Discovery of Light-induced Metastable Martensitic Anomaly Controlled by Single-Cycle Terahertz Pulses

TL;DR

This study demonstrates that single-cycle terahertz pulses can induce a long-lived, non-thermal Martensitic phase in Nb$_3$Sn, significantly exceeding equilibrium stability temperatures through ultrafast, light-driven structural control.

Contribution

It reveals a novel non-thermal, light-induced phase transition mechanism in Nb$_3$Sn driven by terahertz pulses, extending the stability of the Martensitic phase beyond traditional limits.

Findings

Terahertz pulses induce a long-lived Martensitic anomaly in Nb$_3$Sn.

Light-induced phase persists up to ~100 K, over twice the equilibrium temperature.

First-principle simulations link structural fluctuations to THz-driven phonon modes.

Abstract

We report on an ultrafast photoinduced phase transition with a strikingly long-lived Martensitic anomaly driven by above-threshold single-cycle terahertz (THz) pulses in Nb$_3$Sn. A non-thermal, THz-induced depletion of low frequency conductivity indicates increased gap splitting of high energy $\Gamma_{12}$ bands by removal of their degeneracies which enhances the Martensitic phase. In contrast, optical pumping leads to a $\Gamma_{12}$ gap melting. Such light-induced non-equilibrium Martensitic instability persists up to a critical temperature $\sim$100 K, i.e., more than twice the equilibrium temperature, and can be stabilized beyond technologically-relevant, nanosecond timescales. Together with first-principle simulations, we identify a compelling THz tuning of structural fluctuations via E$_u$ phonons to achieve a non-equilibrium ordering at high temperatures far exceeding those for equilibrium states.