Angle-Resolved Polarized Raman Spectroscopy Reveals Anisotropic Phonon Response in UTe2

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Orthorhombic UTe 2 has attracted significant attention due to its potential spin-triplet superconductivity and prospects in topological quantum computing. This study synthesized high-quality superconducting UTe 2 single crystals ( T c ≈ 2.0 K – 2.1 K) through chemical vapor transport (CVT) and molten salt flux (MSF) methods. X-ray diffraction and Laue backscattering confirmed their excellent crystallinity and determined their (001) crystallographic orientation. Room-temperature unpolarized Raman spectroscopy revealed three intrinsic phonon modes: B 1g (∼92 cm –1 ), B 3g 3 (∼119 cm –1 ), and A g 2 (∼139 cm –1 ). Angle-resolved polarized Raman spectroscopy near T c (1.6 K – 3.0 K) observed significant anisotropic responses in all phonon modes, with deviations in polarization dependence from D 2h point group theory. The nonzero intensity of B 3g 3 is attributed to symmetry breaking or spin–orbit coupling (SOC)-driven activation of forbidden modes; the polarization anomaly of A g 2 relates to strong electron–phonon coupling renormalization. Notably near T c (1.6 K – 3.0 K), no abrupt changes in phonon behavior (such as phonon frequency, line width, or symmetry) were observed in both polarized and conventional Raman spectra, indicating that phonon dynamics may not play a primary role in the superconducting mechanism in this system, or their connection is relatively weak. This work establishes a benchmark phonon database for UTe 2, laying the foundation for future exploration of phonon–electron correlation mechanisms under extreme conditions (high magnetic field/pressure).