Over the past two decades, breakthroughs have been made in the growth and exfoliation of monoatomic layers, ushering in a new era of scientific discovery and technological innovation. After graphene, transition metal dichalcogenides (**s) have received extensive attention and become a treasure trove of many novel quantum phenomena. In recent years, a phenomenon called ising superconductivity has been observed in materials such as NBSE2, which is mainly driven by spin-orbit coupling and center-inversion symmetry breaking.
fig. 1 electron–phonon interaction and intra/inter-pocket eliashberg spectral function.
The proximity and interface effects between ising superconductors and other layered materials, such as topological materials, monolayers, and two-dimensional magnetic layered materials, are expected to be applied to quantum information storage and spintronics devices. Recently, in addition to the dominant electroacoustic coupling (EPC), attention has been paid to the possible role of spin fluctuation (SF) in the phenomenon of ising superconductivity, the possibility of the dominance of triplet states has been discussed, and a conjecture about the singlet-triplet Leggett oscillation has been raised. However, these hypotheses have not been quantitatively tested.
fig. 2 superconducting gap without and with spin-fluctuation interaction.
S. from the Department of Physics and Astronomy at George Mason University in Virginia, USADAS et al., based on first-principles calculations, conducted a detailed study on the Ising superconductor NBSE2, and the role of EPC and SF was determined. The authors found that: (1) EPC has strong anisotropy, mainly from k-k' scattering, thus ruling out the possibility of triplet symmetry as an excited state;(2) The superconductivity is significantly weakened by SF, but the anisotropy remains unchanged. (3) The authors found the possibility of the Leggett mode, not between the singlet-triplet states, but in the S++ S channel.
fig. 3 schematic illustration of the ising superconductor pairing symmetry.
Through the self-consistent analysis of the contribution of electroacoustic coupling and spin fluctuation, the authors estimated the average BCS energy gap δBCS, the Leggett mode frequency L, and L 2δBCS, which are close to the experimental results. This study provides a comprehensive quantitative analysis for understanding the superconductivity phenomenon of NBSE2 and other ising superconductors, and provides strong support for future experimental and theoretical research. Related**Recently published on NPJ Computational Materials
fig. 4 analytical solution of the two-gap bcs equations.
editorial summary
unr**eling the ising superconductivity in nbse2: electron-phonon coupling and spin fluctuations
revolutionary progress in the growth and exfoliation of single atomic layers over the last two decades has led to a new era of scientific discoveries and technological innovation. following graphene, transition metal dichalcogenides (*s) h**e taken the spotlight, as a treasure trove for a plethora of novel quantum phenomena. in recent years, a phenomenon called ising superconductivity has been observed in materials such as nbse2, driven primarily by spin-orbit coupling and the absence of inversion symmetry. the proximity and interface effects between ising superconductors and other layered materials, such as topological materials, single-layer **s, and two-dimensional magnetic layered materials, could lead to interesting device applications for quantum information storage and spintronics. recently, attention was called to the possible role that spin fluctuations (sf) play in this phenomenon, in addition to the dominant electron–phonon coupling (epc); the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet leggett oscillations. however, these hypotheses h**e not been put to a quantitative test.
s. das et al. from the department of physics and astronomy, george mason university, usa, conducted an in-depth study on the ising superconductor nbse2, and explored the roles of epc and sf based on first-principles calculations. the authors found that: (1) epc is strongly anisotropic, largely coming from the k−k’ scattering, and therefore excludes triplet symmetry even as an excited state; (2) superconductivity is substantially weakened by sf, but anisotropy remains as above; and, (3) the possibility of a leggett mode was found, not in a singlet–triplet but in an s++ s± channel. based on the self-consistent analytical solution and first-principles calculations including electron–phonon coupling and spin-fluctuation contribution, the authors estimated the **erage bcs gap δbcs, leggett mode frequency ωl, and the ratio ωl/2δbcs, showing good agreement with experimental results. this study provides a fairly comprehensive quantitative analysis for understanding the superconductivity in nbse2 and other ising superconductors, offering valuable insights for future experimental and theoretical research.thisarticle was recently published in npj computational materials
Original text abstract and its translation
electron-phonon coupling and spin fluctuations in the ising superconductor nbse2
s. das, h. paudyal, e. r. margine, d. f. agterberg & i. i. mazin
abstract
ising superconductivity, observed in nbse2 and similar materials, has generated tremendous interest. recently, attention was called to the possible role that spin fluctuations (sf) play in this phenomenon, in addition to the dominant electron–phonon coupling (epc); the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet leggett oscillations. however, these hypotheses h**e not been put to a quantitative test. in this **we report first principle calculations of the epc and also estimate coupling with sf, including full momentum dependence. we find that: (1) epc is strongly anisotropic, largely coming from the k−k′ scattering, and therefore excludes triplet symmetry even as an excited state; (2) superconductivity is substantially weakened by sf, but anisotropy remains as above; and, (3) we do find the possibility of a leggett mode, not in a singlet–triplet but in an s++ s±channel.
Summary:
The ising superconductivity observed in NBSE2 and similar materials is of great concern. More recently, in addition to the dominant electroacoustic coupling (EPC), attention has been paid to the possible role of spin fluctuations (SFs) in this phenomenon, the possibility of the dominance of triplet states has been discussed, and a conjecture about singlet-triplet leggett oscillations has been raised. However, these hypotheses have not been quantitatively tested. In this paper, we report first-principles calculations of electroacoustic coupling and also estimate coupling with spin fluctuations, including full momentum dependence. We found that: (1) EPC is strongly anisotropic and mainly comes from k-k' scattering, so that triplet symmetry is excluded even as an excited state;(2) Superconductivity is significantly weakened by spin fluctuations, but anisotropy still exists. (3) We did find the possibility of a leggett mode, not between a singlet-triplet state, but in the S++ S channel.