Electron-phonon Coupling Mechanism Research Articles

Exploring hot carrier relaxation dynamics in MoSi2N4 monolayer for photocatalytic applications: Insights into electron-phonon coupling mechanisms

The relaxation process of hot carriers in MoSi2N4 monolayer remains unclear due to the need to sample electron–phonon interaction at different momenta. Utilizing density functional theory (DFT) combined with nonadiabatic molecular dynamics (NAMD), we determined that the material possesses an indirect bandgap of approximately 2.33 eV, primarily originating from the d orbitals of inner Mo atoms. NAMD simulations unveil rapid relaxation of hot electrons and holes, exhibiting lifetimes of approximately 166 fs and 146 fs, respectively. The rapid relaxation of hot carriers couples with the vibrations of outer Si and N atoms, with no inter-valley scattering observed between the K and K′ valleys. Notably, the coupling between the d orbitals of inner Mo atoms and the vibrations of outer Si and N atoms plays a pivotal role in determining the relaxation dynamics of hot carriers, shedding light on the intricate interplay between electronic and vibrational modes in this material. Our research reveals the potential application value of MoSi2N4 monolayer material as a photocatalyst and elucidates a relaxation mechanism governing the dynamics of excited carriers.

Charge-Density-Wave Order And Electronic Phase Transitions in a Dilute D-Band Semiconductor.

As one of the most fundamental physical phenomena, charge density wave (CDW) order predominantly occurs in metallic systems such as quasi-one-dimensional (quasi-1D) metals, doped cuprates, and transition metal dichalcogenides, where it is well understood in terms of Fermi surface nesting and electron-phonon coupling mechanisms. On the other hand, CDW phenomena in semiconducting systems, particularly at the low carrier concentration limit, are less common and feature intricate characteristics, which often necessitate the exploration of novel mechanisms, such as electron-hole coupling or Mott physics, to explain. In this study, we combined electrical transport, synchrotron X-ray diffraction and density-functional theory (DFT) calculations to investigate CDW order and a series of hysteretic phase transitions in a dilute d-band semiconductor, BaTiS3 . Our experimental and theoretical findings suggest that the observed CDW order and phase transitions in BaTiS3 may be attributed to both electron-phonon coupling and non-negligible electron-electron interactions in the system. Our work highlights BaTiS3 as a unique platform to explore CDW physics and novel electronic phases in the dilute filling limit and could open new opportunities for developing novel electronic devices. This article is protected by copyright. All rights reserved.

RTS Noise Characterization of Trap Properties in InGaAs nFinFETs

In order to extract and characterize the trap properties in In <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula> Ga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{1}-\textit{x}}$</tex-math> </inline-formula> As nFinFET sensitively and effectively, the time-domain and frequency-domain characteristics of low-frequency noise are studied by the random telegraph signal (RTS) method. It is found that the RTS noise in this study originates from the strong electron–phonon coupling mechanism. The activation energies of traps are extracted from the Arrhenius curves, and the results show that these traps mainly come from extended defects, such as dislocation, etc. Furthermore, the relationship between noise characteristics and gate length is explored, it is found that with the reduction of the gate length, the noise contains more RTS components. The noise behavior of devices with different In content is also investigated, it shows that the average of activation energies, as well as the capture cross section of bulk traps, decrease with the increasing In content in the channel. Overall, it can be concluded that the RTS noise is an effective tool to reveal the defect properties of nano-scaled devices. It can be used to provide theoretical guidance in improving the performance and reliability of devices.

