Layer-dependent optically-induced spin polarization in InSe. (arXiv:2212.05423v1 [cond-mat.mtrl-sci])

2022-12-13T02:29:40+00:00December 13th, 2022|Categories: Publications|Tags: , |

Optical control of spin in semiconductors has been pioneered using nanostructures of III-V and II-VI semiconductors, but the emergence of two-dimensional van der Waals materials offers an alternative low-dimensional platform for spintronic phenomena. Indium selenide (InSe), a group-III monochalcogenide van der Waals material, has shown promise for opto-electronics due to its high electron mobility, tunable direct bandgap, and quantum transport. There are predictions of spin-dependent optical selection rules suggesting potential for all-optical excitation and control of spin in a two-dimensional layered material. Despite these predictions, layer-dependent optical spin phenomena in InSe have yet to be explored. Here, we present measurements of layer-dependent optical spin dynamics in few-layer and bulk InSe. Polarized photoluminescence reveals layer-dependent optical orientation of spin, thereby demonstrating the optical selection rules in few-layer InSe. Spin dynamics are also studied in many-layer InSe using time-resolved Kerr rotation spectroscopy. By applying out-of-plane and in-plane static magnetic fields for polarized emission measurements and Kerr measurements, respectively, the $g$-factor for InSe was extracted. Further investigations are done by calculating precession values using a $textbf{k} cdot textbf{p}$ model, which is supported by textit{ab-initio} density functional theory. Comparison of predicted precession rates with experimental measurements highlights the importance of excitonic effects in InSe for understanding spin dynamics. Optical orientation of spin is an important prerequisite for opto-spintronic phenomena and devices, and these first demonstrations of layer-dependent optical excitation of spins in InSe lay the foundation for combining layer-dependent spin properties with advantageous electronic properties found in this material.

Published in: "arXiv Material Science".

Unveiling the complex structure-property correlation of defects in 2D materials based on high throughput datasets. (arXiv:2212.02110v1 [cond-mat.mtrl-sci])

2022-12-06T02:29:50+00:00December 6th, 2022|Categories: Publications|Tags: , , , , |

Modification of physical properties of materials and design of materials with on-demand characteristics is at the heart of modern technology. Rare application relies on pure materials–most devices and technologies require careful design of materials properties through alloying, creating heterostructures of composites or controllable introduction of defects. At the same time, such designer materials are notoriously difficult for modelling. Thus, it is very tempting to apply machine learning methods for such systems. Unfortunately, there is only a handful of machine learning-friendly material databases available these days. We develop a platform for easy implementation of machine learning techniques to materials design and populate it with datasets on pristine and defected materials. Here we describe datasets of defects in represented 2D materials such as MoS2, WSe2, hBN, GaSe, InSe, and black phosphorous, calculated using DFT. Our study provides a data-driven physical understanding of complex behaviors of defect properties in 2D materials, holding promise for a guide to the development of efficient machine learning models. In addition, with the increasing enrollment of datasets, our database could provide a platform for designing of materials with predetermined properties.

Published in: "arXiv Material Science".

Long-range electrostatic contribution to the electron-phonon couplings and mobilities of two-dimensional materials. (arXiv:2207.10190v1 [cond-mat.mtrl-sci])

2022-07-22T02:29:43+00:00July 22nd, 2022|Categories: Publications|Tags: , , |

Charge transport plays a crucial role in manifold potential applications of two-dimensional materials, including field effect transistors, solar cells, and transparent conductors. At most operating temperatures, charge transport is hindered by scattering of carriers by lattice vibrations. Assessing the intrinsic phonon-limited carrier mobility is thus of paramount importance to identify promising candidates for next-generation devices. Here we provide a framework to efficiently compute the drift and Hall carrier mobility of two-dimensional materials through the Boltzmann transport equation by relying on a Fourier-Wannier interpolation. Building on a recent formulation of long-range contributions to dynamical matrices and phonon dispersions [$href{https://journals.aps.org/prx/abstract/10.1103/PhysRevX.11.041027}{Phys. Rev. X textbf{11}, 041027 (2021)}$], we extend the approach to electron-phonon coupling including the effect of dynamical dipoles and quadrupoles. We study a wide selection of relevant monolayers ranging from SnS$_2$ to MoS$_2$, graphene, BN, InSe, and phosphorene, showing the importance of the current strategy to fully account for the peculiar nature of long-range electrostatics in two dimensions. Interestingly, we discover a non-trivial temperature evolution of the Hall hole mobility in InSe whereby the mobility increases with temperature above 150 K due to the mexican-hat electronic structure of the InSe valence bands. Overall, we find that dynamical quadrupoles are essential and can impact the carrier mobility in excess of 40%.

