Composite fermion liquid at Landau level filling factor 1/2: Bloch ferromagnetism, Luttinger theorem, and particle-hole symmetry*

The ground state of a dilute, two-dimensional electron system has been a topic of intense theoretical and experimental speculation, because the physics here is governed by strong correlations. Back in 1929, Felix Bloch proposed a fully spin-polarized ground state for a low-density fermionic system which is historically the first predicted quantum many-body phase. However, this state eluded experimental realization for the last nine decades. In the first part of my talk, I will present an experimental realization of the elusive interaction-driven spin polarization in a system of unusual suspects, namely composite fermions (CFs). CFs are quasiparticles, each composed of an electron and two flux quanta, formed in the half-filled Landau level of a two-dimensional electron system. As the density of CFs is lowered, the CFs become strongly interacting and make a sudden transition into a ferromagnetic state, which we probe directly via measuring the CF Fermi sea [1]. In the second part, I will discuss the nature of the CF Fermi sea in the presence of strong CF-CF interaction. In particular, the applicability of the Luttinger theorem for the Fermi sea area and particle-hole symmetry will be highlighted [2].

In collaboration with T. Zhao, S. Pu, M. A. Mueed, M. K. Ma, K. A. V. Rosales, Y. J. Chung, L. N. Pfeiffer, K. W. West, K. W. Baldwin, J. K. Jain, and M. Shayegan.

References:

1. Md. S. Hossain et al., Bloch ferromagnetism of composite fermions, Nat. Phys. 17, 48 (2021).

2. Md. S. Hossain et al., Precise experimental test of the Luttinger theorem and particle-hole symmetry for a strongly correlated fermionic system, Phys. Rev. Lett. 125, 046601 (2020).