Two-dimensional Metallic Phase Research Articles

Temperature-dependent resistivity in the doped two-dimensional metallic phase of mTMD bilayers

Two recent experiments from Cornell and Columbia have reported insulator-to-metal transitions in two-dimensional (2D) moir\'e transition metal dichalcogenides (mTMD) induced by doping around half-filling, where the system is a Mott insulator. In the current work, we consider the temperature dependent resistivity of this metallic phase in the doped situation away from half-filling, arguing that it arises from the strongly temperature dependent 2D Friedel oscillations (i.e. finite momentum screening) associated with random quenched charged impurities, leading to the observed strongly increasing linear-in-$T$ resistivity in the metallic phase. Our theory appears to account for the temperature-dependent metallic resistivity for doping around half-filling of the effective moir\'e TMD band, showing that temperature-dependent screened Coulomb disorder is an essential ingredient of doped 2D mTMD physics.

A simple electrochemical route to metallic phase trilayer MoS2: evaluation as electrocatalysts and supercapacitors

The development of a simple, scalable and reproducible technique for the synthesis of two-dimensional metallic phase MoS2nanosheets is of paramount importance in the field of catalysis and energy storage devices.

Cesium growth on the SrTiO3(100) surface

We investigate Cs adsorption on the SrTiO3(100) surface at room temperature by means of Auger electron spectroscopy, low energy electron diffraction, electron energy loss spectroscopy, thermal desorption spectroscopy and work function measurements. Cesium grows in a single amorphous layer, showing different morphology from that on other insulating substrates. The Cs overlayer approximates a two-dimensional metallic phase. No indications for the reduction of the substrate and a Cs–O compound are found. Thermal annealing desorbs part of the metallic Cs, inducing at the same time the surface diffusion of the Cs adatoms to higher binding energy states. The growth and adsorption kinetics of Cs on the STO, shows substantial differences to that of other alkalis such as K and Li. The reasons for that are discussed.

Temperature, electron density and in-plane magnetic field dependence of cyclotron relaxation time in the two-dimensional metallic phase

We have performed cyclotron resonance measurements on two-dimensional electrons in the metallic phase. The temperature, electron density and in-plane magnetic field dependence of cyclotron and transport scattering time are reported for a high-mobility Si/SiGe quantum well.

Cyclotron resonance in the two-dimensional metallic phase of Si quantum wells

We have performed cyclotron resonance measurements on two-dimensional electrons near the metal-insulator transition. Both the cyclotron scattering time τCR and the transport scattering time τt decrease with the electron density. The values of τt/τCR are close to unity, indicating that the scattering mechanism does not depend on scattering angle in the metallic phase. Short-range potential fluctuations seem to play an important role in the appearance of the metallic behavior.

Structural Distortion and Physical Properties in Double-Layered Ruthenate Sr3-xCaxRu2O7

We have investigated the structural, magnetic, and electronic properties of single-crystalline Sr 3- x Ca x Ru 2 O 7 (0 ≤ x ≤3) grown by a floating-zone method. The results of X-ray diffraction, magnetic susceptibility, specific heat, and electrical resistivity measurements reveal that this system shows a novel phase diagram. With increasing Ca content, the enhanced paramagnetism of Sr 3 Ru 2 O 7 is suppressed, and a phase with a ferromagnetic correlation (\(0.5 \lesssim x \lesssim 1.2\)) emerges. This phase adjoins an antiferromagnetic two-dimensional metallic phase (\(1.2 \lesssim x \leq 3.0\)). At the border between these two phases, discontinuous changes in the lattice parameters are observed. In the ferromagnetically correlated phase, the density of states is significantly enhanced. In the antiferromagnetic phase, the magnetic easy axis changes continuously from the c -axis to the a b -plane with increasing Ca content. These magnetic and electronic properties are strongly coupled with structural dist...