Published in: "arXiv Material Science".

Phonon-limited Mobility of 2D Semiconductors: Quadrupole Scattering and Free-carrier Screening. (arXiv:2207.00110v1 [cond-mat.mtrl-sci])

2022-07-04T02:29:18+00:00July 4th, 2022|Categories: Publications|Tags: , |

Two-dimensional (2D) semiconductors have demonstrated great potential for next-generation electronics and optoelectronics. An important property for these applications is the phonon-limited charge carrier mobility. The common approach to calculate the mobility from first principles relies on the interpolation of the electron-phonon coupling (EPC) matrix. However, it neglects the scattering by the dynamical quadrupoles generated by phonons, limiting its accuracy. Here we present a first-principles method to incorporate the quadrupole scattering, which results in a much better interpolation quality and thus a more accurate mobility as exemplified by monolayer MoS2 and InSe. This method also allows for a natural incorporation of the effects of the free carriers, enabling us to efficiently compute the screened EPC and thus the mobility for doped semiconductors. Particularly, we find that the electron mobility of InSe is more sensitive to the carrier concentration than that of MoS2 due to the stronger long-range scattering in intrinsic InSe. With increasing electron concentration, the InSe mobility can reach ~4 times of the intrinsic value, then decrease owing to the involvement of heavier electronic states. Our work provides accurate and efficient methods to calculate the phonon-limited mobility in the intrinsic and doped 2D materials, and improves the fundamental understanding of their transport mechanism.

Published in: "arXiv Material Science".

Cataloguing MoSi$_2$N$_4$ and WSi$_2$N$_4$ van der Waals Heterostructures: An Exceptional Material Platform for Excitonic Solar Cell Applications. (arXiv:2206.11765v1 [cond-mat.mtrl-sci])

2022-06-24T04:30:29+00:00June 24th, 2022|Categories: Publications|Tags: , , |

Two-dimensional (2D) materials van der Waals heterostructures (vdWHs) provides a revolutionary route towards high-performance solar energy conversion devices beyond the conventional silicon-based pn junction solar cells. Despite tremendous research progress accomplished in recent years, the searches of vdWHs with exceptional excitonic solar cell conversion efficiency and optical properties remain an open theoretical and experimental quest. Here we show that the vdWH family composed of MoSi$_2$N$_4$ and WSi$_2$N$_4$ monolayers provides a compelling material platform for developing high-performance ultrathin excitonic solar cells and photonics devices. Using first-principle calculations, we construct and classify 51 types of MoSi$_2$N$_4$ and WSi$_2$N$_4$-based [(Mo,W)Si$_2$N$_4$] vdWHs composed of various metallic, semimetallic, semiconducting, insulating and topological 2D materials. Intriguingly, MoSi$_2$N$_4$/(InSe, WSe$_2$) are identified as Type-II vdWHs with exceptional excitonic solar cell power conversion efficiency reaching well over 20%, which are competitive to state-of-art silicon solar cells. The (Mo,W)Si$_2$N$_4$ vdWH family exhibits strong optical absorption in both the visible and ultraviolet regimes. Exceedingly large peak ultraviolet absorptions over 40%, approaching the maximum absorption limit of a free-standing 2D material, can be achieved in (Mo,W)Si$_2$N$_4$/$alpha_2$-(Mo,W)Ge$_2$P$_4$ vdWHs. Our findings unravel the enormous potential of (Mo,W)Si$_2$N$_4$ vdWHs in designing ultimately compact excitonic solar cell device technology.

