A new way to detect stabilizing properties of optical devices - Phys.org

Two ultrashort laser pulses revealed a difficult-to-measure quantum property in an atomically thin semiconductor. Combining optical measurements with an analytical model yielded a local Berry curvature consistent with theoretical calculations. The approach could help track rapid changes in electronic quantum states, although broader applications require further testing. A crystal can send electrons sideways even without an external magnetic field. Behind that unexpected motion lies Berry curvature, a geometric property of electronic quantum states. Measuring it experimentally, however, has remained considerably harder than calculating it. A collaboration between the universities of Jena and Regensburg has demonstrated an optical approach to that problem. In Nature Photonics, the team describes how ultrashort laser pulses and an analytical model revealed local Berry curvature in tungsten diselenide. The experiment examined a semiconductor layer less than one nanometer thick. Its response to light provided a quantitative estimate that agreed with theoretical predictions.

UC San Diego engineers showed that carefully shaped ultrafast laser beams can reverse magnetization in platinum-cobalt multilayers without an external magnetic field. Shrinking the laser spot changed the underlying switching behavior, allowing polarization-independent reversal in structures containing as many as nine Pt/Co repeats. The work could eventually support faster and denser magnetic storage, but it remains a laboratory demonstration using repeated femtosecond pulses rather than a finished memory device. A magnetic bit normally changes state because a field pushes its orientation from one direction to another. UC San Diego researchers have shown that carefully engineered light can perform that job instead, even in magnetic films thicker than those used in earlier optical-switching experiments. The team shaped ultrafast laser pulses into tightly focused vector beams and used them to reverse magnetization in platinum-cobalt multilayers without an external magnetic field. By shrinking the illuminated region and controlling how light was distributed across it, the researchers could switch between two optical-reversal mechanisms.