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1. Incommensurate charge-stripe correlations in the kagome superconductor CsV3Sb5−xSnx

   https://doi.org/10.1038/s41535-023-00570-x  

   Kautzsch, Linus ; Oey, Yuzki M. ; Li, Hong ; Ren, Zheng ; Ortiz, Brenden R. ; Pokharel, Ganesh ; Seshadri, Ram ; Ruff, Jacob ; Kongruengkit, Terawit ; Harter, John W. ; et al ( July 2023 , npj Quantum Materials)

   The class ofAV₃Sb₅(A=K, Rb, Cs) kagome metals hosts unconventional charge density wave states seemingly intertwined with their low temperature superconducting phases. The nature of the coupling between these two states and the potential presence of nearby, competing charge instabilities however remain open questions. This phenomenology is strikingly highlighted by the formation of two ‘domes’ in the superconducting transition temperature upon hole-doping CsV₃Sb₅. Here we track the evolution of charge correlations upon the suppression of long-range charge density wave order in the first dome and into the second of the hole-doped kagome superconductor CsV₃Sb_5−xSn_x. Initially, hole-doping drives interlayer charge correlations to become short-ranged with their periodicity diminished along the interlayer direction. Beyond the peak of the first superconducting dome, the parent charge density wave state vanishes and incommensurate, quasi-1D charge correlations are stabilized in its place. These competing, unidirectional charge correlations demonstrate an inherent electronic rotational symmetry breaking in CsV₃Sb₅, and reveal a complex landscape of charge correlations within its electronic phase diagram. Our data suggest an inherent 2k_fcharge instability and competing charge orders in theAV₃Sb₅class of kagome superconductors.

    

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2. Two types of charge order with distinct interplay with superconductivity in the kagome material CsV3Sb5

   https://doi.org/10.1038/s42005-022-01011-0  

   Gupta, Ritu ; Das, Debarchan ; Mielke, Charles ; Ritz, Ethan T. ; Hotz, Fabian ; Yin, Qiangwei ; Tu, Zhijun ; Gong, Chunsheng ; Lei, Hechang ; Birol, Turan ; et al ( December 2022 , Communications Physics)

   Abstract The kagome metals of the family A V 3 Sb 5 , featuring a unique structural motif, harbor an array of intriguing phenomena such as chiral charge order and superconductivity. CsV 3 Sb 5 is of particular interest because it displays a double superconducting dome in the region of the temperature-pressure phase diagram where charge order is still present. However, the microscopic origin of such an unusual behavior remains an unsolved issue. Here, to address it, we combine high-pressure, low-temperature muon spin relaxation/rotation with first-principles calculations. We observe a pressure-induced threefold enhancement of the superfluid density, which also displays a double-peak feature, similar to the superconducting critical temperature. This leads to three distinct regions in the phase diagram, each of which features distinct slopes of the linear relation between superfluid density and the critical temperature. These results are attributed to a possible evolution of the charge order pattern from the superimposed tri-hexagonal Star-of-David phase at low pressures (within the first dome) to the staggered tri-hexagonal phase at intermediate pressures (between the first and second domes). Our findings suggest a change in the nature of the charge-ordered state across the phase diagram of CsV 3 Sb 5 , with varying degrees of competition with superconductivity. 

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3. Electron hole asymmetry in the phase diagram of carrier-tuned CsV3Sb5

   https://doi.org/10.3389/femat.2023.1257490  

   Capa_Salinas, Andrea N ; Ortiz, Brenden R ; Bales, Calvin ; Frassineti, Jonathan ; Mitrović, Vesna F ; Wilson, Stephen D ( October 2023 , Frontiers in Electronic Materials)

   In this work, we study the effect of electron doping on the kagome superconductor CsV₃Sb₅. Single crystals and powders of CsV₃Sb_5−xTe_xare synthesized and characterized via magnetic susceptibility, nuclear quadrupole resonance, and x-ray diffraction measurements, where we observe a slight suppression of the charge density wave transition temperature and superconducting temperature with the introduction of electron dopants. In contrast to hole doping, both transitions survive relatively unperturbed up to the solubility limit of Te within the lattice. A comparison is presented between the electronic phase diagrams of electron- and hole-tuned CsV₃Sb₅.

