Application Of Uniaxial Strain Research Articles

First principles predictions of structural, electronic and topological properties of two-dimensional Janus Ti2N2XI (X = Br, Cl) structures.

Motivated by the report of the giant Rashba effect in ternary layered compounds BiTeX, we consider two Janus structured compounds Ti2N2XI (X = Br, Cl) of the same ternary family exhibiting a 1 : 1 : 1 stoichiometric ratio. Broken inversion symmetry in the Janus structure, together with its unique electronic structure exhibiting anti-crossing states formed between Ti-d states and strong spin-orbit coupled I-p states, generates large Rashba cofficients of 2-3 eV Å for these compounds, classifying them as strong Rashba compounds. The anti-crossing features of the first-principles calculated electronic structure also result in non-trivial topology, combining two quantum phenomena - Rashba effect and non-trivial topology - in the same materials. This makes Janus TiNI compounds candidate materials for two-dimensional composite quantum materials. The situation becomes further promising by the fact that the properties are found to exhibit extreme sensitivity and tunability upon application of uniaxial strain.

Rashba and Dresselhaus effects in doped methylammonium lead halide perovskite MAPbI3.

Inorganic-organic lead halide perovskites, particularly methylammonium lead halide (MAPbI3) perovskite, have been regarded as promising materials for optoelectronics and spintronics. However, the practical applications of these perovskites are limited by lead toxicity and instability under air and pressure. This study investigates the substitution of Pb with Sn and Ge in cubic MAPbI3 perovskite. The properties of the resulting hybrid perovskites are compared using state-of-the-art first-principles-based methodologies, viz., density functional theory (DFT) with generalized gradient approximation (PBE) and hybrid functional (HSE06), in conjunction with spin-orbit coupling (SOC). Here, we mainly study the Rashba-Dresselhaus (RD) effect, which arises due to two major mechanisms: (i) the breaking of inversion symmetry (static and dynamic) and (ii) SOC, originating from the presence of heavy elements. We find significant spin-splitting effects in the conduction band minimum and valence band maximum for hybrid perovskites. To gain a deeper understanding of the observed spin-splitting, the spin textures are analyzed, and Rashba coefficients are calculated. We find that the Dresselhaus effect comes into play in substituted hybrid structures in addition to the usual Rashba effect observed in the pristine compound. Additionally, we observe that the strength of Rashba spin-splitting is substantially tuned by the application of uniaxial strain (±5%). Moreover, certain hybrid perovskites exhibit mechanical stability and ductility, making them potential candidates in perovskite-based optoelectronics and spintronics applications.

Theoretical insight of origin of Rashba-Dresselhaus effect in tetragonal and rhombohedral phases of BiFeO3.

The inclusion of the spin-orbit coupling effect in ferroelectric materials with non-centrosymmetry leads to intriguing properties for spintronic applications. In the present work, a comparative study of spin splitting in the bulk electronic energy bands of the tetragonal and rhombohedral phases of BiFeO3 (BFO) in terms of the Rashba and Dresselhaus effects is carried out through first-principles calculations. The obtained spin splittings, particularly at the conduction band minima, are further supplemented with an effective k·p model analysis. For the tetragonal BFO, a dominating pure bulk-type Rashba effect with helical in-plane spin components shown through diagrams is observed, whereas the rhombohedral BFO shows a significant contribution from the out-of-plane spin components and an interplay between the Rashba and Dresselhaus effects is discussed. In addition, tunability of the Rashba parameters with the application of uniaxial strain (±5%) is obtained in tetragonal BFO, in which the Rashba coefficient (αR) doubles with a compressive 5% strain, making tetragonal BFO a suitable candidate for spintronic applications. More importantly, full reversal of the in-plane spin texture is obtained for the opposite polarization states in tetragonal BFO with an activation energy barrier of 1.13 eV.

Tunable interaction between excitons and hybridized magnons in a layered semiconductor.