Strain and Optoelectronic Tuning in Mixed‐Halide Perovskites with Ion Irradiation

AbstractDefects usually behave as imperfections in materials that significantly degrade their performance. However, the unusual optoelectronic performance in metal halide perovskites in the presence of defects opens the way for strain and optoelectronic properties tailoring with ion irradiation. Defects and strain engineering is performed in triple‐cation mixed halide perovskites using proton irradiation at 1 MeV and different fluences. At intermediate fluence, the initial polycrystalline film compressive strain (−0.15%) can be released, improving exciton lifetimes from about 500 ns to ≈1 µs. In contrast, high irradiation fluence is shown to restore compressive strain leading to sample degradation, with lower lifetime values (≈200 ns). Also, the phase segregation occurring under light illumination between bromine‐rich and iodine‐rich regions is shown to be defects‐mediated as the segregation rate increases by a factor of four for high proton irradiation fluence. The irradiation defects are revealed with low‐temperature photoluminescence (PL) through bound exciton radiative recombination mechanisms. The PL temperature dependence gives some insight into electron–phonon coupling mechanism and their modification with ion irradiation.

Aromatic superconductors: Electron-phonon coupling and electronic correlations

&lt;sec&gt;Aromatic superconductors are a new type of high-temperature superconductor discovered in recent years. The superconducting transition temperature (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt;) increases with the size of aromatic molecule increasing, which has attracted widespread attention of experimental and theoretical researchers. The driving mechanism for such a superconductivity, whether it is dominated by electron-phonon coupling or electronic correlation effects, has aroused great interest of many research groups. This paper briefly introduces the rich superconducting phenomena of metal doped aromatic compounds. From the perspectives of electron-phonon coupling or electronic correlations, the superconductivity of aromatic compounds is discussed, which is helpful in exploring aromatic superconductors with higher &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt;. The challenges currently faced in the field are also introduced.&lt;/sec&gt;&lt;sec&gt;The rest of this paper is organized as follows. We first introduce the existence of abundant superconducting phases in the experiment of metal doped aromatic compounds. Different doping concentrations of metal cause superconducting phases with different &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; values, especially the highest &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; value of the superconducting phase increases with the size of aromatic molecule increasing. Theoretical prediction shows that all aromatic hydrocarbon superconductors have a low-&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; superconducting phase in a range of 5–7 K, which is a common feature. For systems with few benzene rings (such as benzene, naphthalene, and phenanthrene crystals), only low-&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; phase of 5–7 K exists, while in systems with multiple benzene rings (such as picene, dibenzopentacene, and others with the number of benzene rings more than 5), there are multiple superconducting phases; the highest &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; in long-benzene-ring system depends not only on the number of benzene rings, but also on the chain size of organic molecule. Further research indicates that low-&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; phase is induced by doping about 2 electrons and has good stability, while high-&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; phase results from doping 3 electrons and has slightly poorer stability.&lt;/sec&gt;&lt;sec&gt;Then, the electron-phonon coupling characteristics and electron-electron exchange correlation effects in aromatic compound superconductors are discussed. For low-&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; phases, the values of electronic density of states at the Fermi level are comparable to each other and relatively low, resulting in weak electron-phonon interactions. However, the &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; value predicted by this electron-phonon coupling mechanism is in good agreement with experimental value, indicating that the electron-phonon coupling is sufficient to describe the superconductivity of low-&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; phases. For high-&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; phases, the big values of electron density of states at the Fermi level imply strong electron-phonon interactions, and this electron-phonon coupling increases with the size of organic molecule increasing. However, the &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; value predicted only by the electron-phonon mechanism is lower than the experimental value. The study of electron-electron exchange correlation effect of aromatic compounds shows that the electronic correlation effect increases with the size of aromatic molecule increasing, which is consistent with the increase of &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; maximum value with the size of aromatic molecule increasing in a long-benzene-ring system. This indicates that the superconductivity of high&lt;i&gt;-T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; phase is driven by both the electron-phonon mechanism and the electronic correlation effect. This understanding of superconductivity is significant for exploring and discovering aromatic superconductors with higher transition temperatures.&lt;/sec&gt;&lt;sec&gt;Finally, comprehensive physical models and methods are required in this paper in order to gain a thorough understanding of the superconductivity of aromatic compound.&lt;/sec&gt;

