Distinct charge density wave instabilities in PrTen (n=2, 3) and ErTe3 investigated via ARPES and XAS

Understanding the origin of distinct charge density wave (CDW) instabilities in layered $R{\mathrm{Te}}_n$ ($n=2$, 3) compounds ($R$, rare earth element) has been an important issue. In this research update, we have investigated the electronic structures of ${\mathrm{PrTe}}_n$ ($n=2$, 3) and ${\mathrm{ErTe}}_3$ layered CDW compounds employing angle-resolved photoemission spectroscopy (ARPES) and soft x-ray absorption spectroscopy (XAS). The trivalent valency of $R^{3+}$ ions is confirmed for ${\mathrm{PrTe}}_n$ ($n=2$, 3) and ${\mathrm{ErTe}}_3$, supporting that $R$-Te slabs serve as charge reservoirs and that the CDW instability occurs in the partially filled Te sheets. Both $R4d\to 4f$ resonant photoemission spectroscopy and photon-energy map measurements provide evidence that $R4f$ electrons do not contribute directly to the CDW formation but that the indirect contribution from Pr $4f$ electrons through the Pr $4f-\mathrm{Te} 5p$ hybridization is feasible in ${\mathrm{PrTe}}_n$ ($n=2$, 3). Circular and linear dichroism ARPES measurements indicate that the chirality of the Te $5p$ orbitals certainly plays a role in the CDW formation of $R{\mathrm{Te}}_3$ ($R=\mathrm{Pr}$, Er) while it is relatively weak in ${\mathrm{PrTe}}_2$, and that the $E_{\mathrm{F}}$-crossing orbitals, responsible for the CDW formation, are ordered in plane (in the $ac$ plane) in all of them. Different CDW-induced Fermi surface reconstructions between $R{\mathrm{Te}}_3$ and $R{\mathrm{Te}}_2$ are due to (i) the existence of two Te sheets and one Te sheet per unit cell in $R{\mathrm{Te}}_3$ and $R{\mathrm{Te}}_2$, respectively, so as to produce different numbers of hole carriers, and (ii) the different lattice parameters of Te sheets in $R{\mathrm{Te}}_n$, leading to the different densities of states at $E_{\mathrm{F}}$.