The interaction between distinct excitations in solids is of both fundamental interest and technological importance. One such interaction is the coupling between an exciton, a Coulomb bound electron-hole pair, and a magnon, a collective spin excitation. The recent emergence of van der Waals magnetic semiconductors1 provides a platform to explore these exciton-magnon interactions and their fundamental properties, such as strong correlation2, as well as their photospintronic and quantum transduction3 applications. Here we demonstrate the precise control of coherent exciton-magnon interactions in the layered magnetic semiconductor CrSBr. We varied the direction of an applied magnetic field relative to the crystal axes, and thus the rotational symmetry of the magnetic system4. Thereby, we tuned not only the exciton coupling to the bright magnon, but also to an optically dark mode via magnon-magnon hybridization. We further modulated the exciton-magnon coupling and the associated magnon dispersion curves through the application of uniaxial strain. At a critical strain, a dispersionless dark magnon band emerged. Our results demonstrate an unprecedented level of control of the opto-mechanical-magnonic coupling, and a step towards the predictable and controllable implementation of hybrid quantum magnonics5-11.

Ab-initio study of topological phase tuning in Half-Heusler YPdBi compound

The topological phase tuning in Half-Heusler alloys could be hosted from trivial to non-trivial states and vice-versa, either with a small variation in the lattice parameter or by introducing the spin-orbit coupling. First principles simulations of the electronic bulk band structure of the YPdBi compound exhibit the topologically non-trivial semimetal state without and with spin-orbit coupling at equilibrium lattice constant due to the single band-inversion at Γ-point. We observed the topological phase tuning from a non-trivial to a trivial state due to the second band-inversion at Γ-point, after applying the hydrostatic pressure of ∼4 GPa. The semimetallic nature of these compounds is protected by the cubic symmetry of the crystal. Thus, by breaking cubic symmetry of the crystal with the application of uniaxial strain along the c-axis and biaxial strain in the ab-plane, we have noticed the topological phase transition from a non-trivial semimetal state to a topological insulator. The importance of half-Heusler compounds lies in their usage as a promising candidate in nanoelectronic applications.

Origin of Rashba Spin Splitting and Strain Tunability in Ferroelectric Bulk CsPbF3

Spin-orbit coupling (SOC) in conjunction with broken inversion symmetry acts as a key ingredient for several intriguing quantum phenomena, viz., Rashba-Dresselhaus (RD) effect. The coexistence of spontaneous polarization and the RD effect in ferroelectric (FE) materials enables the electrical control of spin degrees of freedom. Here, we explore the FE lead halide perovskite CsPbF3 as a potential candidate in the field of spintronics by employing state-of-the-art first-principles-based methodologies, viz., density functional theory (DFT) with semilocal and hybrid functional (HSE06) combined with SOC and many-body perturbation theory (G0W0). For a deeper understanding of the observed spin splitting, the spin textures are analyzed using the k.p model Hamiltonian. We find there is no out-of-plane spin component indicating that the Rashba splitting dominates over Dresselhaus splitting. We also observe that the strength of Rashba spin splitting can be substantially tuned on application of uniaxial strain (±5%). More interestingly, we notice reversible spin textures by switching the FE polarization in CsPbF3 perovskite, making it potent for perovskite-based spintronic applications.

Influence of uniaxial deformation on surface morphology and corrosion performance of chromium-based coatings for packaging steel

Chromium-based coatings on steel, cathodically electroplated from Cr(VI) and Cr(III) electrolytes, were studied to compare their corrosion resistance following application of uniaxial strain. An organic overcoat (PVB) was applied to strained samples and an in-situ scanning Kelvin probe technique was used to determine rates of PVB cathodic disbondment. The Cr(VI) derived coatings were fully resistant to cathodic disbondment post-deformation. The Cr(III) derived coatings exhibited increased rates of cathodic disbondment with increasing uniaxial strain. The Kinetics of cathodic disbondment are explained on the basis of coating morphology produced by deformation, and the exposure of underlying iron. The electrochemical availability of iron is estimated by measuring hydrogen evolution kinetics on cathodically polarised samples.

Designing frustration in two-dimensional magnetic systems via the application of uniaxial strain

First principles are used and combined with Monte Carlo simulations to predict that the application of compressive uniaxial strains in two-dimensional $\mathrm{CrGe}{\mathrm{Te}}_{3}$ can tune the underlying magnetic parameters in such a way that the system undergoes a phase transition from ferromagnetic (FM) to antiferromagnetic (AFM) phases, with the border between these being a region of high frustration. Such latter region can be the playground for fine-tuning the system to exhibit exotic states. Moreover, we also show and explain that such uniaxial strains also dramatically tune the critical temperatures, namely N\'eel temperatures for the AFM phase and Curie temperatures for the FM phase, which is of obvious technological and fundamental significance.