Published : "arXiv Mesoscale and Nanoscale Physics".

Cataloguing MoSi$_2$N$_4$ and WSi$_2$N$_4$ van der Waals Heterostructures: An Exceptional Material Platform for Excitonic Solar Cell Applications. (arXiv:2206.11765v1 [cond-mat.mtrl-sci])

2022-06-24T02:29:21+00:00June 24th, 2022|Categories: Publications|Tags: , , |

Two-dimensional (2D) materials van der Waals heterostructures (vdWHs) provides a revolutionary route towards high-performance solar energy conversion devices beyond the conventional silicon-based pn junction solar cells. Despite tremendous research progress accomplished in recent years, the searches of vdWHs with exceptional excitonic solar cell conversion efficiency and optical properties remain an open theoretical and experimental quest. Here we show that the vdWH family composed of MoSi$_2$N$_4$ and WSi$_2$N$_4$ monolayers provides a compelling material platform for developing high-performance ultrathin excitonic solar cells and photonics devices. Using first-principle calculations, we construct and classify 51 types of MoSi$_2$N$_4$ and WSi$_2$N$_4$-based [(Mo,W)Si$_2$N$_4$] vdWHs composed of various metallic, semimetallic, semiconducting, insulating and topological 2D materials. Intriguingly, MoSi$_2$N$_4$/(InSe, WSe$_2$) are identified as Type-II vdWHs with exceptional excitonic solar cell power conversion efficiency reaching well over 20%, which are competitive to state-of-art silicon solar cells. The (Mo,W)Si$_2$N$_4$ vdWH family exhibits strong optical absorption in both the visible and ultraviolet regimes. Exceedingly large peak ultraviolet absorptions over 40%, approaching the maximum absorption limit of a free-standing 2D material, can be achieved in (Mo,W)Si$_2$N$_4$/$alpha_2$-(Mo,W)Ge$_2$P$_4$ vdWHs. Our findings unravel the enormous potential of (Mo,W)Si$_2$N$_4$ vdWHs in designing ultimately compact excitonic solar cell device technology.

Published in: "arXiv Material Science".

The quantum-well turn into van der Waals: epitaxy of GaSe and InSe heterostructures for optoelectronic devices. (arXiv:2206.06250v1 [cond-mat.mtrl-sci])

2022-06-14T04:30:32+00:00June 14th, 2022|Categories: Publications|Tags: , |

Bandgap engineering and quantum confinement in semiconductor heterostructures provide the means to fine-tune material response to electromagnetic fields and light in a wide range of the spectrum. Nonetheless, forming semiconductor heterostructures on lattice-mismatched substrates has been a challenge for several decades, leading to restrictions for device integration and the lack of efficient devices in important wavelength bands. Here, we show that the van der Waals epitaxy of two-dimensional (2D) GaSe and InSe heterostructures occur on substrates with substantially different lattice parameters, namely silicon and sapphire. The GaSe/InSe heterostructures were applied in the growth of quantum wells and superlattices presenting photoluminescence and absorption related to interband transitions. Moreover, we demonstrate a self-powered photodetector based on this heterostructure on Si that works in the visible-NIR wavelength range. Fabricated at wafer-scale, these results pave the way for an easy integration of optoelectronics based on these layered 2D materials in current Si technology.

Published : "arXiv Mesoscale and Nanoscale Physics".

The quantum-well turn into van der Waals: epitaxy of GaSe and InSe heterostructures for optoelectronic devices. (arXiv:2206.06250v1 [cond-mat.mtrl-sci])

2022-06-14T02:30:10+00:00June 14th, 2022|Categories: Publications|Tags: , |

Bandgap engineering and quantum confinement in semiconductor heterostructures provide the means to fine-tune material response to electromagnetic fields and light in a wide range of the spectrum. Nonetheless, forming semiconductor heterostructures on lattice-mismatched substrates has been a challenge for several decades, leading to restrictions for device integration and the lack of efficient devices in important wavelength bands. Here, we show that the van der Waals epitaxy of two-dimensional (2D) GaSe and InSe heterostructures occur on substrates with substantially different lattice parameters, namely silicon and sapphire. The GaSe/InSe heterostructures were applied in the growth of quantum wells and superlattices presenting photoluminescence and absorption related to interband transitions. Moreover, we demonstrate a self-powered photodetector based on this heterostructure on Si that works in the visible-NIR wavelength range. Fabricated at wafer-scale, these results pave the way for an easy integration of optoelectronics based on these layered 2D materials in current Si technology.

