Shapiro steps in charge-density-wave states driven by ultrasound

TL;DR

This paper demonstrates that ultrasound can induce Shapiro steps in charge-density-wave states, revealing unique coupling effects and potential for sensitive ultrasound detection.

Contribution

It introduces the novel finding that ultrasound can induce and modulate Shapiro steps in charge-density-wave systems, differing from traditional ac voltage effects.

Findings

Ultrasound induces Shapiro steps at integer multiples of frequency.

Ultrasound enhances odd multiple steps more than even ones.

Shapiro steps cause peaks in differential conductance, useful for ultrasound detection.

Abstract

We show that ultrasound can induce the Shapiro steps (SS) in the charge-density-wave (CDW) state. When ultrasound with frequency $\omega$ and a dc voltage are applied, the SS occur at the current $I$ $\propto$ $n\omega$ with integer $n$. Even and odd multiples of SS are represented by two couplings between the CDW and ultrasound. Although an ac voltage bias with frequency $\omega$ induces the SS at $I\propto n\omega$, the ultrasound bias enhances the odd multiples more strongly than the even ones. This is the difference between the ultrasound and the ac voltage. Since the SS cause abrupt peaks in the $dV/dI$, the extreme changes in the $I$-$V$ curve will be applied to a very sensitive ultrasound detector.