Two-dimensional hole transport in ion-gated diamond surfaces: A brief review (Review article)

Abstract

Electrically-conducting diamond is a promising candidate for next-generation electronic, thermal and electrochemical applications. One of the major obstacles towards its exploitation is the strong degradation that some of its key physical properties -such as the carrier mobility and the superconducting transition temperature -undergo upon the introduction of disorder. This makes the two-dimensional hole gas induced at its surface by electric field-effect doping particularly interesting from both a fundamental and an applied perspective, since it strongly reduces the amount of extrinsic disorder with respect to the standard boron substitution. Here, we review the main results achieved so far in controlling the electric transport properties of different field-effect doped diamond surfaces via the ionic gating technique. We analyze how ionic gating can tune their conductivity, carrier density and mobility, and drive the different surfaces across the insulator-to-metal transition. We review their strongly orientation-dependent magnetotransport properties, with a particular focus on the gate-tunable spin-orbit coupling shown by the (100) surface. Finally, we discuss the possibility of field-induced superconductivity in the (110) surface as predicted by density functional theory calculations.

Pressure-Responsive Conductive Poly(vinyl alcohol) Composites Containing Waste Cotton Fibers Biochar

“…Figure 3a shows that σ strongly decreases as the temperature is reduced from T = 350 K to T = 20 K. Unlike in the tea-leaf [24] biochars where σ scaled as a power law of T, here, we observe that σ scales as σ(T) = σ 0 exp(T 0 /T) 1 4 with T 0 ≈ 4500 K, as highlighted by the black dashed line. According to the theory of the insulator-to-metal transition [38][39][40], such a behavior is typical of insulating materials where electric transport occurs via variablerange hopping (VRH) of the three-dimensional (3D) Mott type. This was confirmed by means of Zabrodskii analysis [41] of the reduced activation energy W = d(ln σ)/d(ln T), as shown in Figure 3b.…”

Development of Pressure-Responsive PolyPropylene and Biochar-Based Materials

“…This was quantitatively assessed by considering the scaling of G s with T in log-log scale, as shown in Figure 5b. In addition to the incipient saturation at low T, the biochar samples showed two different power-law scalings (G s ∝ T β ) at intermediate (β 0.07) and high temperatures (β 0.2), with a crossover around T ∼ 90 K. According to the theory of the insulator-to-metal transition (IMT), power-law dependences of the conductivity with temperature are typical of the quantum critical regime of the IMT, with β < 1/3 and β > 1/3 being associated with its metallic and insulating sides, respectively [49,52,53]. In the case of the biochar considered here, β < 1/3 at any T, indicated metallic behavior.…”

Migdal-Eliashberg theory of multi-band high-temperature superconductivity in field-effect-doped hydrogenated (111) diamond

“…Previous density functional theory (DFT) simulations 21,[29][30][31] showed that it is possible to induce a SC phase transition in hydrogenated diamond surfaces by hole-doping in the FET configuration. In these studies, the critical temperature T c was estimated using the McMillan/Allen-Dynes 32,33 formula.…”