This article reviews the static and dynamic properties of spontaneous superstructures formed by electrons. Representations of such electronic crystals are charge density waves (CDW) and spin density waves in inorganic as well as organic low-dimensional materials. A special attention is paid to the collective effects in pinning and sliding of these superstructures, and the glassy properties at low temperature. Charge order and charge disproportionation which occur in organic materials resulting from correlation effects are analysed. Experiments under magnetic field, and more specifically field-induced CDWs are discussed. Properties of meso-and nanostructures of CDWs are also reviewed.

/pdf/electronic-crystals-an-experimental-overview-4myd2tqsgy.pdf

Electronic crystals: an experimental overview

A new two-dimensional (2D) layered material, namely, titanium trisulfide (TiS3) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS3 monolayer is a direct-gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in-plane electron mobility of the 2D TiS3 is highly anisotropic, amounting to about 10 000 cm2 V−1 s−1 in the b direction, which is higher than that of the MoS2 monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS3 possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS3. Both dynamical and thermal stability of the TiS3 monolayer is examined by phonon-spectrum calculation and Born–Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS3 monolayer a promising 2D atomic-layer material for applications in future nanoelectronics.

/pdf/titanium-trisulfide-monolayer-theoretical-prediction-of-a-53pxyjt5ve.pdf

Titanium Trisulfide Monolayer: Theoretical Prediction of a New Direct‐Gap Semiconductor with High and Anisotropic Carrier Mobility

Charge density wave conduction: A novel collective transport phenomenon in solids

Here, we isolate thin TiS3 ribbons, a layered direct band gap semiconductor (1.1 eV, well suited for detection all across the visible spectrum), thus far almost unexplored. We fabricate field effect transistors and study their electrical characteristics and optoelectronic properties. The measured FET characteristics show mobilities up to 2.6 cm^2/Vs and ON/OFF ratios up to 10^4. Under illumination, the TiS3 NR-FETs present an ultrahigh photoresponse of 2910 A/W and fast rise/fall times of ~4 ms. In addition, we measure cutoff frequencies (f3dB) up to 1000 Hz. The strong combination of ultrahigh sensitivity all along the visible spectrum and fast time response of TiS3 nanoribbon transistors put them among the best nanoscale photodetectors to date.

Ultrahigh Photoresponse of Few‐Layer TiS3 Nanoribbon Transistors

Control over the morphology of TiS3 is demonstrated by synthesizing 1D nanoribbons and 2D nanosheets. The nanosheets can be exfoliated down to a single layer. Through extensive characterization of the two morphologies, differences in the electronic properties are found and attributed to a higher density of sulphur vacancies in nanosheets, which, according to density functional theory calculations, leads to an n-type doping.

TiS3 Transistors with Tailored Morphology and Electrical Properties

Charge density wave transition and nonlinear conductivity in NbS3

Disorder effects in the linear chain compound TiS3

Frequency- ($\ensuremath{\omega}$) dependent conductivity measurements are reported on the linear-chain compound orthorhombic Ta${\mathrm{S}}_{3}$. A weak frequency dependence and positive dielectric constant are observed due to one-dimensional fluctuations of charge-density waves (CDW's) above the Peierls transition at ${T}_{P}=215$ K. Below the phase transition the conductivity strongly increases with increasing $\ensuremath{\omega}$, and the dielectric constant is of the order of ${10}^{7}$. The small characteristic energies obtained from the observed $\ensuremath{\omega}$ dependence give direct evidence for the collective mode. When interpreted in terms of a classical model of the pinned CDW, $\ensuremath{\sigma}(\ensuremath{\omega})$ indicates a strongly overdamped response. A tunneling model developed by Bardeen also leads to a consistent description of both $\ensuremath{\sigma}(\ensuremath{\omega})$ and the electric-field- ($E$) dependent dc conductivity $\ensuremath{\sigma}(E)$. In this model the frequency-dependent response is due to both a tunneling contribution and the response of the pinned mode. Below about 130 K the observed frequency dependence suggests the development of a disordered CDW state. These observations are compared with experiments performed on the linear-chain compound Nb${\mathrm{Se}}_{3}$.

C.M. Jackson

Papers

Charge density wave transition and nonlinear conductivity in NbS3

Disorder effects in the linear chain compound TiS3

Charge-density-wave transport in orthorhombic Ta S 3 . II. Frequency-dependent conductivity

High frequency conductivity in the charge density wave semiconductor TaS3

Frequency dependent conductivity in HfTe5 and ZrTe5