Published in: "arXiv Material Science".

A First-Principles Study on the Adsorption of Small Molecules on Arsenene: Comparison of Oxidation Kinetics in Arsenene, Antimonene, Phosphorene and InSe. (arXiv:2203.12218v1 [cond-mat.mtrl-sci])

2022-03-24T02:29:34+00:00March 24th, 2022|Categories: Publications|Tags: , , , , |

Arsenene, a new group V two-dimensional (2D) semiconducting material beyond phosphorene and antimonene, has recently gained an increasing attention owning to its various interesting properties which can be altered or intentionally functionalized by chemical reactions with various molecules. This work provides a systematic study on the interactions of arsenene with the small molecules, including H2, NH3, O2, H2O, NO, and NO2. It is predicted that O2, H2O, NO, and NO2 are strong acceptors, while NH3 serves as a donor. Importantly, it is shown a negligible charge transfer between H2 and arsenene which is ten times lower than that between H2 and phosphorene and about thousand times lower than that between H2 and InSe and antimonene. The calculated energy barrier for O2 splitting on arsenene is found to be as low as 0.67 eV. Thus, pristine arsenene may easily oxidize in ambient conditions as other group V 2D materials. On the other hand, the acceptor role of H2O on arsenene, similarly to the cases of antimonene and InSe, may help to prevent the proton transfer between H2O and O species by forming acids, which suppresses further structural degradation of arsenene. The structural decomposition of the 2D layers upon interaction with the environment may be avoided due to the acceptor role of H2O molecules as the study predicts from the comparison of common group V 2D materials. However, the protection for arsenene is still required due to its strong interaction with other small environmental molecules. The present work renders the possible ways

Published in: "arXiv Material Science".

Designing Ultra-Flat Bands in Twisted Bilayer Materials at Large Twist Angles without specific degree. (arXiv:2202.13791v1 [physics.comp-ph])

2022-03-01T04:30:26+00:00March 1st, 2022|Categories: Publications|Tags: , , , |

Inter-twisted bilayers of two-dimensional (2D) materials can host low-energy flat bands, which offer opportunity to investigate many intriguing physics associated with strong electron correlations. In the existing systems, ultra-flat bands only emerge at very small twist angles less than a few degrees, which poses challenge for experimental study and practical applications. Here, we propose a new design principle to achieve low-energy ultra-flat bands with increased twist angles. The key condition is to have a 2D semiconducting material with large energy difference of band edges controlled by stacking. We show that the interlayer interaction leads to defect-like states under twisting, which forms a flat band in the semiconducting band gap with dispersion strongly suppressed by the large energy barriers in the moire superlattice even for large twist angles. We explicitly demonstrate our idea in bilayer alpha-In2Se3 and bilayer InSe. For bilayer alpha-In2Se3, we show that a twist angle -13.2 degree is sufficient to achieve the band flatness comparable to that of twist bilayer graphene at the magic angle -1.1 degree. In addition, the appearance of ultra-flat bands here is not sensitive to the twist angle as in bilayer graphene, and it can be further controlled by external gate fields. Our finding provides a new route to achieve ultra-flat bands other than reducing the twist angles and paves the way towards engineering such flat bands in a large family of 2D materials.

Published : "arXiv Mesoscale and Nanoscale Physics".

