Pressure Dependence of the Charge-Density-Wave Gap in Rare-Earth Tritellurides

Abstract

We investigate the pressure dependence of the optical properties of CeTe3, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe3. The physical properties of low-dimensional systems have fascinated researchers for a great part of the last century, and have recently become one of the primary centers of interest in condensed matter research. Lowdimensional systems not only experience strong quantum and thermal fluctuations, but also admit ordering tendencies which are difficult to realize in three-dimensional materials. Prominent examples are spin-and chargedensity waves in quasi-one-dimensional compounds [1]. Moreover, the competition among several possible order parameters leads to rich phase diagrams, which can be tuned by external variables as temperature, magnetic field, and both chemical and applied pressure [1,2]. Tunable external parameters also affect the effective dimensionality of the interacting electron gas, which plays an essential role in defining the intrinsic electronic properties of the investigated systems.The rare-earth tri-tellurides RTe 3 (R= La-Tm, excepting Eu [3]) are the latest paramount examples of low dimensional systems exhibiting an incommensurate chargedensity-wave (CDW) state, stable across the available rare-earth series [4,5]. The lattice constant decreases on going from R = La to R = Tm [6,7], i.e. by chemically compressing the lattice, as consequence of the reduced ionic radius of the rare-earth atom. The CDW state in RTe 3 can be then investigated as a function of the inplane lattice constant a, which is directly related to the Te-Te distance in the Te-layers.Recently, we have reported on the first optical measurements of RTe 3 [8]. Our data, collected over an extremely broad spectral range, allowed us to observe both the Drude component and the single-particle peak, ascribed to the contributions due to the free charge carriers and to the excitation across the charge-density-wave gap, respectively. We established a diminishing impact of the charge-density-wave condensate on the electronic properties of RTe 3 with decreasing a across the rare-earth series [8]. On decreasing a, a reduction of the CDW gap together with an enhancement of the metallic (Drude) contribution were observed in the absorption spectrum. This is the consequence of a quenching of the nesting condition, driven by the modification of the Fermi surface (FS) because of the lattice compression [8].We present in this letter infrared optical investigations of the pressure dependence of the optical ...

Pressure suppression of unconventional charge-density-wave state in PrRu4P12studied by optical conductivity

“…The peak shifted to lower energy, and hence the CDW gap decreased, with lattice contraction given by different R elements 34,35 and also by external pressure. [35][36][37] In contrast, as already mentioned, the gap excitation peak of PrRu 4 P 12 decreases only slightly with P . The reason for this behavior is unclear at the present, and it may point to the unconventional nature of CDW state in this compound.…”

“…33 For example, σ(ω) of a series of compounds RTe 3 (R: rare earths) have been studied recently. [35][36][37] A peak was commonly observed in their σ(ω) spectra, whose energy was identified as the CDW gap magnitude. The peak shifted to lower energy, and hence the CDW gap decreased, with lattice contraction given by different R elements 34,35 and also by external pressure.…”

“…[35][36][37] A peak was commonly observed in their σ(ω) spectra, whose energy was identified as the CDW gap magnitude. The peak shifted to lower energy, and hence the CDW gap decreased, with lattice contraction given by different R elements 34,35 and also by external pressure. [35][36][37] In contrast, as already mentioned, the gap excitation peak of PrRu 4 P 12 decreases only slightly with P .…”

“…Such a concept has been applied to analyze the optical data of the RTe 3 compounds. [34][35][36][37] In the case of RTe 3 with layered crystal structure, the CDW had a strong 2D character, driven by a 2D nesting of FS. As a result, the FS nesting was not complete and only a part of FS was gapped.…”

“…To determine the position of the gap excitation peak and its shifts with P , we adapted a previously reported method used to analyze a CDW gap. [34][35][36][37] Namely, the center-of-mass energy (ω CM ) of the three Lorentz oscillators used in the fitting, defined as ω CM = i ω 0,i S i / i S i where i denotes L1, L2, and L3, was regarded as the peak position. As shown in Fig.…”