Scientists at the Federal Polytechnic School of Lausanne (EPFL) have succeeded in measuring an ultrashort time delay in an electron emission without the need for a clock , a discovery that has important implications for fundamental research – without immediate practical purposes – and also for cutting-edge technology, as explained by this European institution, a leader in science and technology, through a statement.
When light collides with certain materials, an emission of electrons takes place. The phenomenon, known by the name of photoemission, was discovered in 1905 by Albert Einstein and made him worthy of the Nobel Prize, but it has not been until recent years that scientists, thanks to advances in laser technology, have been able to approach really at the incredibly short timescales that take place in photoemission.
In this sense, researchers from the EPFL have just discovered an ultrashort time lag in a photoemission by measuring the spin of the photoemitted electrons – when the general belief is that the emission of electrons is instantaneous – without having to use ultrashort laser pulses . Photoemission has been confirmed as an important phenomenon by creating a foundation platform for the latest spectroscopic techniques, allowing scientists to study the properties of electrons in solids. One of them is spin – rotation – an intrinsic quantum property of these elementary particles by which they give the impression that they rotate around their axis. The degree to which this axis aligns in a specific direction is called spin polarization, and it is what gives certain materials, such as iron, magnetic properties.
The work carried out by an EPFL team, in the laboratory of scientist Hugo Dil, with whom a group of German researchers have collaborated, has recently been published in the journal Physical Review Letters . And he has shown that, during photoemission, the spin polarization of the emitted electrons can be related to the photoemission delay times . But the most important thing is that they have done it without resorting to a watch. To achieve this, scientists have used a type of photoemission spectroscopy with which they have measured the spin of electrons photoemitted by a copper crystal.
“With the laser, you can directly measure the time lag between different processes, but it is difficult to determine the moment when a process begins, that is, zero time”, explains Mauro Fanciulli, from Hugo Dil’s team and main author of the Article. “However, with our experience, we have measured time in an indirect way, and thus we have not had that problem: we have been able to access one of the shortest time scales ever measured. The two techniques (spin and laser) are complementary. , and together they can provide a whole new field of information, “he adds.
Hugo Dil points out that this work could trigger future fundamental and applied research. “It has to do with the nature of time itself, and will allow us to understand the details of the photoemission process, but it can also be used in photoemission spectroscopy on interesting materials,” he adds. These materials include graphene and high-temperature superconductors , on which these researchers will focus their studies soon.