    

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4. Phonon mixing in the charge density wave state of ScV6Sn6

   https://doi.org/10.1038/s41535-023-00590-7  

   Gu, Yanhong ; Ritz, Ethan T. ; Meier, William R. ; Blockmon, Avery ; Smith, Kevin ; Madhogaria, Richa Pokharel ; Mozaffari, Shirin ; Mandrus, David ; Birol, Turan ; Musfeldt, Janice L. ( December 2023 , npj Quantum Materials)

   Kagomé metals are widely recognized, versatile platforms for exploring topological properties, unconventional electronic correlations, magnetic frustration, and superconductivity. In theRV₆Sn₆family of materials (R= Sc, Y, Lu), ScV₆Sn₆hosts an unusual charge density wave ground state as well as structural similarities with theAV₃Sb₅system (A= K, Cs, Rb). In this work, we combine Raman scattering spectroscopy with first-principles lattice dynamics calculations to reveal phonon mixing processes in the charge density wave state of ScV₆Sn₆. In the low temperature phase, we find at least four new peaks in the vicinity of the V-containing totally symmetric mode near 240 cm⁻¹suggesting that the density wave acts to mix modes ofP6/mmmand$$R\bar{3}m$$$R\overline{3}m$symmetry - a result that we quantify by projecting phonons of the high symmetry state onto those of the lower symmetry structure. We also test the stability of the short-range ordered density wave state under compression and propose that both physical and chemical pressure quench the effect. We discuss these findings in terms of symmetry and the structure-property trends that can be unraveled in this system.

    

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5. Absence of E2g Nematic Instability and Dominant A1g Response in the Kagome Metal CsV3Sb5

   https://doi.org/10.1103/PhysRevX.14.031015  

   Liu, Zhaoyu ; Shi, Yue ; Jiang, Qianni ; Rosenberg, Elliott W ; DeStefano, Jonathan M ; Liu, Jinjin ; Hu, Chaowei ; Zhao, Yuzhou ; Wang, Zhiwei ; Yao, Yugui ; et al ( July 2024 , Physical Review X)

   Ever since the discovery of the charge density wave (CDW) transition in the kagome metal${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, the nature of its symmetry breaking has been under intense debate. While evidence suggests that the rotational symmetry is already broken at the CDW transition temperature ($T_{\mathrm{CDW}}$), an additional electronic nematic instability well below$T_{\mathrm{CDW}}$has been reported based on the diverging elastoresistivity coefficient in the anisotropic channel ($m_{E_{2g}}$). Verifying the existence of a nematic transition below$T_{\mathrm{CDW}}$is not only critical for establishing the correct description of the CDW order parameter, but also important for understanding low-temperature superconductivity. Here, we report elastoresistivity measurements of${\mathrm{CsV}}_3{\mathrm{Sb}}_5$using three different techniques probing both isotropic and anisotropic symmetry channels. Contrary to previous reports, we find the anisotropic elastoresistivity coefficient$m_{E_{2g}}$is temperature independent, except for a step jump at$T_{\mathrm{CDW}}$. The absence of nematic fluctuations is further substantiated by measurements of the elastocaloric effect, which show no enhancement associated with nematic susceptibility. On the other hand, the symmetric elastoresistivity coefficient$m_{A_{1g}}$increases below$T_{\mathrm{CDW}}$, reaching a peak value of 90 at$T^{*}=20\mathrm{K}$. Our results strongly indicate that the phase transition at$T^{*}$is not nematic in nature and the previously reported diverging elastoresistivity is due to the contamination from the$A_{1g}$channel.