Temperature Dependence Of Linewidth Research Articles

Interplay of Phonon Directionality and Emission Polarization in Two-Dimensional Layered Metal Halide Perovskites.

ConspectusLayered metal halide perovskites represent a natural quantum well system for charge carriers that provides rich physics, and the organic encapsulation of the inorganic metal halide layers not only increases their stability in devices but also provides an immense freedom to design their functionality. Intriguingly, these organic moieties strongly impact the optical, electrical, and mechanical properties, not only through their dielectric, elastic, and chemical properties but also because of induced mechanical distortions in the inorganic lattice. This tunability makes two-dimensional layered perovskites (2DLPs) highly attractive as light emitters. Common consensus is that exciton-phonon coupling plays an important role in radiative recombination. For bulk and some two-dimensional (2D) materials, the band edge emission broadening can be described by the classic models for polar inorganic semiconductors, while for the temperature dependence of the self-trapped exciton emission, an analysis developed for color centers has been successfully applied. For many 2DLPs these approaches do not work because of the complexity of their vibrational spectra. However, their emission is still strongly determined by phonons, and therefore, an adequate understanding of the electron-phonon coupling needs to be developed.With polarized and angle-resolved Raman spectroscopy studies on single 2DLP flakes based on different ammonium molecules as organic cations, in 2020 we revealed very rich phonon spectra in the low-frequency regime. Although the phonon bands at low frequency can generally be attributed to the vibrations of the inorganic lattice, we found very different responses by only changing the type of organic cations. In addition, the intensity of the different phonon modes depended strongly on the angle of the linearly polarized excitation beam with respect to the in-plane axes of the octahedron lattice. In 2022, we mapped this angular dependence of the phonon modes, which allowed identification of the directionality of the different lattice vibrations. By correlating the phonon spectra with the temperature-dependent emission for a set of 2DLPs that featured very different self-trapped exciton (STE) emission, we demonstrated that the exciton relaxation cannot be related to coupling with a single (longitudinal-optical) phonon band and that several phonon bands should be involved in the emission process. To gain insights into the exciton-phonon coupling effects on the band edge emission, we performed both angle-resolved polarized emission and Raman spectroscopy on single 2D lead iodide perovskite microcrystals. These experiments revealed the impact of the organic cations on the linear polarization of the emission and corroborated that multiple phonon bands should be involved in the radiative recombination process. Analysis of the temperature-dependent line width broadening of the band edge emission showed that for many systems, the behavior cannot be described by assuming the involvement of only one phonon mode in the electron-phonon coupling process. Our studies revealed a wealth of highly directional low-frequency phonons in 2DLPs from which several bands are involved in the emission process, which leads to diverse optical and vibrational properties depending on the type of organic cation in the material.

Evidence of strong and mode-selective electron–phonon coupling in the topological superconductor candidate 2M-WS2

The interaction between lattice vibrations and electrons plays a key role in various aspects of condensed matter physics — including electron hydrodynamics, strange metal behavior, and high-temperature superconductivity. In this study, we present systematic investigations using Raman scattering and angle-resolved photoemission spectroscopy (ARPES) to examine the phononic and electronic subsystems of the topological superconductor candidate 2M-WS2. Raman scattering exhibits an anomalous nonmonotonic temperature dependence of phonon linewidths, indicative of strong phonon–electron scattering over phonon–phonon scattering. The ARPES results demonstrate pronounced dispersion anomalies (kinks) at multiple binding energies within both bulk and topological surface states, indicating a robust and mode-selective coupling between the electronic states and various phonon modes. These experimental findings align with previous calculations of the Eliashberg function, providing a deeper understanding of the highest superconducting transition temperature observed in 2M-WS2 (8.8 K) among all transition metal dichalcogenides as induced by electron–phonon coupling. Furthermore, our results may offer valuable insights into other properties of 2M-WS2 and guide the search for high-temperature topological superconductors.

