave equation for an electron confined in a cylindrical potential well offers the possibility to analyze the confinement behavior of an electron executing one- or two-dimensional motion in the three-dimensional space within the framework of the same mathematical model. Some low-lying electronic states with different symmetries have been considered and the corresponding wave functions have been calculated; the behavior of their nodes and their peak positions with respect to the parameters of the cylindrical well has been analyzed. Additionally, the momentum distributions of electrons in these states have been calculated. The limiting cases of the ratio of the cylinder length H and its radius R0 have been considered; when the cylinder length H significantly exceeds its radius R0 and when the cylinder radius is much greater than its length. The cylindrical quantum confinement effects on the momentum distribution of electrons in these potential wells have been analyzed. The possible application of the results obtained here for the description of the general features in the behavior of electrons in nanowires with metallic type of conductivity (or nanotubes) and ultrathin epitaxial films (or graphene sheets) are discussed. Possible experiments are suggested where the quantum confinement can be manifested.

physics.atom-ph↗

arXiv2016

Doubly-charged Negative Ion of C60 Molecule

Within the Dirac- and Lorentz-bubble potential models an electronic structure of the doubly-charged negative ion has been studied by a variational method. It is shown that even in the first approximation of this method when a trial wave function of the two electrons is represented as a product of one-electron functions the total energy of the system is negative, a manifestation of the existence of a stable state of the doubly-charged negative ion in these models. The second electron affinity of C60 according to estimation is about 1 eV. The photodetachment cross sections of this ion have been calculated as well. Near threshold behavior of cross section is found to exhibit peculiar and interesting behavior. The first cross section accompanied by the transformation of the doubly-charged negative ion into a singly-charged one is exponentially small near the process threshold. The second cross section corresponds to the photodetachment of a singly-charged ion; it increases at the threshold as a power function of the kinetic energy of the photoelectron. These cross sections are of the same order as the photodetachment cross sections of atomic ions with the same electron affinity. AMS (MOS) Subject Classification. 70G75, 81V10, 81V55

physics.atom-ph↗

arXiv2016

Model Potentials for a C60 Shell

The spatial distribution of electric charges forming a square well potential has been analyzed. It is shown that this potential is created by two concentric spheres with a double layer of charges. A C60 shell potential has been calculated under the assumption that it is formed by the averaged charge density of a neutral atom. It is further demonstrated that the phenomenological potentials simulating the C60 shell potential belong to a family of potentials with a non-flat bottom. Two possible types of C60 model potentials are proposed and their parameters have been calculated. AMS (MOS) Subject Classification. 62P35, 81V55

physics.atom-ph↗

arXiv2016

Scaling behavior of the thermopower of the archetypical heavy-fermion metal $\rm{YbRh_2Si_2}$

We reveal and explain a scaling behavior of the thermopower $S/T$ exhibiting by the archetypical heavy-fermion (HF) metal $\rm{YbRh_2Si_2}$ under the application of magnetic field $B$ at temperatures $T$. We show that the same scaling is demonstrated by such different HF compounds as $β$-${\rm YbAlB_4}$ and the strongly correlated layered cobalt oxide $\rm [BiBa_{0.66}K_{0.36}O_{2}]CoO_{2}$. Using $\rm{YbRh_2Si_2}$ as an example, we demonstrate that the scaling behavior of $S/T$ is violated at the antiferromagnetic phase transition, while both the residual resistivity $ρ_0$ and the density of states $N$ experience jumps at the phase transition, making the thermopower experience two jumps and change its sign. Our elucidation is based on flattening of the single-particle spectrum that profoundly affects $ρ_0$ and $N$. To depict the main features of the $S/T$ behavior, we construct the $T-B$ schematic phase diagram of $\rm{YbRh_2Si_2}$. Our calculated $S/T$ for the HF compounds are in good agreement with experimental facts and support our observations.

cond-mat.str-el↗

arXiv2015

Core-Polarization and Relativistic Effects in Electron Affinity Calculations for Atoms: A Complex Angular Momentum Investigation

Core-polarization interactions are investigated in low-energy electron elastic scattering from the atoms In,Sn,Eu,Au and At through the calculation of their electron affinities. The complex angular momentum method wherein is embedded the vital electron-electron correlations is used. The core-polarization effects are studied through the well investigated rational function approximation of the Thomas-Fermi potential,which can be analytically continued into the complex plane. The EAs are extracted from the large resonance peaks in the calculated low-energy electron atom scattering total cross sections and compared with those from measurements and sophisticated theoretical methods. It is concluded that when the electron-electron correlation effects and core polarization interactions are accounted for adequately the importance of relativity on the calculation of the electron affinities of atoms can be assessed. For At, relativistic effects are estimated to contribute a maximum of about 3.6 percent to its (non-relativistic) calculated electron affinity.

