NMR evidence for a Peierls transition in the layered square-net compound LaAgSb${}_2$

Abstract

We measured the central ($1/2\leftrightarrow -1/2$) and first satellite ($\pm 3/2\leftrightarrow \pm 1/2$) lines of the \la\ NMR spectra as a function of temperature in LaAgSb${}_2$, in order to elucidate the origin and nature of the charge-density-wave (CDW) transitions at $T_{\text{CDW1}}=207$ K and $T_{\text{CDW2}}=186$ K. In the normal state, the Knight shift K reveals a fairly linear relationship with decreasing temperature, which is ascribed to a pseudogap in the spin excitation spectrum, pointing towards the material being an unconventional metal. Upon further cooling, K decreases more steeply below $T_{\text{CDW1}}$, indicative of the partial Fermi surface gap opening on top of the pseudogap. The most remarkable finding in our study is a clear splitting of the satellite lines at $T_{\text{CDW1}}$ observed for $H\parallel c$, whose temperature dependence behaves as the BCS order parameter in the weak-coupling limit, evidencing that the CDW transition induces the periodic lattice distortion. Our NMR findings therefore demonstrate that the CDW transition in LaAgSb${}_2$ is of Peierls type, being driven by the electronic instability in the vicinity of the Fermi level.

5 pages, 3 figures, published in PRB

References in corpus (5)

• Fermi surface nesting and the origin of Charge Density Waves in metals
• Pseudogap and charge density waves in two dimensions
• Infrared Measurement of the Pseudogap in P-Doped and Co-Doped BaFe2As2 High-Temperature Superconductors
• Revealing extremely low energy amplitude modes in the charge-density-wave compound LaAgSb${}_2$
• Interplay of charge density waves, disorder, and superconductivity in 2$H$-TaSe${}_2$ elucidated by NMR