Double superconducting dome and triple enhancement of Tc in the kagome superconductor CsV3Sb5 under high pressure

Abstract: CsV3Sb5 is a newly discovered Z2 topological kagome metal showing the coexistence of a charge density wave (CDW)-like order at T* = 94 K and superconductivity (SC) at Tc = 2.5 K at ambient pressure. Here we study the interplay between CDW and SC in CsV3Sb5 via measurements of resistivity and magnetic susceptibility under hydrostatic pressures. We find that the CDW transition decreases with pressure and experience a subtle modification at Pc1 = 0.6-0.9 GPa before it vanishes completely at Pc2 = 2 GPa. Correspondingly, Tc(P) displays an unusual M-shaped double dome character with two maxima around Pc1 and Pc2, respectively, leading to a tripled enhancement of Tc to about 8 K at 2 GPa. The obtained temperature-pressure phase diagram resembles those of many unconventional superconductors, illustrating an intimated competition between CDW-like order and SC. The competition is found to be particularly strong for the intermediate pressure range Pc1 <= P <= Pc2 as evidenced by the broad superconducting transition and reduced superconducting volume fraction. This work not only demonstrates the potential to raise the Tc of the V-based kagome superconductors, but also offers more insights into the rich physics related to the electronic correlations in this novel family of topological kagome metals.

• The paper reveals that applying hydrostatic pressure suppresses the charge density wave order, paving the way for a double superconducting dome.
• The paper demonstrates that the superconducting Tc increases from 2.5 K to approximately 8 K, marking a threefold enhancement at key pressure points.
• The paper identifies quantum criticality through pressure-induced variations in the upper critical field, underscoring strong electron correlation effects.

Double Superconducting Dome and Charge Density Wave Competition in CsV₃Sb₅ Under Pressure

The research paper presents an in-depth investigation into the unconventional superconducting behavior of the newly discovered kagome superconductor CsV₃Sb₅, emphasizing the interplay between charge density wave (CDW) and superconductivity (SC) under varying pressures. CsV₃Sb₅ is particularly notable due to its layered structure with hexagonal symmetry, belonging to a novel category of topological kagome metals that exhibit fascinating quantum phenomena such as nontrivial band topology and CDW-like order.

At ambient conditions, CsV₃Sb₅ transitions into a superconducting state at a critical temperature (T_c) of 2.5 K, in tandem with a CDW-like transition at a temperature (T*) of 94 K. The applied study examines the dynamics between these two competing phases under hydrostatic pressure, tracing the evolution of resistivity and magnetic susceptibility.

Key Observations and Results

1. Pressure-Induced CDW Suppression: It is observed that the CDW-like order gradually diminishes with increasing pressure and disappears completely at around 2 GPa. This suppression aligns with a distinct change in resistivity behavior, signaling the transition from a kink-like anomaly at lower pressures to a hump-like feature at intermediate pressures.
2. Double Superconducting Dome:
   • The superconducting T_c manifests an M-shaped double dome with two evident maxima at specific pressure points, 0.8 GPa and 2 GPa. Notably, T_c is enhanced to approximately 8 K at 2 GPa, representing a threefold increase from its value at ambient pressure.
   • The variation in superconducting transition width indicates significant competition between the CDW and SC phases, contributing to the broadened transition range at intermediate pressures.
3. Quantum Criticality Indicators: The paper presents evidence for quantum critical behavior, marked by changes in the upper critical field (μ₀H_c2) and its pressure-dependent double peak structure. Such findings suggest enhanced electronic mass near quantum critical points, a phenomenon known to characterize systems with strong electron correlations.

Implications and Future Outlook

This study elucidates the pressure-dependent modifications in the electronic structure of CsV₃Sb₅, portraying a complex but insightful representation of competing electronic orders that bear semblance to other unconventional superconductors such as heavy-fermion systems and iron-based superconductors. The M-shaped superconducting dome further emphasizes the potential that external pressures hold in tuning superconducting properties, with potential implications for enhancing superconductivity applications.

The observed interplay between CDW and SC phases in CsV₃Sb₅ underlines the necessity of probing further into the underlying mechanisms of electronic correlation. Future research may focus on exploring the nature of the pressure-induced CDW state, investigating possible hidden quantum critical points, and leveraging this interplay to discover new superconducting materials.

This work also supports research into pressure as a tool for manipulating the quantum states within superconductors, thereby providing an avenue for experimental methodologies aimed at uncovering new high-T_c materials within the kagome family and beyond. The exploration of kagome metals continues to be a fertile ground for understanding intricate quantum phenomena, with this work positioning CsV₃Sb₅ as a promising candidate for further theoretical and practical investigations.