[Paper Review] Superconductivity in quasi-one-dimensional K$_2$Cr$_3$As$_3$

Jin‐Ke Bao, Jiyong Liu+11 more|arXiv (Cornell University)|Nov 29, 2014

Iron-based superconductors research1 citations

TL;DR

This study reports bulk superconductivity at 6.1 K in quasi-one-dimensional K₂Cr₃As₃, a chromium pnictide with double-walled subnano-tubes of face-sharing Cr₆/₂(As₆/₂) octahedra. The material exhibits strong electron correlations (γ = 70–75 mJ K⁻² mol⁻¹), non-Fermi liquid resistivity, and an upper critical field exceeding the Pauli limit by 3–4×, indicating unconventional superconductivity in a Q1D correlated system.

ABSTRACT

We report the discovery of bulk superconductivity (SC) at 6.1 K in a quasi-one-dimensional (Q1D) chromium pnictide K$_2$Cr$_3$As$_3$ which contains [(Cr$_3$As$_3$)$^{2-}$]$_{\infty}$ double-walled subnano-tubes with face-sharing Cr$_{6/2}$ (As$_{6/2}$) octahedron linear chains in the inner (outer) wall. The material has a large electronic specific-heat coefficient of 70$\sim$75 mJ K$^{-2}$ mol$^{-1}$, indicating significantly strong electron correlations. Signature of non-Fermi liquid behavior is shown by the linear temperature dependence of resistivity in a broad temperature range from 7 to 300 K. Unconventional SC is preliminarily manifested by the estimated upper critical field exceeding the Pauli limit by a factor of three to four. The title compound represents a rare example that possibly unconventional SC emerges in a Q1D system with strong electron correlations.

Motivation & Objective

• To investigate superconducting properties in the quasi-one-dimensional chromium pnictide K₂Cr₃As₃.
• To determine the nature of superconductivity in a system with strong electron correlations and low dimensionality.
• To assess whether unconventional superconductivity emerges in a Q1D correlated electron system.
• To characterize electronic correlations and normal-state behavior via specific heat and resistivity measurements.

Proposed method

• Synthesis of high-quality single crystals of K₂Cr₃As₃ via solid-state reaction and annealing.
• Measurement of electrical resistivity from 7 to 300 K to probe normal-state electronic behavior.
• Determination of the electronic specific-heat coefficient (γ) via low-temperature heat capacity measurements.
• Analysis of the upper critical field (Hc2) to assess the superconducting pairing symmetry.
• Comparison of Hc2 with the Pauli paramagnetic limit to infer unconventional pairing.
• Structural characterization to confirm the presence of [(Cr₃As₃)²⁻]∞ double-walled subnano-tubes with face-sharing octahedral chains.

Experimental results

Research questions

• RQ1 Does bulk superconductivity exist in the quasi-one-dimensional K₂Cr₃As₃ system?
• RQ2 What is the strength of electron correlations in K₂Cr₃As₃, as indicated by the electronic specific-heat coefficient?
• RQ3 Does the normal state exhibit non-Fermi liquid behavior, as evidenced by linear resistivity?
• RQ4 Is the superconducting state unconventional, as suggested by an upper critical field exceeding the Pauli limit?
• RQ5 Can unconventional superconductivity be stabilized in a quasi-one-dimensional correlated electron system?

Key findings

• Bulk superconductivity is observed at Tc = 6.1 K in K₂Cr₃As₃, confirmed by zero resistivity and Meissner effect.
• The electronic specific-heat coefficient γ is measured at 70–75 mJ K⁻² mol⁻¹, indicating strong electron correlations.
• Resistivity shows linear temperature dependence from 7 to 300 K, signaling non-Fermi liquid behavior in the normal state.
• The upper critical field Hc2 exceeds the Pauli paramagnetic limit by a factor of three to four, suggesting unconventional superconducting pairing.
• The system features a quasi-one-dimensional structure with double-walled subnano-tubes of face-sharing Cr₆/₂(As₆/₂) octahedra.
• K₂Cr₃As₃ represents a rare example of unconventional superconductivity in a Q1D correlated system.