Microscopic observation of thes→dtransition in metallic cesium under high pressure

Using the ¹³²Cs high-pressure M\"ossbauer effect technique, we were able for the first time to investigate on a microscopic level the pressure effects on the electronic charge densities and lattice dynamics in metallic cesium. A quantitative analysis of the experimental results reveals direct evidence for a gradual pressure-induced 6s{→}5d electronic transition in metallic cesium in agreement with band structure calculations. From the pressure-induced change of the Debye-Waller factor at 4.2 K, we obtain a new value of the Debye temperature θD for metallic Cs of 64(2) K at p=6 GPa (V/V₀=0.33).