Measuring Valley Polarization in Two-Dimensional Materials with Second-Harmonic Spectroscopy

  title={Measuring Valley Polarization in Two-Dimensional Materials with Second-Harmonic Spectroscopy},
  author={Yi Wei Ho and Henrique G. Rosa and Ivan A. Verzhbitskiy and Manuel J. L. F. Rodrigues and Takashi Taniguchi and Kenji Watanabe and Goki Eda and Vitor M. Pereira and Jos{\'e} Viana‐Gomes},
  journal={ACS Photonics},
Inducing a population imbalance at different valleys of an electronic system lowers its effective rotational symmetry. We introduce a technique to measure such valley imbalance (a valley polarization) that directly exploits this symmetry reduction as well as the unique fingerprints it has in the polarization-dependent second-harmonic generation. We describe the principle and detection scheme in the context of hexagonal two-dimensional crystals, which include graphene-based systems and the… 
13 Citations

Figures from this paper

Probing valley population imbalance in transition metal dichalcogenides via temperature-dependent second harmonic generation imaging

Degenerate minima in momentum space—valleys—provide an additional degree of freedom that can be used for information transport and storage. Notably, such minima naturally exist in the band structure

All-optical polarization and amplitude modulation of second-harmonic generation in atomically thin semiconductors

Second-harmonic generation is of paramount importance in several fields of science and technology, including frequency conversion, self-referencing of frequency combs, nonlinear spectroscopy and

An on-Si directional second harmonic generation amplifier for MoS2/WS2 heterostructure

Transition metal dichalcogenides (TMD) heterostructure is widely applied for second harmonic generation (SHG) and holds great promises for laser source, nonlinear switch, and optical logic gate.

Harmonic Generation in Low‐Dimensional Materials

Low‐dimensional materials (LDMs) provide an unprecedented avenue having the potential to disruptively revolutionize the information and communication technologies. The rise of nonlinear photonics in

Berry curvature, orbital magnetization, and Nernst effect in biased bilayer WSe2

A valley-contrasting Berry curvature in bilayer transition metal dichalcogenides with spin-orbit coupling can generate valley magnetization when the inversion symmetry is broken, for example, by an

Optical Harmonic Generation in 2D Materials

2D materials are emerging as ideal candidates for fundamental investigations and new technologies due to their unique optoelectronic properties. Giant nonlinear susceptibility and perfect phase

Parametric Nonlinear Optics with Layered Materials and Related Heterostructures

Nonlinear optics is of crucial importance in several fields of science and technology with applications in frequency conversion, entangled‐photon generation, self‐referencing of frequency combs,

Second harmonic generation at the edge of a two-dimensional electron gas

We show that driving a two-dimensional electron gas by an in-plane electric field oscillating at the frequency ω gives rise to an electric current at 2 ω flowing near the edge of the system. This

Nonlinear spectroscopy of excitonic states in transition metal dichalcogenides

Yaroslav V. Zhumagulov, 2, ∗ Vyacheslav D. Neverov, 2, † Alexander E. Lukyanov, 2 Dmitry R. Gulevich, Andrey V. Krasavin, Alexei Vagov, 4, 5 and Vasili Perebeinos ‡ University of Regensburg,



Second harmonic spectroscopy to optically detect valley polarization in 2D materials

Valley polarization (VP), an induced imbalance in the populations of a multi-valley electronic system, allows emission of second harmonic (SH) light even in centrosymmetric crystals such as graphene.

Characterization of the second- and third-harmonic optical susceptibilities of atomically thin tungsten diselenide

The first detailed characterization of the sheet third-harmonic optical susceptibility, χ(3)s, of tungsten diselenide (WSe2) is reported, in very good agreement on the order of magnitude with recent reports for WSe2, which asserts the robustness of the values for |χ( 3)s|.

Valley polarization in MoS2 monolayers by optical pumping.

It is demonstrated that optical pumping with circularly polarized light can achieve a valley polarization of 30% in pristine monolayer MoS(2), demonstrating the viability of optical valley control and valley-based electronic and optoelectronic applications in MoS (2) monolayers.

Valley-dependent optoelectronics from inversion symmetry breaking

Inversion symmetry breaking allows contrasted circular dichroism in different $k$-space regions, which takes the extreme form of optical selection rules for interband transitions at high symmetry

Electrical control of the valley Hall effect in bilayer MoS2 transistors.

It is shown that the valley Hall effect in bilayer MoS2 transistors can be controlled with a gate voltage, which is consistent with symmetry-dependent Berry curvature and valley Hall conductivity in bilayers MoS 2.

Valley excitons in two-dimensional semiconductors

Monolayer group-VIB transition-metal dichalcogenides have recently emerged as a new class of semiconductors in the two-dimensional limit. The attractive properties include the visible range direct

Long valley relaxation time of free carriers in monolayer WSe 2

Monolayer transition metal dichalcogenids (TMDs) feature valley degree of freedom, giant spinorbit coupling and spin-valley locking. These exotic natures stimulate efforts of exploring the potential

Optically initialized robust valley-polarized holes in monolayer WSe2

It is demonstrated that robust valley-polarized holes in monolayer WSe2 can be initialized by optical pumping, which opens up the possibility to realize room-temperature valleytronics based on transition metal dichalcogenides.

Many-body effects in valleytronics: direct measurement of valley lifetimes in single-layer MoS2.

Direct measurements of valley relaxation dynamics in single layer MoS2 are reported by using ultrafast transient absorption spectroscopy, showing that strong Coulomb interactions significantly impact valley population dynamics and biexcitons form with more than an order of magnitude larger binding energy compared to conventional semiconductors.

Probing of valley polarization in graphene via optical second-harmonic generation

Valley polarization in graphene breaks inversion symmetry and therefore leads to second-harmonic generation. We present a complete theory of this effect within a single-particle approximation. It is