skip to main content

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Thursday, February 13 until 2:00 AM ET on Friday, February 14 due to maintenance. We apologize for the inconvenience.


Title: Screening induced crossover between phonon- and plasmon-mediated pairing in layered superconductors
Abstract

Two-dimensional (2D) metals can host gapless plasmonic excitations that strongly couple to electrons and thus may significantly affect superconductivity. To investigate the dynamical interplay of the electron–electron and electron–phonon interactions in the theory of 2D superconductivity, we apply a full momentum- and frequency-dependent one-loop theory treating electron–phonon, electron–plasmon, and phonon–plasmon coupling with the same accuracy. We tune the strength of the Coulomb interaction by varying the external screeningεextto the layered superconductor and find three distinct regions. At weak screening, superconductivity is mediated by plasmons. In the opposite limit conventional electron–phonon interactions dominate. In between, we find a suppressed superconducting state. Our results show that even in conventional electron–phonon coupled layered materials, superconductivity can be significantly enhanced by the electron–plasmon coupling in a manner that can be controlled by the external screening.

 
more » « less
PAR ID:
10465023
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
IOP Publishing
Date Published:
Journal Name:
2D Materials
Volume:
10
Issue:
4
ISSN:
2053-1583
Page Range / eLocation ID:
Article No. 045031
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We measure the thermal electron energization in 1D and 2D particle-in-cell simulations of quasi-perpendicular, low-beta (βp= 0.25) collisionless ion–electron shocks with mass ratiomi/me= 200, fast Mach numberMms=1–4, and upstream magnetic field angleθBn= 55°–85° from the shock normalnˆ. It is known that shock electron heating is described by an ambipolar,B-parallel electric potential jump, Δϕ, that scales roughly linearly with the electron temperature jump. Our simulations haveΔϕ/(0.5miush2)0.1–0.2 in units of the pre-shock ions’ bulk kinetic energy, in agreement with prior measurements and simulations. Different ways to measureϕ, including the use of de Hoffmann–Teller frame fields, agree to tens-of-percent accuracy. Neglecting off-diagonal electron pressure tensor terms can lead to a systematic underestimate ofϕin our low-βpshocks. We further focus on twoθBn= 65° shocks: aMs=4(MA=1.8) case with a long, 30diprecursor of whistler waves alongnˆ, and aMs=7(MA=3.2) case with a shorter, 5diprecursor of whistlers oblique to bothnˆandB;diis the ion skin depth. Within the precursors,ϕhas a secular rise toward the shock along multiple whistler wavelengths and also has localized spikes within magnetic troughs. In a 1D simulation of theMs=4,θBn= 65° case,ϕshows a weak dependence on the electron plasma-to-cyclotron frequency ratioωpece, andϕdecreases by a factor of 2 asmi/meis raised to the true proton–electron value of 1836.

     
    more » « less
  2. Abstract

    The polarization of the cosmic microwave background is rich in information but obscured by foreground emission from the Milky Way’s interstellar medium (ISM). To uncover relationships between the underlying turbulent ISM and the foreground power spectra, we simulated a suite of driven, magnetized, turbulent models of the ISM, varying the fluid properties via the sonic Mach number,MS, and magnetic (Alfvén) Mach number,MA. We measure the power spectra of density (ρ), velocity (v), magnetic field (H), total projected intensity (T), parity-even polarization (E), and parity-odd polarization (B). We find that the slopes of all six quantities increase withMS. Most increase withMA, while the magnetic field spectrum steepens withMA. By comparing spectral slopes ofEandBto those measured by Planck, we infer typical values ofMSandMAfor the ISM. As the fluid velocity increases,MS>4, the ratio of BB power to EE power increases to approach a constant value near the Planck-observed value of ∼0.5, regardless of the magnetic field strength. We also examine correlation coefficients between projected quantities, and find thatrTE≈ 0.3, in agreement with Planck, for appropriate combinations ofMSandMA. Finally, we consider parity-violating correlationsrTBandrEB.

     
    more » « less
  3. Abstract

    We present a survey of 1D kinetic particle-in-cell simulations of quasi-parallel nonrelativistic shocks to identify the environments favorable for electron acceleration. We explore an unprecedented range of shock speedsvsh≈ 0.067–0.267c, Alfvén Mach numbersMA=540, sonic Mach numbersMs=5160, as well as the proton-to-electron mass ratiosmi/me= 16–1836. We find that high Alfvén Mach number shocks can channel a large fraction of their kinetic energy into nonthermal particles, self-sustaining magnetic turbulence and acceleration to larger and larger energies. The fraction of injected particles is ≲0.5% for electrons and ≈1% for protons, and the corresponding energy efficiencies are ≲2% and ≈10%, respectively. The extent of the nonthermal tail is sensitive to the Alfvén Mach number; whenMA10, the nonthermal electron distribution exhibits minimal growth beyond the average momentum of the downstream thermal protons, independently of the proton-to-electron mass ratio. Acceleration is slow for shocks with low sonic Mach numbers, yet nonthermal electrons still achieve momenta exceeding the downstream thermal proton momentum when the shock Alfvén Mach number is large enough. We provide simulation-based parameterizations of the transition from thermal to nonthermal distribution in the downstream (found at a momentum aroundpi,e/mivsh3mi,e/mi), as well as the ratio of nonthermal electron to proton number density. The results are applicable to many different environments and are important for modeling shock-powered nonthermal radiation.

     
    more » « less
  4. Abstract

    Fe3+δGeTe2(FGT) has proved to be an interesting van der Waals (vdW) ferromagnetic compound with a tunable Curie temperature (TC). However, the underlying mechanism for varyingTCremains elusive. Here, we systematically investigate and compare low-temperature magnetic properties of single crystalline FGT samples that exhibitTCs ranging from 160 K to 205 K. Spin stiffness (D) and spin excitation gap (Δ) are extracted using Bloch’s theory for crystals with varying Fe content. Compared to Cr-based vdW ferromagnets, FGT compounds have higher spin stiffness values but lower spin wave excitation gaps. We discuss the implication of these relationships in Fe–Fe ion magnetic interactions in FGT unit cells. The itinerancy of magnetic electrons is measured and discussed under the Rhodes–Wohlfarth ratio (RWR) and the Takahashi theory.

     
    more » « less
  5. Abstract

    We survey 20 reconnection outflow events observed by Magnetospheric MultiScale in the low-βand high-Alfvén-speed regime of the Earth’s magnetotail to investigate the scaling of ion bulk heating produced by reconnection. The range of inflow Alfvén speeds (800–4000 km s−1) and inflow ionβ(0.002–1) covered by this study is in a plasma regime that could be applicable to the solar corona and flare environments. We find that the observed ion heating increases with increasing inflow (upstream) Alfvén speed,VA, based on the reconnecting magnetic field and the upstream plasma density. However, ion heating does not increase linearly as a function of available magnetic energy per particle,miVA2. Instead, the heating increases progressively less asmiVA2rises. This is in contrast to a previous study using the same data set, which found that electron heating in this high-Alfvén-speed and low-βregime scales linearly withmiVA2, with a scaling factor nearly identical to that found for the low-VAand high-βmagnetopause. Consequently, the ion-to-electron heating ratio in reconnection exhausts decreases with increasing upstreamVA, suggesting that the energy partition between ions and electrons in reconnection exhausts could be a function of the available magnetic energy per particle. Finally, we find that the observed difference in ion and electron heating scaling may be consistent with the predicted effects of a trapping potential in the exhaust, which enhances electron heating, but reduces ion heating.

     
    more » « less