Charge density wave depinning and switching in NbSe3

We have investigated the relation between charge density wave (CDW) depinning and switching in NbSe₃. In the lower CDW state we observe that the critical electric field at which switching occurs is independent of temperature. We also observe that the differential resistance of the sample is independent of applied dc bias beyond the switching threshold, and corresponds to the high-field limit of the pure resistance. We interpret our results in terms of a temperature dependent CDW domain structure in the crystal.     

Charge density wave in kagome superconductor AV3Sb5

The kagome lattice is one of the most important platforms to investigate quantum many-body physics.For example,owing to its special lattice,the kagome lattice has a standard geometric frustration phenomenon in quantum magnetism.How to utilize this simple lattice to uncover the unconventional quantum phenomenon attracts great attention.     

Charge density wave transition and nonlinear conductivity in NbS3

We report dc conductivity (σ) measurements on the linear chain compound NbS₃. The temperature dependence of σ indicates a phase trànsition at T_MI = 155 K with strong one-dimensional fluctuations above T_MI. Below T_MI the conductivity is strongly increasing with increasing electric field above a threshold field E_T, and is also strongly frequency dependent. We argue that the nonlinear conductivity is due to sliding charge density waves.     

Charge density wave commensurability in 2H-TaS2 and AgxTaS2

The charge density wave transition in 2H-TaS₂near 75 K has been observed to be incommensurate, using electron diffraction, with $\text{q}{}^1\text{= (}\text{0.338}\text{±}\text{0.002}\text{)a}{}^1{}_0$ along the 〈10.0〉 directions which, within the experimental uncertainty, remains temperature independent to about 14 K. Incommensurate charge density formation is also observed in Ag_xTaS₂ samples for $\text{x?}\text{0.26}$ with an increase in q¹ to $\text{(}\text{0.347}\text{±}\text{0.002}\text{)a}{}^1{}_0$ when x?0.26. Within the experimental error q¹ appears to be temperature independent to 25 K.     

Charge density wave and excitonic magnetic polarons in CeTe2

Mechanisms of anomalous magnetic and transport properties in CeTe₂ observed recently on single-crystal samples are studied by comparing with the nonmagnetic reference material LaTe₂, as well as other typical low carrier-density systems such as Ce monopnictides, doped Eu chalcogenides and Yb₄As₃. The present system is unique on the point of low-carrier semimetal due to CDW of near perfect nesting, which is shown to be nearly independent of the spin–orbit splitting. The large residual resistivity indicates the giant molecular scattering due to excitonic states forming the distorted Wigner crystal, similar to Yb₄As₃. At low temperatures, induced magnetic polarons cause unusual novel transport properties with a sharp peak of resistivity without any anomaly on other physical properties. This is attributed to a sharp glassy transition from an antiferromagnetic short-range ordering to the ferromagnetic ordering of the magnetic polarons within each CeTe double layer sandwiching the mono Te layer. It is shown that, similar to Ce monopnictides, the type strong nonlinear p–f mixing is the origin of the main anomalous magnetic properties. Lattice polarons are essential for the stable excitonic states in LaXc₂, as well as in CeTe₂ in the ferromagnetic state.     

Charge density wave transport in (TaSe4)2I

We report non linear transport properties below the metal-insulat transition temperature T_° = 263 K in the halogened metal transition tetrachalcogenide (TaSe₄)₂I. These non linear properties are similar to those of NbSe₃ and TaS₃ and indicate that (TaSe₄)₂I is a new compound exhibiting charge density wave transport.     

Quasiperiodic noise voltage and metastability in the charge density wave conductivity of K0.30MoO3

Slow relaxation phenomena as well as quasiperiodic noise have been studied in the non linear regime of conductivity which takes place above a well defined threshold electric field in the semiconducting incommensurate phase of the quasi one-dimensional blue bronze K_0.30MoO₃. The noise frequencies are found to be proportional to the excess current attributed to the charge density wave (CDW). In some temperature range, the CDW current is found to decrease logarithmically vs time. These results indicate the presence of metastable states related to domains and domain walls.     

Charge density wave instability in the quasi two-dimensional metal γ-Mo4011

Transport and specific heat properties have been studied on the orthorhombic molybdenum oxide γ-Mo₄0₁₁. The anisotropy of the electrical resistivity establishes that this compound is a quasi two-dimensional metal, as expected from crystal structure data. Both the resistivity and the thermopower show that an electronic transition, probably due to a charge density wave instability takes place at T_c = 100 K. Low temperature specific heat data provide an estimation of the Debye temperature and of the electronic density of states in the low temperature metallic phase.     

Broad band noise associated with the current carrying charge density wave state in TaS3

We report the observation of low frequency broad band noise in the current carrying charge density wave (CDW) state of orthorhombic TaS₃. The noise amplitude is proportional to the number of condensed electrons, and we suggest that the broad band noise reflects the dynamics of the internal deformations of the CDW condensate.     

Charge density waves in nanocrystalline thin films of blue bronze K0.3MoO3

Thin granular films of charge density wave (CDW) system K_0.3MoO₃ were prepared by pulsed laser deposition and investigated by various standard characterization methods such as GI-XRD, electric transport, TOF-ERDA, AFM and UV–visible spectroscopy. While all these methods indicate that the thin films consist of nanometer grains of K_0.3MoO₃, it is only the non-destructive femtosecond time-resolved spectroscopy (fsTRS) that demonstrates the charge density wave nature of the ground state and therefore proves directly the presence of K_0.3MoO₃. Furthermore, the comparison of the fsTRS data obtained in thin films and in single crystals shows the reduction of the charge density wave transition temperature and of the photoinduced signal strength in granular thin films with respect to single crystals, which is attributed to the granularity and crystal growth morphology. Our results establish fsTRS technique as the essential tool for the detection and characterization of complex ground states in nano-sized systems.     

