Temperature-dependent ultrasonic study on parity-violating phase transitions of d- and l-alanine single crystals

Abstract

Ultrasonic technology was utilized to probe the molecular parity violation on phase transitions of alanine enantiomers. Temperature-dependent longitudinal ultrasonic attenuation and velocity were measured in D- and L-alanine single crystals in the range of 200 K to 290 K. The D-alanine crystal showed a reversible second-order phase transition at 247 K, which was accompanied by a pronounced attenuation peak during both heating and cooling. The L-alanine crystal had a step-like attenuation transition also around 247 K, with a thermal hysteresis. Based on the established obvious difference of electron and nucleus spin properties between alanine enantiomers during the phase transition processes, which were unraveled by temperature dependent DC-magnetic susceptibility and ¹H CRAMPS ssNMR spectra experiments, spin-phonon coupling is proposed to account for the different ultrasonic velocity and attenuation behaviors between D- and L-alanine crystals near the transition temperature. The present ultrasonic study will mutually support and further correlate itself with previously conducted magnetic susceptibility and ssNMR spectra measurements in the perspective of both electron and nucleus spin properties of enantiomers.