Fermi-liquid Effects Research Articles

Spontaneous splitting of d -wave surface states: Competition between circulating currents and edge magnetization

Pair-breaking edges of d-wave superconductors feature Andreev bound states at the Fermi energy. Since these states are energetically highly unfavorable they are susceptible to effects that shift them to finite energy. We investigate the free energy of two different mechanisms: spontaneous phase gradients in the superconducting order parameter and surface ferromagnetism caused by Fermi liquid interaction effects. We find that the surface magnetization appears at lower temperatures than the spontaneous current flow of the phase-crystal state. The magnetic state can, however, be energetically favorable at lower temperatures for sufficiently strong Fermi liquid effects. Thus, first-order transitions between the two states as function of system temperature are possible, suggesting a rich low-temperature phase diagram in d-wave superconductors. Published by the American Physical Society 2024

Generation of pure superconducting spin current in magnetic heterostructures via nonlocally induced magnetism due to Landau Fermi liquid effects

We propose a mechanism for the generation of pure superconducting spin-current carried by equal-spin triplet Cooper pairs in a superconductor (S) sandwiched between a ferromagnet (F) and a normal metal (N$_{\rm so}$) with intrinsic spin-orbit coupling. We show that in the presence of Landau Fermi-liquid interactions the superconducting proximity effect can induce non-locally a ferromagnetic exchange field in the normal layer, which disappears above the superconducting transition temperature of the structure. The internal Landau Fermi-liquid exchange field leads to the onset of a spin supercurrent associated with the generation of long-range spin-triplet superconducting correlations in the trilayer. We demonstrate that the magnitude of the spin supercurrent as well as the induced magnetic order in the N$_{\rm so}$ layer depends critically on the superconducting proximity effect between the S layer and the F and N$_{\rm so}$ layers and the magnitude of the relevant Landau Fermi-liquid interaction parameter. We investigate the effect of spin flip processes on this mechanism. Our results demonstrate the crucial role of Landau Fermi-liquid interaction in combination with spin-orbit coupling for the creation of spin supercurrent in superconducting spintronics, and give a possible explanation of a recent experiment utilizing spin-pumping via ferromagnetic resonance [Jeon $\it{ et}$ $\it{al.}$, Nat. Mat. ${\bf 17}$, 499 (2018)].

Fermi liquid effects and quasiparticle mass renormalization in a system of two-dimensional electrons with strong interaction

The dependence of the quasiparticle Fermi energy on the electron density is investigated by analyzing the radiative recombination spectra of two-dimensional electrons with photoexcited holes bound at remote acceptors. In this way, the electron-density dependence of the renormalized mass of quasiparticles is determined. It is established that, as the electron density decreases (the parameter rs increases to 4.5), the density-of-states effective mass of quasiparticles increases by 35% as compared to the cyclotron mass of the electron. It is shown that, in a perpendicular magnetic field, the concept of quasiparticles in a two-dimensional Fermi liquid is applicable not only near the Fermi level but also deeply below the Fermi surface, even to the bottom of the quantum-confinement subband, because the broadening of excitations remains considerably smaller than their energy.

Allowance for Fermi liquid effects in the theory of electron states in “epitaxial graphene-metallic substrate” systems

The problem of taking into account Fermi liquid effects in the theory of electron states of epitaxial graphene formed on a metallic substrate is considered on the basis of the Anderson-Newns model. Analytic expressions were obtained for charge transition in the “epitaxial graphene plus size-quantized film” system. Fermi liquid effects are shown to play a significant role in the theory of electron states in the system being considered.

Neutrino emission from spin waves in neutron spin-triplet superfluid

The linear response of a neutron spin-triplet superfluid onto external weak axial-vector field is studied for the case of 3P2 pairing with a projection of the total angular momentum mj=0. The problem is considered in BCS approximation discarding Fermi-liquid effects. The anomalous axial-vector vertices of neutron quasiparticles possess singularities at some frequencies which specify existence of undamped spin-density waves in the Cooper condensate. The spin waves are of a low excitation energy and are kinematically able to decay into neutrino pairs through neutral weak currents. The calculation predicts significant energy losses from within a neutron star at lowest temperatures when all other mechanisms of neutrino emission are killed by the neutron and proton superfluidity.

Neutrino emission from triplet pairing of neutrons in neutron stars

Neutrino emission due to the pair breaking and formation processes in the bulk triplet superfluid in neutron stars is investigated with taking into account of anomalous weak interactions. We consider the problem in the BCS approximation discarding Fermi-liquid effects. In this approach we derive self-consistent equations for anomalous vector and axial-vector vertices of weak interactions taking into account the $^{3}P_{2}- ^{3}F_{2}$ mixing. Further we simplify the problem and consider the pure $^{3}P_{2}$ pairing with $m_{j}=0$, as is adopted in the minimal cooling paradigm. As was expected because of current conservation we have obtained a large suppression of the neutrino emissivity in the vector channel. More exactly, the neutrino emission through the vector channel vanishes in the nonrelativistic limit $V_F=0$. The axial channel is also found to be moderately suppressed. The total neutrino emissivity is suppressed by a factor of $1.9\times10^{-1}$ relative to original estimates using bare weak vertices.