Two-dimensional spin-filtered chiral network model for theZ2quantum spin-Hall effect

The effects of static disorder on the ${\mathbb{Z}}_{2}$ quantum spin-Hall effect for noninteracting electrons propagating in two-dimensional space are studied numerically. A two-dimensional time-reversal symmetric network model is constructed to account for the effects of static disorder on the propagation of noninteracting electrons subjected to spin-orbit couplings. This network model is different from past network models belonging to the symplectic symmetry class in that the propagating modes along the links of the network can be arranged into an odd number of Kramers doublet. It is found that (1) a two-dimensional metallic phase of finite extent is embedded in a ${\mathbb{Z}}_{2}$ insulating phase in parameter space and (2) the quantum phase transitions between the metallic and ${\mathbb{Z}}_{2}$ insulating phases belong to the conventional symplectic universality class in two space dimensions.

Metallic phases of a C 70 single layer adsorbed on Cu(1 1 1) doped with sodium

The electronic properties of a C 70 single layer chemisorbed on Cu(1 1 1) surface, in which the charge state has been modified by Na doping, were studied via synchrotron radiation photoemission and absorption spectroscopy. A two-dimensional metallic phase is observed in the whole range of charge states investigated (from 1 up to 3 electrons/C 70). Moreover, all the results suggest that the orientation of the molecules, with the C 5v axis perpendicular to the surface, is not affected by Na doping.

Scaling limits for the two-dimensional metal-insulator transition atB=0in Si-MOSFET’s

We have examined data on the density-driven conductivity transition at $B=0$ in Si-MOSFET's. Data from this transition can be arranged such that it appears to collapse into certain one-parameter scaling forms. This fact has been used to support the idea that a quantum phase transition to a two-dimensional metallic phase is occurring in these systems. Here we present a quantitative analysis on the compatibility of the data with such a quantum phase transition. For this purpose, we developed a self-consistent nonlinear regression method, which extracts all scaling parameters with statistical error estimates in single unbiased fits. By carefully tracking sources of error and statistical uncertainties in the experimental data, we are able to determine the normalized mean-square deviation, ${\ensuremath{\chi}}^{2},$ of such fits. Using ${\ensuremath{\chi}}^{2}$ as a quantitative measure of goodness of fit, we analyzed E-field scaling in three different samples. We also investigated the variation of the fitted parameters and ${\ensuremath{\chi}}^{2}$ as automated truncations are imposed on the data. We determined that individual fits can show quantitative agreement with scaling. However, this agreement is sensitive to truncation. For example, we found larger variation in fitted parameters, even within a single sample, than our statistical error estimates suggest.

Quantum Hall effect in the highly spin-polarized electron system

Transport study of high electron mobility modulation-doped heterostructures of CdMnTe/CdMgTe : I shows that the magnetic ions and the associated giant-spin splitting leave the quantization precision of the Hall plateaus unchanged. Positive magnetoresistance in weak magnetic fields is dominated by a spin effect. Properties of the observed two-dimensional metallic phase support its electron–electron interaction origin.

Breakdown of the anomalous two-dimensional metallic phase in a parallel magnetic field

We report on magnetotransport studies of the 2D metallic phase in high-mobility Si-MOSFETs. We have observed that the magnetic field applied in the 2D plane suppresses the metallic state, causing the resistivity to increase dramatically by more than 30 times. Over the existence range of the metallic state, we have found three distinct types of magnetoresistance behaviour, related to the corresponding quantum corrections to the conductivity. Our data suggest that the unusual metallic state is a consequence of both spin- and Coulomb-interaction effects.

Erratum: Instability of the two-dimensional metallic phase to a parallel magnetic field [JETP Lett. 65, No. 12, 932–937 (25 June 1997)

Erratum: Instability of the two-dimensional metallic phase to a parallel magnetic field [JETP Lett. 65, No. 12, 932–937 (25 June 1997)

Instability of the two-dimensional metallic phase to a parallel magnetic field

We report on magnetotransport studies of the unusual two-dimensional metallic phase in high mobility Si-MOS structures. We have observed that the magnetic field applied in the 2D plane suppresses the metallic state, causing the resistivity to increase dramatically by more than 30 times. Over the total existence range of the metallic state, we have found three distinct types of the magnetoresistance, related to the corresponding quantum corrections to the conductivity. Our data suggest that the unusual metallic state is a consequence of both spin- and Coulomb-interaction effects.