A.I. Bezuglyj and S.I. Shevchenko, Order parameter phase locking as a cause of a zero bias peak in the differential tunneling conductance of bilayers with electron-hole pairing, Low Temp. Phys. 30, (2004) [Fiz. Nizk. Temp. 30, 282-288, (2004)] DOI: https://doi.org/10.1063/1.1645179.