The mystery of the alkali metals; the induced anomalous Hall effect in thin Cs films

Sandwiches made from Fe and Cs films are investigated as a function of the magnetic field and the Cs thickness. Conduction electrons which cross from the Fe to the Cs are marked by a drift velocity component perpendicular to the electric field. The anomalous Hall effect in the Fe provides this "non-diagonal" kick to the electrons that cross from the Fe into the Cs. The ballistic propagation of the conduction electrons can be monitored as a function of the Cs film thickness. The free propagation into the Cs is measured in terms of the non-diagonal conductance L-xy which we denote as the "induced anomalous Hall conductance" L-xy(0). For a normal (non-magnetic) metal in contact with Fe, L-xy increases with the thickness of the normal metal until the film thickness exceeds (half) the mean free path of the conduction electrons. For Cs on top of Fe the induced anomalous Hall conductance increases up to a Cs coverage of about 100 A, then, in contrast to other non-magnetic metals, L-xy(0) decreases for larger Cs coverage and approaches zero. This behavior cannot be explained with the free electron model. The strange behavior of the induced AHC in Cs films adds an even more challenging mystery to the already poorly understood properties of thin Cs films. These results defy explanation in the free electron model.