Demonstrating Kondo behavior by temperature-dependent scanning tunneling spectroscopy

The Kondo effect describes the scattering of conduction electrons by magnetic impurities, manifesting as an electronic resonance at the Fermi energy with a distinctive temperature evolution. In this Letter, we present a critical evaluation of the current methodology employed to demonstrate Kondo behavior in transport measurements, underscoring the limitations of established theoretical frameworks and the influence of extrinsic broadening. We introduce an approach for analyzing spectroscopic indicators of the Kondo effect, employing the Hurwitz-Fano lineshape as a model for the Kondo resonance in the presence of extrinsic broadening. Through precise scanning tunneling spectroscopy measurements on an exemplary spin-1/2 Kondo system, phenalenyl on Au(111), we demonstrate the efficacy of our proposed protocol in extracting accurate intrinsic Kondo linewidths from finite-temperature measurements. The extracted linewidths exhibit a robust fit with a recently derived expression for the temperature-dependent intrinsic Kondo linewidth, providing compelling evidence for the validity of the underlying theory. Published by the American Physical Society 2024

Plasmon Excitations across the Charge-Density-Wave Transition in Single-Layer TiSe2.

1T-TiSe2 is believed to possess a soft electronic mode, i.e., plasmon or exciton, that might be responsible for the exciton condensation and charge-density-wave (CDW) transition. Here, we explore collective electronic excitations in single-layer 1T-TiSe2 by using the ab initio electromagnetic linear response and unveil intricate scattering pathways of the two-dimensional (2D) plasmon mode near the CDW phase. We found the dominant role of plasmon-phonon scattering, which in combination with the CDW gap excitations leads to the anomalous temperature dependence of the plasmon line width across the CDW transition. Below the transition temperature TCDW a strong hybridization between the 2D plasmon and CDW excitations is obtained. These optical features are highly tunable due to temperature-dependent CDW-related modifications of electronic structure and electron-phonon coupling and make CDW-bearing systems potentially interesting for applications in optoelectronics and low-loss plasmonics.

Thermalization rate of polaritons in strongly-coupled molecular systems

Abstract Polariton thermalization is a key process in achieving light–matter Bose–Einstein condensation, spanning from solid-state semiconductor microcavities at cryogenic temperatures to surface plasmon nanocavities with molecules at room temperature. Originated from the matter component of polariton states, the microscopic mechanisms of thermalization are closely tied to specific material properties. In this work, we investigate polariton thermalization in strongly-coupled molecular systems. We develop a microscopic theory addressing polariton thermalization through electron-phonon interactions (known as exciton-vibration coupling) with low-energy molecular vibrations. This theory presents a simple analytical method to calculate the temperature-dependent polariton thermalization rate, utilizing experimentally accessible spectral properties of bare molecules, such as the Stokes shift and temperature-dependent linewidth of photoluminescence, in conjunction with well-known parameters of optical cavities. Our findings demonstrate qualitative agreement with recent experimental reports of nonequilibrium polariton condensation in both ground and excited states, and explain the thermalization bottleneck effect observed at low temperatures. This study showcases the significance of vibrational degrees of freedom in polariton condensation and offers practical guidance for future experiments, including the selection of suitable material systems and cavity designs.

An electron paramagnetic resonance study of the electron transport in heavily Si-doped high Al content AlxGa1−xN

High Al mole fraction AlGaN is an ultrawide bandgap semiconductor with potential applications in power electronics and deep UV detectors. Although n-type material is achievable with Si-doping, the role of Si is controversial, particularly for AlxGa1−xN with x > 0.8. For this paper, AlGaN films were grown by plasma-assisted molecular beam epitaxy onto bulk AlN substrates and doped with 1018–1020 cm−3 Si. We examine electron transport in heavily Si-doped AlxGa1−xN with x ≥ 0.65 using magnetic resonance, which allows us to probe the neutral donors directly rather than the free carriers and avoids complications due to electrical contacts. Transport was studied through the temperature-dependent linewidth of the electron paramagnetic resonance (EPR) signature for the neutral donor. Analysis shows evidence of hopping conductivity in the most lightly doped samples and impurity band formation in the most heavily doped ones. The EPR results, which are consistent with Hall measurements performed on the same samples, are promising for the development of highly conducting high Al content AlGaN.

