Energy gaps in the failed high-Tc superconductor La1:875Ba0:125CuO4

A central issue in high-T-c superconductivity is the nature of the normal-state gap (pseudogap) 1 in the underdoped regime and its relationship with superconductivity. Despite persistent efforts, theoretical ideas for the pseudogap evolve around fluctuating superconductivity(2), competing order(3-8) and spectral weight suppression due to many-body effects(9). Recently, although some experiments in the superconducting state indicate a distinction between the superconducting gap and pseudogap(10-14), others in the normal state, either by extrapolation from high-temperature data(15) or directly from La1:875Ba0:125CuO4 (LBCO-1/8) at low temperature(16), suggest the ground-state pseudogap is a single gap of d-wave(17) form. Here, we report angle-resolved photoemission data from LBCO-1=8, collected with improved experimental conditions, that reveal the ground-state pseudogap has a pronounced deviation from the simple d-wave form. It contains two distinct components: a d-wave component within an extended region around the node and the other abruptly enhanced close to the antinode, pointing to a dual nature of the pseudogap in this failed high-T-c superconductor that involves a possible precursor-pairing energy scale around the node and another of different but unknown origin near the antinode.