This paper proposes 0-1-A-Ā LUT, a new programmable logic using atom switches, and a delay-optimal mapping algorithm for it. Atom switch is a non-volatile memory device of very small geometry which is fabricated between metal layers of a VLSI, and it can be used as a switch device of very small on-resistance and parasitic capacitance. While considerable area reduction of Look Up Tables (LUTs) used in conventional Field Programmable Gate Arrays (FPGAs) has been achieved by simply replacing each SRAM element with a memory element using a pair of atom switches, our 0-1-A-Ā LUT achieves further area and delay reduction. Unlike the conventional atom-switch-based LUT in which all k input signals are fed to a MUX, one of input signals is fed to the switch array, resulting area reduction due to the reduced number of inputs of the MUX from 2^k to 2^k-1, as well as delay reduction due to reduced fanout load of the input buffers. Since the fanout of this input buffers depends on the mapped logic function, this paper also proposes technology mapping algorithms to select logic function of fewer number of fanouts of input buffers to achieve further delay reduction. From our experiments, the circuit delay using our k-LUT is 0.94% smaller in the best case compared with using the conventional atom-switch-based k-LUT.