Ab initio study on the atomic and electronic structures of twisted InSe bilayer. (arXiv:2202.12812v1 [cond-mat.mtrl-sci])

2022-02-28T02:29:23+00:00February 28th, 2022|Categories: Publications|Tags: , , |

The electronic properties of the twisted InSe bilayer are studied by large-scale density functional theory. Spectral Function Unfolding reveals that the electronic structure of the twisted system can be described in terms of a combination of features of the bandstructures of the aligned InSe bilayer with different stacking configurations, enabling predictions of the band gap and the effective mass for holes. The effective mass for holes in the twisted InSe bilayer is shown to be influenced primarily by the interlayer distance. The intralayer and interlayer exciton binding energies are thus calculated based on a model recently developed by Ruiz-Tijerina et al. We apply similar analysis to the trilayer heterostructure InSe/hBN/InSe: its electronic structure is shown to be well-described by the superposition of band structures of two InSe monolayers with a small coupling through the hBN layer.

Published in: "arXiv Material Science".

Spatially-Resolved Band Gap and Dielectric Function in 2D Materials from Electron Energy Loss Spectroscopy. (arXiv:2202.12572v1 [cond-mat.mtrl-sci])

2022-02-28T02:29:18+00:00February 28th, 2022|Categories: Publications|Tags: , |

The electronic properties of two-dimensional (2D) materials depend sensitively on the underlying atomic arrangement down to the monolayer level. Here we present a novel strategy for the determination of the band gap and complex dielectric function in 2D materials achieving a spatial resolution down to a few nanometers. This approach is based on machine learning techniques developed in particle physics and makes possible the automated processing and interpretation of spectral images from electron energy-loss spectroscopy (EELS). Individual spectra are classified as a function of the thickness with $K$-means clustering and then used to train a deep-learning model of the zero-loss peak background. As a proof-of-concept we assess the band gap and dielectric function of InSe flakes and polytypic WS$_2$ nanoflowers, and correlate these electrical properties with the local thickness. Our flexible approach is generalizable to other nanostructured materials and to higher-dimensional spectroscopies, and is made available as a new release of the open-source EELSfitter framework.

Published in: "arXiv Material Science".

Moire flat bands in twisted 2D hexagonal vdW material. (arXiv:2110.07962v1 [cond-mat.mtrl-sci])

2021-10-18T02:29:24+00:00October 18th, 2021|Categories: Publications|Tags: , , , |

Moire superlattices in twisted bilayer graphene (TBG) and its derived structures can host exotic correlated quantum phenomena because the narrow moire flat minibands in those systems effectively enhance the electron-electron interaction. Correlated phenomena are also observed in 2H-transitional metal dichalcogenides moire superlattices. However, the number of moire systems that have been explored in experiments are still very limited. Here we theoretically investigate a series of two-dimensional (2D) twisted bilayer hexagonal materials (TBHMs) beyond TBG at fixed angles of 7.34 and 67.34 degree with 22 2D van der Waals (vdW) layered materials that are commonly studied in experiments. First-principles calculations are employed to systemically study the moire minibands in these systems. We find that flat bands with narrow bandwidth generally exist in these systems. Some of the systems such as twisted bilayer In2Se3, InSe, GaSe, GaS and PtS2 even host ultra-flat bands with bandwidth less than 20 meV even for such large angles, which make them especially appealing for further experimental investigations. We further analysis the characters of moire flat bands and provides guidance for further exploration of 2D moire superlattices that could host strong electron correlations.

Published in: "arXiv Material Science".

Identifying atomically thin crystals with diffusively reflected light. (arXiv:2106.12419v1 [cond-mat.mes-hall])

2021-06-24T04:30:21+00:00June 24th, 2021|Categories: Publications|Tags: , , , |

The field of two-dimensional materials has been developing at an impressive pace, with atomically thin crystals of an increasing number of different compounds that have become available, together with techniques enabling their assembly into functional heterostructures. The strategy to detect these atomically thin crystals has however remained unchanged since the discovery of graphene. Such an absence of evolution is starting to pose problems because for many of the 2D materials of current interest the optical contrast provided by the commonly used detection procedure is insufficient to identify the presence of individual monolayers or to determine unambiguously the thickness of atomically thin multilayers. Here we explore an alternative detection strategy, in which the enhancement of optical contrast originates from the use of optically inhomogeneous substrates, leading to diffusively reflected light. Owing to its peculiar polarization properties and to its angular distribution, diffusively reflected light allows a strong contrast enhancement to be achieved through the implementation of suitable illumination-detection schemes. We validate this conclusion by carrying out a detailed quantitative analysis of optical contrast, which fully reproduces our experimental observations on over 60 WSe$_2$ mono-, bi-, and trilayers. We further validate the proposed strategy by extending our analysis to atomically thin phosphorene, InSe, and graphene crystals. Our conclusion is that the use of diffusively reflected light to detect and identify atomically thin layers is an interesting alternative to the common detection scheme based on Fabry-Perot interference, because it enables atomically thin layers to be detected on substrates others than the commonly used

