Valley Zeeman Splitting and Valley Polarization of Neutral and Charged Excitons in Monolayer MoTe₂ at High Magnetic Fields

Semiconducting transition metal dichalcogenides (TMDCs) give rise to interesting new phenomena in external magnetic fields, such as valley Zeeman splitting and magnetic-field-induced valley polarization. These effects have been reported for monolayers (MLs) of the transition metal diselenides MoSe₂ and WSe₂ and, more recently, for disulfides MoS₂ and WS₂. Here, we present helicity-resolved magneto-photoluminescence and magneto-reflectance contrast measurements for MLs of the telluride member of the semiconducting TMDCs, 2H-MoTe₂, in magnetic fields up to 29 T in Faraday geometry. Well-resolved valley Zeeman splittings for the neutral A and B excitons (X_A⁰ and X_B⁰) and the charged exciton X^± are observed with effective g-factors of −4.6 ± 0.2, – 3.8 ± 0.6, and −4.5 ± 0.3, respectively. The magnetic field induced valley polarization of X_A⁰ and X^± reaches 78% and 36%, respectively, at a magnetic field of 29 T

High-Angular Momentum Excitations in Collinear Antiferromagnet FePS₃

We report on magneto-optical studies of the quasi-two-dimensional van der Waals antiferromagnet FePS3. Our measurements reveal an excitation that closely resembles the antiferromagnetic resonance mode typical of easy-axis antiferromagnets; nevertheless, it displays an unusual, four-times larger Zeeman splitting in an applied magnetic field. We identify this excitation with an |Sz| = 4 multipolar magnona single-ion 4-magnon bound statethat corresponds to a full reversal of a single magnetic moment of the Fe2+ ion. We argue that condensation of multipolar magnons in large-spin materials with a strong magnetic anisotropy can produce new exotic states

Electrical Switch to the Resonant Magneto-Phonon Effect in Graphene

We report a comprehensive study of the tuning with electric fields of the resonant magneto-exciton optical phonon coupling in gated graphene. For magnetic fields around <i>B</i> ∼ 25 T that correspond to the range of the fundamental magneto-phonon resonance, the electron–phonon coupling can be switched on and off by tuning the position of the Fermi level in order to Pauli block the two fundamental inter-Landau level excitations. The effects of such a profound change in the electronic excitation spectrum are traced through investigations of the optical phonon response in polarization resolved magneto-Raman scattering experiments. We report on the observation of a splitting of the phonon feature with satellite peaks developing at particular values of the Landau level filling factor on the low or on the high energy side of the phonon, depending on the relative energy of the discrete electronic excitation and of the optical phonon. Shifts of the phonon energy as large as ±60 cm^–1 are observed close to the resonance. The intraband electronic excitation, the cyclotron resonance, is shown to play a relevant role in the observed spectral evolution of the phonon response

Le Grand écho du Nord de la France

16 janvier 19091909/01/16 (A91,N16).Appartient à l’ensemble documentaire : NordPdeC

Crystal-Phase Quantum Wires: One-Dimensional Heterostructures with Atomically Flat Interfaces

In semiconductor quantum-wire heterostructures, interface roughness leads to exciton localization and to a radiative decay rate much smaller than that expected for structures with flat interfaces. Here, we uncover the electronic and optical properties of the one-dimensional extended defects that form at the intersection between stacking faults and inversion domain boundaries in GaN nanowires. We show that they act as crystal-phase quantum wires, a novel one-dimensional quantum system with atomically flat interfaces. These quantum wires efficiently capture excitons whose radiative decay gives rise to an optical doublet at 3.36 eV at 4.2 K. The binding energy of excitons confined in crystal-phase quantum wires is measured to be more than twice larger than that of the bulk. As a result of their unprecedented interface quality, these crystal-phase quantum wires constitute a model system for the study of one-dimensional excitons

Observation of a Biexciton Wigner Molecule by Fractional Optical Aharonov-Bohm Oscillations in a Single Quantum Ring

The Aharonov-Bohm effect in ring structures in the presence of electronic correlation and disorder is an open issue. We report novel oscillations of a strongly correlated exciton pair, similar to a Wigner molecule, in a single nanoquantum ring, where the emission energy changes abruptly at the transition magnetic field with a fractional oscillation period compared to that of the exciton, a so-called fractional optical Aharonov-Bohm oscillation. We have also observed modulated optical Aharonov-Bohm oscillations of an electron–hole pair and an anticrossing of the photoluminescence spectrum at the transition magnetic field, which are associated with disorder effects such as localization, built-in electric field, and impurities