Contactless pulsed tunneling spectroscopy of exciton superfluid phase in a quantum Hall bilayer*

A quantum Hall (QH) bilayer with sufficiently small interlayer separation d is predicted to host an exciton superfluid phase. Here, we use a contactless pulsed tunneling technique to search for novel superfluid properties of the QH bilayer. As our method does not require ohmic contacts to the layers, it permits access the entire range of density imbalances (Δν) at a total filling factor ν_T = 1. At a small magnetic field (d/l_B = 1.49), zero-bias interlayer tunneling is maximized at Δν = 0 and is consistent with prior DC tunneling measurements. On the other hand, at a larger magnetic field (d/l_B = 1.82), we observe the maximum of zero-bias tunneling near a full density imbalance Δν = 1. The observed behavior near Δν = 1 contradicts the simple theoretical expectation, based on the pseudospin stiffness going to zero, that the system would evolve into a trivial ν = 1 QH-state in one layer. In addition to the full density imbalance dependence, future pulse tunneling measurements can reveal high-frequency dynamical response of the exciton superfluid phase.