Published : "arXiv Mesoscale and Nanoscale Physics".

Broadband Photocurrent Spectroscopy and Temperature Dependence of Band-gap of Few-Layer Indium Selenide. (arXiv:2104.04877v1 [cond-mat.mes-hall])

2021-04-13T04:30:23+00:00April 13th, 2021|Categories: Publications|Tags: , |

Understanding broadband photoconductive behaviour in two dimensional layered materials are important in order to utilize them for a variety of opto-electronic applications. Here we present our results of photocurrent spectroscopy measurements performed on few layer Indium Selenide (InSe) flakes. Temperature (T) dependent (40 K < T < 300 K) photocurrent spectroscopy was performed in order to estimate the band-gap energies E_g(T) of InSe at various temperatures. Our measurements indicate that room temperature E_g value for InSe flake was ~ 1.254 eV, which increased to a value of ~ 1.275 eV at low temperatures. The estimation of Debye temperatures by analysing the observed experimental variation of E_g as a function of T using several theoretical models is presented and discussed.

Published : "arXiv Mesoscale and Nanoscale Physics".

Weak ferroelectric charge transfer in layer-asymmetric bilayers of 2D semiconductors. (arXiv:2103.06093v1 [cond-mat.mes-hall])

2021-03-11T04:30:20+00:00March 11th, 2021|Categories: Publications|Tags: |

In bilayers of two-dimensional (2D) semiconductors with stacking arrangements which lack inversion symmetry charge transfer between the layers due to layer-asymmetric interband hybridisation can generate a potential difference between the layers. When analyzed using crystalline density functional theory codes, the related difference between vacuum energies above and below the bilayer would contradict the periodicity of supercell boundary conditions. Here, we resolve this constraint by two means: (a) by constructing a larger supercell, including two mirror reflected images of the bilayer separated by a further vacuum, and (b) by using a background dipole correction. We use both methods to compare bilayers of transition metal dichalcogenides (TMDs) – in particular, WSe$_2$ – for which we find a substantial stacking-dependent charge transfer, and InSe, for which the charge transfer is found to be negligibly small. The information obtained about TMDs is then used to map potentials generated by the interlayer charge transfer across the moir’e superlattice in twistronic bilayers.

Published : "arXiv Mesoscale and Nanoscale Physics".

Optoelectronic characteristics and application of black phosphorus and its analogs. (arXiv:2102.13316v1 [physics.optics])

2021-03-01T02:29:26+00:00March 1st, 2021|Categories: Publications|Tags: , , , , |

The tunable bandgap from 0.3 eV to 2 eV of black phosphorus (BP) makes it to fill the gap in graphene. When studying the properties of BP more comprehensive, scientists have discovered that many two-dimensional materials, such as tellurene, antimonene, bismuthene, indium selenide and tin sulfide, have similar structures and properties to black phosphorus thus called black phosphorus analogs. In this review, we briefly introduce preparation methods of black phosphorus and its analogs, with emphasis on the method of mechanical exfoliation (ME), liquid phase exfoliation (LPE) and chemical vapor deposition (CVD). And their characterization and properties according to their classification of single-element materials and multi-element materials are described. We focus on the performance of passively mode-locked fiber lasers using BP and its analogs as saturable absorbers (SA) and demonstrated this part through classification of working wavelength. Finally, we introduce the application of BP and its analogs, and discuss their future research prospects.

Published in: "arXiv Material Science".

