Spin effects in the nu_T = 1 bilayer system

P. GIUDICI; K. MURAKI; N. KUMADA

Sapporo

Encuentro; Autumn meeting of the Japanese physical society; 2007

One major issue involved in the quantum Hall (QH) bilayer system at totalfilling factor nu_T = 1 [1] is the nature of its phase transition between the QH andcompressible states that occurs as a function of the interlayer coupling d/l_B [2](with d and l_B the interlayer distance and the magnetic length, respectively).Applying an in-plane field B in the regime of negligible tunneling we demonstratethat, contrary to the common belief, the phase boundary strongly depends on thespin degree of freedom. As B = B_TOT*sin(µ) is applied (by tilting the sampleby an angle µ away from the external field B_TOT) we observe that the phaseboundary to the compressible state largely shifts towards higher values of d/l_B,from d/l_B = 1.90 at B_TOT = 3 T (B = 0) until it saturates at d/l_B = 2.33 forB_TOT = 8 T. Using a simple analytic model considering the Coulomb and Zeemanenergies of the competing phases, we can quantitatively describe our results andestablish a new phase diagram including spin degree of freedom. The excellentagreement between the model and experiment confirms that the increased Zeemanenergy makes the partially polarized compressible state energetically unfavorable,moving the boundary to higher values of d/l_B; the saturation at B_TOT = 8 Tcorresponds to the full polarization of the compressible state. Our results clearlydemonstrate that the interpretations of previous experiments on nu_T = 1 bilayersystem reported heretofore, including the standard d/l_B vs Delta_SAS phase diagram,must be modified to incorporate the spin effects. In the presentation, its profoundimplications as to the nature of the phase transition will be discussed.[1] S. M. Girvin and A. H. MacDonald, Perspectives in Quantum Hall E®ects (Wiley, New York, 1997), edited by A. Pinczuk and S. Das Sarma.[2] S. Q. Murphy et al., Phys. Rev. Lett. 72, 728 (1994).