Fermi Liquid Picture Research Articles

How heat propagates in liquid 3He

In Landau’s Fermi liquid picture, transport is governed by scattering between quasi-particles. The normal liquid 3He conforms to this picture but only at very low temperature. Here, we show that the deviation from the standard behavior is concomitant with the fermion-fermion scattering time falling below the Planckian time, ℏkBT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{\\hslash }{{k}_{{{{{{{{\\rm{B}}}}}}}}}T}$$\\end{document} and the thermal diffusivity of this quantum liquid is bounded by a minimum set by fundamental physical constants and observed in classical liquids. This points to collective excitations (a sound mode) as carriers of heat. We propose that this mode has a wavevector of 2kF and a mean free path equal to the de Broglie thermal length. This would provide an additional conducting channel with a T 1/2 temperature dependence, matching what is observed by experiments. The experimental data from 0.007 K to 3 K can be accounted for, with a margin of 10%, if thermal conductivity is the sum of two contributions: one by quasi-particles (varying as the inverse of temperature) and another by sound (following the square root of temperature).

Method to Reveal and Investigate Almost 2D Fermi Surfaces in Layered Conductors: Universal Resistivity in a Parallel Magnetic Field

We suggested an original method to investigate the Fermi surfaces (FSs) in the quasi-two-dimensional conductors some time ago [A.G. Lebed and N.N. Bagmet, Phys. Rev. B 55, R8654 (1997)]. It was based on a consideration of a perpendicular conductivity in quasi-two-dimensional metals in parallel magnetic fields in the framework of the Boltzmann kinetic equation, where it was shown that the conductivity was independent on impurities. In this paper, we demonstrate that the above mentioned result is much more general than the kinetic equation and can be obtained even in a fully quantum mechanical case. We suggest to investigate this possible phenomenon in the quasi-two-dimensional organic, high-{{T}_{c}}, and some others superconductors in a metallic phase to judge if the Fermi liquid picture is valid for them or not. If the Fermi liquid picture is valid, then study of the perpendicular resistivity in the rotated parallel magnetic field allows to extract important information about the two-dimensional Fermi surfaces.

Magnetotransport in overdoped La2−xSrxCuO4 : Effect of anisotropic scattering

We revisit the Hall effect and magnetoresistivity by incorporating the anisotropic scattering caused by apical oxygen vacancies in overdoped La-based cuprates. The theoretical calculations within the Fermi liquid picture agree well with a handful of anomalous magneto-transport data, better than the results using an isotropic scattering rate alone. In particular, we obtain the upturn of Hall coefficient $R_H$ with decreasing temperature $T$, the initial drop of $R_H$ in magnetic field $B$ in all overdoped regimes, the linear resistivity $\rho$ versus $B$ near the van Hove doping level, the temperature dependence of the magnetoresistivity ratio, and the violation of Kohler's law. These results suggest that many of the anomalous transport behaviors in overdoped La$_{2-x}$Sr$_x$CuO$_4$ could actually be understood within the Fermi liquid picture.

First-principles prediction of the Landau parameter for Fermi liquids near the unitarity limit

This paper explores the behavior of systems of cold fermions as they approach unitary above the critical temperature. Symmetry arguments indicate that at unitarity the Fermi-liquid picture breaks down. As we move away from unitarity, by decreasing the scattering length, the dilaton, the Goldstone boson resulting from the spontaneous breaking of Schrodinger symmetry by the Fermi sea, becomes gapped. At energies below this gap, the interaction between quasiparticles will be dominated by dilaton exchange. The dilaton mass can, in turn, be related via anomaly matching to the scattering length and contact parameter within the confines of a systematic expansion. We use this relation to predict that the quasiparticle width is given by the expression $\mathrm{\ensuremath{\Gamma}}(E,T)=\frac{8m}{9\ensuremath{\pi}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathcal{C}}}^{2}}(\sqrt{\frac{m}{{m}^{★}}}\frac{a{\ensuremath{\mu}}_{F}^{2}}{4\ensuremath{\hbar}{E}_{F}^{2}}{)}^{2}({E}^{2}+{\ensuremath{\pi}}^{2}{k}_{B}^{2}{T}^{2})$ where $a$ is the the scattering length, ${m}_{★}$ is the effective mass, and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathcal{C}}$ is the dimensionless contact parameter. This prediction is valid for ${(\frac{{E}_{F}}{E})}^{2}\ensuremath{\gg}a{k}_{f}\ensuremath{\gg}1$.

