Solid State Physics Laboratory

About: Solid State Physics Laboratory is a facility organization based out in Delhi, India. It is known for research contribution in the topics: Quantum dot & Dielectric. The organization has 1754 authors who have published 2597 publications receiving 50601 citations.

Superconducting critical fields and anisotropy of a MgB2 single crystal

Abstract: Using a double axis vibrating sample magnetometer, we have made detailed magnetic measurements of the lower critical field Hc1 for fields parallel to the two crystallographic directions of MgB2 single crystals. Additionally, using a novel Hall probe magnetometer we have measured high precision magnetization loops, from which we directly determine the upper critical field Hc2 for both field orientations. Our results suggest that Hc1 is much larger than most previous estimates and that consequently the Ginzburg–Landau parameter κ is very low (less than 5). We find the anisotropy parameter γ ~ 2, independent of temperature over the measured range.

ESR on UV Irradiated Lead Halides at 80° K

Abstract: Results are presented of electron spin resonance measurements on uv irradiated single crystals of PbCl2, PbBr2, and PbI2 at liquid nitrogen temperature. Both pure single crystals and PbBr2 crystals doped with Tl+, Ag+, Cu+, and Bi+++ ions are studied. The ESR spectra indicate that Pb+ ions occur as an initial step in the photochemical decomposition. These ions are probably present in clusters of two or three and coagulate to metallic lead particles. The ESR signals due to the conduction electrons of these small lead particles are studied. Some hole centres which are formed during the irradiation are also described. The experiments show that the ambient conditions of the crystals are much more important in the photolysis process than the presence of foreign ions. Es werden Ergebnisse von Elektronenspinresonanz-Messungen an UV-bestrahlten PbCl2-, PbBr2- und PbI2-Einkristallen bei der Temperatur des flussigen Stickstoffs mitgeteilt. Reine, sowie mit Tl+, Ag+, Cu+ und Bi+++ dotierte PbBr2-Einkristalle werden untersucht. Die ESR-Spektren weisen darauf hin, das Pb+-Ionen als Anfangsstufe der photochemischen Zersetzung auftreten. Diese Ionen sind wahrscheinlich als Paare und Tripel vorhanden und koagulieren als metallische Bleiteilchen. ESR-Signale, die von den Leitungselektronen dieser kleinen Bleiteilchen hervorgerufen werden, werden analysiert. Weiterhin werden einige wahrend der Bestrahlung gebildete Loch-Zentren beschrieben. Die experimentellen Ergebnisse weisen darauf hin, das die Umgebungsbedingungen der Kristalle fur den Photolyseprozes wichtiger sind als die Anwesenheit von Fremdionen.

Gap Opening in Twisted Double Bilayer Graphene by Crystal Fields

Abstract: Crystal fields occur due to a potential difference between chemically different atomic species. In van der Waals heterostructures such fields are naturally present perpendicular to the planes. It has been realized recently that twisted graphene multilayers provide powerful playgrounds to engineer electronic properties by the number of layers, the twist angle, applied electric biases, electronic interactions, and elastic relaxations, but crystal fields have not received the attention they deserve. Here, we show that the band structure of large-angle twisted double bilayer graphene is strongly modified by crystal fields. In particular, we experimentally demonstrate that twisted double bilayer graphene, encapsulated between hBN layers, exhibits an intrinsic band gap. By the application of an external field, the gaps in the individual bilayers can be closed, allowing to determine the crystal fields. We find that crystal fields point from the outer to the inner layers with strengths in the bottom/top bilayer [Formula: see text] = 0.13 V/nm ≈ [Formula: see text] = 0.12 V/nm. We show both by means of first-principles calculations and low energy models that crystal fields open a band gap in the ground state. Our results put forward a physical scenario in which a crystal field effect in carbon substantially impacts the low energy properties of twisted double bilayer graphene, suggesting that such contributions must be taken into account in other regimes to faithfully predict the electronic properties of twisted graphene multilayers.