Role of Layer Thickness and Field-Effect Mobility on Photoresponsivity of Indium Selenide (InSe) Based Phototransistors. (arXiv:2102.00365v1 [physics.app-ph])

2021-02-02T02:29:43+00:00February 2nd, 2021|Categories: Publications|Tags: , |

Understanding and optimizing the properties of photoactive two-dimensional (2D) Van der Waals solids are crucial for developing optoelectronics applications. Here we present a detailed investigation of layer dependent photoconductive behavior of InSe based field-effect transistors (FETs). InSe based FETs with five different channel thickness (t, 20 nm < t < 100 nm) were investigated with a continuous laser source of {lambda} = 658 nm (1.88 eV) over a wide range of illumination power of 22.8 nW < P < 1.29 {mu}W. All the devices studied, showed signatures of photogating, however, our investigations suggest that the photoresponsivities are strongly dependent on the thickness of the conductive channel. A correlation between the field-effect mobility ({mu}FE) values (as a function of channel thickness, t) and photoresponsivity (R) indicates that in general R increases with increasing {mu}FE (decreasing t) and vice versa. The maximum responsivity of ~ 7.84 A/W and ~ 0.59 A/W was obtained for the device with t = 20 nm and t = 100 nm respectively. These values could substantially increase under the application of a gate voltage. The structure-property correlation-based studies presented here indicate the possibility of tuning the optical properties of InSe based photo-FETs for a variety of applications related to photodetector and/or active layers in solar cells.

Published in: "arXiv Material Science".

Layer- and Gate-tunable Spin-Orbit Coupling in a High Mobility Few-Layer Semiconductor. (arXiv:2012.00937v1 [cond-mat.mes-hall])

2020-12-03T02:29:31+00:00December 3rd, 2020|Categories: Publications|Tags: |

Spin-orbit coupling (SOC) is a relativistic effect, where an electron moving in an electric field experiences an effective magnetic field in its rest frame. In crystals without inversion symmetry, it lifts the spin degeneracy and leads to many magnetic, spintronic and topological phenomena and applications. In bulk materials, SOC strength is a constant that cannot be modified. Here we demonstrate SOC and intrinsic spin-splitting in atomically thin InSe, which can be modified over an unprecedentedly large range. From quantum oscillations, we establish that the SOC parameter alpha is thickness-dependent; it can be continuously modulated over a wide range by an out-of-plane electric field, achieving intrinsic spin splitting tunable between 0 and 20 meV. Surprisingly, alpha could be enhanced by an order of magnitude in some devices, suggesting that SOC can be further manipulated. Our work highlights the extraordinary tunability of SOC in 2D materials, which can be harnessed for in operando spintronic and topological devices and applications.

Published in: "arXiv Material Science".

Intercorrelated ferroelectrics in 2D van der Waals materials. (arXiv:2011.10914v1 [cond-mat.mtrl-sci])

2020-11-24T02:29:39+00:00November 24th, 2020|Categories: Publications|Tags: , , , , |

2D intercorrelated ferroelectrics, exhibiting a coupled in-plane and out-of-plane ferroelectricity, is a fundamental phenomenon in the field of condensed-mater physics. The current research is based on the paradigm of bi-directional inversion asymmetry in single-layers, which restricts 2D intercorrelated ferroelectrics to extremely few systems. Herein, we propose a new scheme for achieving 2D intercorrelated ferroelectrics using van der Waals (vdW) interaction, and apply this scheme to a vast family of 2D vdW materials. Using first-principles, we demonstrate that 2D vdW multilayers-for example, BN, MoS2, InSe, CdS, PtSe2, TI2O, SnS2, Ti2CO2 etc.- can exhibit coupled in-plane and out-of-plane ferroelectricity, thus yielding 2D intercorrelated ferroelectricsferroelectric physics. We further predict that such intercorrelated ferroelectrics could demonstrate many distinct properties, for example, electrical full control of spin textures in trilayer PtSe2 and electrical permanent control of valley-contrasting physics in four-layer VS2. Our finding opens a new direction for 2D intercorrelated ferroelectric research.

Published in: "arXiv Material Science".

Some say, that 2D Research is the best website in the world.