Measuring Dislocation Density in Aluminum with Resonant Ultrasound Spectroscopy

Dislocations in a material will, when present in enough numbers, change the speed of propagation of elastic waves. Consequently, two material samples, differing only in dislocation density, will have different elastic constants, a quantity that can be measured using Resonant Ultrasound Spectroscopy. Measurements of this effect on aluminum samples are reported. They compare well with the predictions of the theory.Comment: 4 pages, 2 figure

Elastic Tensor of YNi_2B_2C

The complete elastic tensor of YNi_2B_2C was determined by application of the resonant ultrasound spectroscopy technique to a single-crystal sample. Elastic constants were found to be in good agreement with partial results obtained from `time-of-flight' measurements performed on samples cut from the same ingot. From the measured constants, the bulk modulus and Debye temperature are calculated.Comment: 5 pages, 3 figure

One-Component Order Parameter in URu2_2Si2_2 Uncovered by Resonant Ultrasound Spectroscopy and Machine Learning

The unusual correlated state that emerges in URu$_2$Si$_2$ below T$_{HO}$ = 17.5 K is known as "hidden order" because even basic characteristics of the order parameter, such as its dimensionality (whether it has one component or two), are "hidden". We use resonant ultrasound spectroscopy to measure the symmetry-resolved elastic anomalies across T$_{HO}$. We observe no anomalies in the shear elastic moduli, providing strong thermodynamic evidence for a one-component order parameter. We develop a machine learning framework that reaches this conclusion directly from the raw data, even in a crystal that is too small for traditional resonant ultrasound. Our result rules out a broad class of theories of hidden order based on two-component order parameters, and constrains the nature of the fluctuations from which unconventional superconductivity emerges at lower temperature. Our machine learning framework is a powerful new tool for classifying the ubiquitous competing orders in correlated electron systems

Elastic and thermodynamic properties of the shape-memory alloy AuZn

The current work reports on the elastic shear moduli, internal friction, and the specific heat of the B2 cubic ordered alloy AuZn as a function of temperature. Measurements were made on single-crystal and polycrystalline samples using Resonant Ultrasound Spectroscopy (RUS), semi-adiabatic calorimetry and stress-strain measurements. Our results confirm that this alloy exhibits the shape-memory effect and a phase transition at 64.75 K that appears to be continuous (second-order) from the specific heat data. It is argued that the combination of equiatomic composition and a low transformation temperature constrain the chemical potential and its derivatives to exhibit behavior that lies at the borderline between that of a first-order (discontinuous) and a continuous phase transition. The acoustic dissipation does not peak at the transtion temperature as expected, but shows a maximum well into the low-temperature phase. The Debye temeprature value of 219 K, obtained from the low-temperature specific heat data is in favorable agreement with that determined from the acoustic data (207 K) above the transition.Comment: 25 pages, 6 figures, submitted to Phys. Rev.

High magnetic field thermal-expansion and elastic properties of CeRhIn5_5

We report high magnetic field thermal-expansion and magnetostriction results on CeRhIn$_5$ single crystals. Several transitions, both first and second order, are observed when the field is applied perpendicular to the crystallographic c-axis. The magnetic field dependence of the thermal-expansion coefficient above 15 K, where the magnetic correlations are negligible, can be explained supposing an almost pure $| \pm 5/2>$ ground state doublet, in apparent contradiction with neutron scattering experiments. Although the spin-lattice interaction is relevant in this compound, the effect of the magnetic correlations on the elastic properties is relatively weak, as revealed by resonant ultrasound spectroscopy experiments.Comment: 5 pages, 6 figure

Elastic Tensor of Sr2_2RuO4_4

The six independent elastic constants of Sr$_2$RuO$_4$ were determined using resonant ultrasound spectroscopy on a high-quality single-crystal specimen. The constants are in excellent agreement with those obtained from pulse-echo experiments performed on a sample cut from the same ingot. A calculation of the Debye temperature using the measured constants agrees well with values obtained from both specific heat and M\"{o}ssbauer measurements.Comment: 4 pages, 2 figures, 2 tables, submitted to PR