Observation of Magnetic Proximity Effect Using Resonant Optical Spectroscopy of an Electrically Tunable ${\mathrm{MoSe}}_{2}/{\mathrm{CrBr}}_{3}$ Heterostructure

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Observation of Magnetic Proximity Effect Using Resonant Optical Spectroscopy of an Electrically Tunable ${MoSe}_{2} / {CrBr}_{3}$ Heterostructure

Livio Ciorciaro, Martin Kroner, Kenji Watanabe, Takashi Taniguchi, and Atac Imamoglu

Phys. Rev. Lett. 124, 197401 – Published 14 May 2020; Erratum Phys. Rev. Lett. 130, 019901 (2023)

Abstract

van der Waals heterostructures combining two-dimensional magnetic and semiconducting layers constitute a promising platform for interfacing magnetism, electronics, and optics. Here, we use resonant optical reflection spectroscopy to observe the magnetic proximity effect in a gate-tunable ${MoSe}_{2} / {CrBr}_{3}$ heterostructure. The high quality of the interface leads to a giant zero-field splitting of the $K$ and $K^{'}$ valley excitons in ${MoSe}_{2}$ , equivalent to an external magnetic field of 12 T, with a weak but distinct electric field dependence that hints at potential for electrical control of magnetization. The magnetic proximity effect allows us to use resonant optical spectroscopy to fully characterize the ${CrBr}_{3}$ magnet, determining the easy-axis coercive field, the magnetic anisotropy energy, and critical exponents associated with spin susceptibility and magnetization.

Received 6 February 2020
Accepted 9 April 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.197401

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Excitons Magnetic interactions Magnetic phase transitions Magnetism

Transition metal dichalcogenides

Magneto-optical Kerr effect Photoluminescence Reflectivity

Condensed Matter, Materials & Applied Physics

Erratum

Erratum: Observation of Magnetic Proximity Effect Using Resonant Optical Spectroscopy of an Electrically Tunable ${MoSe}_{2} / {CrBr}_{3}$ Heterostructure [Phys. Rev. Lett. 124, 197401 (2020)]

Livio Ciorciaro, Martin Kroner, Kenji Watanabe, Takashi Taniguchi, and Atac Imamoglu

Phys. Rev. Lett. 130, 019901 (2023)

Authors & Affiliations

Livio Ciorciaro ^1,*, Martin Kroner ¹, Kenji Watanabe ², Takashi Taniguchi², and Atac Imamoglu ¹

¹Institut für Quantenelektronik, ETH Zürich, Auguste-Piccard-Hof 1, 8093 Zürich, Switzerland
²National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan

^*livioc@phys.ethz.ch

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Vol. 124, Iss. 19 — 15 May 2020

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Figure 1
(a) Schematic of the layer structure of the device and electrical connectivity. A bilayer ${CrBr}_{3}$ and monolayer ${MoSe}_{2}$ are encapsulated in $h − BN$ . Monolayer graphene flakes are used as top and bottom gates and as contact to ${MoSe}_{2}$ . The stack is placed on a transparent ${SiO}_{2}$ substrate. (b) Optical micrograph of the device, with ${MoSe}_{2}$ and ${CrBr}_{3}$ outlined in blue and green, respectively.
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Figure 2
(a) Reflection spectrum of bare undoped ${MoSe}_{2}$ . (b) Reflection spectra in $σ^{-}$ and $σ^{+}$ polarization of the undoped ${MoSe}_{2} / {CrBr}_{3}$ heterostructure at $B = 0$ . The $K$ and $K^{'}$ valley excitons are split by 2.9 meV. (c),(d) Hysteresis of the reflection of a $σ^{+} / σ^{-}$ polarized laser tuned to the low-frequency tail of the ${MoSe}_{2}$ exciton in the heterostructure as marked by the vertical line in panel (b). (e) Measurement of the ${CrBr}_{3}$ magnetization hysteresis using the MOKE. The apparent offset from zero of the magnetic field in both measurements is due to a stray field from a ferromagnetic component in the cryostat.
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Figure 3
(a) Gate dependence of the bare ${MoSe}_{2}$ reflection spectrum. The appearance of attractive and repulsive polaron lines at positive and negative voltages shows the flake can be $n$ doped and $p$ doped. (b) Gate dependence of the reflection spectrum of the heterostructure in $σ^{-}$ polarization. Because of the type-II band alignment, ${MoSe}_{2}$ cannot be $n$ doped anymore, as signified by the persistence of the exciton line at positive voltages. Inset: Reflection spectra in the $p$ -doped regime, as indicated by the dashed line. The attractive polaron lines show the same splitting as the exciton lines. The $x$ ticks are identical to the parent axis, the $y$ -tick separation is 0.1. (c) Schematic of the type-II band alignment of ${MoSe}_{2}$ and ${CrBr}_{3}$ with chemical potential $μ$ for positive and negative gate voltages. Exchange coupling leads to valley splitting in the conduction band of ${MoSe}_{2}$ . (d),(e) Dependence of the valley splitting $Δ$ and FWHM of the exciton lines on the out-of-plane electric field. Both the splitting and FWHM are tunable, indicating a modification of the tunneling rate across the ${MoSe}_{2} / {CrBr}_{3}$ interface.
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Figure 4
(a) Fitted exciton peak positions from polarization-resolved reflection spectra as function of in-plane magnetic field. The splitting collapses around 0.3 T, indicating the transition to in-plane magnetization of ${CrBr}_{3}$ . (b) Exciton valley splitting as function of in-plane magnetic field. The fitted model using a macroscopic magnetic moment with anisotropy is in excellent agreement with the experimental data. (c) Magnetization of ${CrBr}_{3}$ as a function of temperature. Round data points are extracted from polarization-resolved reflection spectra of ${MoSe}_{2}$ and triangular data points are extracted from MOKE measurements. A fit of the form $m (T) = A {(1 - T / T_{C})}^{β}$ yields values for the critical temperature $T_{C}$ and critical exponent $β$ . (d) Magnetic susceptibility as a function of temperature extracted from spectra and MOKE measurements. A fit of the form $χ (T) = B {(T / T_{C} - 1)}^{- γ}$ yields the critical exponent $γ$ .
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Physical Review Letters

Observation of Magnetic Proximity Effect Using Resonant Optical Spectroscopy of an Electrically Tunable MoSe2/CrBr3 Heterostructure

Livio Ciorciaro, Martin Kroner, Kenji Watanabe, Takashi Taniguchi, and Atac Imamoglu

Phys. Rev. Lett. 124, 197401 – Published 14 May 2020; Erratum Phys. Rev. Lett. 130, 019901 (2023)

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Erratum: Observation of Magnetic Proximity Effect Using Resonant Optical Spectroscopy of an Electrically Tunable MoSe2/CrBr3 Heterostructure [Phys. Rev. Lett. 124, 197401 (2020)]

Livio Ciorciaro, Martin Kroner, Kenji Watanabe, Takashi Taniguchi, and Atac Imamoglu

Phys. Rev. Lett. 130, 019901 (2023)

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Observation of Magnetic Proximity Effect Using Resonant Optical Spectroscopy of an Electrically Tunable ${MoSe}_{2} / {CrBr}_{3}$ Heterostructure

Erratum: Observation of Magnetic Proximity Effect Using Resonant Optical Spectroscopy of an Electrically Tunable ${MoSe}_{2} / {CrBr}_{3}$ Heterostructure [Phys. Rev. Lett. 124, 197401 (2020)]