Multiparticle scattering and breakdown of the Wiedemann-Franz law at a junction of N interacting quantum wires

We analyze the charge and thermal transport at a junction of interacting quantum wires close to equilibrium. Within the framework of Tomonaga-Luttinger liquids, we compute the thermal conductance for a wide class of boundary conditions and detail the physical processes leading to the breakdown of the Wiedemann-Franz law at the junction. We show how connecting external reservoirs to the quantum wires affects the conductance tensors close to the various fixed points of the phase diagram of the junction. We therefore distinguish two types of violation of the Wiedemann-Franz law: a ``trivial'' one, independent of the junction dynamics and arising from the breakdown of the Fermi-liquid picture in the wire, and a junction-related counterpart, arising from multiparticle scattering processes at the junction.

Sign-problem-free variant of the complex Sachdev-Ye-Kitaev model

We construct a sign-problem free variant of the complex Sachdev-Ye-Kitaev (SYK) model which keeps all the essential properties of the SYK model, including the analytic solvability in the large-$N$ limit and being maximally chaotic. In addition to the number of complex fermions $N$, our model has an additional parameter $M$ controlling the number of terms in the Hamiltonian which we take $M \to \infty$ with keeping $M/N$ constant in the large-$N$ limit. While our model respects global $U(1)$ symmetry associated with the fermion number conservation, both the large-$N$ limit and the sign-problem free nature become explicit in the Majorana representation. We present a detailed analysis on our model, i.e., the random matrix classification based on the symmetry analysis, analytic approach, and the quantum Monte Carlo simulations. All these analysis show that our model exhibit a non-Fermi liquid (NFL) physics, a gapless fermionic system lying beyond the conventional Fermi liquid picture.

Magnetotransport in overdoped La2−xSrxCuO4 : Fermi liquid approach

Recently, several experiments on La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) challenged the Fermi liquid picture for overdoped cuprates, and stimulated intensive debates [1]. In this work, we study the magnetotransport phenomena in such systems based on the Fermi liquid assumption. The Hall coefficient $R_H$ and magnetoresistivity $\rho_{xx}$ are investigated near the van Hove singularity $x_{\tiny\text{VHS}}\approx0.2$ across which the Fermi surface topology changes from hole- to electron-like. Our main findings are: (1) $R_H$ depends on the magnetic field $B$ and drops from positive to negative values with increasing $B$ in the doping regime $x_{\tiny\text{VHS}}<x\lesssim0.3$; (2) $\rho_{xx}$ grows up as $B^2$ at small $B$ and saturates at large $B$, while in the transition regime a "nearly linear" behavior shows up. Our results can be further tested by future magnetotransport experiments in the overdoped LSCO.

Many-body exchange-correlation effects in MoS2 monolayer: The key role of nonlocal dielectric screening

We calculate the quasiparticle properties of $\rm{MoS_2}$ monolayer at $T=0$ considering the dynamical electron-electron interaction effect within random-phase-approximation (RPA). The calculations are carried out for an electron-doped slab of $\rm{MoS_2}$ monolayer using a minimal massive Dirac Hamiltonian and the quasi-two-dimensional nature of the Coulomb interaction in this system is taken into account considering a modified interaction of Keldysh type. Having calculated the real and imaginary parts of the retarded self-energy, we find the spectral function and discuss the impact of extrinsic variables such as the dielectric medium and the charge carrier density on the appearance and position of the quasiparticle peaks. We also report the results of the renormalization constant and the effective Fermi velocity calculations in a broad range of the coupling constant and carrier density. We show that the effective Fermi velocity obtained solving the self-consistent Dyson equation has an absolutely different behavior from the one found from the on-shell approximation. Our results show that the nonlocal dielectric screening of the monolayer tends to stabilize the Fermi liquid picture in $\rm{MoS_2}$ monolayer and that the interaction strength parameter of this system is a multivariable function of the coupling constant, carrier density, and also the screening length.

