Superconductivity in Pd-intercalated charge-density-wave rare earth poly-tellurides RETe_n

Abstract

The interplay between magnetism and superconductivity is one of the dominant themes in the study of unconventional superconductors, such as high-T c cuprates, iron pnictides and heavy fermions 1-3 . In such systems, the same d-or f-electrons tend to form magnetically ordered states and participate in building up a high density of states at the Fermi level, which is responsible for the superconductivity. Charge-density-wave (CDW) is another fascinating collective quantum phenomenon in some low dimensional materials, like the prototypical transition-metal poly-chalcogenides, in which CDW instability is frequently found to accompany with superconducting transition at low temperatures 4 . Remarkably, similar to the antiferromagnetic superconductors, superconductivity can also be achieved upon suppression of CDW order via chemical doping or applied pressure in 1T-TiSe 2 (ref. 5, 6). However, in these CDW superconductors, the two ground states are believed to occur in different parts of Fermi surface (FS) sheets, derived mainly from chalcogen p-states and transition metal d-states, respectively.The origin of superconductivity and its interplay with CDW instability has not yet been unambiguously determined. Here we report on the discovery of bulk superconductivity in Pd-intercalated CDW R E Te n (R E =rare earth; n=2.5, 3) compounds, which belong to a large family of rare-earth poly-chalcogenides with CDW instability usually developing in the planar square nets of tellurium at remarkably high transition temperature and the electronic properties are also dominated by chalcogen p-orbitals. Our study demonstrates that the intercalation of palladium leads to the suppression of the CDW order and the emergence of the superconductivity. Our finding could provide an ideal model system for comprehensive studies of the interplay between CDW and superconductivity.

Disorder-induced suppression of charge density wave order: STM study of Pd-intercalated ErTe3

“…Single-crystal x-ray diffraction on the same crystals confirmed the increase in the b-axis lattice constant consistent with Pd atoms intercalating between the van der Waals bonded Te bilayer [14]. DFT calculations also show this to be the most favorable location for intercalation [12]. No surface Pd atoms were observed for low intercalations, presumably due to the high volatility of the Pd atoms upon cleaving at room temperature.…”

“…It was recently suggested that Pd-intercalated RTe 3 (R = rare earth element) might be such a model system [12][13][14]. Here we explicitly study the case R = Er.…”

Suppression of charge density wave order by disorder in Pd-intercalated ErTe$_3$

“…Also, it is worth noting that all measurements point to a truly incommensurate CDW in all members of the RTe 3 family, with no observation of a lock-in transition to a commensurate wavevector at low temperatures. 35,36 Polycrystalline samples of Pd x RTe 3 (R=Y, La, Pr, Sm, Gd, Tb, Dy, Ho, Er, Tm) have been reported previously 37 , and it was established that for high enough x, the material superconducts with T c ≈2-3 K regardless of the chosen rare earth. Single crystal measurements have only previously been reported in Pd x HoTe 3 38 , and only the remnant of the first CDW transition was observed.…”

Incommensurate 2kF density wave quantum criticality in two-dimensional metals

“…In some of these compounds the CDW transition temperature can be tuned to zero across a potential quantum critical point by intercalation or applying pressure, indicating that electronic correlations could be the main driving force behind the CDW transition [35]. Moreover, some of these materials become superconducting at low temperatures in the vicinity of the putative CDW quantum critical point [36][37][38]. One of our aims is to provide clear experimental signatures of an incommensurate 2k F CDW quantum phase transition, which would allow to settle the question if the incommensurate CDW transition in materials like NbSe 2 is driven by electronic correlations, or by a different mechanism, such as the coupling to phonons.…”