Electronic Structure Correspondence of Singlet-Triplet Scale Separation in Strained Sr2RuO4

At a temperature of roughly 1 K, Sr2RuO4 undergoes a transition from a normal Fermi liquid to a superconducting phase. Even while the former is relatively simple and well understood, the superconducting state has not even been understood after 25 years of study. More recently, it has been found that critical temperatures can be enhanced by the application of uniaxial strain, up to a critical strain, after which it falls off. In this work, we take an “instability” approach and seek divergences in susceptibilities. This provides an unbiased way to distinguish tendencies to competing ground states. We show that in the unstrained compound, the singlet and triplet instabilities of the normal Fermi liquid phase are closely spaced. Under uniaxial strain, electrons residing on all orbitals contributing to the Fermiology become more coherent, while the electrons of the Ru-dxy character become heavier, and the electrons of the Ru-dxz,yz characters become lighter. In the process, Im χ(q,ω) increases rapidly around q = (0.3,0.3,0)2π/a and q = (0.5,0.25,0)2π/a, while it gets suppressed at all other commensurate vectors, in particular at q = 0, which is essential for spin-triplet superconductivity. We observe that the magnetic anisotropy under strain drops smoothly, which is concomitant with the increment in singlet instability. Thus, the triplet superconducting instability remains the lagging instability of the system, and the singlet instability enhances under strain, leading to a large energy-scale separation between these competing instabilities. However, since this happens even without spin-orbit coupling, we believe it is primarily the enhancement in the spin fluctuation glue around quasi-anti-ferromagnetic vectors that drives the Cooper pairing instead of the magnetic anisotropy. At large strain, an instability to a spin density wave overtakes the superconducting one. The analysis relies on a high-fidelity, ab initio description of the one-particle properties and two-particle susceptibilities, based on the quasiparticle self-consistent GW approximation augmented by dynamical mean field theory. This approach is described and its high fidelity confirmed by comparing to observed one- and two-particle properties.

Half metallicity and ferromagnetism of vanadium nitride nanoribbons: a first-principles study.

Half metallic materials with intrinsic ferromagnetism are identified as the pillar of next generation spintronic devices. In search of new low-dimensional materials with these excellent properties, herein we systematically study the electronic and magnetic properties of edge dependent (armchair (ac) and zigzag (zz)) vanadium nitride nanoribbons (VNNRs) using density functional theory (DFT) based calculations. Both the ac and zz VNNRs show robust ferromagnetism and extensive half-metallicity with large band gaps (3.9-4.3 eV for ac and 2.5-3.0 eV for zz VNNRs) for the down spin channel. Interestingly, even with the application of uniaxial strain (both tensile and compressive) along the axis of the ribbons, VNNRs retain their extensive half metallicity with a large spin band gap and robust ferromagnetic behavior. Spin dependent electronic transport reveals the 100% spin filtering efficiency of nanoribbons, in both the free state and under applied strain, which support the robust half metallicity of VNNRs. Our study of VNNRs on a MoS2 substrate also shows half metallicity along with high stability, indicating the usage of MoS2 as a substrate for the synthesis of VNNRs. All these results guide the potential application of VNNRs in spintronic devices.

Revealing the single electron pocket of FeSe in a single orthorhombic domain

We measure the electronic structure of FeSe from within individual orthorhombic domains. Enabled by an angle-resolved photoemission spectroscopy beamline with a highly focused beamspot (nano-ARPES), we identify clear stripe-like orthorhombic domains in FeSe with a length scale of approximately 1-5~$\mu$m. Our photoemission measurements of the Fermi surface and band structure within individual domains reveal a single electron pocket at the Brillouin zone corner. This result provides clear evidence for a one-electron pocket electronic structure of FeSe, observed without the application of uniaxial strain, and calls for further theoretical insight into this unusual Fermi surface topology. Our results also showcase the potential of nano-ARPES for the study of correlated materials with local domain structures.

Tunable phonon nanocapacitor built by carbon schwarzite based host-guest system

The ability to control monochromatic and coherent phonons is crucial for many phonon-related applications but remains very challenging. Here, we demonstrate a promising phonon nanocapacitor for storing and emitting phonons, built by the carbon schwarzite based host-guest system (HGS). This phonon nanocapacitor takes advantage of the inherently strong phonon confinement of the hybridized modes in HGS. The monochromaticity and coherence of the stored phonons are well demonstrated via the ultralong phonon lifetime and coherent time. More interestingly, the frequency of the nanocapacitor is widely tunable from gigahertz to several terahertz by engineering the host-guest interaction. Finally, the stored phonons with different polarizations can be emitted separately with the application of uniaxial strain along a particular direction. This work may provide new opportunities for studying the coherent wave effect of phonons.