Liquid-Liquid Phase Transitions in Silicon.

We use computationally simple neutral pseudoatom ("average atom") density functional theory (DFT) and standard DFT to elucidate liquid-liquid phase transitions (LPTs) in liquid silicon. An ionization-driven transition and three LPTs including the known LPT near 2.5 g/cm^{3} are found. They are robust even to 1eV. The pair distributions functions, pair potentials, electrical conductivities, and compressibilites are reported. The LPTs are elucidated within a Fermi liquid picture of electron scattering at the Fermi energy that complements the transient covalent bonding picture.

Electronic properties of the Dirac and Weyl systems with first- and higher-order dispersion in non-Fermi-liquid picture

We investigate the non-Fermi-liquid behaviors of the 2D and 3D Dirac/Weyl systems with low-order and higher order dispersion. The self-energy correction, symmetry, free energy, optical conductivity, density of states, and spectral function are studied. We found that, for Dirac/Weyl systems with higher order dispersion, the non-Fermi-liquid features remain even at finite chemical potential, and they are distinct from the ones in Fermi-liquid picture and the conventional non-Fermi-liquid picture. The power law dependence of the physical observables on the energy as well as the logarithmic renormalizations due to the long-range Coulomb interaction are showed. The Landau damping of the longitudinal excitations within random-phase-approximation (RPA) for the non-Fermi-liquid case are also discussed.

Modern Physics of the Condensed State: Strong Correlations and Quantum Topology

The topic of the review is the application of new ideas of unconventional quantum states to the physics of condensed matter, in particular of solid state, in the context of modern field theory. A comparison is made with classical papers on many-electron theory, including the formalism of many-electron operators. The essentially many-particle nature of the ground state, individual and collective excitations, and quantum fluctuations in the systems under consideration, as well as quantum phase transitions are discussed with an emphasis on topological aspects and with allowance for the effects of frustration. Variational approaches and representations of auxiliary particles, corresponding mean-field approximation and gauge field theory, confinement-deconfinement problem, violation of the Fermi-liquid picture, and exotic non-Fermi-liquid states are considered. An overview is given of the modern theory of entangled topological states, formation of spin liquid, strings and string networks.

Anomalous normal-state resistivity in superconducting La2−xCexCuO4 : Fermi liquid or strange metal?

We present experimental results for the in-plane resistivity of the electron-doped cuprate superconductor $La_{2-x}Ce_xCuO_4$ above its transition temperature $T_c$ as a function of Ce doping x and temperature. For the doping x between 0.11 and 0.17, where $T_c$ varies from 30 K (x=0.11) to 5 K (x=0.17), we find that the resistivity shows an approximate $T^2$ behavior for all values of doping over the measurement range from 100 K to 400 K. The coefficient of the $T^2$ resistivity term decreases with increasing x following the trend in $T_c$. We analyze our data theoretically and posit that n-type cuprates are better thought of as strange metals. Although the quadratic temperature dependence appears to be in naive agreement with the Fermi liquid (FL) expectations, the fact that the measured resistivity is large and no phonon-induced linear-in-T resistivity manifests itself even at 400 K argue against a standard normal metal Fermi liquid picture being applicable. We discuss possible origins of the strange metal behavior.