Temperature dependence of growth-sector-dependent Raman spectra of boron-doped diamonds synthesized at high-pressure high-temperature

Single crystals of boron-doped diamond (BDD) were synthesized by the temperature gradient method in high-pressure and high-temperature conditions in the Fe–Al–B–C system, and multisectoral diamond plates were extracted. Temperature-dependent (77–600 K) high-resolution Raman spectroscopic studies have been carried out to investigate the behavior of anharmonic phonon decay in the {001}, {113}, and {111} growth sectors of multisectoral diamond plates with different content of boron impurities (⩽80 ppm) and compare with the data for undoped IIa diamond. Micro-Fourier transform infrared spectroscopy was used to estimate the spatial distribution of uncompensated boron impurity [Na-Nd] in BDD plates by analyzing boron-related absorption peaks. The plates were shown to have non-uniform growth-sector-dependent content of uncompensated boron impurity in the range from 1.1 × 1018 to 1.4 × 1019 cm−3. The effects of anharmonic decay (damping) of optical phonons in BDD are studied by modeling the temperature dependence of phonon frequency and linewidth of the diamond’s F2g and boron-induced vibrational modes. The extrapolated zero-temperature optical phonon linewidth and frequency and the anharmonic nature of their linear relationship are determined as a function of the growth sector and boron doping. The predominant mechanisms and parameters of the anharmonic decay of optical phonons are determined, which is of fundamental importance for the thermal conductivity of semiconductor materials. The anharmonic phonon decay remained the predominant process at higher temperatures, irrespective of the doping level.

Photophysical Properties of S = 5/2 Zigzag-1D (2-Bromoethylammonium)3MnBr5 Antiferromagnet.

It has been challenging to design multifunctional lead-free organic-inorganic hybrid halides that can exhibit fascinating magnetic and photoluminescence properties since the dimensionality of the compounds has a contrasting impact on them. In this context, our newly synthesized compound (2-bromoethylammonium)3MnBr5 (BEAMBr) crystallizes in the monoclinic C2/c space group with corner-sharing zigzag 1D chains of MnBr6 distorted octahedra. Intriguingly, it exhibits a long-range antiferromagnetic ordering at low temperature (∼2.5 K) along with a typical low-dimensional broad magnetic susceptibility hump. The magnetic properties modeled by the exact diagonalization approach indicate strong intrachain and weak interchain interactions with J1 = -50.1 K, J2 = -13.0 K, and J' = -1.25 K, respectively, suggesting excellent one-dimensionality. In addition, BEAMBr displays orange-red emission with a photoluminescence quantum yield of 15.2%. Interestingly, electron-phonon coupling was observed in this soft distorted compound with coupling strength γLO = 128.3 meV, confirmed from the analysis of temperature-dependent emission line width broadening and Raman spectra.

Charge transport in protic ionic liquids: Effect of protonation state in 1-methylimidazolium – acetate/trifluoroacetate mixtures