physics.atom-ph↗

arXiv2015

Heavy fermion spin liquid in herbertsmithite

We analyze recent heat capacity measurements in herbertsmithite $\rm ZnCu_3(OH)_6Cl_2$ single crystal samples subjected to strong magnetic fields. We show that the temperature dependence of specific heat $C_{mag}$ formed by quantum spin liquid at different magnetic fields $B$ resembles the electronic heat capacity $C_{el}$ of the HF metal $\rm YbRh_2Si_2$. We demonstrate that the spinon effective mass $M^*_{mag}\propto C_{mag}/T$ exhibits a scaling behavior like that of $C_{el}/T$. We also show that the recent measurements of $C_{mag}$ are compatible with those obtained on powder samples. These observations allow us to conclude that $\rm ZnCu_3(OH)_6Cl_2$ holds a stable strongly correlated quantum spin liquid, and a possible gap in the spectra of spinon excitations is absent even under the application of very high magnetic fields of 18 T.

cond-mat.str-el↗

arXiv2014

Comment on "Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice" (Punk, M., Chowdhury, D. & Sachdev, S. Nature Physics 10, 289-293 (2014))

The authors of a recent paper evidently take the view that the whole of progress made toward a theoretical understanding of the physics of quantum spin liquids (QSL) is associated with models of the kind proposed and applied in their present work. As motivation for this work, they observe that in contrast to existing theoretical models of both gapped and gapless spin liquids, which give rise to sharp dispersive features in the dynamic structure factor, the measured dynamic structure factor reveals an excitation continuum that is remarkably flat as a function of frequency. They go on to assert that "so far, the only theoretical model for a spin liquid state on the kagome lattice which naturally gives rise to a flat excitation band at low energies consists of the $Z_2$ spin liquids". Here we point out that there already exists a different and demonstrably successful approach to the QSL problem that does naturally feature a flat band.

cond-mat.str-el↗

arXiv2014

General properties of phase diagrams of heavy-fermion metals

We study the temperature-magnetic field T-B phase diagrams of heavy fermion (HF) metals, and show that at sufficiently high temperatures outside the ordered phase the crossover temperature T*(B), regarded as the energy scale, follows a linear B-dependence, crossing the origin of the T-B phase diagram. This behavior of T*(B) constitutes the general property, and is formed by the presence of fermion condensation quantum phase transition hidden within the ordered phase. Our result is in good agreement with the experimental T-B phase diagram of the HF metals YbRh2Si2, Yb(Rh{0.93}Co{0.07})2Si2, and Yb(Rh{0.94}Ir{0.06})2Si2. To support our observations, we analyze the isothermal magnetization M, and demonstrate that dM/dT exhibits a universal temperature behavior over magnetic field scaling. The obtained results are in good agreement with the corresponding data collected on YbRh2Si2 as a function of magnetic field at different temperatures under hydrostatic pressure.

cond-mat.str-el↗

arXiv2013

Heat transport in magnetic fields by quantum spin liquid in the organic insulators EtMe3Sb[Pd(dmit)2]2 and κ-(BEDT-TTF)2Cu2(CN)3

Measurements of the low-temperature thermal conductivity collected on insulators with geometrical frustration produce important experimental facts shedding light on the nature of quantum spin liquid composed of spinons. We employ a model of strongly correlated quantum spin liquid located near the fermion condensation phase transition to analyze the exciting measurements of the low-temperature thermal conductivity in magnetic fields collected on the organic insulators EtMe3Sb[Pd(dmit)_2]2 and κ-(BEDT-TTF)2Cu2(CN)3. Our analysis of the conductivity allows us to reveal a strong dependence of the effective mass of spinons on magnetic fields, to detect a scaling behavior of the conductivity, and to relate it to both the spin-lattice relaxation rate and the magnetoresistivity. Our calculations and observations are in a good agreement with experimental data.

cond-mat.str-el↗

arXiv2013

Flat Bands and Enigma of Metamagnetic Quantum Critical Regime in Sr3Ru2O7

Understanding the nature of field-tuned metamagnetic quantum criticality in the ruthenate Sr3Ru2O7 has presented a significant challenge within condensed matter physics. It is known from experiments that the entropy within the ordered phase forms a peak, and is unexpectedly higher than that outside, while the magnetoresistivity experiences steep jumps near the ordered phase. We find a challenging connection between Sr3Ru2O7 and heavy-fermion metals expressing universal physics that transcends microscopic details. Our construction of the T-B phase diagram of Sr3Ru2O7 permits us to explain main features of the experimental one, and unambiguously implies an interpretation of its extraordinary low-temperature thermodynamic in terms of fermion condensation quantum phase transition leading to the formation of a flat band at the restricted range of magnetic fields B. We show that it is the flat band that generates both the entropy peak and the resistivity jumps at the QCPs.

cond-mat.str-el↗