Fermi Liquid Model Research Articles

Heavy-fermion metallic state and Mott transition induced by Li-ion intercalation in LiV2O4 epitaxial films

The spinel-type ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ exhibits heavy-fermion metallic behaviors at low temperatures, but the effect of composition modulation on them is unknown. We realized the epitaxial growth of highly crystalline ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ films and conducted the electrochemical Li-ion intercalation (electron doping) to investigate systematic variation of transport properties in ${\mathrm{Li}}_{1+x}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$. We found that adjustment of Li content during pulsed-laser deposition was important to obtain films exhibiting the heavy-fermion metallic behavior comparable to that of a bulk single crystal. At low doping regime $(x\ensuremath{\le}0.5)$, resistivity increased with increasing electron filling. The slope of their linear ${T}^{2}$ dependence also increased in accordance of a Fermi-liquid model. At high doping regime $(x>0.5)$, a Mott transition was observed over a range of Li content where a new spinel phase and the original one coexisted. The results revealed that the electron doping induced enhancement of the electron correlation and the resultant Mott transition.

Positive Magnetoresistance and Chiral Anomaly in Exfoliated Type-II Weyl Semimetal Td-WTe2.

Layered van der Waals semimetallic -WTe, exhibiting intriguing properties which include non-saturating extreme positive magnetoresistance (MR) and tunable chiral anomaly, has emerged as a model topological type-II Weyl semimetal system. Here, ∼45 nm thick mechanically exfoliated flakes of -WTe are studied via atomic force microscopy, Raman spectroscopy, low-T/high- magnetotransport measurements and optical reflectivity. The contribution of anisotropy of the Fermi liquid state to the origin of the large positive transverse and the signature of chiral anomaly of the type-II Weyl Fermions are reported. The samples are found to be stable in air and no oxidation or degradation of the electronic properties is observed. A transverse ∼1200 % and an average carrier mobility of 5000 cmVs at for an applied perpendicular field are established. The system follows a Fermi liquid model for and the anisotropy of the Fermi surface is concluded to be at the origin of the observed positive MR. Optical reflectivity measurements confirm the anisotropy of the electronic behaviour. The relative orientation of the crystal axes and of the applied electric and magnetic fields is proven to determine the observed chiral anomaly in the in-plane magnetotransport. The observed chiral anomaly in the WTe flakes is found to persist up to , a temperature at least four times higher than the ones reported to date.

Fermi liquid theory sheds light on hot electron-hole liquid in 1L−MoS2

Room-temperature electron-hole liquid has recently been experimentally identified in low-dimensional transition metal dichalcogenides. Here, the authors demonstrate that a first-principles Fermi liquid model effectively predicts the photoluminescence response of this phenomenon. Using density functional theory, in conjunction with previous Raman and photoluminescence spectroscopy results, they present a consistent quantitative picture of the electron-hole liquid phase transition in suspended, heat-strained 1$L$-MoS${}_{2}$ monolayers. They show a 23-fold increase in photoluminescence per unit of direct gap carrier density and 9:1 indirect-direct hole population ratio at high strain.

Effect of high angular momentum on η/s of nuclear matter

The shear viscosity ($\ensuremath{\eta}$) of nuclear matter is investigated in different nuclei (nuclear mass $A\ensuremath{\approx}59--194$) using experimental giant dipole resonance (GDR) width ($\mathrm{\ensuremath{\Gamma}}$) at high angular momenta ($J=12--54$ $\ensuremath{\hbar}$) and temperatures ($T=1.2--2.1$ MeV) collected from the existing literature. $\ensuremath{\eta}$, calculated from $\mathrm{\ensuremath{\Gamma}}$, is found to increase with $T$ and $J$. We show that critical temperature included fluctuation model (CTFM) successfully describes $J$-induced $\ensuremath{\eta}$ even beyond critical angular momentum ${J}_{c}$ at different values of $T$. However, the Fermi liquid drop model (FLDM) could not explain the data at higher angular momenta. We propose the addition of a $J$-dependent term with the FLDM $\ensuremath{\eta}$ to improve the prediction at such high-$J$ region. The $\ensuremath{\eta}/s$ ratio, highly important for measuring fluidity, is calculated using $\ensuremath{\eta}$ and the entropy density $s$. The latter is estimated using the Fermi gas formula. Interestingly, the experimental value of the ratio is independent of $J$ and $A$ and comes within 2.6--6.0 $\ensuremath{\hbar}/4\ensuremath{\pi}{k}_{\mathrm{B}}$, which is very close to those of a partonic system like quark gluon plasma at high temperature.

