This graphic depicts an ultrashort pulse of terahertz light (yellow arrow) distorting a manganite crystal lattice. Around where the light hits, the diamond-like shaped arrangement of manganese (blue) and oxygen (red) atoms changes to become more square-like, a distortion that also alters the material’s magnetism, which is indicated by the direction of red and blue arrows shown over the manganese atoms. The extremely brief duration and high intensity of the LCLS X-ray laser pulses allowed the team to take stop-action images used to measure the material’s altered magnetism. Image: Jörg Harms, Max-Planck Department for Structural Dynamics, Center for Free Electron Laser Science |
Scientists
have found a way to distort the atomic arrangement and change the
magnetic properties of an important class of electronic materials with
ultra-short pulses of terahertz (mid-infrared) laser light without
heating the material up. While the achievement is currently of purely
scientific interest, the researchers say this new approach control could
ultimately lead to extremely fast, low-energy, non-volatile computer
memory chips or data-switching devices.
Working
at the SLAC National Accelerator Laboratory’s Linear Coherent Light
Source (LCLS), the scientists aimed intense, 130-femtosecond-long pulses
of terahertz light at samples of manganite, a class of complex
manganese-oxide compounds that has many desirable electronic and
magnetic properties.
With
each flash, the material’s atoms shimmied and shifted positions,
although the overall temperature of the solid barely changed. The
scientists then used X-ray laser pulses from the LCLS’s Soft X-ray
Materials Science (SXR) instrument to measure the material’s altered
magnetism.
Rapid
light-induced switching of manganite magnetism has been known for many
years, said physicist Michael Först of the Max Planck Department of
Structural Dynamics (MPSD) in Hamburg, Germany, one of the leaders of
the international research group. However, earlier efforts to trigger
this switch with higher-energy, near-visible lasers heated the
materials, which greatly limits potential applications.
The
latest LCLS experiments confirm that terahertz light only distorts the
lattice enough to rearrange the electronic and magnetic properties while
not generating extra heat.
The
research team was led by scientists from the MPSD (Först and Andrea
Cavalleri) and Brookhaven National Laboratory (Ron Tobey and John Hill),
and included researchers from England and SLAC. They published their
results last month in Physical Review B.
SLAC co-authors are Bill Schlotter and Josh Turner, SXR instrument
scientists; Wei-Sheng Lee and Rob Moore of the Stanford Institute for
Materials & Energy Science (SIMES), and Mariano Trigo of Photon
Ultrafast Laser Science and Engineering (PULSE).
“We
will come back to LCLS later this year to use the X-ray Pump Probe
instrument to measure terahertz-light-driven atomic displacements
directly,” said Först. In recent years, his same group of MPSD
scientists has also used terahertz light pulses to shake materials into a
superconducting state and to change insulators into metals.
Future
research aims to explore the phenomenon more deeply and start
developing capabilities essential for applications, such as
reverse-switching techniques, materials that can switch magnetically at
room temperature or higher, and a laser source suitable for using on
chips.
Driving magnetic order in a manganite by ultrafast lattice excitation