Two-gap superconductivity in a Janus MoSH monolayer

Hydrides under ultrahigh pressure, such as ${\mathrm{H}}_{3}\mathrm{S}$ and ${\mathrm{LaH}}_{10}$, can achieve coveted superconducting critical temperatures via the conventional electron-phonon coupling mechanism. In this work, we report first-principles investigation of high-temperature phonon-mediated superconductivity in a two-dimensional metal hydride, namely, the Janus MoSH monolayer. The MoSH sheet is a recently synthesized intermediate in realizing Janus transition metal dichalcogenides by involving stripping the top-layer S of ${\mathrm{MoS}}_{2}$ with H atoms [X. Wan et al., ACS Nano 15, 20319 (2021); A. Y. Lu et al., Nat. Nanotechnol. 12, 744 (2017)]. We find coupling of electrons from $\mathrm{Mo}\text{\ensuremath{-}}d$ orbitals around the Fermi level to ultrahigh frequency H- and S-derived phonons, analogous to superconducting hydrides of ${\mathrm{H}}_{3}\mathrm{S}$ and ${\mathrm{LaH}}_{10}$. This leads to strong coupling two-gap superconductivity with the calculated critical temperature ${T}_{c}$ being about 28.58 K at atmosphere pressure. The presence of soft phonon bands from the Mo in-plane vibrations, in cooperation with the electron susceptibility, accounts for the strong electron-phonon coupling of the MoSH monolayer. By further aligning the Fermi level via doping, the ${T}_{c}$ can be boosted to 37.31 K, close to the McMillan limit (39 K). Thus, our work points out a real metal hydride for the realization of two-dimensional high-temperature superconductivity at atmosphere pressure and facilitates further studies on new families of Janus transition-metal sulfhydrates.

Real-time first-principles calculations of ultrafast carrier dynamics of SnSe/TiO2 heterojunction under Li+ implantation

Ion implantation has been widely used in biomaterials, alloys, and semiconductors modification. Basing on the studying of trapping states in the equilibrium state, we investigate the ultrafast carrier dynamics of SnSe/TiO2 and SnSe/Li/TiO2 heterojunctions under Li+ implantation by the real-time time-dependent density functional theory. The special type II band alignment and Li+ interfacial states in SnSe/TiO2 heterojunction effectively facilitate the exciton dissociation in a benign process and suppresses the interfacial nonradiative recombination. By monitoring the instantaneous ion–solid interaction energy, electronic stropping power and the excitation electron evolution, we find that atomic reconstruction introduced by the Li inserting layer changes the charge density and crystal potential field in the injection channel, and thus weakens the violent oscillation force and electron excitation on the Ti and O atoms. There exists a weaker and shorter charge excitation at the interface for SnSe/Li/TiO2 implantation system, which suggests that the Li ion layer weakens the e–ph coupling between the interface electrons and the moving ion. Meanwhile, only the hot electrons are produced in the interface region, reducing the probability of carrier recombination. These results provide an understanding for the behavior of carriers in SnSe based heterojunctions and the electron–phonon coupling mechanism at the phase/grain boundary under ion implantation.

Tc up to 23.6 K and robust superconductivity in the transition metal δ−Ti phase at megabar pressure

We report a record high superconducting transition temperature ($T_{\rm c}$) up to 23.6 K under high pressure in the elemental metal Ti, one of the top ten most abundant elements in Earth's crust. The $T_{\rm c}$ increases monotonically from 2.3 K at 40.3 GPa to 23.6 K at 144.9 GPa, which surpasses all known records from elemental metals reported so far. With further compression, a robust $T_{\rm c}$ of ~23 K is observed between 144.9 and 183 GPa in the $\delta$-Ti phase. The pressure-dependent $T_{\rm c}$ can be well described by the conventional electron-phonon coupling (EPC) mechanism. Density Functional Theory calculations show the Fermi nesting and the phonon softening of optical branches at the $\gamma$-Ti to $\delta$-Ti phase transition pressure enhance EPC, which results in the record high $T_{\rm c}$. We attribute the robust superconductivity in $\delta$-Ti to the apparent robustness of its strong EPC against lattice compression. These results provide new insight into exploring new high-$T_{\rm c}$ elemental metals and Ti-based superconducting alloys.

