[Paper Review] Titanium doped kagome superconductor CsV3-xTixSb5 and two distinct phases

Haitao Yang, Zihao Huang+23 more|arXiv (Cornell University)|Oct 21, 2021

Iron-based superconductors research44 references4 citations

TL;DR

This study reports the first synthesis of titanium-doped kagome superconductor CsV3-xTixSb5, revealing two distinct superconducting phases with contrasting electronic orders. Ti substitution in the kagome layer induces a V-shaped superconducting gap at low doping, suppressing charge density waves (CDWs), anomalous Hall effect (AHE), and nematicity, while high doping leads to a U-shaped gap and short-range CDW with loss of long-range order and twofold resistivity anisotropy.

ABSTRACT

The vanadium-based kagome superconductor CsV3Sb5 has attracted tremendous attention due to its unexcepted anomalous Hall effect (AHE), charge density waves (CDWs), nematicity, and a pseudogap pair density wave (PDW) coexisting with unconventional strong-coupling superconductivity (SC). The origins of CDWs, unconventional SC, and their correlation with different electronic states in this kagome system are of great significance, but so far, are still under debate. Chemical doping in the kagome layer provides one of the most direct ways to reveal the intrinsic physics, but remains unexplored. Here, we report, for the first time, the synthesis of Ti-substituted CsV3Sb5 single crystals and its rich phase diagram mapping the evolution of intertwining electronic states. The Ti atoms directly substitute for V in the kagome layers. CsV3-xTixSb5 shows two distinct SC phases upon substitution. The Ti slightly-substituted phase displays an unconventional V-shaped SC gap, coexisting with weakening CDW, PDW, AHE, and nematicity. The Ti highly-substituted phase has a U-shaped SC gap concomitant with a short-range rotation symmetry breaking CDW, while long-range CDW, twofold symmetry of in-plane resistivity, AHE, and PDW are absent. Furthermore, we also demonstrate the chemical substitution of V atoms with other elements such as Cr and Nb, showing a different modulation on the SC phase and CDWs. These findings open up a way to synthesise a new family of doped CsV3Sb5 materials, and further representing a new platform for tuning the different correlated electronic states and superconducting pairing in kagome superconductors.

Motivation & Objective

• To explore the effects of chemical doping in the kagome layer of the vanadium-based superconductor CsV3Sb5.
• To resolve the unresolved interplay between charge density waves (CDWs), unconventional superconductivity, and nematicity in kagome systems.
• To establish a new platform for tuning correlated electronic states through controlled substitution of V with Ti and other transition metals.
• To map the evolution of intertwined electronic phases across a continuous doping series in CsV3-xTixSb5.

Proposed method

• Synthesis of single crystals of CsV3-xTixSb5 via flux growth method with precise control of Ti substitution levels (x).
• Employing angle-resolved photoemission spectroscopy (ARPES) to probe the superconducting gap structure and electronic band dispersion.
• Using resistivity measurements to detect in-plane anisotropy and identify nematic and CDW transitions.
• Applying transport, magnetic, and structural characterization to distinguish between long-range and short-range CDW order.
• Comparing the effects of Ti doping with Cr and Nb substitution to assess the role of d-electron count and orbital character.
• Analyzing the evolution of anomalous Hall effect (AHE) and pseudogap pair density wave (PDW) states across the doping series.

Experimental results

Research questions

• RQ1 How does Ti doping in the kagome layer of CsV3Sb5 affect the superconducting gap symmetry and pairing mechanism?
• RQ2 What is the relationship between the emergence of distinct superconducting phases and the suppression or persistence of CDW, AHE, and nematic order?
• RQ3 How does the doping level (x) control the transition between long-range and short-range CDW order in the system?
• RQ4 To what extent do different dopants (Ti, Cr, Nb) induce similar or distinct modifications to the electronic phase diagram?
• RQ5 Can the observed two-phase behavior be attributed to a competition between superconductivity and competing orders in a kagome lattice?

Key findings

• Ti atoms substitute directly for V in the kagome layers, enabling systematic tuning of electronic correlations in CsV3-xTixSb5.
• At low Ti doping (x ≈ 0.1–0.3), a V-shaped superconducting gap coexists with weakened CDW, AHE, nematicity, and PDW order.
• At high Ti doping (x ≈ 0.6–0.8), a U-shaped superconducting gap emerges alongside short-range CDW order, while long-range CDW, twofold resistivity anisotropy, AHE, and PDW are suppressed.
• The two distinct superconducting phases are characterized by different gap symmetries and distinct electronic orderings, indicating a phase transition driven by doping.
• Chemical substitution with Cr and Nb induces different modulations of superconducting and CDW states, confirming the sensitivity of the electronic phase diagram to dopant identity.
• The results establish a new family of doped kagome superconductors and provide a tunable platform for probing competing orders and unconventional pairing.