Possible precursor phenomenon to superconducting transition in niobium: Anomalous behavior of shear modulus at low temperatures

Abstract

Niobium is an important superconducting element widely used in many applications. There is a long history of interest in the microscopic origins of superconducting mechanism of this material. However, the precise prediction of material specific properties of superconductors including niobium still remains one of the great challenges of modern condensed matter physics. One of the obstacles that limit us in calculating, for example, superconducting transition temperature is the lack of enough knowledge of materials in the normal state. Here the author shows experimental evidence for a precursor phenomenon to superconducting transition in niobium. The temperature variation of the tetragonal shear modulus C′=(C11−C12)∕2, of a single-crystal niobium in the normally conducting state under a strong magnetic field and at ambient pressure was measured by a contact-free ultrasonic method. Anomalous decrease in C′, just a few degrees above the known superconducting transition temperature Tc9.26K, was observed and it continued to decrease down to 4.22K, contrary to the usual tendency of the temperature variation of the elastic constants of metals, an increase with the decreasing temperature. No such anomalous decrease in elastic constants of normally conducting metallic elements at low temperatures and at ambient pressure have been observed until now. Since C′ is a key factor in explaining the structural instability which is related to the strength of the electron-phonon coupling and the occurrence of high-Tc, it can be considered that the start of decrease in C′ just a few degrees above the Tc, is a precursor phenomenon to superconducting transition in niobium.

Source-reported materials — not catalogue approval

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