Acoustoelectric current in graphene due to electron deformation potential and piezoelectric phonon couplings

Recent studies strongly indicate that graphene can be used as a channel material for converting surface acoustic waves to acoustoelectric current, which is a resource for various exciting technological applications. On the theoretical side, studies on phonon amplification/attenuation and acoustoelectric current at low temperatures in graphene have reported approximate analytical results under exceedingly simplifying conditions using the Boltzmann transport equation. Overcoming the earlier simplifying assumptions, we investigate both numerically and analytically the governing kinetic equations for amplification/attenuation and acoustoelectric current, taking into account the piezoelectric and deformation potential electron phonon coupling mechanism in the semi classical Boltzmann transport formalism approach, and obtain analytical results that are in reasonable agreement with the reported experimental results.

Charge transport in cove-type graphene nanoribbons: The role of quasiparticles

Previous reports indicate that cove-type graphene nanoribbons (CGNR) may present high intrinsic charge mobility of almost 15,000 cm2/Vs. Still, with experimental estimates varying from 150 to 15,000 cm2/Vs. Typically, theoretical mobilities are obtained from methods such as the Drude-Smith model, which tends to neglect the electron-phonon coupling mechanism, or the Boltzmann transport equation, that considers only acoustic phonons. As such, more thorough approaches are needed. In this work, we simulated charge transport in 4-CGNR by explicitly contemplating the lattice collective behavior. The nanoribbon is simulated by a two-dimensional Su-Schrieffer-Heeger (SSH) tight-binding model with electron-phonon coupling and considering all phonon modes. Results show the rise of two quasiparticles: polaron and bipolaron. We probed their dynamical properties by including the presence of an external electric field. Findings indicate that each carrier has a characteristic transport regime that is deeply related to phonon collision interactions. Model derived mobilities for polarons and bipolarons reach up to 18,000 cm2/Vs and 1500 cm2/Vs, respectively. Furthermore, calculations reveal the carriers to be highly efficient charge transporters, with a field independent low effective mass and notable mobility, delivering a better performance than other narrow GNRs. All presented features place the CGNR as a potential base material of future high-quality organic-based optoelectronic devices. The work also contributes to the theoretical understanding of transport physics in highly confined materials.

Theory-directed discovery of high-temperature superconductivity in clathrate hydrides at high pressure

Theory-directed discovery of high-temperature superconductivity in clathrate hydrides at high pressure

Electronic Structure and Superconductivity of Compressed Metal Tetrahydrides.

Tetrahydrides crystallizing in the ThCr2 Si2 structure type have been predicted to become stable for a plethora of metals under pressure, and some have recently been synthesized. Through detailed first-principles investigations we show that the metal atoms within these symmetry MH4 compounds may be divalent, trivalent or tetravalent. The valence of the metal atom and its radius govern the bonding and electronic structure of these phases, and their evolution under pressure. The factors important for enhancing superconductivity include a large number of hydrogenic states at the Fermi level, and the presence of quasi-molecular H units whose bonds have been stretched and weakened (but not broken) via electron transfer from the electropositive metal, and via a Kubas-like interaction with the metal. Analysis of the microscopic mechanism of superconductivity in MgH4 , ScH4 and ZrH4 reveals that phonon modes involving a coupled libration and stretch of the H units leading to the formation of more complex hydrogenic motifs are important contributors towards the electron phonon coupling mechanism. In the divalent hydride MgH4 , modes associated with motions of the hydridic hydrogen atoms are also key contributors, and soften substantially at lower pressures.

MgPd2Sb : A Mg-based Heusler-type superconductor

We report the synthesis and physical properties of a full Heusler compound, MgPd$_2$Sb, which we found to show superconductivity below $T_c$ = 2.2 K. MgPd$_2$Sb was obtained by a two-step solid-state reaction method and its purity and cubic crystal structure (Fm-3m, a=6.4523(1) \r{A}) were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The results show that MgPd$_2$Sb is a type-II, weak coupling superconductor ($\lambda_{e-p}$ = 0.53). The observed pressure dependence of $T_c$ ($\Delta T_c / p \approx $ -0.23 K/GPa) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons, and electron-phonon coupling in MgPd$_2$Sb were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters tothose of all reported Heusler-type superconductors.