Despite the potential to overcome slow charge transport in ionic liquids by decoupling charge transport from mass transport in protic ionic liquids (PILs), the average proton distribution and the contribution of proton conduction to the overall charge transport in PILs has not been fully established. To elucidate the predominant underlying molecular species in the PILs and the molecular dynamics of the PILs, we study the dipolar response and conductivity using dielectric relaxation (DR) spectroscopy and the nucleis chemical environment and molecular mobility using nuclear magnetic resonance (NMR) spectroscopy of prototypical PILs based on 1–methylimidazolium as Brønsted base. To elucidate the effect of the acidity of the Brønsted acid we gradually vary the composition of the PILs from 1–methylimidazoliumacetate [MimH][AcO] to 1–methylimidazoliumtrifluoroacetate [MimH][TFA]. Both, 15N-NMR chemical shifts and the sample conductivities suggest that in neat [MimH][AcO] electro-neutral molecular species dominate, consistent with earlier findings. The dipolar response of these molecular species as detected via the DR spectra is stronger than what one would expect based on the molecular dipole moments estimated from density functional theory calculations, which points to the formation of an extended hydrogen-bonded network. Upon addition of [MimH][TFA], this dipolar response is reduced as the degree of protonation of 1–methylimidazolium gradually increases, which is apparent from the conductance and 15N chemical shifts. Interestingly, diffusion ordered NMR spectroscopy indicates protons to become more mobile than the constituting acid and base molecules, consistent with Grotthuss-like proton transport. To vary the immediate environment of the PILs, we study solutions of the PIL mixtures in aprotic dimethylformamide (DMF) and protic methanol (MeOH) as two limiting cases. We find that [MimH][AcO] exclusively forms electroneutral species in DMF, as evident from the negligible conductivity, while with increasing TFA content the fraction of charged molecular species increases. Although these ionic species give rise to a finite conductivity, demonstrating the presence of mobile ions, a large fraction of these ions is bound in [MimH][TFA] ion-pairs, as detected in the DR spectra. Yet, temperature dependent 1H-NMR linewidths of the acidic proton signals suggest proton exchange to occur on the NMR timescale, presumably between [MimH]+ and [Mim]. Conversely, in MeOH we find no evidence for the presence of ion-pairs, while the high conductivity of these solutions shows that MeOH can efficiently solvate ions and may participate in proton transfer. Together, our results highlight the sensitivity of protonation equilibria to the immediate environment and of proton dynamics to these protonation equilibria. Our results show that tuning these equilibria using PIL mixtures can provide routes to tailor the contribution of proton transport to charge transport in PILs.

Dephasing by optical phonons in GaN defect single-photon emitters

Single-photon defect emitters (SPEs), especially those with magnetically and optically addressable spin states, in technologically mature wide bandgap semiconductors are attractive for realizing integrated platforms for quantum applications. Broadening of the zero phonon line (ZPL) caused by dephasing in solid state SPEs limits the indistinguishability of the emitted photons. Dephasing also limits the use of defect states in quantum information processing, sensing, and metrology. In most defect emitters, such as those in SiC and diamond, interaction with low-energy acoustic phonons determines the temperature dependence of the dephasing rate and the resulting broadening of the ZPL with the temperature obeys a power law. GaN hosts bright and stable single-photon emitters in the 600–700 nm wavelength range with strong ZPLs even at room temperature. In this work, we study the temperature dependence of the ZPL spectra of GaN SPEs integrated with solid immersion lenses with the goal of understanding the relevant dephasing mechanisms. At temperatures below ~ 50 K, the ZPL lineshape is found to be Gaussian and the ZPL linewidth is temperature independent and dominated by spectral diffusion. Above ~ 50 K, the linewidth increases monotonically with the temperature and the lineshape evolves into a Lorentzian. Quite remarkably, the temperature dependence of the linewidth does not follow a power law. We propose a model in which dephasing caused by absorption/emission of optical phonons in an elastic Raman process determines the temperature dependence of the lineshape and the linewidth. Our model explains the temperature dependence of the ZPL linewidth and lineshape in the entire 10–270 K temperature range explored in this work. The ~ 19 meV optical phonon energy extracted by fitting the model to the data matches remarkably well the ~ 18 meV zone center energy of the lowest optical phonon band (E_{2}(low)) in GaN. Our work sheds light on the mechanisms responsible for linewidth broadening in GaN SPEs. Since a low energy optical phonon band (E_{2}(low)) is a feature of most group III–V nitrides with a wurtzite crystal structure, including hBN and AlN, we expect our proposed mechanism to play an important role in defect emitters in these materials as well.

Glycan Stability and Flexibility: Thermodynamic and Kinetic Characterization of Nonconventional Hydrogen Bonding in Lewis Antigens.

We provide evidence for CH-based nonconventional hydrogen bonds (H-bonds) for 10 Lewis antigens and two of their rhamnose analogues. We also characterize the thermodynamics and kinetics of the H-bonds in these molecules and present a plausible explanation for the presence of nonconventional H-bonds in Lewis antigens. Using an alternative method to simultaneously fit a series of temperature-dependent fast exchange nuclear magnetic resonance (NMR) spectra, we determined that the H-bonded conformation is favored by ∼1 kcal/mol over the non-H-bonded conformation. Additionally, a comparison of temperature-dependent 13C linewidths in various Lewis antigens and the two rhamnose analogues reveals H-bonds between the carbonyl oxygen of the N-acetyl group of N-acetylglucosamine and the OH2 group of galactose/fucose. The data presented herein provide insight into the contribution of nonconventional H-bonding to molecular structure and could therefore be used for the rational design of therapeutics.