Topological nonlinear anomalous Nernst effect in strained transition metal dichalcogenides

We theoretically analyze the non-linear anomalous Nernst effect as the second-order response of temperature gradient by using the semiclassical framework of electron dynamics. We find that a non-linear current can be generated transverse to the applied temperature gradient in time-reversal-symmetry materials with broken inversion symmetry. This effect has a quantum origin arising from the Berry curvature of states near the Fermi surface. We discuss the non-linear Nernst effect in transition metal dichalcogenides~(TMDCs) under the application of uniaxial strain. In particular, we predict that under fixed chemical potential in TMDCs, the non-linear Nernst current exhibits a transition from $\textbf{j}^\text{dip}_\text{A}\sim T^{-2}$ temperature dependence in low temperature regime to a linear $T$-dependence in high temperature.

Membrane Mechanical Properties Regulate the Effect of Strain on Spontaneous Electrophysiology in Human iPSC-Derived Neurons

Peripheral nerves contain neuron fibers vital for movement and sensation and are subject to continuous elongation and compression during everyday movement. At supraphysiological strains conduction blocks occur, resulting in permanent or temporary loss of function. The mechanisms underpinning these alterations in electrophysiological activity remain unclear; however, there is evidence that both ion channels and network synapses may be affected through cell membrane transmitted strain. The aim of this work was to quantify the changes in spontaneous activity resulting from application of uniaxial strain in a human iPS-derived motor neuron culture model, and to investigate the role of cell membrane mechanical properties during cell straining. Increasing strain in a custom-built cell-stretching device caused a linear decrease in spontaneous activity, and no immediate recovery of activity was observed after strain release. Imaging neuronal membranes with c-Laurdan showed changes to the lipid order in neural membranes during deformation with a decrease in lipid packing. Neural cell membrane stiffness can be modulated by increasing cholesterol content, resulting in reduced stretch-induced decrease of membrane lipid packing and in a reduced decrease in spontaneous activity caused by mechanical strain. Together these results indicate that the mechanism whereby cell injury causes impaired transmission of neural impulses may be governed by the mechanical state of the cell membrane, and contribute to establishing a direct relationship between neural uniaxial straining and loss of spontaneous neural activity.

First demonstration of improvement in hole conductivity in c-plane III-Nitrides through application of uniaxial strain

Hole transport in III-Nitrides (III-Ns) is dominantly dependent on the large effective mass of holes and thus, results in a low hole mobility. First principle band structure calculations suggest that under uniaxial strain, the valence band degeneracy can be broken and the light hole band with lower hole effective mass can be obtained as the topmost valence band. In this work, we experimentally demonstrate the improvement in hole conductivity under the application of uniaxial strain in III-Ns. We obtained approximately 25%–50% lower sheet resistance with uniaxially strained InGaN layers compared to planar biaxially strained InGaN layers.

Strain engineering of antimonene by a first-principles study: Mechanical and electronic properties

In this work, we investigate the mechanical and electronic properties of monolayer antimonene in its most stable beta-phase using first-principles calculations. The upper region of its valence band is found to solely consist of lone pair p-orbital states, which are by nature more delocalized than the d-orbital states in transition metal dichalcogenides, implying superior transport performance of antimonene. The Young's and shear moduli of beta-antimonene are observed to be ~25% higher than those of bulk antimony, while the hexagonal lattice constant of the monolayer reduces significantly (~5%) from that in bulk, indicative of strong inter-layer coupling. The ideal tensile test of beta-antimonene under applied uniaxial strain highlights ideal strengths of 6 GPa and 8 GPa, corresponding to critical strains of 15% and 17% in the zigzag and armchair directions, respectively. During the deformation process, the structural integrity of the material is shown to be better preserved, albeit moderately, in the armchair direction. Interestingly, the application of uniaxial strain in the zigzag and armchair directions unveil direction-dependent trends in the electronic band structure. We find that the nature of the band gap remains insensitive to strain in the zigzag direction, while strain in the armchair direction activates an indirect-direct band gap transition at a critical strain of 4%, owing to a band switching mechanism. The curvature of the conduction band minimum increases during the transition, which suggests a lighter effective mass of electrons in the direct-gap configuration than in the free-standing state of equilibrium. The work function of free-standing beta-antimonene is 4.59 eV and it attains a maximum value of 5.07 eV under an applied biaxial strain of 4%.

