Interchain-frustration-induced metallic state in quasi-one-dimensional Mott insulators

Charge Density Wave and Superconductivity in BaSbTe2S Heterolayer Crystal with 2D Te Square Nets

Low-dimensional materials with charge density waves (CDW) are attractive for their potential to exhibit superconductivity and nontrivial topological electronic features. Here we report the two-dimensional (2D) chalcogenide, BaSbTe2S which acts as a new platform hosting these phenomena. The crystal structure of BaSbTe2S is composed of alternating atomically thin Te square-net layers and double rock-salt type [(SbTeS)2]2- slabs separated with Ba2+ atoms. Due to the electronic instability of the Te square net, an incommensurately modulated structure is triggered and confirmed by both single-crystal X-ray diffraction, electron diffraction, and the presence of an energy bandgap in this compound. Our first-principles electronic structure analysis and investigation of structural dynamical instability suggest that the Te network plays a dominant role in its origin. The incommensurate structure is refined with a modulation vector of q = 0.351(1)b* using an orthorhombic cell of a = 4.4696(5) Å, b = 4.4680(5) Å, and c = 15.999(2) Å under superspace group Pmm2(0β0)000 at 293 K. The modulation vector q varies as a function of both occupancy of Te in the square net and temperature, indicating the CDW order can be modulated by local distortions. The CDW can be suppressed by pressure, leading to the emergence of superconductivity with a Tc up to 7.5 K at 13.6 GPa, suggesting a competition between the CDW order and superconductivity. Furthermore, electrical transport under the magnetic field reveals the existence of compensated high mobility electron- and hole-bands near the Fermi surface (μ ∼600-3500 cm2V-1s-1), suggesting Dirac-like band dispersion.

Dimensional-crossover-driven Mott transition in the frustrated Hubbard model

We study the Mott transition in a frustrated Hubbard model with next-nearest neighbor hopping at half-filling. The interplay between interaction, dimensionality, and geometric frustration closes the one-dimensional Mott gap and gives rise to a metallic phase with Fermi surface pockets. We argue that they emerge as a consequence of remnant one-dimensional umklapp scattering at the momenta with vanishing interchain hopping matrix elements. In this pseudogap phase, enhanced d-wave pairing correlations are driven by antiferromagnetic fluctuations. Within the adopted cluster dynamical mean-field theory on the 8 × 2 cluster and down to our lowest temperatures, the transition from one to two dimensions is continuous.

Recent progress in high-pressure studies on organic conductors

Recent high-pressure studies of organic conductors and superconductors are reviewed. The discovery of the highest T_c superconductivity among organics under high pressure has triggered the further progress of the high-pressure research. Owing to this finding, various organic conductors with the strong electron correlation were investigated under high pressures. This review includes the pressure techniques using the cubic anvil apparatus, as well as high-pressure studies of the organic conductors up to 10 GPa showing extraordinary temperature and pressure dependent transport phenomena.