Impact of the organic cation on the band-edge emission of two-dimensional lead-bromide perovskites.

Organic-inorganic low-dimensional layered metal-halide perovskites are semiconductors in which the optoelectronic properties can be tuned by the material composition and the design of the layered architecture. While the electronic band structure is mainly determined by the inorganic octahedra lattice, the binding and conformation of the organic cations induces related lattice distortions that can break the symmetry and lead to the splitting of the exciton energy levels, and influence the dielectric confinement. Furthermore, organic-induced lattice deformations lead to offsets in k-space (where k is the wavevector) that go along with the exciton energy level splitting. Hence, the electronic transitions between these levels require the momentum contribution of phonons, and contributions of phonons in the exciton recombination dynamics result in thermal broadening of the emission linewidth. In this work, we investigate the band-edge emission of two-dimensional Ruddlesden-Popper lead-bromide perovskites synthesized with different organic cations that vary in their binding head group and their alkyl chain length. We find several peaks in the low-temperature photoluminescence spectra, and the number of peaks in the band-edge emission and their decay dynamics depend strongly on the type of organic cation in the material, which we relate to the difference in the inorganic lattice distortions that the cations induce. For two-dimensional layered perovskites with mainly in-plane distortions, induced by short primary ammonium molecules, we find a two-fold splitting of the band edge emission at low temperatures. If also out-of-plane distortions are present, as for the long-chain primary ammoniums, a three-fold splitting is observed. Interestingly, the low-energy peaks of the split series merge into the highest energy peak with increasing temperature. Thermal broadening analysis of the temperature-dependent photoluminescence linewidth in the structures with out-of-plane distortions yields energies that are larger than those reported for the inorganic lattice phonons. This indicates the involvement of either high-frequency oscillations involving the organic cations, or the broadening might be related to higher order phonon scattering processes in the excitonic recombination process. The strong directionality of the phonon modes in the octahedral lattice could promote the involvement of multiple electron-phonon scattering processes in the exciton relaxation dynamics, for example involving modes with orthogonal directionality.

Significant Anharmonicity of Thermal Transport in Amorphous Silica at High Temperature

Amorphous Silica The significant anharmonicity, including temperature-dependent linewidths and frequency shifts of the vibrational modes in amorphous silica, is discussed in article number 2200217 by Bing-Yang Cao and Lei Yang. The anharmonic frequency shifts notably affect the strength of coupling between pairs of vibrational modes and dictate the positive temperature dependence at high temperatures, whereas the increasing linewidths with the rising temperature are of minor importance.

Insights into the Effect of Lithium Doping on the Deep Eutectic Solvent Choline Chloride:Urea.

Choline-based deep eutectic solvents (DESs) are potential candidates to replace flammable organic solvent electrolytes in lithium-ion batteries (LIBs). The effect of the addition of a lithium salt on the structure and dynamics of the material needs to be clarified before it enters the battery. Here, the archetypical DES choline chloride:urea at 1:2 mole fraction has been added with lithium chloride at two different concentrations and the effect of the additional cation has been evaluated with respect to the non-doped system via multinuclear NMR techniques. 1H and 7Li spin-lattice relaxation times and diffusion coefficients have been measured between 298 K and 373 K and revealed a decrease in both rotational and translational mobility of the species after LiCl doping at a given temperature. Temperature dependent 35Cl linewidths reflect the viscosity increase upon LiCl addition, yet keep track of the lithium complexation. Quantitative indicators such as correlation times and activation energies give indirect insights into the intermolecular interactions of the mixtures, while lithium single-jump distance and transference number shed light into the lithium transport, being then of help in the design of future DES electrolytes.

Superradiance and Exciton Delocalization in Perovskite Quantum Dot Superlattices.

