Extracting correlation length in Mott insulators by strong-field driving

The break-down of a Mott-insulator when subjected to intense laser fields is characterized by the formation of elementary charge excitations known as doublon-hole pairs. This break-down is furthermore evidenced by the production of high harmonics that can be experimentally measured. Recently, we investigated coupling a metal to the Mott insulator in an interface environment to study the effect this had on the production of these doublon-hole pairs and the resultant high harmonics at the interface.



We found that interfacial coupling of a metal to the Mott insulator enhances high harmonic production inside the insulator and suggested an increase in the doublon-hole correlation length as the physical mechanism behind this lowered threshold for dielectric break-down. Here, we present an approach for extracting the doublon-hole correlation length of a Mott insulator to verify this hypothesis. The method is based on a dynamical calculation of the Mott insulator's rate of charge production in response to an applied strong-field laser pulse. We find that the correlation length does in fact increase drastically with increased interfacial coupling, in support of our hypothesis, which signifies the metal's role in the enhancement of charge fluctuations in the insulator.



We confirm our conclusions using Density Matrix Renormalization Group (DMRG) calculations. The proposed method further allows one to experimentally access the doublon-hole correlation length through measurable observables, such as differential reflectivity or the high harmonic generation (HHG) spectrum.