Thermopower and the Fractional Quantized Hall Effect in the N=1 Landau Level

Having recently eliminated an issue involving long thermal time constants [1], we are now able to resolve diffusion thermopower deep into the fractional quantized Hall effect (FQHE) regime. In this talk we report measurements of thermopower in the first excited (N=1) Landau level as a continuous function of magnetic field down to temperatures as low as 30mK. Above 50mK we can clearly resolve the $\nu$ = 5/2 as well as $\nu$ = 7/3, 8/3, and 14/5 FQHEs in both the electrical and thermoelectrical transport. Below 50mK a prominent feature of the electrical transport in the first excited Landau level is the Re-entrant Integer Quantized Hall Effect (RIQHE) which is associated with insulating collective phases [2]. In this temperature regime the thermopower exhibits a series of intriguing sign reversals that are as yet not fully understood. We will conclude with a brief discussion of the connection between thermopower and the entropy of the 2D electron system. This connection is invoked by a recent prediction [3] of the thermopower at $\nu$ = 5/2, which assumes the ground state is the non-Abelian Moore-Read paired composite fermion state.\\[4pt] [1] Chickering, Phys. Rev. B 81, 245319 (2010)\\[0pt] [2] Eisenstein, Phys. Rev. Lett. 88, 076801 (2002)\\[0pt] [3] Yang, Phys. Rev. B 79, 115317 (2009)