The newly discovered kagome metals AV₃Sb₅ (A = K, Rb, Cs) have aroused tremendous research interest as a novel platform to study the interplay between nontrivial band topology, superconductivity (SC) and charge-density-wave (CDW) order [1-4]. At ambient conditions, these materials crystallize into a layered structure with hexagonal symmetry (space group P6/mmm), inset of Fig. 1(a), consisting of A layer and V-Sb slab stacked alternatively along the c-axis. The most prominent feature of this structure is the presence of quasi-2D ideal kagome layers of V ions coordinated by Sb. These compounds are metallic and enter a superconducting ground state below T_c = 0.93, 0.92, and 2.5 K for A= K, Rb, and Cs [2-4], respectively. In the normal state, their transport and magnetic properties exhibit a clear anomaly at T* = 78, 104, and 94 K, respectively, due to the formation of CDW-like order as revealed by the x-ray diffraction and scanning tunning microscopy measurements [2-4]. The charge order in KV₃Sb₅ has been found to display a chiral anisotropy [5], which can lead to giant anomalous Hall effect in the absence of magnetic order or local moments [6,7]. It was also argued as a strong precursor of unconventional SC. Moreover, angle-resolved photoemission spectroscopy measurements and density-functional-theory calculations have characterized their normal state as a Z₂ topological metal with multiple Dirac nodal points near the Fermi level [1,4], consistent with the observations of Shubnikov-de Haas quantum oscillations and small Fermi surfaces (FSs) with low effective mass in RbV₃Sb₅ [3].

Fig. 1. Temperature-pressure phase diagram of CsV₃Sb₃. Pressure dependence of the transition temperatures for (a) the CDW-like order and (b) superconductivity. The color scale in (a) represents the sign of Δ(dρ/dT) around T*, which changes sign near P_c1 due to the modification of CDW order. Inset of (a) shows the crystal structure of CsV₃Sb₃. The yellow region between P_c1 and P_c2 in (b) corresponds to a relatively broad superconducting transition.

At present, the topologically related phenomena and SC have been actively studied in these AV₃Sb₅ compounds, but the rich physics related to the electron correlation, especially the relationship between the intertwined electronic orders, has been barely revealed. In this regard, it is interesting to unveil the correlation between the CDW-like order and SC commonly observed in these AV₃Sb₅ materials. Thus, we have chosen to study CsV₃Sb₅ with the highest T_c among this series of compounds by applying a high-pressure approach, which has been widely used in disentangling the competing electronic orders of strongly correlated metals. The interplay between CDW and SC in CsV₃Sb₅ was studied via measurements of resistivity, DC and AC magnetic susceptibility under various pressures up to 6.6 GPa [8]. We find that the CDW transition decreases with pressure and experience a subtle modification at P_c1 ≈ 0.6-0.9 GPa before it vanishes completely at P_c2 ≈ 2 GPa. Correspondingly, T_c(P) displays an unusual M-shaped double dome with two maxima around P_c1 and P_c2, respectively, leading to a tripled enhancement of T_c to about 8 K at 2 GPa. The obtained temperature-pressure phase diagram, Fig. 1, 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 P_c1 ≤ P ≤ P_c2 as evidenced by the broad superconducting transition and reduced superconducting volume fraction. The modification of CDW order around P_c1 has been discussed based on the band structure calculations. Our work not only demonstrates the potential to raise T_c of the V-based kagome superconductors, but also offers more insights into the rich physics related to the electron correlations in this novel family of topological kagome metals.

References

• [1] B. R. Ortiz, L. C. Gomes, J. R. Morey et al., Phys. Rev. Mater. 3, 094407 (2019).
• [2] B. R. Ortiz, E. Kenney, P.M. Sarte et al., Phys. Rev. Mater. 5, 034801 (2021).
• [3] Q.W. Yin, Z. J. Tu, C. S. Gong et al., Chin. Phys. Lett. 38, 037403 (2021).
• [4] B. R. Ortiz, S. M. L. Teicher, Y. Hu et al., Phys. Rev. Lett. 125, 247002 (2020).
• [5] Y. X. Jiang, J. X. Yin, M. M. Denner et al., Nature Mater. 20, 1353 (2021).
• [6] S. Y. Yang, Y. J. Wang, B. R. Ortiz et al., Sci. Adv. 6, eabb6003 (2020).
• [7] E. M. Kenney, B. R. Ortiz, C. N. Wang et al., J. Phys. Condens. Matter. 33, 235801 (2021).
• [8] K. Y. Chen, N. N. Wang, Q. W. Yin et al., Phys. Rev. Lett. 126, 247001 (2021).

Authors

• K. Y. Chen^a, N. N. Wang^a, Q. W. Yin^b, Y. H. Gu^a, K. Jiang^a, Z. J. Tu^b, C. S. Gong^b, Y. Uwatoko, J. P. Sun^a, H. C. Lei^b, J. P. Hu^a, and J.-G. Cheng^a
• ^aInstitute of Physics, Chinese Academy of Science
• ^bRenmin University of China