Shear-modulus change belowT_cin YBa₂Cu₃O_7−x

Abstract

The ultrasonic transverse-wave velocity in the high-Tc metal-oxide superconductor YBa2Cu3O7−x between 275 and 4 K was measured. Above Tc the velocity shows normal behavior: during cooling, it displays a monotonic increase with decreasing slope. During cooling below Tc the shear modulus departs from normal behavior, increasing as ΔG /G = b [1 − (T/Tc)n, where n = 3. These results depart dramatically from those expected for a simple second-order normal-superconducting phase transition.

A brief review of recent superconductivity research at NIST

“…A check on this is to compare elastic and thermal Debye characteristic temperatures. Elastic constants were measured as the specimens were cooled through the transition temperature [ 107 – 110 ]. Samples run in helium gave reproducible results suggesting that these measurements represented intrinsic material properties.…”

“…Below T C , contrary to expectation, G apparently increases. However, a reentrant-softening model reconciles this apparent anomaly [ 107 ].…”

Fracture and Deformation -- technical activities - 1988

“…Principle of probe operation. 24 Measurements of probe admittance can be made to characterize material in proximity to the probe. The admittance is the ratio of current flowing in the receiver electrodes divided by the potential difference.…”

“…Using ultrasonic methods, we determined the complete set of elastic constants, from 5 to 295 K, of several high-T c metal-oxide superconductors: Y-Ba-Cu-0, Ho-Ba-Cu-0, Eu-Ba-Cu-0 [publications [23][24][25][29][30][31]. Focusing on the yttrium oxide, we studied six specimens prepared at four laboratories.…”

Reentrant Softening in Copper-Oxide Superconductors

“…TEMPERATURE, K Figure 1 shows our low-temperature shear-modulus, G(T), measurements reported previously. 5 The discontinuity at 65 K was taken to be Tc.…”