Giant Paramagnetism-Induced Valley Polarization of Electrons in Charge-Tunable Monolayer MoSe2

Abstract

For applications exploiting the valley pseudospin degree of freedom in transition metal dichalcogenide monolayers, efficient preparation of electrons or holes in a single valley is essential. Here, we show that a magnetic field of 7 Tesla leads to a nearcomplete valley polarization of electrons in MoSe 2 monolayer with a density 1.6 × 10 12 cm −2 ; in the absence of exchange interactions favoring single-valley occupancy, a similar degree of valley polarization would have required a pseudospin g-factor exceeding 40. To investigate the magnetic response, we use polarization resolved photoluminescence as well as resonant reflection measurements. In the latter, we observe gate voltage dependent transfer of oscillator strength from the exciton to the attractiveFermi-polaron: stark differences in the spectrum of the two light helicities provide a confirmation of valley polarization. Our findings suggest an interaction induced giant paramagnetic response of MoSe 2 , which paves the way for valleytronics applications. Hall effect [10,11] as well as a modification of the exciton spectrum [12,13]. Investigation of one of the most interesting features of this material system, namely the valley pseudospin degree of freedom [14,15], has been hampered by the difficulty in obtaining a high-degree of valley polarization of free electrons or holes [16]. While circularly polarized excitation ensures that the excitons are generated in a single valley [17][18][19], significant transfer of valley polarization from excitons to itinerant electrons or holes has not been observed.Here, we report a strong paramagnetic response of a two dimensional electron system (2DES) in a charge-tunable monolayer MoSe 2 sandwiched between two hexagonal boron-nitride (hBN) layers (Fig. 1A). Figure 1B shows the corresponding single-particle energy-band diagram when an external arXiv:1701.01964v1 [cond-mat.mes-hall]

Enhanced Valley Zeeman Splitting in Fe-Doped Monolayer MoS2

“…8 Therefore, the possibility of electron doping leading to the increase in g eff factor is ruled out. 8,18,19,43 We also measured Zeeman-type spin splitting of defect emission in monolayer MoS 2 (see Supplementary Information Fig. S8c-f).…”

Realization of an Electrically Tunable Narrow-Bandwidth Atomically Thin Mirror Using MonolayerMoSe2

“…3(b)]. Even though the optical response of the attractive polaron is relatively modest, its strong dependence on the valley polarization of electrons and its large g factor exceeding 15 [25] Figure 3(c) shows the dependence of maximal extinction (black dots) and the corresponding linewidth (red squares) for several values of the transmission path NA, close to the same spot we used to obtain the data depicted in Fig. 2(b).…”

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

“…Our measurements suggest that the neutral exciton g factor of MoS 2 MLs might be intrinsically smaller (in magnitude) than for diselenide MLs and is different from the commonly observed value g X ≈ −4 [43][44][45]47,48]. Variations in the measured neutral exciton g factor can have different reasons: (i) different strain in CVD-grown MLs as compared to encapsulated monolayers may play a role, (ii) comparing g factors in samples of different origin with different electron concentrations is difficult due to the possible impact of many-body interactions [10,85,86], (iii) eventually, in unprotected samples with considerably broader linewidth, magnetoreflectivity may provide a g factor that is an average of exciton and trion g factors.…”

“…The g factor, closely related to the effective mass tensor, also gives a fingerprint of the impact of different bands on the optical transitions [45,48,84]. In addition, spectacular effects are expected for monolayers with tunable electron density, where the evolution of the valley polarization and the valley Zeeman splitting has been interpreted in terms of a Fermi-polaron model for excitonic transitions; i.e., the simple definitions of neutral exciton and trion are replaced by the attractive and repulsive polaron [10,85,86].…”