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arXiv · 2204.08638

Possible quadrupole-order-driven commensurate-incommensurate phase transition in B20 CoGe

S. -H. Baek·V. A. Sidorov·A. V. Nikolaev·T. Klimczuk·F. Ronning·A. V. Tsvyashchenko
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Abstract

The B20-type cobalt germanide CoGe was investigated by measuring the specific heat, resistivity, and $^{59}$Co nuclear magnetic resonance (NMR). We observed a phase transition at $T_Q=13.7$ K, evidenced by a very narrow peak of the specific heat and sharp changes of the nuclear spin-spin ($T_2^{-1}$) and spin-lattice ($T_1^{-1}$) relaxation rates. The fact that the entropy release is extremely small and the Knight shift is almost independent of temperature down to low temperatures as anticipated in a paramagnetic metal indicates that the $T_Q$ transition is of non-magnetic origin. In addition, we detected a crossover scale $T_0\sim30$ K below which the resistivity and the NMR linewidth increase, and $T_1^{-1}$ is progressively distributed in space, that is, a static and dynamical spatial inhomogeneity develops. While the order parameter for the $T_Q$ transition remains an open question, a group-theoretical analysis suggests that the finite electric quadrupole density arising from the low local site symmetry at cobalt sites could drive the crystal symmetry lowering from the P2$_1$3 symmetry that is commensurate to the R3 symmetry with an incommensurate wavevector, which fairly well accounts for the $T_Q$ transition. The quadrupole-order-driven commensurate-incommensurate phase transition may be another remarkable phenomenon arising from the structural chirality inherent in the noncentrosymmetric B20 family.

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S. -H. Baek, V. A. Sidorov, A. V. Nikolaev, T. Klimczuk, F. Ronning, A. V. Tsvyashchenko. 2022-04-19. Possible quadrupole-order-driven commensurate-incommensurate phase transition in B20 CoGe. https://doi.org/10.1103/physrevb.105.165132

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