Multiparticle Effects in the Spectrum of Collective Excitations of Strongly Interacting Two-Dimensional Electron Systems (Brief Review)

Extraordinary multiparticle effects in quantizing magnetic fields that are manifested in strongly interacting two-dimensional electron systems in MgZnO/ZnO heterostructures have been reviewed. They are studied by the method of inelastic light scattering on two-dimensional systems with unique properties: strong Coulomb interaction characterized by the Wigner–Seitz parameters $${{r}_{s}} > 5$$ and a high mobility. Studies are focused on the properties of collective excitations in strong magnetic fields corresponding to the integer quantum Hall effect regime. Many results for the structure of the ground state and multiparticle contributions to the energy of collective excitations are far beyond the commonly accepted concepts of the microscopic structure of states of the quantum Hall effect in weakly interacting systems. Although any strict theory of two-dimensional electron systems at $${{r}_{s}} \gg 1$$ is absent, experimental results are adequately described by the calculations by the exact diagonalization method and the Fermi liquid model.

The collective excitation of nuclear matter in a bosonized Landau Fermi liquid model

The collective excitation of nuclear matter is analyzed in a bosonized Landau Fermi liquid model. When the nonlinear self-interacting terms of scalar mesons are included in Walecka model, the collective excitation energy of nuclear matter can be obtained self-consistently, and the calculation results are consistent with the corresponding experimental data of the nucleus P208b when the quantum number of the orientation of the total spin m is zero. The cases with the nonzero m values are also studied, and it is found that the collective excitation energy of nuclear matter decreases with the absolute value of m increasing when the total spin is conserved. Moreover, four kinds of collective excitation modes of nuclear matter are discussed when the isospin and spin of nucleons are taken into account. The direct interaction between two nucleons near Fermi surface only changes the effective nucleon mass and Fermi velocity, while the exchange interaction plays an critical role in the collective excitation of nuclear matter.

Emergent mystery in the Kondo insulator samarium hexaboride

Samarium hexaboride (SmB6) is an example of a Kondo insulator, in which strong electron correlations cause a band gap to open. SmB6 hosts both a bulk insulating state and a conductive surface state. Within a Fermi-liquid framework, the strongly correlated ground-state electronic structure can be mapped to a simple state resembling a topological insulator. Although uncertainties remain, many experiments provide compelling evidence that the conductive surface states have a topological origin. However, the bulk behaviour is less well understood and some experiments indicate bulk in-gap states. This has inspired the development of many theories that predict the emergence of new bulk quantum phases beyond Landau’s Fermi-liquid model. We review the current progress on understanding both the surface and the bulk states, especially the experimental evidence for each. A mystery centres on the existence of the bulk in-gap states and why they appear in some experiments but not others. Adding to the mystery is why quantum oscillations in SmB6 appear only in magnetization but not in resistivity. We conclude by elaborating on three questions: why SmB6 is worth studying, what can be done to move forwards and what other correlated insulators could give additional insight. The Kondo insulator samarium hexaboride is the first experimentally demonstrated example of a strongly correlated topological insulator. This article reviews the topological theory and experimental evidence, including a mystery as to the origin of quantum oscillations and their relation to possible unconventional bulk in-gap states.

