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Tuning an electron spin is like tuning a guitar, but with a laser and a lot of mirrors.
PHOTO CREDIT: Patrick Odenthal
Schematic of the ultrafast optics experiment. An initial laser pulse aligns an electron spin along the beam path; the electron spin precesses in an external magnetic field; another time delayed laser pulse detects the spin precession by rotation of its polarization plane (North or Up, South or Down). Upper left: the material structure of the hybrid perovskites. Lower right: typical data shows oscillations induced by spin precession.
First, the researchers formed a thin film from the hybrid perovskite methyl-ammonium lead iodine (CH3NH3PbI3) and placed it in front of an ultrafast laser that shoots very short light pulses 80 million times a second. The researchers are the first to use light to set the electron’s spin orientation and observe the spin precession in this material.
They split the laser into two beams; the first one hit the film to set the electron spin in the desired direction. The second beam bends through a series of mirrors like a pinball machine before hitting the perovskite film at increasing time intervals to measure how long the electron held the spin in the prepared direction.
They found that the perovskite has a surprisingly long spin lifetime — up to nanosecond. The spin flips many times during one nanosecond, which means a lot information can be easily stored and manipulated during that time.
Once they determined the long spin lifetime, the researchers tested how well they could manipulate the spin with a magnetic field.
“The spin is like the compass. The compass spins in this magnetic field perpendicular to that compass, and eventually it will stop spinning,” says Li. “Say you set the spin to ‘up,’ and you call that ‘one.’ When you expose it to the magnetic field, the spin changes direction. If it rotated 180 degrees, it changes from one to zero. If it rotated 360 degrees, it goes from one to one.”
They found that they could rotate the spin more than 10 turns by exposing the electron to different strengths of magnetic field.
The potential for this material is enormous, says Vardeny. It could process data faster and increase random-access memory.
“I’m telling you, it’s a miracle material,” says Vardeny.
Li and Vardeny conducted the research with first authors Patrick Odenthal and William Talmadge, Nathan Gundlach, Chuang Zhang and Dali Sun from the Department of Physics & Astronomy at the University of Utah; Zhi-Gang Yu of the ISP/ Applied Sciences Laboratory at Washington State University; and Ruizhi Wang, who is now at the School of Electronic and Optical Engineering at Nanjing University of Science and Technology.
The work was supported by a start-up grant from the University of Utah and the United States Department of Energy Office of Science grant DES0014579. The National Science Foundation Material Science and Engineering Center at the University of Utah (DMR-1121252) supported perovskite growth and facilities.
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