Achieving superradiance in solids is challenging due to fast dephasing processes from inherent disorder and thermal fluctuations. Perovskite quantum dots (QDs) are an exciting class of exciton emitters with large oscillator strength and high quantum efficiency, making them promising for solid-state superradiance. However, a thorough understanding of the competition between coherence and dephasing from phonon scattering and energetic disorder is currently unavailable. Here, we present an investigation of exciton coherence in perovskite QD solids using temperature-dependent photoluminescence line width and lifetime measurements. Our results demonstrate that excitons are coherently delocalized over 3 QDs at 11 K in superlattices leading to superradiant emission. Scattering from optical phonons leads to the loss of coherence and exciton localization to a single QD at temperatures above 100 K. At low temperatures, static disorder and defects limit exciton coherence. These results highlight the promise and challenge in achieving coherence in perovskite QD solids.

Electron Spin Resonance Study of Hydrogen‐Free Germanium‐Doped Diamond‐Like Carbon Films

Hydrogen‐free germanium (Ge)‐doped diamond‐like carbon (DLC) films deposited on SiO2 substrates are studied by electron spin resonance (ESR) technique at T = 5–295 K. The Ge‐free and DLC films with 1 and 2.5 at% Ge content having low cytotoxicity are investigated. A single Lorentzian ESR line resulting from exchange interaction between localized (LE) and nonlocalized electrons (NE) is observed. The spin susceptibility temperature dependence deviates from the Curie–Weiss law at T > 75 K due to Pauli contribution caused by NE. The antiferromagnetic low‐temperature spin ordering in DLC films, decreasing with Ge content, is observed. The LE contribution is significant for Ge‐free and DLC:1%Ge, whereas NE makes the main contribution to DLC:2.5%Ge. The LEs are related to sp 2/sp carbon‐related centers, while the NEs are assigned with electrons in the sp 3 orbital. The correlation between the sp 3/sp 2 ratio and the shift of g‐factor for NE to lower values with Ge doping is established. The Korringa relaxation model is provided for the ESR linewidth temperature dependence. The higher density of LE states on Fermi energy level caused by Ge doping of DLC films is proposed.

Zero-Dimensional (Piperidinium)2MnBr4: Ring Puckering-Induced Isostructural Transition and Strong Electron-Phonon Coupling-Mediated Self-Trapped Exciton Emission.

We report on the synthesis, structure, and photophysical properties of a lead-free organic-inorganic hybrid halide, (Piperidinium)2MnBr4 (PipMBr). It crystallizes in a monoclinic P21/n structure, with isolated MnBr4 tetrahedra representing a zero-dimensional compound. It undergoes a reversible isostructural transition at 422/417 K in the heating/cooling cycle owing to the hydrogen-bonding rearrangement mediated by ring puckering of piperidinium cations. This compound exhibits green emission with a photoluminescence quantum yield of 51%. Interestingly, strong electron-longitudinal optical phonon coupling with γLO of 237 meV is evidenced from the broadening of the temperature-dependent emission linewidth and the Raman spectrum. Such strong electron-phonon coupling and a relatively low Debye temperature (137 K) suggest the self-trapped exciton emission in this compound.

Spin-Orbit-Torque Efficiency and Current-Driven Coherent Magnetic Dynamics in a Pt / Ni /Py Trilayer-Based Spin Hall Nano-Oscillator