On the nonlinear charge density wave conductivity of TaS3

The conductivity of the charge-density-wave semiconductor TaS₃ is shown to consist of temperature dependent ohmic, and field dependent but temperature independent, contributions at temperatures below the Peierls transition T_P = 215 K. The field dependent conductivity can be described by a tunneling formalism proposed by Bardeen.     

High frequency conductivity in the charge density wave semiconductor TaS3

We report the observation of frequency dependent conductivity σ (ω) in the charge density wave (CDW) semiconductor TaS₃. Based on σ (ω) and other evidences, we sugest that three different temperature regions occur in this compound: 1-D fluctuating CDW region above T_MI, a coherent CDW state below T_MI, and a CDW glass state at low temperatures.     

Polarized infrared reflectivity study in charge density wave conductor Tl0.3MoO3

Polarized infrared reflectivity measurements between 300 and 10 K have been carried out on charge density waves (CDW) conductor blue bronze Tl_0.3MoO₃. Three important features are observed: (i) A bump at 1155 cm⁻¹ in the reflectivity spectra of Tl_0.3MoO₃ at 300 K is a precursor of the Peierls gap due to optical excitations across a pseudogap, and this kind of Peierls-like gap opens gradually with decreasing temperature from 180 to 160 K. (ii) The three sharp modes as “triplet” of infrared reflectivity between 800 and 1000 cm⁻¹ of Tl_0.3MoO₃ along [1 0 2] axis show red shift compared to K_0.3MoO₃ and Rb_0.3MoO₃, which is assigned to the increase of the distance of Mo-O bond with the substitution of thallium ions. (iii) Two peaks at about 514 and 644 cm⁻¹ in the far-infrared reflectivity spectra of Tl_0.3MoO₃ along [1 0 2] direction are suggested to be the electronic transitions from the valence band to the midgap state and from occupied midgap state to the conduction band, respectively.     

Charge density wave transport in a novel inorganic chain compound, (TaSe4)2I

We report the observation of nonlinear conductivity with a well-defined threshold electric field E_T, and frequency dependent ac conductivity, in a novel linear chain compound, (TaSe₄)₂I. The material undergoes a phase transition to a semiconducting phase at T ～ 260 K, and nonlinear and frequency dependent transport is observed below this temperature. We argue that the material is a new example of collective mode transport provided by a Peierls-Fröhlich charge density wave condensate.     

Charge density waves in 2HNbSe2

The formation of a weak superlattice in transmission electron diffraction patterns of the hexagonal layered superconductor 2HNbSe₂ below 35 K is reported. Based on the temperature dependence of the superlattice reflexion intensity down to 17 K and by comparison with related layer materials, an interpretation of these effects in terms of a charge density wave coupled to a periodic lattice distortion is proposed.     

Pressure dependence on the charge density wave transitions in monoclinic TaS3

The resistivity of one-dimensional TaS₃ in the monoclinic structure has been measured under pressure. It is shown that the upper charge density wave transition at 240 K at ambient pressure increases at the rate of +9.9 K/kbar and the lower one at 160 K decreases at the rate of -0.5 K/kbar.     

Photo-induced enhancement of charge density wave current in the quasi-one-dimensional conductor TaS3

In the near vicinity of Peierls transition temperature T_P, we have measured the V-I characteristics of the quasi-one-dimensional conductor TaS₃ under dark and photo-irradiation conditions. It is found that a significant enhancement of CDW current occurs only around the threshold voltage V_t under photo-irradiation. This effect can be interpreted as a result of screening of pinning potential for CDW condensate by photo-excited quasi-particles (QP's). Further the distribution of pinning potential intensity is reflected in the behavior of V-I characteristics near V_t. Our finding suggests that the strength of pinning potential can be controlled by the photo-excited QP's in quasi-1D conductors.     

Effects of radiation damage on the charge density wave transitions in NbSe3

We have measured the electrical resistivity of NbSe₃ samples which have been radiation damaged with 2.5 MeV protons up to a defect concentration of 0.5%. We find that, unlike substitutional impurities, the defects do not destroy the charge density wave (CDW) transitions and the samples do not go superconducting. The defects become more effective scatterers below the CDW transitions so that the defect resistivity is temperature dependent. The defects pin the CDWs randomly so that carriers in the unnested regions can be scattered by the CDW. This leads to an enhancement of the defect resistivity. The resistivity of the highly damaged samples is still increasing with decreasing temperatures to below 1 K.     

Charge ordering characteristics in Y0.5Ca0.5MnO3 manganite

The charge ordering characteristics in Y_0.5Ca_0.5MnO₃ manganite, prepared by sol–gel process, have been investigated experimentally. It is found that the superlattice diffractions appear in the electron diffraction patterns recorded at low temperatures, while only basic Brag diffraction spots can be observed when temperature is higher than 300 K. This provides direct evidence for the existence of charge ordering in Y_0.5Ca_0.5MnO₃. The magnetization and specific heat measurements indicate the charge ordering temperature of Y_0.5Ca_0.5MnO₃ is 290 K, around which both the magnetization and specific heat reveal anomalous behaviors. We also observed that the MnO bond length changed remarkably and the effective number of carriers reduced prominently with decreasing temperature around charge ordering temperature through transform infrared spectra measurements.     

Anomalous ultrasonic velocity of the transverse wave in KH3(SeO3)2

The ultrasonic velocity of the transverse wave with q = [010] and ξ = [001] measured as a function of temperature at 5 MHz in centrosymmetric KH₃(SeO₃)₂ shows a large anomaly with a tendency to approach zero at the transition temperature.