1. Scientific Achievement
Studies of superconductors in the Meissner state by optical NV - MagnetoScope
N. M. Nusran, K. R. Joshi, K. Cho and M. A. Tanatar, R. Prozorov
Spatial variation of the magnetic induction
Probing near the edge to determine Hc1
Scientific Achievement
Direct spatially – resolved study of the Meissner state, performed by using optical sensing of magnetic fields with NV centers in diamond
Significance and Impact
Observed non-trivial behavior cooling - dependent Meissner effect ranging from expected diamagnetic to paramagnetic.
First direct evidence for predicted “corner cutting” by Abrikosov vortices.
Direct determination of the first penetration field.
Research Details
Built functional low – temperature setup that uses ensembles of NV – centers in diamond for non-perturbative vector-field measurements with diffraction-limited spatial resolution.
Found strong correlation between sample surface quality determined from SEM images and the observed results.
arXiv:
CaKFe4As4
T = 5 K
Ba(Fe1-xCox)2As2
Zettl, LBNL ECMP; Cromie LBNL - PB
Berkeley Lab scientists have experimentally observed “atomic collapse” for the first time, confirming decades-old predictions and providing important insights for future graphene devices.
For more than 70 years, theorists have predicted that electrons in atoms with very large nuclei should behave completely differently than those in regular atoms. Instead of making stable orbits around the nuclei, these ultra-relativistic electrons should spiral into and out of the nuclear region and have some chance to escape — a phenomenon that has come to be known as atomic collapse.
Confirmation of atomic collapse has proved elusive because of the difficulty in making nuclei with nearly twice as many protons as the largest known element. To get around this problem the researchers took advantage of the special properties of graphene, in which the nuclear charge threshold for atomic collapse is much lower. The researchers assembled a cluster of charged calcium atoms on graphene using a scanning-tunneling microscope (STM), with pairs of Ca atoms playing the same role that protons play in regular atomic nuclei.
Using an STM, the researchers directly imaged how electrons behaved around the artificial nuclei as they increased the nuclear charge to the supercritical limit, thereby observing the signature of atomic collapse in good agreement with theory.
In addition to confirming basic relativistic quantum mechanics predictions, this exotic phenomenon will help illuminate the role of defects and dopants in future graphene devices.