Strong electron-lattice coupling and orbital fluctuations in iron pnictide superconductor Ba(Fe1-xCox)2As2

TL;DR

This study investigates the elastic properties and orbital fluctuations in Ba(Fe1-xCox)2As2, revealing complex frequency-dependent anomalies in elastic moduli related to structural transitions, with new high-frequency measurements providing more reliable data.

Contribution

The paper reports on frequency-dependent ultrasonic measurements of elastic moduli in Ba(Fe1-xCox)2As2, highlighting the importance of high-frequency data for accurate interpretation of structural anomalies.

Findings

C66 shows softening toward the structural transition temperature TS.

Anomalies in C44 and (C11-C12)/2 diminish at higher frequencies.

High-frequency measurements yield more reliable elastic data.

Abstract

This paper has been withdrawn by the author due to some experimental mistakes. In this paper, we reported that C66, C44 and (C11-C12)/2 show remarkable softening toward the structural transition temperature TS. The data reported in this paper were acquired using the ultrasonic frequency lower than 25 MHz. Recently, we performed high-frequency measurements for the same system. We found that the anomaly of C44 and (C11-C12)/2 tend to disappear rapidly with increasing the frequency. On the other hand, C66 anomaly is still there at high frequencies. Therefore, we concluded that the observed anomalies in C44 and (C11-C12)/2 are not true. They would be ascribed to certain influence by the large softening of C66. So, we have checked our data through careful measurements by using ultrasonic frequency higher than 60 MHz, so far. Then, it has been found that C66 shows still nice softening toward TS, but that its temperature dependence is slightly different from the results of this paper. We have accumulated reliable data now. They will be reported in near future.