Valley polarization assisted spin polarization in two dimensions

Renard, V.; Piot, B. A.; Waintal, Xavier; Fleury, Geneviève; Cooper, D. L.; Niida, Y; Tregurtha, D; Fujiwara, Akira; Hirayama, Y.; Takashina, Kei

doi:10.1038/ncomms8230

Cited by 31 publications

(18 citation statements)

References 52 publications

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“…We observe a strongly enhanced valley magnetic response, which can be understood as a consequence of a step rise in the exchange interaction strength that is highly sensitive to the number of internal degrees of freedom 21,22,24 . Our result opens up new possibilities of exploring strongly interacting electron systems with multiple internal degrees of freedom beyond the conventional multi-valley semiconductor quantum wells of Si [25][26][27][28][29] and AlAs 30,31 .…”

mentioning

confidence: 92%

Strongly Interaction-Enhanced Valley Magnetic Response in Monolayer WSe2

2018

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Coulomb interaction between electrons lies at the heart of magnetism in solids 1, 2 . In contrast to conventional two-dimensional (2D) systems, electrons in monolayer transition metal dichalcogenides (TMDs) possess coupled spin and valley degrees of freedom by the spin-orbit interaction 3, 4 . The electrons are also strongly interacting even in the high-density regime because of the weak dielectric screening in two dimensions and a large band mass 5,6 . The combination of these properties presents a unique platform for exploring spin and valley magnetism in 2D electron liquids. Here we report an observation by magneto-photoluminescence spectroscopy of a nonlinear valley Zeeman effect, correlated with an over fourfold enhancement in the exciton g-factor in monolayer WSe 2 . The effect occurs when the Fermi level crosses the spin-split upper conduction band, corresponding to a change of the spin-valley degeneracy from 2 to 4. The enhancement increases, shows no sign of saturation as the sample temperature decreases. Our result suggests the possibility of rich manybody ground states in monolayer TMDs with multiple internal degrees of freedom.Electrons in monolayer transition metal dichalcogenide (TMD) semiconductors with a honeycomb lattice structure possess a two-fold valley degree of freedom, corresponding to the K and K' point of the Brillouin zone [3][4][5] . Because of the strong spinorbit interaction, the bands are spin split with the valley and spin locked to satisfy the time reversal symmetry 3-5 (Fig. 1a). Similar to the spin, the valley carries a magnetic moment and has been proposed as a new type of information carriers 3,7 . Several new valley dependent phenomena, including the valley contrasting optical selection rules [8][9][10][11][12] , valley Zeeman effect [13][14][15][16][17][18] and valley Hall effect 19,20 , have emerged in the independentparticle picture and provided means to manipulate the valley polarization. In particular, the valley exciton splitting in an out-of-plane magnetic field has been shown to depend linearly on the field up to 65 Tesla 18 and an exciton g-factor between -2 and -4 has been reported for various monolayer TMDs 6, 13-18 . On the other hand, even in the relatively high-density regime (~ 5×10 !" cm -2 ), electrons in monolayer TMDs are strongly interacting with the Coulomb energy (~ 100's meV) dominating all other energy scales (Fermi energy, conduction band spin splitting at K/K' ~ 10's meV for WSe 2 ) 6 . The valley magnetic response of the independent-particle picture is thus expected to be modified by the strong electron-electron interaction and the system may even develop a magnetically ordered ground state [21][22][23][24] . A unique scenario emerges when the Fermi level crosses the spin-split upper conduction band (Fig. 1a), where the spin-valley degeneracy ! ! changes from 2 to 4 ( ! and ! stand for the spin and valley degeneracy, respectively) 6 . We observe a strongly enhanced valley magnetic response, which can be understood as a consequence of a step rise in ...

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confidence: 92%

Strongly Interaction-Enhanced Valley Magnetic Response in Monolayer WSe2

2018

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“…A plenty of exotic properties such as quantum spin/valley anomalous Hall effect [8][9][10] , valleydependent optoelectronics 11 , spin/valley polarization of plasmons [12][13][14] , magneto-optical conductivity 15 , electrical transport of valley carriers 16 have been explored in the valley-polarized systems. Moreover, valley polarization may interplay with spin polarization, especially to enhance spin polarization 17,18 . Research efforts have been devoted to experimetally measuring valley currents, although disentangling valley currents from the currents carried by edge eigenstates remains challenging 19,20 .…”

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confidence: 99%

Valley splitting in the van der Waals heterostructure WSe2/CrI3 : The role of atom superposition

et al. 2019

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Recent experiment shows that the K ′ K valley degeneracy can be lifted in a monolayer WSe2 deposited on a layered ferromagnetic substrate of CrI3. In this work, we take a van der Waals heterostructure WSe2/CrI3 to model the monolayer WSe2 on the CrI3 substrate and investigate the effects underpinning the K ′ K valley splitting based on first-principles calculations. We demonstrate that the interfacial atom superposition plays an important role and a W-Cr superposition is essential for a relatively large valley splitting. The results indicate inevitable sample-to-sample variations in the K ′ K valley splitting in the WSe2/CrI3. Furthermore, we show that the K ′ K valley splitting can be tuned in a trilayer CrI3/WSe2/CrI3 from nearly zero to more than two times of that in the bilayer WSe2/CrI3 by manipulating the layer alignment.

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“…Therefore, the behaviour of the polarization field B c is affected by the disorder potential in accordance with refs. 24 , 26 . Good agreement between our experimental data for B c and the calculations for the clean limit 24 gives evidence that the electron properties studied in our samples are only weakly sensitive to the residual disorder and the clean limit has been reached in our samples.…”

Section: Introductionmentioning

confidence: 99%

Indication of band flattening at the Fermi level in a strongly correlated electron system

Mel'nikov

Shashkin

Dolgopolov

et al. 2017

Sci Rep

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Using ultra-high quality SiGe/Si/SiGe quantum wells at millikelvin temperatures, we experimentally compare the energy-averaged effective mass, m, with that at the Fermi level, m F, and verify that the behaviours of these measured values are qualitatively different. With decreasing electron density (or increasing interaction strength), the mass at the Fermi level monotonically increases in the entire range of electron densities, while the energy-averaged mass saturates at low densities. The qualitatively different behaviour reveals a precursor to the interaction-induced single-particle spectrum flattening at the Fermi level in this electron system.

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Valley polarization assisted spin polarization in two dimensions

Cited by 31 publications

References 52 publications

Strongly Interaction-Enhanced Valley Magnetic Response in Monolayer WSe2

Strongly Interaction-Enhanced Valley Magnetic Response in Monolayer WSe2

Valley splitting in the van der Waals heterostructure WSe2/CrI3 : The role of atom superposition

Indication of band flattening at the Fermi level in a strongly correlated electron system

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