Single-layer semiconducting transition-metal dichalcogenides (TMDs), lacking point inversion symmetry, provide an efficient platform for valleytronics, where the electronic, magnetic, valley and lattice degrees of freedom can be selectively manipulated by using polarized light. This task is however thought to be limited in parent bulk compounds where the point inversion symmetry is restored. Exploiting the underlying quantum physics in bulk materials is thus one of the biggest paradigmatic challenges.
Here we show that a sizable optical Kerr rotation can be efficiently generated in a wide energy range on ultrafast timescales in bulk WSe2, by means of circularly-polarized light. We rationalize these findings as a result of the hidden spin/layer/valley quantum entanglement. The spectral analysis reveals clear features at the three characteristic frequencies corresponding to the A-, B- and C-exciton edges. The origin and the relative sign of all these features is shown to stem from the selective Pauli blocking of intralayer and interlayer optical transitions. The long lifetime of the broadband Kerr response (~500 fs) provides a strong indication that coupled photo-induced electron and hole densities survive in bulk compounds longer than previously expected. The present report demonstrates that a hidden quantum entanglement is operative also in bulk centrosymmetric layered materials, opening the way for an effective exploitation of bulk WSe2 in optoelectronic applications.

Emmanuele Cappelluti, got the Degree in Physics at University La Sapienza, of Rome (Italy) in 1996, and the Ph.D. in Physics at Max-Planck-Institut FKF, Stuttgart (Germany) in 1999.
After the Ph.D. studies he came back to Italy where he got a research position in 2004.
He also spent two-years at ICMM-CSIC in Madrid (Spain).