Pressure-Induced Superconductivity in the Charge-Density-Wave Compound LaTe_(2-x)Sb_(x)(x=0 and 0.4)

Magnetic CeTe_(2)achieving superconductivity under external pressure has received considerable attention.The intermingling of 4f and 5d electrons from Ce raised the speculation of an unconventional pairing mechanism arising from magnetic fluctuations.Here,we address this speculation using a nonmagnetic 4f-electron-free LaTe_(2)as an example.No structural phase transition can be observed up to 35 GPa in the in situ synchrotron diffraction patterns.Subsequent high-pressure electrical measurements show that LaTe_(2)exhibits superconductivity at20 Gpa with its T_(c)(4.5 K)being two times higher than its Ce-counterpart.Detailed theoretical calculations reveal that charge transfer from the 4p orbitals of the planar square Te-Te network to the 5d orbitals of La is responsible for the emergence of superconductivity in LaTe_(2),as confirmed by Hall experiments.Furthermore,we study the modulation of q_(CDW)by Sb substitution and find a record high T_(c)^(onset)~6.5 K in LaTe_(1.6)Sb_(0.4).Our work provides an informative clue to comprehend the role of 5d-4p hybridization in the relationship between charge density wave(CDW)and superconductivity in these RETe_(2)(RE=rare-earth elements)compounds.

First-Principles Study of Hole-Doped Superconductors RNiO_(2)(R=Nd,La,and Pr)

Recent experiments have found that in contrast to the nonsuperconducting bulk RNiO_(2)(R=Nd,La,and Pr),the strontium-doped R_(1−x)Sr_(x)NiO_(2)thin films show superconductivity with the critical temperature T_(c)of 9–15K at x=0.2,whose origin of superconductivity deserves further investigation.Based on first-principles calculations,we study the electronic structure,lattice dynamics,and electron–phonon coupling(EPC)of the undoped and doped RNiO_(2)(R=Nd,La,and Pr)at the experimental doping level.Our results show that the EPC-derived T_(c)’s are all about 0K in the undoped and doped RNiO_(2).The electron–phonon coupling strength is too small to account for the observed superconductivity.We hence propose that the electron–phonon interaction can not be the exclusive origin of the superconductivity in RNiO_(2)(R=Nd,La,and Pr).

Exploring charge and spin fluctuations in infinite-layer cuprate SrCuO_(2)from a phonon perspective

The infinite-layer cuprate ACu O_(2)(A=Ca,Sr,Ba)possesses the simplest crystal structure among numerous cuprate superconductors and can serve as a prototypical system to explore the unconventional superconductivity.Based on the first-principles electronic structure calculations,we have studied the electronic and magnetic properties of the infinite-layer cuprate SrCuO_(2)from a phonon perspective.We find that interesting fluctuations of charges,electrical dipoles,and local magnetic moments can be induced by the atomic displacements of phonon modes in SrCuO_(2)upon the hole doping.Among all optical phonon modes of SrCuO_(2)in the antiferromagnetic Néel state,only the A_(1g)mode that involves the full-breathing O vibrations along the Cu-O bonds can cause significant fluctuations of local magnetic moments on O atoms and dramatic charge redistributions between Cu and O atoms.Notably,due to the atomic displacements of the A_(1g)mode,both the charge fluctuations on Cu and the electrical dipoles on O show a dome-like evolution with increasing hole doping,quite similar to the experimentally observed behavior of the superconducting T_(c);in comparison,the fluctuations of local magnetic moments on O display a monotonic enhancement along with the hole doping.Further analyses indicate that around the optimal doping,there exists a large softening in the frequency of the A_(1g)phonon mode and a van Hove singularity in the electronic structure close to the Fermi level,suggesting potential electron-phonon coupling.Our work reveals the important role of the full-breathing O phonon mode playing in the infinite-layer SrCuO_(2),which may provide new insights in understanding the cuprate superconductivity.