Microscopic description of localization-delocalization transitions in BaFe2S3

Unusual metallic states involving breakdown of the standard Fermi-liquid picture of long-lived quasiparticles in well-defined band states emerge at low temperatures near correlation-driven Mott transitions. Prominent examples are ill-understood metallic states in $d$- and $f$-band compounds near Mott-like transitions. Finding of superconductivity in solid O$_{2}$ on the border of an insulator-metal transition at high pressures close to 96~GPa is thus truly remarkable. Neither the insulator-metal transition nor superconductivity are understood satisfactorily. Here, we undertake a first step in this direction by focussing on the pressure-driven insulator-metal transition using a combination of first-principles density-functional and many-body calculations. We report a striking result: the finding of an orbital-selective Mott transition in a pure $p$-band elemental system. We apply our theory to understand extant structural and transport data across the transition, and make a specific two-fluid prediction that is open to future test. Based thereupon, we propose a novel scenario where soft multiband modes built from microscopically coexisting itinerant and localized electronic states are natural candidates for the pairing glue in pressurized O$_{2}$.

Quantum self-organization and nuclear collectivities

The quantum self-organization is introduced as one of the major underlying mechanisms of the quantum many-body systems. In the case of atomic nuclei as an example, two types of the motion of nucleons, single-particle states and collective modes, dominate the structure of the nucleus. The outcome of the collective mode is determined basically by the balance between the effect of the mode-driving force (e.g., quadrupole force for the ellipsoidal deformation) and the resistance power against it. The single-particle energies are one of the sources to produce such resistance power: a coherent collective motion is more hindered by larger gaps between relevant single particle states. Thus, the single-particle state and the collective mode are “enemies” each other. However, the nuclear forces are demonstrated to be rich enough so as to enhance relevant collective mode by reducing the resistance power by changing singleparticle energies for each eigenstate through monopole interactions. This will be verified with the concrete example taken from Zr isotopes. Thus, when the quantum self-organization occurs, single-particle energies can be self-organized, being enhanced by (i) two quantum liquids, e.g., protons and neutrons, (ii) two major force components, e.g., quadrupole interaction (to drive collective mode) and monopole interaction (to control resistance). In other words, atomic nuclei are not necessarily like simple rigid vases containing almost free nucleons, in contrast to the naïve Fermi liquid picture. Type II shell evolution is considered to be a simple visible case involving excitations across a (sub)magic gap. The quantum self-organization becomes more important in heavier nuclei where the number of active orbits and the number of active nucleons are larger. The quantum self-organization is a general phenomenon, and is expected to be found in other quantum systems.

Single-particle states vs. collective modes: friends or enemies ?

The quantum self-organization is introduced as one of the major underlying mechanisms of the quantum many-body systems. In the case of atomic nuclei as an example, two types of the motion of nucleons, single-particle states and collective modes, dominate the structure of the nucleus. The collective mode arises as the balance between the effect of the mode-driving force (e.g., quadrupole force for the ellipsoidal deformation) and the resistance power against it. The single-particle energies are one of the sources to produce such resistance power: a coherent collective motion is more hindered by larger spacings between relevant single particle states. Thus, the single-particle state and the collective mode are “enemies” against each other. However, the nuclear forces are rich enough so as to enhance relevant collective mode by reducing the resistance power by changing single-particle energies for each eigenstate through monopole interactions. This will be verified with the concrete example taken from Zr isotopes. Thus, the quantum self-organization occurs: single-particle energies can be self-organized by (i) two quantum liquids, e.g., protons and neutrons, (ii) monopole interaction (to control resistance). In other words, atomic nuclei are not necessarily like simple rigid vases containing almost free nucleons, in contrast to the naïve Fermi liquid picture. Type II shell evolution is considered to be a simple visible case involving excitations across a (sub)magic gap. The quantum self-organization becomes more important in heavier nuclei where the number of active orbits and the number of active nucleons are larger.

