Superconducting energy gap of $2H$-NbSe${}_2$ in phonon spectroscopy

Abstract

We present a high energy-resolution inelastic x-ray scattering data investigation of the charge-density-wave (CDW) soft phonon mode upon entering the superconducting state in $2H$-NbSe${}_2$. Measurements were done close to the CDW ordering wavevector ${\mathbf{q}}_{CDW}$ at $\mathbf{q}={\mathbf{q}}_{CDW}+(0,0,l)$,$0.15\le l\le 0.5$, for $T=10\mathrm{K}$ (CDW order) and $3.8\mathrm{K}$ (CDW order + superconductivity). We observe changes of the phonon lineshape that are characteristic for systems with strong electron-phonon coupling in the presence of a superconducting energy gap $2{\Delta }_c$ and from which we can demonstrate an $l$-dependence of the superconducting gap. Reversely, our data imply that the CDW energy gap is strongly localized along the $c^{\ast }$ direction. The confinement of the CDW gap to a very small momentum region explains the rather low competition and easy coexistence of CDW order and superconductivity in $2H$-NbSe${}_2$. However, the energy gained by opening ${\Delta }_{CDW}$ seems to be too small to be the driving force of the phase transition at $T_{CDW}=33\mathrm{K}$ , which is better described as an electron-phonon coupling driven structural phase transition.

References in corpus (6)

• Two energy gaps and Fermi surface 'arcs' in NbSe2
• Quasi-Particle Spectra, Charge-Density-Wave, Superconductivity and Electron-Phonon Coupling in 2H-NbSe2
• A quantum phase transition from triangular to stripe charge order in NbSe${}_2$
• Charge Order from Orbital-dependent Coupling Evidenced by NbSe${}_2$
• Pressure dependence of the charge-density-wave and superconducting states in GdTe${}_3$, TbTe${}_3$ and DyTe${}_3$
• Superconductivity-Induced Distortions of Phonon Lineshapes in Niobium

Cited by in corpus (2)

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