Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userElectric field exfoliation and high-T$_{text{C}}$ superconductivity in field-effect hole-doped hydrogenated diamond (111)
152
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We investigate the possible occurrence of field-effect induced superconductivity in the hydrogenated $(111)$ diamond surface by first-principles calculations. By computing the band alignment between bulk diamond and the hydrogenated surface we show that the electric field exfoliates the sample, separating the electronic states at the valence band top from the bulk projected ones. At the hole doping values considered here, ranging from $n=2.84times10^{13}$cm$^{-2}$ to $n=6times 10^{14} $ cm$^{-2}$, the valence band top is composed of up to three electronic bands hosting holes with different effective masses. These bands resemble those of the undoped surface, but they are heavily modified by the electric field and differ substantially from a rigid doping picture. We calculate superconducting properties by including the effects of charging of the slab and of the electric field on the structural properties, electronic structure, phonon dispersion and electron-phonon coupling. We find that at doping as large as $n=6times 10^{14} $ cm$^{-2}$, the electron-phonon interaction is $lambda=0.81$ and superconductivity emerges with $T_{text{C}}approx 29-36$K. Superconductivity is mostly supported by in-plane diamond phonon vibrations and to a lesser extent by some out-of-plane vibrations. The relevant electron-phonon scattering processes involve both intra and interband scattering so that superconductivity is multiband in nature.
rate research
Read More
We perform single- and multi-band Migdal-Eliashberg (ME) calculations with parameters exctracted from density functional theory (DFT) simulations to study superconductivity in the electric-field-induced 2-dimensional hole gas at the hydrogenated (111) diamond surface. We show that according to the Eliashberg theory it is possible to induce a high-T$_{text{c}}$ superconducting phase when the system is field-effect doped to a surface hole concentration of $6times10^{14},$cm$^{-2}$, where the Fermi level crosses three valence bands. Starting from the band-resolved electron-phonon spectral functions $alpha^2F_{jj}(omega)$ computed ab initio, we iteratively solve the self-consistent isotropic Migdal-Eliashberg equations, in both the single-band and the multi-band formulations, in the approximation of a constant density of states at the Fermi level. In the single-band formulation, we find T$_{text{c}}approx40,$K, which is enhanced between $4%$ and $8%$ when the multi-band nature of the system is taken into account. We also compute the multi-band-sensistive quasiparticle density of states to act as a guideline for future experimental works.
We show the possibility of inducing a superconductive phase transition in tetrahedrally coordinated semiconductors via field-effect (FET) doping by taking as an example the hydrogenated (111) silicon surface. We perform density functional theory computations of the electronic and vibrational properties of the system in the proper FET geometry, by taking into account the applied electric field and the induced charge density. Using a simplified superconductive model at $q=Gamma$ and the McMillan/Allen-Dynes formula, we get an estimate of the superconductive critical temperature. We observe that, by heavily doping with holes at $n_{dop}=6cdot10^{14}$ cm$^{-2}$, we get an electron-phonon coupling constant of $lambda_{Si}=0.98$ and a superconductive phase transition at $T_{text{c}}in[8.94;10.91]$ K, with $mu^*in[0.08;0.12]$.
The layered lithium borocarbide LiBC, isovalent with and structurally similar to the superconductor MgB2, is an insulator due to the modulation within the hexagonal layers (BC vs. B2). We show that hole-doping of LiBC results in Fermi surfaces of B-C p sigma character that couple very strongly to B-C bond stretching modes, precisely the features that lead to superconductivity at Tc = 40 K in MgB2. Comparison of Li{0.5}BC with MgB2 indicates the former to be a prime candidate for electron-phonon coupled superconductivity at substantially higher temperature than in MgB2.
Superconductivity of boron-doped diamond, reported recently at T_c=4 K, is investigated exploiting its electronic and vibrational analogies to MgB2. The deformation potential of the hole states arising from the C-C bond stretch mode is 60% larger than the corresponding quantity in MgB2 that drives its high Tc, leading to very large electron-phonon matrix elements. The calculated coupling strength lambda ~ 0.5 leads to T_c in the 5-10 K range and makes phonon coupling the likely mechanism. Higher doping should increase T_c somewhat, but effects of three dimensionality primarily on the density of states keep doped diamond from having a T_c closer to that of MgB2.
We investigated the effect of nanoscale-C doping on the critical current density Jc and irreversibility field Birr of Fe-sheathed MgB2 tapes prepared by the in-situ powder-in-tube method. The tapes were heat treated at 600-950C for 1 h. Higher values of Jc and Birr were seen for 5 at.%C-doped MgB2 tapes at higher sintering temperatures, where substantial substitution of boron for carbon occurred. The C-doped samples sintered at 950C showed the highest Birr, for example, at 4.2 K, the Birr reached 22.9 T. In particular, at 20 K, Birr for the C-doped tape achieved 9 T, which is comparable to the upper critical field of the commercial NbTi at 4.2 K. This role of nano-sized C particles can be very beneficial in the fabrication of MgB2 tapes for magnetic resonance imaging applications at 20 K.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
