Magnetic field microscopy with ultra cold atoms reveals details of current flow

03. Mar 2008  — An international team of scientists at the TU-Wien / Universität Heidelberg / Ben-Gurion University, used ultra cold atom magnetic field microscopy to probe current flow patterns in thin gold films with unprecedented sensitivity.


Magnetic field microscopy with ultra cold atoms reveals details of current flow


Scheme of the Ultra Cold Atom Magnetic Field Microscope:
An highly elongated, quasi one dimensional cloud of ultra cold (T~100nK)  or Bose-Condensed Rubidium atoms is positioned above the current carrying wire on an atom chip.   The current in the wire modifies the magnetic trapping potential. Current flow deviations lead to a potential roughness of the atom trap and consequently to a modified density of the trapped atomic cloud.  Imaging the atom cloud reveals the magnetic field profile. Scanning the cloud across the wire allows registering a full magnetic field map.

 

The physics of ultra cold atoms and matter waves enables the application of new sensitive probes for many different fields of science. Up to now inertial sensing (measuring rotations and accelerations) and atomic clocks were the main application. The study ‘Long-Range Order in Electronic Transport through Disordered Metal Films’, published in Science on Feb, 29th, is the first direct application of ultra cold atoms as a probe for solid state science.  

The team of scientists at the TU-Wien/Universität Heidelberg lead by Jörg Schmiedmayer, in collaboration with the Group of Ron Folman at the Ben-Gurion University of the Negev at Béer Sheva (Israel), used ultra cold atom magnetic field microscopy on an atom chip to probe minute changes in the magnetic field direction which allow the reconstruction of the current flow patterns in thin planar conductors with unprecedented sensitivity. Directional changes of the current flow at the level of below 10 µrad can be imaged with 3 micrometer resolution.  

The new study published in Science revealed surprising phenomena in the current flow in thin gold films.  

- The current flow irregularities exhibit of long range correlations showing organized patterns oriented at ±45º relative to the mean current flow, even at room temperature and at length scales of tens of microns, orders of magnitude larger than the tens of nanometer scale given by the diffusion length or the grain size. These patterns are the direct visualization of the fundamental properties of current flow around defects.  

- Even more surprising the amplitude of these current direction fluctuations scales contrary to what is expected from the measured parameters of the gold films: thinner films with larger grains show smaller directional variations that are much too small to be explained by the measured surface roughness.  

This study is the first direct application of ultra cold atoms as a sensor for a solid-state science problem. It demonstrates that the new method reveals information complementary to that offered by traditional probes. The present study opens the road for a rich spectrum of new experimental studies on the interplay between disorder and transport. 

Long-Range Order in Electronic Transport through Disordered Metal Films
S. Aigner, L. Della Pietra, Y. Japha, O. Entin-Wohlman, T. David, R. Salem, R. Folman, J. Schmiedmayer
Science 319 1226 (2008) 

Other literature on magnetic field microscopy
S. Wildermuth et al., Nature, 435, 440 (2005).
S. Wildermuth et al., Appl. Phys. Lett., 88, 264103 (2006). 

Overview on Atom Chip science:
R. Folman et al., Advances of Atomic and Molecular and Optical Physics,
48, 263 (2002).

Science Vol 319