Combined impact of resonance bond engineering and Peierls distortion on electronic density of states in bulk Ge₂Sb₂Te_(5-5x)Se_{5x p}phase change materials

We report studies on bulk Ge₂Sb₂Te_(5-5x)Se_5x (GSST) phase change material (PCM) single crystals, where x represents the amount of Selenium (Se) substituting Tellurium (Te) in Ge₂Sb₂Te₅. Using results from photoemission spectroscopy, x-ray diffraction and Raman scattering experiments together with numerical simulations. we explore tunability of resonance bonding (RB) and its impact on the electronic structure of GSST in the crystalline phase. We present direct evidence for (i) finite electronic density of states (DOS) at the chemical potential for all measured x as expected in the crystalline phase, and (ii) an unusual suppression in the DOS with increasing x over an energy range comparable to the entire valence band. Using numerical works, we show that these observations can naturally be interpreted by a gradual weakening of resonance bonding accompanied by an enhancement in Peierls-type distortion with increasing substitution of Te by Se, which is counterintuitive since the modification in RB of a PCM is commonly perceived to occur during crystal to amorphous transition.