Evolution of superconductivity and charge order in pressurized RbV3Sb5

The kagome metals AV3Sb5 (A = K, Rb, Cs) under ambient pressure exhibit an unusual charge order, from which superconductivity emerges. In this work, by applying hydrostatic pressure using a liquid pressure medium and carrying out electrical resistance measurements for RbV3Sb5, we find the charge order becomes suppressed under a modest pressure p c (1.4 < p c < 1.6 GPa), while the superconducting transition temperature T c is maximized. T c is then gradually weakened with further increase of pressure and reaches a minimum around 14.3 GPa, before exhibiting another maximum around 22.8 GPa, signifying the presence of a second superconducting dome. Distinct behaviors in the normal state resistance are found to be associated with the second superconducting dome, similar to KV3Sb5. Our findings point to qualitatively similar temperature-pressure phase diagrams in KV3Sb5 and RbV3Sb5, and suggest a close link between the second superconducting dome and the high-pressure normal state resistance.

Tri-Hexagonal charge order in kagome metal CsV3Sb5 revealed by 121Sb NQR

We report 121Sb nuclear quadrupole resonance (NQR) measurements on kagome superconductor CsV3Sb5 with T c = 2.5 K. 121Sb NQR spectra split after a charge density wave (CDW) transition at 94 K, which demonstrates a commensurate CDW state. The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first order phase transition. The CDW order exhibits Tri-Hexagonal deformation with a lateral shift between the adjacent kagome layers, which is consistent with 2×2×2 superlattice modulation. The superconducting state coexists with CDW order and shows a conventional s-wave behavior in the bulk state.

Tuning Charge Order in (TMTTF)2X by Partial Anion Substitution

In the quasi-one-dimensional (TMTTF)2X compounds with effectively quarter-filled bands, electronic charge order is stabilized from the delicate interplay of Coulomb repulsion and electronic bandwidth. The correlation strength is commonly tuned by physical pressure or chemical substitution with stoichiometric ratios of anions and cations. Here, we investigate the charge-ordered state through partial substitution of the anions in (TMTTF)2[AsF6]1−x[SbF6]x with x≈0.3, determined from the intensity of infrared vibrations, which is sufficient to suppress the spin-Peierls state. Our dc transport experiments reveal a transition temperature TCO = 120 K and charge gap ΔCO=430 K between the values of the two parent compounds (TMTTF)2AsF6 and (TMTTF)2SbF6. Upon plotting the two parameters for different (TMTTF)2X, we find a universal relationship between TCO and ΔCO yielding that the energy gap vanishes for transition temperatures TCO≤60 K. While these quantities indicate that the macroscopic correlation strength is continuously tuned, our vibrational spectroscopy results probing the local charge disproportionation suggest that 2δ is modulated on a microscopic level.

Observation of Possible Nonlinear Anomalous Hall Effect in Organic Two-Dimensional Dirac Fermion System

We report the observation of nonlinear anomalous Hall effect (NLAHE) in the multilayered organic conductor α-(BEDT-TTF)2I3 in the charge order (CO) insulating phase just under the critical pressure for transition into two-dimensional (2D) massless Dirac fermion (DF) phase. We successfully extracted the finite nonlinear Hall voltage proportional to square current at zero magnetic field. The observed NLAHE features, current direction dependence and correlation with CO, are consistent with the previous estimation assuming 2D massive DF with a pair of tilted Dirac cones. This is the first observation of topological transport in organic conductors, and also the first example of NLAHE in the electronic phase with spontaneous symmetry breaking.