We experimentally study the current-induced effective spin-orbit torque (SOT) efficiency and the spectral characteristics of current-driven coherent magnetic dynamics in spin Hall nano-oscillators (SHNOs) based on the $\mathrm{Pt}$/$\mathrm{Ni}$/Py trilayer. We determine that the $\mathrm{Pt}$/$\mathrm{Ni}$/Py trilayer structure has an effective dampinglike torque efficiency ${\ensuremath{\xi}}_{\mathrm{DL}}\ensuremath{\sim}0.055$, comparable with the $\mathrm{Pt}$/$\mathrm{Co}$ and $\mathrm{Pt}$/$\mathrm{Fe}$ bilayer systems with a strong interfacial spin-orbit coupling and magnetic proximity effect. Furthermore, the microwave-generation spectra show that the $\mathrm{Pt}$/$\mathrm{Ni}$/Py-based SHNOs exhibit a single nonlinear self-localized bullet mode with a frequency below ${f}_{\mathrm{FMR}}$ and a significant current-dependent frequency red shift due to its strong nonlinear effect, which is very similar to that in $\mathrm{Pt}$/Py-based SHNOs, at low oblique angles $\ensuremath{\varphi}\ensuremath{\le}\phantom{\rule{0.2em}{0ex}}{50}^{\ensuremath{\circ}}$. In contrast, at high oblique angles $\ensuremath{\varphi}\ensuremath{\ge}\phantom{\rule{0.2em}{0ex}}{55}^{\ensuremath{\circ}}$, the spectra show two oscillating peaks with very similar field-, current-, and temperature-dependent behaviors, which suggests the spatial coexistence of two same-type nonlinear self-localized bullet modes at certain currents and magnetic fields. Additionally, the observed linear temperature dependence of the minimum line width, which resembles the thermal broadening of single-mode oscillation, further confirms that two localized bullet modes are independent, spatially separated, and lack thermally activated mode-transition behavior. Our results provide valuable information for the electronic control of coherent magnetic dynamics by combining bulk and interfacial spin-orbit coupling effects in the magnetic heterostructures.

Layered SnSe nanoflakes with anharmonic phonon properties and memristive characteristics

Understanding the phonon anharmonicity and temperature-dependent behavior of phonons that affect the thermal transport properties in 2D materials is crucial for developing efficient thermoelectric and memristor devices. SnSe has attracted significant interest because of its potential applications for developing such novel devices. Here, orthorhombic SnSe nanoflakes with a thickness of less than 100 nm and oriented along the [100] crystal axis were obtained using physical vapor transport at atmospheric pressure. Polarization-resolved Raman spectroscopy of SnSe nanoflakes was performed at a temperature of 5 K. Temperature-dependent frequencies and linewidths of Raman modes in tin selenide were fitted according to the anharmonic phonon coupling theory. The results indicate that both two and three order processes are responsible for the phonon decay in tin selenide. The memristive property was confirmed by electrical measurements of SnSe devices. SnSe memristors have an operating current of 10−4 A, similar to other transition-metal dichalcogenide memristors, but are more energy efficient than memristors based on defect migration, with a threshold voltage of 3 V.

Evidence of phase stability, topological phonon and temperature-induced topological phase transition in rocksalt SnS and SnSe

Both SnS and SnSe have been experimentally and theoretically confirmed as topological crystalline insulators in native rocksalt structure. Here, phononic structure, thermodynamic properties and temperature dependent electron–phonon interaction (EPI) have investigated for both the materials in rocksalt phase. Previously performed theoretical studies have predicted the phase instability of SnS in this crystal structure at ambient condition. But, after a detailed study performing on the phonon calculation of SnS, we have predicted the phase stability of SnS with considering the Sn 4p orbitals as valence states in ab-initio calculation. The importance of long range Coulomb forces along with the themodynamical properties are also described in detailed for both materials. The computed value of Debye temperature () for SnS (SnSe) is ∼315.0 K (∼201.7 K). The preliminary evidence of topological phonon is found along X–W direction, where the linear band touching is observed as compared to type II Weyl phononic material ZnSe (Liu et al 2021 Phys. Rev. B 103 094306). The topological phase transition is seen for these materials due to EPI, where non-linear temperature dependent bandgap is estimated. The predicted value of transition temperature for SnS (SnSe) is found to be ∼700 K, where after this temperature the non-trivial to trivial topological phase is seen. The strength of EPI shows more stronger impact on the electronic structure of SnS than SnSe material. The reason of non-linear behaviour of bandgap with rise in temperature is discussed with the help of temperature dependent linewidths and lineshifts of conduction band and valence band due to EPI. The present study reveals the phase stability of SnS along with the comparative study of thermal effect on EPI of SnS and SnSe. Further, the possibility of temperature induced topological phase transition provides one of important behaviour to apply these two materials for device making application.