Multi-electron anisotropic quantum dots/TMDCs/CNT families under magnetic field: analytical treatment to first Brillouin zone by Fermi liquid model

Acute Coulomb interaction of the two-dimensional systems has drawn special attention due to its unusual logarithmic Green function expansion. As the number of electrons (N) increases, Pauli Exclusion principle emerges inevitably with rapidly growing electronic correlations. Quantum dot, Transition metal dichalcogenides (TMDC) and Carbon nanotube (CNT) families of 2-D anisotropic mesoscopic systems are rich habitats of electrons. Schrödinger equations of such electrons in electrical confinement and transverse magnetic field can be recast in self-adjoint Whittaker-M functions facilitating each Coulomb interaction to terminable, exact and single summed Lauricella function via Chu-Vandermonde identity. For , multipoles of Green function expansion also succumb to terminable, single-summed, analytical integrals by inserting discretised closure relations. Thus, multi-configuration Slater determinantal states are employed for strong correlation of Fermi liquid model of first Brillouin zone (FBZ) within giga-units of reciprocal lattices (mesoscopic scale). Chemical potential, addition energies of WS, GaAs and model systems of dielectric constant have set benchmark at low and high confinement potentials, as a function of magnetic field and density of electrons. Because of sharp falls in surface integrals of both Newman and Dirichlet forms of Green function, Coulomb interaction takes to (or leads to) multipole expansion of generic coordinates. Formation of composite-fermions may be anticipated. At the most, octupole is sufficient for the convergence.

Magnetosonic Waves in a Two-Dimensional Electron Fermi Liquid

The properties of highly viscous fluids at high frequencies become similar to those of amorphous solids. In particular, the propagation of not only longitudinal acoustic waves (plasmons in the case of an electron fluid), but also transverse acoustic waves associated with shear deformations becomes possible. In this work, the formation of transverse acoustic waves at high frequencies in a two-dimensional electron fluid in a magnetic field is studied. Consideration is performed within Landau’s Fermi-liquid model. It is shown that the dynamics of Fermi-liquid excitations is described by hydrodynamic equations at a rather strong quasiparticle interaction. The Navier–Stokes equation and expressions for high-frequency shear viscosity coefficients are derived. Based on the equations obtained, dispersion laws are calculated for transverse and longitudinal magnetosonic waves. It is shown that the cyclotron frequency entering the viscosity coefficients and the dispersion relation of transverse magnetosonic waves is renormalized and typically becomes lower than the ordinary cyclotron frequency determining cyclotron resonance. The latter fact was apparently observed in the photoresistance of high-mobility GaAs quantum wells in which two-dimensional electrons form a viscous fluid.

Two-dimensional Fermi liquid dynamics with density-density and quadrupolar interactions

We consider a Fermi liquid model with density-density as well as quadrupolar forward scattering interactions parametrized by the Landau parameters $F_0$ and $F_2$. Using bosonization and a decimation technique, we compute collective modes and spectral functions for a huge range of interactions, ranging from strong repulsion to strong attraction in either angular momentum channels. We present a dynamical phase diagram showing a region of parameters where the collective modes structure changes abruptly, possibly signaling a dynamical phase transition.

A comparative study on the influence of the addition of different nano-oxide particles on the thermopower of (Bi,Pb)-2223 superconductor

Solid-state reaction technique was used to prepare superconductor samples with nominal composition of (SnO2)x(Bi,Pb)-2223 and (NiO)x(Bi,Pb)-2223, where 0.0 ≤ x ≤ 0.2 wt%. The prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The impact of SnO2 and NiO nanoparticles addition on the thermopower of (Bi,Pb)-2223 was measured using a standard differential technique. The Seebeck coefficient values in the presence of NiO nanoparticles were about 5–37.9% higher than those obtained with the addition of SnO2 nanoparticles. Higher values of Seebeck coefficients result in a wide variety of applications of these superconductors such as electronics and thermoelectric devices. The obtained results were analyzed according to the two-band model (Fermi-liquid model) and the two-band model with an extra linear term. The Fermi velocity (υF), Fermi energy, Fermi temperature (TF), Fermi wavenumber (KF), Fermi wavelength (λF) as well as the carrier concentration (N/V) values were calculated and discussed as a function of the nanoparticles content.

