Present models of the superconducting-to-normal transition in transition-edgesensors (TESs) do not describe the current distribution within a biased TES.This distribution is complicated by normal-metal features that are integral toTES design. We present a model with one free parameter that describes theevolution of the current distribution with bias. To probe the currentdistribution experimentally, we fabricated TES devices with different currentreturn geometries. Devices where the current return geometry mirrors currentflow within the device have sharper transitions, thus allowing for a directtest of the current-flow model. Measurements from these devices show thatcurrent meanders through a TES low in the resistive transition but flows acrossthe normal-metal features by 40% of the normal-state resistance. Comparison oftransition sharpness between device designs reveals that self-induced magneticfields play an important role in determining the width of the superconductingtransition. [http://dx.doi.org/10.1063/1.4771984]
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