The mechanism of charge density wave in Pt-based layered superconductors: SrPt2As2 and LaPt2Si2

Abstract

The intriguing coexistence of the charge density wave (CDW) and superconductivity in SrPt2As2 and LaPt2Si2 has been investigated based on the ab initio density functional theory band structure and phonon calculations. We have found that the CDW instabilities for both cases arise from the q-dependent electron-phonon coupling with quasi-nesting feature of the Fermi surface. The band structure obtained by the band-unfolding technique reveals the sizable q-dependent electron-phonon coupling responsible for the CDW instability. The local split distortions of Pt atoms in the [As-Pt-As] layers play an essential role in driving the five-fold supercell CDW instability as well as the phonon softening instability in SrPt2As2. By contrast, the CDW and phonon softening instabilities in LaPt2Si2 occur without split distortions of Pt atoms. The phonon calculations suggest that the CDW and the superconductivity coexist in [X-Pt-X] layers (X = As or Si) for both cases.

Charge density wave with anomalous temperature dependence in UPt2Si2

“…Our calculation shows that about 90% of displacement is in the ab plane of the Si(2)-Pt(2)-Si(2) layer, in agreement with previously reported putative disorder [11]. It is interesting that the lattice modulation of sandwiched metallic layers is quite ubiquitous [23] as in the Pt-based layered superconductor LaPt 2 Si 2 [24][25][26]. It should be, however, noted that the period of the LaPt 2 Si 2 superstructure is close to 3 unit cells compared to the ≈5 unit cell periodicity in UPt 2 Si 2 .…”

Evolution of charge density wave order and superconductivity under pressure in LaPt2Si2

“…Furthermore, CDW order is detected in arXiv:2004.03111v1 [cond-mat.supr-con] 7 Apr 2020 other physical quantities such as the thermopower and thermal conductivity [22]. First principles calculations suggest that the Fermi surface of LaPt 2 Si 2 is quasi twodimensional, and that there is coexistence of CDW order and SC in the [Si2-Pt1-Si2] layer [23,24]. The coexistence of the two orders and a partially opened CDW gap on the Fermi surface were confirmed by nuclear magnetic resonance (NMR) experiments [25].…”

Possibility of charge density wave transition in a SrPt2Sb2superconductor

“…However, the other compounds show similar T c between 1.3 and 2.1 K, regardless of the CDW order, which indicates that there is no close correlation between superconductivity and the CDW. In addition, SrPt 2 As 2 and other CaBe 2 Ge 2 -type materials have similar electronic structures, as determined from band calculations [37,38,39,29,26]. The main contributors to the DOS at the Fermi energy are the d states of Pt ions in the As-Pt-As layer of SrPt 2 As 2 [37,38,26].…”

“…Imre et al ascribed the CDW order to Peierls instability using band structure calculations [23]. Kim et al ascribed this to momentum-dependent electron-phonon coupling using band structure calculations [26]; a weak nesting feature and evidence of a sizable electron-phonon interaction were found. However, the origin is still under debate.…”