title: Breaking of valley degeneracy by magnetic field in monolayer MoSe2.
abstract: Using polarization-resolved photoluminescence spectroscopy, we investigate the breaking of valley degeneracy by an out-of-plane magnetic field in back-gated monolayer MoSe2 devices. We observe a linear splitting of -0.22  meV/T between luminescence peak energies in σ+ and σ- emission for both neutral and charged excitons. The optical selection rules of monolayer MoSe2 couple the photon handedness to the exciton valley degree of freedom; so this splitting demonstrates valley degeneracy breaking. In addition, we find that the luminescence handedness can be controlled with a magnetic field to a degree that depends on the back-gate voltage. An applied magnetic field, therefore, provides effective strategies for control over the valley degree of freedom.
authors: Department of Physics, Cornell University, Ithaca, New York 14853, USA.
authors: David
authors: D
authors: MacNeill
authors: Department of Physics, Cornell University, Ithaca, New York 14853, USA.
authors: Colin
authors: C
authors: Heikes
authors: Department of Physics, Cornell University, Ithaca, New York 14853, USA and Kavli Institute at Cornell, Cornell University, Ithaca, New York 14853, USA.
authors: Kin Fai
authors: KF
authors: Mak
authors: Department of Physics, Cornell University, Ithaca, New York 14853, USA.
authors: Zachary
authors: Z
authors: Anderson
authors: Department of Physics, University of Konstanz, D-78464 Konstanz, Germany.
authors: Andor
authors: A
authors: Kormányos
authors: Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom.
authors: Viktor
authors: V
authors: Zólyomi
authors: Kavli Institute at Cornell, Cornell University, Ithaca, New York 14853, USA and Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.
authors: Jiwoong
authors: J
authors: Park
authors: Department of Physics, Cornell University, Ithaca, New York 14853, USA and Kavli Institute at Cornell, Cornell University, Ithaca, New York 14853, USA.
authors: Daniel C
authors: DC
authors: Ralph