- Singer, A;
- Patel, SKK;
- Kukreja, R;
- Uhlíř, V;
- Wingert, J;
- Festersen, S;
- Zhu, D;
- Glownia, JM;
- Lemke, HT;
- Nelson, S;
- Kozina, M;
- Rossnagel, K;
- Bauer, M;
- Murphy, BM;
- Magnussen, OM;
- Fullerton, EE;
- Shpyrko, OG
Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing an efficient mechanism to selectively transform a broad excitation of the electronic order into a well-defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance order parameters in other systems with coupled degrees of freedom.