Effect Of Charge Density Wave Research Articles

Effect of Charge Density Wave on the Electronic Transport in Graphene

Effect of Charge Density Wave on the Electronic Transport in Graphene

Enhanced Low-Temperature Thermoelectric Performance in (PbSe)1+δ(VSe2)1 Heterostructures due to Highly Correlated Electrons in Charge Density Waves.

We explore the effect of charge density wave (CDW) on the in-plane thermoelectric transport properties of (PbSe)1+δ(VSe2)1 and (PbSe)1+δ(VSe2)2 heterostructures. In (PbSe)1+δ(VSe2)1 we observe an abrupt 86% increase in the Seebeck coefficient, 245% increase in the power factor, and a slight decrease in resistivity over the CDW transition. This behavior is not observed in (PbSe)1+δ(VSe2)2 and is rather unusual compared to the general trend observed in other materials. The abrupt transition causes a deviation from the Mott relationship through correlated electron states. Raman spectra of the (PbSe)1+δ(VSe2)1 material show the emergence of additional peaks below the CDW transition temperature associated with VSe2 material. Temperature-dependent in-plane X-ray diffraction (XRD) spectra show a change in the in-plane thermal expansion of VSe2 in (PbSe)1+δ(VSe2)1 due to lattice distortion. The increase in the power factor and decrease in the resistivity due to CDW suggest a potential mechanism for enhancing the thermoelectric performance at the low temperature region.

Quantum oscillations and magnetoresistance in type-II Weyl semimetals: Effect of a field-induced charge density wave

Recent experiments on type-II Weyl semimetals such as WTe$_2$, MoTe$_2$, Mo$_x$W$_{1-x}$Te$_2$ and WP$_2$ reveal remarkable transport properties in presence of a strong magnetic field, including an extremely large magnetoresistance and an unusual temperature dependence. Here, we investigate magnetotransport via the Kubo formula in a minimal model of a type-II Weyl semimetal taking into account the effect of a charge density wave (CDW) transition, which can arise even at weak coupling in the presence of a strong magnetic field because of the special Landau level dispersion of type-II Weyl systems. Consistent with experimental measurements we find an extremely large magnetoresistance with close to $B^2$ scaling at particle-hole compensation, while in the extreme quantum limit there is a transition to a qualitatively new scaling with approximately $B^{0.75}$. We also investigate the Shubnikov-de Haas effect and find that the amplitude of the resistivity quantum oscillations are greatly enhanced below the CDW transition temperature which is accompanied by an unusual non-monotonous (non-Lifshitz-Kosevich) temperature dependence.

Angle-/temperature-dependence of Raman scattering in layered NbSe3 crystal

Distinguishing the lattice vibrational modes of different Raman peaks and further studying the temperature-dependent behaviour of the different Raman modes are fundamental subjects for Raman spectroscopy of single crystal. Herein, we conducted a comprehensive study of angle- and temperature-dependant Raman scattering behaviour in high-crystalline NbSe3 layers prepared by chemical vapour transport method. The polarization experiments performed on NbSe3’s (100) crystal surface revealed that the Raman peaks could be clearly identified as Ag and Bg vibrational modes, indicating significantly anisotropic structure. Meanwhile, the effect of charge density wave (CDW) transition on the lattice vibrational behaviour was studied by investigating temperature-dependent Raman scattering spectra above and below the CDW transition temperature. It was observed that Raman shifts versus temperature for the four prominent Raman peaks of NbSe3 which belonged to Ag vibrational mode exhibited linear softening behaviour as the temperature increased from 83k to 293k. The temperature coefficient of Raman peaks fitted by Grüneisen model further confirmed the anharmonicity of the lattice in NbSe3 crystal, suggesting that the changes of ionic positions across the CDW transition has small effect on its Raman scattering behaviour.

"Graphene-Like" Exfoliation and Characterization of the Atomically-Thin Films of Titanium Ditelluride

We used a "graphene-like" mechanical exfoliation to obtain atomically thin films of TiTe2. The building blocks of titanium ditelluride are atomic tri-layers separated by the van der Waals gaps. The exfoliation procedure allows one to obtain the few-atom-thick films with strong confinement of charge carriers and phonons. We have verified the crystallinity of the exfoliated films and fabricated the back-gated field-effect devices. The current - voltage characteristics of the TiTe2 devices revealed strong non-linearity, which can indicate the charge-density wave effects. The obtained results are important for the proposed application of TiTe2 for the charge-density wave devices and thermoelectric energy conversion.