Магнитозвуковые волны в двумерной электронной ферми-жидкости

The properties of highly viscous fluids at high frequencies become similar to the properties of amorphous solids. In particular, it becomes possible to propagate not only longitudinal sound waves (plasmons for the case of an electron fluid), but also transverse sound waves associated with shear deformations. In this work, transverse sound waves at high frequencies in a twodimensional electron liquid in a magnetic field are studied. The consideration was carried out in the framework of the Landau Fermi-liquid model. It is shown that for a sufficiently large interaction between quasiparticles, the dynamics of excitations of a Fermi liquid is described by the equations of hydrodynamics. The Navier-Stokes equation and expressions for high-frequency shear viscosity coefficients are derived. Based on the equations obtained, the dispersion laws are calculated for transverse and longitudinal magnetosonic waves. It is shown that the cyclotron frequency, which enters in the viscosity coefficients and the dispersion law of transverse magnetosonic waves, is renormalized and typically becomes less than the usual cyclotron frequency, which determines the cyclotron resonance. The latter fact was apparently observed in the photoresistance of highly mobile GaAs quantum wells, in which two-dimensional electrons form a viscous fluid.

Optical Asymmetry and Nonlinear Light Scattering from Colloidal Gold Nanorods.

A systematic study is presented of the intensity-dependent nonlinear light scattering spectra of gold nanorods under resonant excitation of the longitudinal surface plasmon resonance (SPR). The spectra exhibit features due to coherent second and third harmonic generation as well as a broadband feature that has been previously attributed to multiphoton photoluminescence arising primarily from interband optical transitions in the gold. A detailed study of the spectral dependence of the scaling of the scattered light with excitation intensity shows unexpected scaling behavior of the coherent signals, which is quantitatively accounted for by optically induced damping of the SPR mode through a Fermi liquid model of the electronic scattering. The broadband feature is shown to arise not from luminescence, but from scattering of the second-order longitudinal SPR mode with the electron gas, where efficient excitation of the second order mode arises from an optical asymmetry of the nanorod. The electronic-temperature-dependent plasmon damping and the Fermi-Dirac distribution together determine the intensity dependence of the broadband emission, and the structure-dependent absorption spectrum determines the spectral shape through the fluctuation-dissipation theorem. Hence a complete self-consistent picture of both coherent and incoherent light scattering is obtained with a single set of physical parameters.

Possibility for conventional superconductivity in Sr0.1Bi2Se3 from high-pressure transport studies

SrxBi2Se3 is recently reported to be a superconductor derived from topological insulator Bi2Se3. It shows a maximum resistive Tc of 3.25 K at ambient pressure. We report magnetic (up to 1 GPa) and transport properties (up to 8 Gpa) under pressure for single crystalline Sr0.1Bi2Se3 superconductor. Magnetic measurements show that Tc decreases from ∼2.6 K (0 GPa) to ∼1.9 K (0.81 GPa). Similar behavior is observed in transport properties as well without much change in the metallic characteristics in normal-state resistivity. No reentrant superconducting phase (Zhou Y. et al., Phys. Rev. B, 93 (2016) 144514) is observed at high pressure. Normal-state resistivity near Tc is explained by Fermi liquid model. Band structure calculations indicate decreasing density of states at Fermi level with pressure. In consonance with transition temperature suppression in conventional BCS low-Tc superconductors, the pressure effect in SrxBi2Se3 is well accounted by pressure-induced band broadening.

Memory-function conductivity formula and transport coefficients in underdoped cuprates

The two-band memory-function conductivity formula is derived from the quantum kinetic equation in the pseudogap state of underdoped cuprates. The conduction electrons are described by using the adiabatic version of the nested Fermi liquid model, and the effects of Mott correlations are taken into account phenomenologically. The linear dependence of the low-temperature effective number of conduction electrons on the doping level δ (for not too large δ) is found to be in agreement with experimental observation. The momentum distribution function turns out to play an important role in describing temperature effects. The closing of the antiferromagnetic pseudogap at temperatures of the order of room temperature is shown to be a direct consequence of a relatively large width of the quasiparticle peak in this distribution function. The coupling of conduction electrons to external magnetic fields is included in the two-band transport equations in the usual semiclassical way. It is shown that the low-temperature Hall number is proportional to δ as well (again for not too large δ) and that it exhibits singular behaviour when the Fermi surface changes from the hole-like shape into the electron-like shape.