Microscopic description of insulator-metal transition in high-pressure oxygen

Unusual metallic states involving breakdown of the standard Fermi-liquid picture of long-lived quasiparticles in well-defined band states emerge at low temperatures near correlation-driven Mott transitions. Prominent examples are ill-understood metallic states in d- and f-band compounds near Mott-like transitions. Finding of superconductivity in solid O2 on the border of an insulator-metal transition at high pressures close to 96 GPa is thus truly remarkable. Neither the insulator-metal transition nor superconductivity are understood satisfactorily. Here, we undertake a first step in this direction by focussing on the pressure-driven insulator-metal transition using a combination of first-principles density-functional and many-body calculations. We report a striking result: the finding of an orbital-selective Mott transition in a pure p-band elemental system. We apply our theory to understand extant structural and transport data across the transition, and make a specific two-fluid prediction that is open to future test. Based thereupon, we propose a novel scenario where soft multiband modes built from microscopically coexisting itinerant and localized electronic states are natural candidates for the pairing glue in pressurized O2.

Non-Fermi-liquid magic angle effects in high magnetic fields

We investigate a theoretical problem of electron-electron interactions in an inclined magnetic field in a quasi-one-dimensional (Q1D) conductor. We show that they result in strong non-Fermi-liquid corrections to a specific heat, provided that the direction of the magnetic field is far from the so-called Lebed's magic angles (LMAs). If magnetic field is directed close to one of the LMAs, the specific heat corrections become small and the Fermi-liquid picture restores. As a result, we predict Fermi-liquid--non-Fermi-liquid angular crossovers in the vicinities of the LMA directions of the field. We suggest to perform the corresponding experiment in the Q1D conductor ${(\mathrm{Per})}_{2}\mathrm{Au}{(\mathrm{mnt})}_{2}$ under pressure in magnetic fields of the order of $H\ensuremath{\simeq}25\phantom{\rule{0.28em}{0ex}}\text{T}$.

Transport of Dirac electrons in a random magnetic field in topological heterostructures

We consider the proximity effect between Dirac states at the surface of a topological insulator and a ferromagnet with easy plane anisotropy, which is described by the \emph{XY}-model and undergoes a Berezinskii-Kosterlitz-Thouless (BKT) phase transition. The surface states of the topological insulator interacting with classical magnetic fluctuations of the ferromagnet can be mapped onto the problem of Dirac fermions in a random magnetic field. However, this analogy is only partial in the presence of electron-hole asymmetry or warping of the Dirac dispersion, which results in screening of magnetic fluctuations. Scattering at magnetic fluctuations influences the behavior of the surface resistivity as a function of temperature. Near the BKT phase transition temperature we find that the resistivity of surface states scales linearly with temperature and has a clear maximum which becomes more pronounced as the Fermi energy decreases. Additionally at low temperatures we find linear resistivity, usually associated with non-Fermi liquid behavior, however here it appears entirely within the Fermi liquid picture.

Decoherence of Impurities in a Fermi Sea of Ultracold Atoms

We investigate the decoherence of ^{40}K impurities interacting with a three-dimensional Fermi sea of ^{6}Li across an interspecies Feshbach resonance. The decoherence is measured as a function of the interaction strength and temperature using a spin-echo atom interferometry method. For weak to moderate interaction strengths, we interpret our measurements in terms of scattering of K quasiparticles by the Fermi sea and find very good agreement with a Fermi liquid calculation. For strong interactions, we observe significant enhancement of the decoherence rate, which is largely independent of temperature, pointing to behavior that is beyond the scattering of quasiparticles in the Fermi liquid picture.

High pressure synthesis of a new phase of YbAg2: Structure, valence of Yb and properties

The new phase of YbAg2 was obtained using high-pressure and high-temperature reaction. YbAg2 crystallizes in the MgZn2 structure (the space group P63/mmc space group, No 194) with a = 5.68153(3) Å and c = 9.31995(7) Å and the unit cell volume V = 260.54(3) Å3. The XANES analysis showed that the valence state of Yb is +2.8. The low-temperature dependences of the electrical resistivity and magnetic susceptibility can be adequately described by a T2 term that supports the Fermi-liquid picture. The Kadowaki–Woods relation gives a low value of the degeneracy (N = 2).