“Graphene-Like” Exfoliation of Quasi-2D Crystals of Titanium Ditelluride: A New Route to Charge Density Wave Materials

ABSTRACTWe used a “graphene-like” mechanical exfoliation to obtain atomically thin films of TiTe2. The building blocks of titanium ditelluride are atomic tri-layers separated by the van der Waals gaps. The exfoliation procedure allows one to obtain the few-atom-thick films with strong confinement of charge carriers and phonons. We have verified the crystallinity of the exfoliated films and fabricated the back-gated field-effect devices. The current – voltage characteristics of the TiTe2 devices revealed strong non-linearity, which suggests the charge-density wave effects. The obtained results are important for the proposed application of TiTe2 for the charge-density wave devices and thermoelectric energy conversion.

Evidence of circulating charge density wave current: Shapiro interference inNbSe3topological crystals

We investigate the topological effect of charge density wave (CDW). We found a ``beat'' Shapiro step structure in ${\text{NbSe}}_{3}$ topological (ring) crystals. We interpreted it as an evidence of the circulating CDW current that flows in the rings and modifies the CDW fundamental frequency, namely, narrow-band-noise frequency. This result also implied that a precursor of Fr\"ohlich's CDW supercurrent emerged in the ring system.

Charge density wave circulating current in NbSe3 rings observed by measuring Shapiro interference

We investigate topological effect of charge density wave (CDW). The Shapiro step measurement was performed on NbSe3 topological (ring) crystals. We found that a beat-like splitting of Shapiro step spectrum. These results suggest that the circulating CDW current flows in the ring, and modifies the CDW fundamental frequency, namely narrow-band-noise frequency.

Effect of charge density waves on the tunnel spectra of the Bi2Sr2CaCu2O8+δ superconductor

The differential tunnel conductance GS of the junction between a normal metal and a superconductor with a charge density wave (CDW) is calculated as a function of the voltage V across the junction. The results are averaged over the spread of superconducting and CDW energy gaps in the nanoscale-inhomogeneous superconductor. It is shown that, if both order parameters are nonzero, a dip-hump structure is formed beyond the superconducting gap of GS(V). If the phase of the CDW order parameter is not equal to π/2, a dip-hump structure will appear solely or mainly for one sign of the bias polarity. The results agree with the experimental data for Bi2Sr2CaCu2O8+δ and other high-temperature oxides

Modulation of the transverse current effect of charge density waves inK0.3MoO3

The effect of a single-particle current transverse to the conducting chains on the charge-density wave (CDW) dynamics in ${\mathrm{K}}_{0.3}{\mathrm{MoO}}_{3}$ was studied. Our results are qualitatively consistent with the theoretical prediction and previous experimental results in ${\mathrm{NbSe}}_{3},$ but, in our case the modulated depinning threshold falls off much slower. In addition, the anomalous transverse current dependences of the threshold and the single-particle resistance in blue bronze also cannot be explained with the geometric effect proposed recently.

Effect of charge-density wave on superconducting critical temperature

The effect of charge density wave(CDW) on superconducting critical temperature( T c ) is examined within a meanfield approximation. When the band structure does not satisfy the perfect-nesting condition for the commensurate CDW, the metallic CDW states can appear. We study the phase diagrams of the imperfect-nesting CDW with the both cases of canonical and grand-canonical ensembles. We compare two cases and calculate the T c . on two phase diagrams. The behavior of the T c and the CDW gap on our simple model shows the qualitavive similarity to the obsreved one in the real system, BaPb 1− x Bi x O 3 .

Effect of charge-density waves on the x-ray emission edges of simple metals.

A theory of the x-ray emission edges of simple metals has been formulated in which the electrons are in a charge-density-wave ground state. The theory can explain the experimental data in the edge region of both sodium and lithium. Since the Na data were not well understood by previous theories, the present theory offers a resolution of a long-standing problem and provides further evidence of the existence of charge density waves in alkali metals.

Effect of charge-density waves on the magnetic susceptibility of niobium triselenide

The magnetic susceptibility of a model charge-density wave (CDW) system is discussed. It is found that the orbital part of the susceptibility can be large and paramagnetic due to mixing of states above and below the CDW energy gaps by the magnetic field. The paramagnetic contribution is anisotropic and depends on the square of the sine of the angle between the magnetic field $\stackrel{\ensuremath{\rightarrow}}{H}$ and the CDW wave vector $\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}}$. The relevance of these findings to recent measurements of the susceptibility of niobium triselenide is discussed.

Charge density wave effects, structural effects and charge transfer in the layered compound TaS2

Charge density wave effects, structural effects and charge transfer in the layered compound TaS2

Sign and amplitude of charge density waves in 1T-TaS 2 and TaSe 2

The effect of charge density waves has been observed in X-ray photoelectron spectra of 1T-TaS 2 and TaSe 2 as a perturbation of the core-electron binding energies. In the commensurate CDW range the Ta 4f levels show a marked splitting; in the quasi-commensurate and incommensurate states they show broadening of magnitude comparable to this splitting.