Semiclassical approaches to nuclear dynamics

The extended Gutzwiller trajectory approach is presented for the semiclassical description of nuclear collective dynamics, in line with the main topics of the fruitful activity of V.G. Solovjov. Within the Fermi-liquid droplet model, the leptodermous effective surface approximation was applied to calculations of energies, sum rules and transition densities for the neutron-proton asymmetry of the isovector giant-dipole resonance and found to be in good agreement with the experimental data. By using the Strutinsky shell correction method, the semiclassical collective transport coefficients such as nuclear inertia, friction, stiffness, and moments of inertia can be derived beyond the quantum perturbation approximation of the response function theory and the cranking model.The averaged particle-number dependence of the low-lying collective vibrational states are described in good agreement with basic experimental data, mainly due to an enhancement of the collective inertia as compared to its irrotational flow value. Shell components of the moment of inertia are derived in terms of the periodic-orbit free-energy shell corrections. A good agreement between the semiclassical extended Thomas-Fermi moments of inertia with shell corrections and the quantum results is obtained for different nuclear deformations and particle numbers. Shell effects are shown to be exponentially dampted out with increasing temperature in all the transport coefficients.

Slope-dependent nuclear-symmetry energy within the effective-surface approximation

The effective-surface approximation is extended taking into account derivatives of the symmetry-energy density per particle with respect to the mean particle density. The isoscalar and isovector particle densities in this extended effective-surface approximation are derived. The improved expressions of the surface symmetry energy, in particular, its surface tension coefficients in the sharp-edged proton-neutron asymmetric nuclei take into account important gradient terms of the energy density functional. For most Skyrme forces the surface symmetry-energy constants and the corresponding neutron skins and isovector stiffnesses are calculated as functions of the Swiatecki derivative of the nongradient term of the symmetry-energy density per particle with respect to the isoscalar density. Using the analytical isovector surface-energy constants in the framework of the Fermi-liquid droplet model we find energies and sum rules of the isovector giant-dipole resonance structure in a reasonable agreement with the experimental data, and they are compared with other theoretical approaches.

Derivative corrections to the symmetry energy and the isovector dipole-resonance structure in nuclei

The effective surface approximation is extended accounting for derivatives of the symmetry energy density per particle. The new expressions for the isovector surface energy constants are used for calculations of improved energies and sum rules of the isovector dipole-resonance strength structure within the Fermi-liquid droplet model. Our results are in reasonable agreement with experimental data and with other theoretical approaches.

Decrease of Ca3Co4O9+δ thermal conductivity by Yb-doping

In this study, the effect of Yb-substitution on the structural, electrical and thermal transport properties of the Ca3Co4O9+δ system has been investigated in the low temperature region (between 10 and 300K). The resistivity of samples increases with raising the Yb-concentration in the system. All the samples show a metal-semiconductor transition below 85K. In the analysis based on Strongly Correlated Fermi Liquid Model, an increased bandwidth and a reduced electronic correlation are found. It has also been found that the energy gap, E0, value also decreases with Yb-substitution. The samples show positive thermoelectric power, indicating that dominant charge carriers are holes in all the samples. The thermoelectric power value decreases with Yb-substitution. From Mott equation, it is determined that the Fermi energy and hole concentration decrease in the Yb-susbtituted samples, compared to the undoped ones. Thermal conductivity, κ, is decreased in about 50% of the measured in undoped samples for the 0.01 and 0.03 Yb-doped samples at 300K. Highest figure of merit, ZT, value is found to be 5.4 10−3 at 300K for the unsubstituted sample and the ZT value decreases by the substitution.

General analysis of the angle-resolved photoemission line shape for strongly correlated electron systems

In many cases the standard perturbation approach appears to be too simple to describe precisely the angle-resolved photoemission spectrum of a strongly correlated electron system. In particular, to describe the momentum asymmetry observed in the photoemission spectra of high-${T}_{c}$ cuprates, a phenomenological approach based on an extremely correlated Fermi-liquid model has been recently introduced. Here we analyze the general structure of the Green's function of quasiparticles in strongly correlated electron systems and stress that it is defined not only by the self-energy of Hubbard quasiparticles but also by a strength operator. The latter leads to an additional odd momentum contribution to the spectral function and alone can explain the observed asymmetry. So, the asymmetry of the angle-resolved photoemission spectra can be a measure of the strength of electron correlations in materials.