Optimized superconductivity in the vicinity of a nematic quantum critical point in the kagome superconductor Cs(V1-xTix)3Sb5.

CsV3Sb5 exhibits superconductivity at Tc = 3.2 K after undergoing intriguing two high-temperature transitions: charge density wave order at ~98 K and electronic nematic order at Tnem ~ 35 K. Here, we investigate nematic susceptibility in single crystals of Cs(V1-xTix)3Sb5 (x = 0.00-0.06) where double-dome-shaped superconducting phase diagram is realized. The nematic susceptibility typically exhibits the Curie‒Weiss behaviour above Tnem, which is monotonically decreased with x. Moreover, the Curie‒Weiss temperature is systematically suppressed from ~30 K for x = 0 to ~4 K for x = 0.0075, resulting in a sign change at x = ~0.009. Furthermore, the Curie constant reaches a maximum at x = 0.01, suggesting drastically enhanced nematic susceptibility near a putative nematic quantum critical point (NQCP) at x = ~0.009. Strikingly, Tc is enhanced up to ~4.1 K with full Meissner shielding realized at x = ~0.0075-0.01, forming the first superconducting dome near the NQCP. Our findings directly point to a vital role of nematic fluctuations in enhancing the superconducting properties of Cs(V1-xTix)3Sb5.

Effect of Threading Dislocations on the Electronic Structure of La-Doped BaSnO3 Thin Films.

In spite of great application potential as transparent n-type oxides with high electrical mobility at room temperature, threading dislocations (TDs) often found in the (Ba,La)SnO3 (BLSO) films can limit their intrinsic properties so that their role in the physical properties of BLSO films need to be properly understood. The electrical properties and electronic structure of BLSO films grown on SrTiO3 (001) (STO) and BaSnO3 (001) (BSO) substrates are comparatively studied to investigate the effect of the TDs. In the BLSO/STO films with TD density of ~1.32 × 1011 cm-2, n-type carrier density ne and electron mobility are significantly reduced, as compared with the BLSO/BSO films with nearly no TDs. This indicates that TDs play the role of scattering-centers as well as acceptor-centers to reduce n-type carriers. Moreover, in the BLSO/STO films, both binding energies of an Sn 3d core level and a valence band maximum are reduced, being qualitatively consistent with the Fermi level shift with the reduced n-type carriers. However, the reduced binding energies of the Sn 3d core level and the valence band maximum are clearly different as 0.39 and 0.19 eV, respectively, suggesting that the band gap renormalization preexisting in proportion to ne is further suppressed to restore the band gap in the BLSO/STO films with the TDs.

Possible Persistence of Multiferroic Order down to Bilayer Limit of van der Waals Material NiI2.

Realizing a state of matter in two dimensions has repeatedly proven a novel route of discovering new physical phenomena. Van der Waals (vdW) materials have been at the center of these now extensive research activities. They offer a natural way of producing a monolayer of matter simply by mechanical exfoliation. This work demonstrates that the possible multiferroic state with coexisting antiferromagnetic and ferroelectric orders persists down to the bilayer flake of NiI2. By exploiting the optical second-harmonic generation technique, both magnitude and direction of the ferroelectric order, arising from the cycloidal spin order, are successfully traced. The possible multiferroic state's transition temperature decreases from 58 K for the bulk to about 20 K for the bilayer. Our observation will spur extensive efforts to demonstrate multifunctionality in vdW materials, which have been tried mostly by using heterostructures of singly ferroic ones until now.