Engineering the Electronic Structure of Tin Sulfide Nanoribbons: A Computational Study

We have investigated the structure, stability, and the electronic properties of bare and edge-hydrogenated tin sulfide nanoribbons (SnSNRs) using first-principles density functional theory calculation. In contrast with the 2D sheet of SnS, which is an indirect band-gap semiconductor, bare 1D SnSNRs are either metallic (in the case of zigzag (zz) edge termination) or direct/indirect band-gap semiconductors (in the case of armchair (ac) edge termination) in nature. The edge-hydrogenated zigzag nanoribbons are direct band-gap semiconductors and the edge-hydrogenated armchair nanoribbons are direct/indirect band-gap semiconductors depending on width. The edge-hydrogenated nanoribbons have low edge energies and quite high mechanical strength, indicating their energetic as well as mechanical stabilities. Moreover, armchair SnSNRs can tolerate very high expansive strain (∼65%) due to their morphological transformation from puckered to buckled ones. On the application of uniaxial strain (both expansive and compre...

Strain-enhanced optical absorbance of topological insulator films

Topological insulator films are promising materials for optoelectronics due to a strong optical absorption and a thickness dependent band gap of the topological surface states. They are superior candidates for photodetector applications in the THz-infrared spectrum, with a potential performance higher than graphene. Using a first-principles $k\cdot p$ Hamiltonian, incorporating all symmetry-allowed terms to second order in the wave vector $k$, first order in the strain $\epsilon$ and of order $\epsilon k$, we demonstrate significantly improved optoelectronic performance due to strain. For Bi$_2$Se$_3$ films of variable thickness, the surface state band gap, and thereby the optical absorption, can be effectively tuned by application of uniaxial strain, $\epsilon_{zz}$, leading to a divergent band edge absorbance for $\epsilon_{zz}\gtrsim 6\%$. Shear strain breaks the crystal symmetry and leads to an absorbance varying significantly with polarization direction. Remarkably, the directional average of the absorbance always increases with strain, independent of material parameters.

Uniaxial strain induced optical properties of complex type-II InGaAs/InAs/GaAsSb nano-scale heterostructure

Semiconducting heterostructures offer an extra degree of flexibility in terms of tuning of optical gain and transition energies or wavelengths. Modifications in the wave functions and alterations in optical transitions in binary and ternary QW (quantum well) heterostructures due to external uniaxial strain provide valuable insights on the optical characteristics of the heterostructure. In this paper, we have reported the effect of uniaxial strain along [001], [100] and [110] on the optical properties such as optical gain, and optical transition energies of W − shaped complex type-II InGaAs/InAs/GaAsSb nano-scale heterostructure consisting of two quantum wells of InAs material using the six band k.p theory. On the basis of results obtained in the work, it can be reported that the TE and TM optical gain can be enhanced by application of uniaxial strain along [110] only. It is also reported that application of strain along [001] is useful for improvement of TE optical gain while strain along [100] is useful for TM optical gain. Thus, for the type-II InGaAs/InAs/GaAsSb nano-heterostructure TE and TM gain and as well as transition energies can be controlled by the application of uniaxial strain along the choice of direction.

The effects of different possible modes of uniaxial strain on the tunability of electronic and band structures in $$\text {MoS}_2$$ MoS 2 monolayer nanosheet via first-principles density functional theory

Ab-initio density functional theory-based calculations have been performed on monolayer (ML) $$\text {MoS}_2$$ nanosheet to study the variation of its electronic properties with the application of uniaxial tensile and compressive strain along its two non-equivalent lattice directions, namely, the zig-zag and the arm-chair directions. Among all the strain types considered in this study, uniaxial tensile strain applied along the zig-zag direction is found to be the most efficacious, inducing a greater tunability in the band gap over a large energy range (from 1.689 to 0.772 eV corresponding to 0–9% of applied strain), followed by uniaxial tensile strain along arm-chair direction. In contrast, the ML– $$\text {MoS}_2$$ nanosheet is found to be less sensitive to the compressive strain applied uniaxially along both the arm-chair as well as zig-zag directions. Moreover, the charges on Mo and S atoms are not found to undergo considerable changes under the application of uniaxial strain, as the atomic motion along the other direction is free from any constraint.