About the ground state structure and superconductivity of the [formula omitted] compound

In the present investigation, based on density functional theory computational approach, we show how the experimentally accepted AlB2-like structure of the SrAlGe compound is suggested to be dynamically unstable at 0 K. We propose a stable configuration that is deduced from the detailed analysis of the phonon spectrum with a doubled unit cell and buckled AlGe layers. It allows to closely reproduce the experimental critical superconducting temperature assuming a phonon mediated superconductivity as described within BCS theory. A soft puckering mode is identified both as the cause for the structural instability and as the main contributor in the electron-phonon coupling constant. From the detailed study of the electronic structure, we show how a peierls-like distortion with the crystal symmetry lowering, affecting mainly the Al-pz orbitals, is correlated with the puckering and with the electron-phonon coupling mechanism.

Superconductivity in alkaline earth metal doped boron hydrides

Effects of alkaline earth metal atoms doping in boron hydrides at high pressure are investigated by first-principles calculations. The calculated results showed that doping with Mg, Ca, Ba, and Sr in B8H16 at 50 GPa is thermodynamically favorable and dynamically stable. The doping changes the B8H16 from a semiconductor to a metal with substantial electronic density-of-state around the Fermi level. The superconductivity of the alkaline earth metal doped B8H16 is studied based on electron-phonon coupling mechanism. The calculated critical superconducting transition temperatures (Tc) range from 10 to 25 K at 50 GPa upon doping. These results suggest that doping metal atoms in boron hydrides is an efficient way in designing superconducting materials.

Pressure-Driven Structural Phase Transitions and Superconductivity of Ternary Hydride MgVH6

A systematic investigation of ternary hydride MgVH6 within the pressure range of 0–200 GPa has been performed by means of the particle swarm optimization algorithm and density functional theory. Results of an extensive structure search and full relaxation further indicate that three new phases, P21/m, C2/m, and Pmn21, appear successively with the increasing of pressure, which contain two first-order structural phase transitions from P21/m to C2/m about 32 GPa and from C2/m to Pmn21 about 93 GPa. Three phases are all metallic phases by analyzing their band structures and density of electronic states and are also dynamically and mechanically stable based on their phonon spectra and elastic properties. More importantly, the electron–phonon coupling calculation indicates that MgVH6 with Pmn21 symmetry is a promising superconductor with an estimated superconducting transition temperature of 27.6 K at 150 GPa, which is similar to the superconducting transition temperature of 35 K at 300 GPa of ternary hydride LaSH6 (Phys. Rev. B 2019, 100, 184502). Further analysis of the electron–phonon coupling mechanism shows that the superconductivity is mainly derived from the strong electron–phonon interaction of heavier transition metal V atoms.

Impact of novel electron-phonon coupling mechanisms on valley physics in two-dimensional materials

We systematically study the impact of various electron-acoustic-phonon coupling mechanisms on valley physics in two-dimensional materials. In the static strain limit, we find that Dirac cone tilt and deformation potential have analogous valley Hall response since they fall into the same universality class of pseudospin structure. However, such argument fails for the coupling mechanism with position-dependent Fermi velocity. For the isotropic case, a significant valley Hall effect occurs near charge neutrality similar to the bond-length change, whereas for the anisotropic case, the geometric valley transport is suppressed, akin to the deformation potential. Gap opening mechanism by nonuniform strain is found to totally inhibit the valley Hall transport, even if the dynamics of strains are introduced. By varying gate voltage, a tunable phonon-assisted valley Hall response can be realized, which paves a way toward rich phenomena and new functionalities of valley acoustoelectronics.

