A peculiar feature of the majority of three-dimensional topological insulator surface states studied experimentally thus far, namely their particle-hole asymmetry, makes quantum oscillations (Shubnikov-de Haas and de Haas-van Alphen oscillations) in these materials particularly rich. I show that this peculiarity can be exploited to measure the Chern number and detect topological phase transitions in topological insulator surface states from the quantum spin Hall phase to the quantum anomalous Hall phase. I consider the behavior of quantum oscillations in topological insulator thin-film surface states in the presence of a topological exciton condensate or hybridization between the two surfaces. As a function of Zeeman field, the Chern number and phase transition from a quantum spin Hall to a quantum anomalous Hall phase can be measured using standard techniques. This effect relies necessarily on the particle-hole asymmetry, which is ubiquitous in currently known materials that exhibit topological insulator surface states. 7-9 coming slightly later than ARPES, allowed complementary confirmation of the 2D nature of the surface states, as well as, it was hoped, a quantitative measurement of the Berry phase. [8][9][10][11][12][13][14][15][16] The conclusive determination of the Berry phase turned out to be unexpectedly subtle 17 and has not, to date, been accomplished. Topological insulators are characterized by their gapless surface states, which are protected from time-reversal invariant perturbations. 18,19 If time-reversal symmetry is broken, however, a gap can be opened on the surface of a topological insulator. This can be achieved through a Zeeman field or by coating the surface of the topological insulator with a ferromagnetic layer, 3 as shown in Fig. 1. The topological insulator surface then becomes a quantum anomalous Hall insulator, so named because it supports a single chiral edge state on each surface. 20 Experimental verification of this phase has proved elusive.A second gap-opening mechanism in topological insulators can occur in a thin film. The two surface states can hybridize, [21][22][23][24] or interactions between them can lead to a nonzero excitonic order parameter, 25,26 as depicted in Fig. 1. The two band gaps-one magnetic and one thin film inducedcan compete in an antibonding state of the topological insulator and add in the bonding state. In this case, a topological phase transition can occur, namely from the quantum anomalous Hall phase (QAH) to the quantum spin Hall phase (QSH).
26This topological phase transition can be quantified by the first Chern number, which is zero in the QSH phase and is 1 in the QAH phase.
27In this article, I demonstrate [see Eq. (9)] that quantum oscillation experiments can measure whether a topological insulator is in the quantum spin Hall (QSH) or quantum anomalous Hall (QAH) phase and can detect topological phase transitions between the two. Curiously, these experiments rely on the seemingly inert, yet so-far ubiquitous particlehole asymmetric spectrum of to...