APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011;
Dallas, Texas
Session J2: Force Probes of Materials' Structure and Function
11:15 AM–2:15 PM,
Tuesday, March 22, 2011
Room: Ballroom A2
Sponsoring
Unit:
DCMP
Chair: Chris Hammel, Ohio State University
Abstract ID: BAPS.2011.MAR.J2.3
Abstract: J2.00003 : Magnetic force microscopy of superconductors: vortex manipulation and measuring the penetration depth
12:27 PM–1:03 PM
Preview Abstract
Abstract
Author:
Ophir Auslaender
(Technion - Israel Institute of Technology)
We use a low temperature magnetic force microscope (MFM) to image
superconductors. The interaction between the magnetic tip and
individual vortices allows us to both image vortices and to
manipulate them. The manipulation results depend on sample
thickness and on the superconducting properties. Here I
concentrate on YBa$_2$Cu$_3$O$_{6+x}$ (YBCO) samples and on
Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$, an underdoped pnictide. In
thin films, if the force exerted by the tip is strong enough to
overcome the pinning potential a vortex jumps as a whole to a new
pinning site. The behavior in thick YBCO single crystals depends
on the doping level. In a slightly overdoped sample
vortices stretch rather than jump when we perturb them strongly
[1]. The dragging distance in this crystal is anisotropic: it is
easier to drag vortices along the Cu-O chains than across them,
consistent with the tilt modulus and the pinning potential being
weaker along the chains. We also find that when we ``wiggle'' the
top of a vortex we can drag it significantly farther than when we
do not, giving rise to a striking dynamic anisotropy between the
fast and the slow directions of the scan pattern. In an
underdoped YBCO single crystal, where superconductivity is so
anisotropic that a vortex should be viewed as a stack of two
dimensional pancakes, we show that vortices kink rather than tilt
when we perturb them [2]. Since the discovery of the pnictides, a
new family of high temperature superconductors, we have also been
developing ways to determine the absolute
value of the magnetic penetration depth, which is notoriously
difficult to measure, as well as its dependence on temperature.
For that we either use the Meissner repulsion of the magnetic MFM
tip from the sample or the magnetic interaction between the tip
and the magnetic field from a vortex. The temperature dependence
that we find allows us to comment on the symmetry
of the order parameter [3].
\\[4pt]
Work done in collaboration with Lan Luan and Kathryn A. Moler
(Stanford)\\[4pt]
[1] O. M. Auslaender et al., Nat. Phys. 5, 35 (2009).\\[0pt]
[2] Lan Luan et al., Phys. Rev. B 79, 214530 (2009).\\[0pt]
[3] Lan Luan et al., Phys. Rev. B 81, 100501 (2010).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.J2.3