Superfluid response and the neutrino emissivity of baryon matter: Fermi-liquid effects

The linear response of a nonrelativistic superfluid baryon system on an external weak field is investigated while taking into account the Fermi-liquid interactions. We generalize the theory developed by Leggett for a superfluid Fermi-liquid at finite temperature to the case of time-like momentum transfer typical of the problem of neutrino emission from neutron stars. A space-like kinematics is also analyzed for completeness and compared with known results. We use the obtained response functions to derive the neutrino energy losses caused by recombination of broken pairs in the electrically neutral superfluid baryon matter. We find that the dominant neutrino radiation occurs through the axial-vector neutral currents. The emissivity is found to be of the same order as in the BCS approximation, but the details of its temperature dependence are modified by the Fermi-liquid interactions. The role of electromagnetic correlations in the pairing case of protons interacting with the electron background is discussed in the conclusion.

Fermi-liquid effects in the gapless state of marginally thin superconducting films

We present low-temperature tunneling density-of-states measurements in Al films in high parallel magnetic fields. The thickness range of the films, $t=6--9\text{ }\text{nm}$, was chosen so that the orbital and Zeeman contributions to their parallel critical fields were comparable. In this quasispin paramagnetically limited configuration, the field produces a significant suppression of the gap, and at high fields the gapless state is reached. By comparing measured and calculated tunneling spectra we are able to extract the value of the antisymmetric Fermi-liquid parameter ${G}^{0}$ and thereby deduce the quasiparticle density dependence of the effective parameter ${G}_{\text{eff}}^{0}$ across the gapless state.

Enhancement of paramagnetic effects during spin alignment in 2D semiconductors

Effects of magnetic ordering associated with the Coulomb exchange interaction of free electrons in a 2D Fermi system are considered. It is shown that the paramagnetic response is substantially enhanced by Fermi-liquid effects. The phase transition to a state with spontaneous polarization of spins can be observed when Heisenberg parameter J is not smaller than μF/3.06 (approximately one-third of the Fermi energy) and not larger than half the Fermi energy (J ≤ μF/2).

Fermi-liquid effects in the Hubbard model

Properties of an electronic system with a very strong electron-electron interaction are studied. The equation of state is obtained, and the temperature and concentration dependences of the hydrodynamic sound and magnetic susceptibility are calculated. A low-temperature domain of instability corresponding to phase segregation is found. This domain is located inside the wide region of Cooper instability. The equation for zero-sound oscillations is obtained with regard to the substantial anisotropy of the energy spectrum.

Neutrino emission from ungapped quark matter

We study neutrino emission from a normal, ungapped, quark phase in the core of a compact star. Neutrino emission from noninteracting quark matter leads to an emissivity that scales as $ϵ\ensuremath{\sim}{T}^{7}$. We show that the emissivity is enhanced by a combination of Fermi liquid and non-Fermi liquid effects. Fermi liquid effects lead to an emissivity that scales as $ϵ\ensuremath{\sim}{\ensuremath{\alpha}}_{s}{T}^{6}$, as originally shown by Iwamoto. We demonstrate that non-Fermi liquid effects further enhance the rate, leading to $ϵ\ensuremath{\sim}{\ensuremath{\alpha}}_{s}^{3}{T}^{6}\mathrm{log}(m/T{)}^{2}$, where $m$ is the electric screening scale and $m\ensuremath{\gg}T$ under the conditions found in compact stars. We show, however, that combined with non-Fermi liquid effects in the specific heat the enhancement in the emissivity only leads to a modest reduction in the temperature of the star at late times. Our results confirm existing bounds on the presence of ungapped quark matter in compact stars. We also discuss neutrino emission from superconducting phases with ungapped fermionic excitations.

Fermi-liquid effects in transresistivity in quantum Hall double layers near ν=1/2

We present theoretical studies of the temperature and magnetic field dependences of the Coulomb drag transresistivity between two parallel layers of two-dimensional electron gases in the quantum Hall regime near half-filling of the lowest Landau level. It is shown that Fermi-liquid interactions between the relevant quasi-particles can significantly affect the transresistivity, providing its independence of the interlayer spacing for spacings that take values reported in the experiments. The obtained results agree with the experimental evidence.

