Swee Kuan Goh

Superconductivity can coexist or compete with other orders such as magnetism or density waves. Optimizing superconductivity requires identifying competing orders that may disrupt Cooper pair coherence. Here, we use the self-field critical current ( I _{c, s f} ) to probe pressure-tuned superconductivity in the kagome superconductor RbV ₃ Sb ₅ . As pressure destabilizes the charge-density wave (CDW) state, I _c,sf drastically enhances, peaking near the critical pressure where the CDW state is completely suppressed at zero temperature. Surprisingly, a weaker I _c,sf peak emerges within the CDW phase. Near the pressure of the weaker peak, the superconducting phase transition temperature shifts from an increasing trend with pressure to a near plateau. Our analysis suggests the possibility of a sudden change in the CDW pattern or a Lifshitz transition, highlighting the need for microscopic examinations of the CDW state for understanding the pressure evolution of superconductivity in RbV ₃ Sb ₅ .

1. Kagome metals AV 3 Sb 5 (A = K, Rb, Cs) feature an electronic band structure characterized by van Hove singularities, Dirac points, and flat bands, establishing them as prime platforms for inves...

Superconductors that can be mechanically exfoliated are an interesting platform for exploring superconducting properties tuned by layer thickness. These layered superconductors are also expected to exhibit sensitivity to applied pressure. While pressure has been demonstrated to be an effective way of tuning bulk superconductors, analogous studies on superconducting thin flakes have been limited due to technical challenges. In particular, spectroscopic measurements under pressure remain insufficiently explored. In this work, we functionalized the diamond anvil cell technique for point-contact Andreev reflection spectroscopy (PCAR) measurement on thin-flake materials under pressure, offering the opportunity to obtain spectroscopic information on superconductivity. To validate the feasibility of this method, we have conducted PCAR measurements on iron-selenide thin flakes to extract temperature-dependent superconducting gap values under ambient and high pressure. Combine with the proven magnetotransport capability, our method provides a conceptually simple tool for a detailed examination of thin-flake superconductors under pressure.

Superconductors that can be mechanically exfoliated are an interesting platform for exploring superconducting properties tuned by layer thickness. These layered superconductors are also expected to exhibit sensitivity to applied pressure. While pressure has been demonstrated to be an effective way of tuning bulk superconductors, analogous studies on superconducting thin flakes have been limited due to technical challenges. In particular, spectroscopic measurements under pressure remain insufficiently explored. In this work, we functionalized the diamond anvil cell technique for point-contact Andreev reflection spectroscopy (PCAR) measurement on thin-flake materials under pressure, offering the opportunity to obtain spectroscopic information on superconductivity. To validate the feasibility of this method, we have conducted PCAR measurements on iron-selenide thin flakes to extract temperature-dependent superconducting gap values under ambient and high pressure. Combined with the proven magnetotransport capability, our method provides a conceptually simple tool for a detailed examination of thin-flake superconductors under pressure.

Kagome metal AV3Sb5 (A = K, Rb, Cs) has emerged as an intriguing platform for exploring the interplay between superconductivity and other quantum states. Among the three compounds, RbV3Sb5 has a notably lower superconducting critical temperature (Tc) at ambient pressure, posing challenges in exploring the superconducting state. For instance, the upper critical field (Hc2) is small and thus difficult to measure accurately against other control parameters. Hence, enhancing superconductivity would facilitate Hc2 measurements, providing insights into key superconducting properties such as the dimensionality. In this Letter, we report the tuning of the Tc in RbV3Sb5 through the application of biaxial strain. Utilizing a negative thermal expansion material ZrW2O8 as a substrate, we achieve a substantial biaxial strain of ɛ = 1.50%, resulting in a remarkable 75% enhancement in Tc. We investigate the Hc2 as a function of temperature, revealing a transition from multi-band to single-band superconductivity with increasing tensile strain. In addition, we study the Hc2 as a function of field angle, revealing a plausible correlation between the Tc enhancement and the change in dimensionality of the superconductivity under tensile strain. Further analysis quantitatively illustrates a transition toward two-dimensional superconductivity in RbV3Sb5 when subjected to tensile strain. Our work demonstrates that the application of biaxial strain allows for the tuning of both the Tc and superconducting dimensionality in RbV3Sb5.