Advanced McMillan’s equation and its application for the analysis of highly-compressed superconductors

Any theory of electron-phonon mediated superconductivity requires knowledge of the full phonon spectrum in order to calculate superconducting transition temperature, Tc. However, there is currently no experimental technique for measuring in highly-compressed near-room-temperature (NRT) superconductors. In this paper, we propose to advance McMillan’s approach (1968 Phys Rev 167 331), which utilises the Debye temperature (an integrated parameter for the full phonon spectrum), deduced via the fit of experimentally measured temperature-dependent resistance data R(T) to the Bloch-Grüneisen equation for highly-compressed black phosphorous, boron, GeAs, SiH4, HxS, DxS, LaHx, and LaDy. By utilizing the relations between Tc, Tθ, and the electron-phonon coupling strength constant λe-ph (which can be computed from first-principles calculations), it is possible to affirm/disprove the electron-phonon coupling mechanism in given superconductors. We show that computed λe-ph for highly-compressed black phosphorous, boron, GeAs, SiH4, and for one sample of LaH10 are in a good agreement with λe-ph values deduced from experimental data. A remarkable constancy of for H3S at different ageing stages is also found. We also show that if the phonon spectra of two isotopic counterparts share an identical shape (or, in the case of highly-compressed superconductors, the same material at different pressures), then within electron-phonon phenomenology, these materials should obey the relation of Tθ,1/Tθ,2 = Tc,1/Tc,2 = ωln,1/ωln,2 (where subscripts 1 and 2 designate two isotopic counterparts). We further report that H3S-D3S pair ratios of Tc,H3S/Tc,D3S = ωln,H3S/ωln,D3S = 1.27 are largely different from deduced Tθ,H3S/Tθ,D3S = 1.65. This implies that NRT superconductivity in H3S-D3S systems originates from more than one mechanism, where the electron-phonon coupling lifts Tc in H3S vs D3S, but the primary origin for the NRT background of Tc ∼ 150 K in both H3S and D3S remains to be discovered.

Isotope effect in superconducting lanthanum hydride under high compression

Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of LaH$_{10}$ under megabar pressure. Specifically, the isotope effect of $T_{\rm c}$ was measured by the replacement of hydrogen (H) with deuterium (D), demonstrating a driving role of phonons in the observed room-temperature SC. Herein, based on the first-principles calculations within the harmonic approximation, we reveal that (i) the identical electron-phonon coupling constants of fcc LaH$_{10}$ and LaD$_{10}$ decrease monotonously with increasing pressure and (ii) the isotope effect of $T_{\rm c}$ is nearly proportional to $M^{-{\alpha}}$ ($M$: ionic mass) with ${\alpha}$ ${\approx}$ 0.465, irrespective of pressure. The predicted value of ${\alpha}$ agrees well with the experimental one (${\alpha}=0.46$) measured at around 150 GPa. Thus, our findings provide a theoretical confirmation of the conventional electron-phonon coupling mechanism in a newly discovered room-temperature superconductor of compressed LaH$_{10}$.

Strong charge-density-wave order of large-area 2D metallic VSe2 nanosheets discovered by temperature-dependent Raman spectra

High-quality and large-area 1T-VSe2 nanosheets with different thicknesses on flat mica substrates are grown by ambient-pressure chemical vapor deposition. Temperature-dependent Raman spectra between 90 and 350 K have been performed to investigate the phenomena of the charge density wave (CDW) order. It can be found that the frequency of the A1g mode increases with the decreasing temperature. When the temperature reaches 110 K, the A1g mode abruptly converts to a low wavenumber. This phenomenon proves the CDW formation of VSe2 with the 5 nm thickness. It can be interpreted as arising from an enhanced electron–phonon coupling mechanism. Moreover, variable temperature-dependent Raman spectra for VSe2 with different thicknesses showed that the phase transition temperature gradually increased with the thickness. In addition, the CDW phase transition has also been detected by the abrupt change of the resistance, and its slope is located at about 112 K. The present results can be helpful for the potential applications of VSe2 crystals, such as spintronics devices and supercapacitors.