The Effect of Interband Excitations on Time-Resolved Two-Photon Photoemission via a Localized State at a Metal Surface

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The effect of' interband excitations on tiune-resolved two-plaoton photoeraaission from anadsorbate-strrf'ace systen? is investigated. The systeuaa is asstruaaed to be co?aaposed of two stub-bands in the btrlk and a localized state of the adsorbate, xvhicl'x is in resonance xvith the trpperenergy strbband. In the txvo-jchoton photoetnission process, first, an electron in tlae lower energysubbazud is excited into the Iocatlized state by the PLIIIIP photon, and strbseqtrently excited abovethe V&CVlLll11 level by the probe photon, The first excitation can be divided into two processes,i.e., the direct and tlae indirect one inxzolx'ing the interl*and excitatiora. The excitation probabilitydtre to the latter process reaches a tnaxinatrun at a certaita photon energy because of tnonaenttrnaconservation. A two-photon photoermission spectrtrrta slaows a peak dtre to the indirect process atan energy position where the initial state is fixed, as well as one dtre to the direct process xvherethe interuaaediate state is fixed. The taaaxitaatrrn of' the cross-correlation trace of' the purnp andprobe ptrlses (the ptrraap-probe delay dependence of the photoelectron intensity) at the formerpeak shows little shift coraupared to that at tlae latter otae. The intensity of the peak dtre to their'xdirect process increases as the ptrlse dtrration is decreased.
社団法人日本物理学会の論文
1998-06-15