Spontaneous Lattice Distortion in the Spin-Triplet Superconductor Cu_{x}Bi_{2}Se_{3}

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Doped topological insulators like Cu_xBi_2Se_3 are platforms for studying topological superconductivity.
• Understanding the interplay between superconductivity and crystal lattice is crucial.

Purpose of the Study:

• Investigate the coupling between the superconducting order parameter and crystal lattice in Cu_xBi_2Se_3.
• Characterize lattice distortions associated with superconductivity onset.

Main Methods:

• Synchrotron x-ray diffraction measurements were performed on Cu_xBi_2Se_3 samples with varying doping levels (0.24≤x≤0.46).
• Nematic diamagnetic susceptibility was used to determine the orientation of the superconducting order parameter (d vector).

Main Results:

• A sizable lattice distortion (∼100 ppm) was observed in crystals where the d vector tilted from high-symmetry directions, coinciding with superconductivity onset.
• No significant lattice change was found when the d vector aligned with high-symmetry directions.
• A chiral superconducting state was suggested in highly doped (x=0.46) samples due to isotropic diamagnetic susceptibility and absence of lattice distortion.

Conclusions:

• Lattice distortion is a powerful diagnostic tool for identifying nematic superconductivity with a two-component order parameter.
• The findings provide evidence for an odd-parity E_u order parameter coupled to the trigonal lattice.
• The study highlights the complex relationship between crystal structure and exotic superconducting states in topological materials.