Fermi-liquid theory for anisotropic superconductors

This article develops a quantitative quasiparticle model of the low-temperature properties of d-wave superconductors which incorporates both Fermi-liquid effects and band-structure effects. The Fermi-liquid interaction effects are found to be classifiable into strong and negligible renormalizaton effects, for symmetric and antisymmetric combinations of the energies of $k\uparrow$ and $-k\downarrow$ quasiparticles, respectively. A particularly important conclusion is that the leading clean-limit temperature-dependent correction to the superfluid density is not renormalized by Fermi-liquid interactions, but is subject to a Fermi velocity (or mass) renormalization effect. This leads to difficulties in accounting for the penetration depth measurements with physically acceptable parameters, and hence reopens the question of the quantitative validity of the quasiparticle picture.

Anomalous Fermi Liquid Effects in Two-Dimensional Hubbard Model near Half-Filling

The Landau parameters F 0 s , F 0 a , F 1 s and F 1 a in the two-dimensional Hubbard model are calculated by the second order perturbation method of Abrikosov-Khalatnikov. The following points are revealed as the half-filling is approached: (1) F 0 a changes its sign from negative to positive, if the Coulomb interaction U is strong enough, i.e., \(U/t\gtrsim 2.0 \). This means that the spin density oscillations, zero spin-sound, can propagate there; (2) F 1 s changes its sign from positive to negative, so that we can understand, on the basis of the anisotropic Fermi liquid theory, the behavior of the Drude weight whose magnitude decreases as the half-filling is approached even if there were no mass enhancement; (3) From the results of F 0 s and F 0 a , it is shown that both the charge and spin susceptibility decrease rapidly close to the half-filling. The latter is regarded as the so-called spin-gap behavior.

About the role of the Fermi-liquid effects on the acoustic transparency in layered conductors

About the role of the Fermi-liquid effects on the acoustic transparency in layered conductors

Cyclotron resonance in the organic conductor (BEDO-TTF)2ReO4(H2O) in the millimeter wavelength band

Resonant microwave absorption in a (BEDO-TTF)2ReO4(H2O) organic conductor single crystal at a temperature of 1.9 K, a magnetic field of up to 70 kOe, and in the frequency band between 30 and 120 GHz has been studied. A spectral component due to the cyclotron resonance (CR) of two-dimensional charge carriers has been identified for ν⩾80 GHz and H⩾10 kOe. The effective mass m(ω) increases with the frequency from m≈0.8m 0 at ν=80 GHz to m≈0.95m 0 at ν=120 GHz. Measurements of the CR line position and FWHM as functions of frequency yield an independently determined imaginary part of the memory function M(ω), which controls the dynamic magnetoconductivity, and the relaxation time τ(ν=100 GHz)≈2.9×10−11 s, which is more than thirty times the value of this parameter in the low-frequency limit τ(ν→0). The anomalous behavior of the CR line position and FWHM is caused by the dispersion of both real and imaginary parts of M(ω), which are probably due to strong Fermi-liquid effects.

Quasiclassical theory of vortices in3He-B

We report weak-coupling numerical calculations of the order parameter and the free energy of isolated vortices in superfluid3He in the framework of the quasiclassical theory of superfluid Fermi-liquids. Unlike earlier work with the Ginzburg-Landau theory, our results are not restricted to the vicinity ofT c. We show that Fermi-liquid effects play an important role at lower temperatures. It appears there is a transition from the double core vortex to an A-phase-core vortex at the vapor pressure just above 0.5Tc.

Vortices in superfluid 3He-B at low temperatures

We report numerical calculations of the order parameter and free energy of an isolated vortex in superfluid 3He-B. Three types of vortices are investigated at low pressures and for all temperatures. Fermi-liquid effects on the supercurrent and the order parameter are discussed within the framework of the quasiclassical theory. Numerical calculations of the vortex energies indicate a vortex core transition at low temperature in weak-coupling theory.

On the Fermi liquid effects in the upper critical field of NbN thin films

The temperature dependence of the upper critical field reveals that NbN is a paramagnetism limited superconductor with significant electron-electron exchange and correlation potential arising from the Fermi liquid effects, in sharp contrast to the strong spin-orbit scattering effects expected from the relatively high atomic number of Nb and the low electron density of states at the Fermi energy of NbN. The results also indicate that while the normal state resistivity of the films can be altered in a controlled manner, it does not correlate to the spin-orbit scattering rate directly.

Inertial mass of a moving singularity in a Fermi superfluid.

The authors consider the problem of the inertial mass of vortex lines and related singularities in both neutral and charged s-wave Fermi superfluids at T = O, taking into account the difference between amplitude and phase motion, Fermi liquid effects and electromagnetic screening. Their results are consistant with earlier estimates as regards order of magnitude, but differ from them in detail.