Experimental Evidence of the Existence of a Nonstationary Coherent Crystal State in Bismuth

The excitation of a bismuth (Bi) crystal by intense ultrashort laser pulses at liquid-helium temperature leads to consistent motion of atoms and variations in the electron density. At various time instants over an interval reaching several dosen picoseconds, atoms in the Bi lattice exhibit sequential pairing in the real and reciprocal spaces. This behavior may correspond to the formation of a coherent crystal-a special state of matter that combines the properties of a solid and quantum fluid. Experimental data showing evidence of the possible existence of this unusual state are presented and analyzed.