RESUMO
Polarons can control carrier mobility and can also be used in the design of quantum devices. Although much effort has been directed into investigating the nature of polarons, observation of defect-related polarons is challenging due to electron-defect scattering. Here we explore the polaronic behavior of nitrogen-vacancy (NV) centers in a diamond crystal using an ultrafast pump-probe technique. A 10-fs optical pulse acts as a source of high electric field exceeding the dielectric breakdown threshold, in turn exerting a force on the NV charge distribution and polar optical phonons. The electronic and phononic responses are enhanced by an order of magnitude for a low density of NV centers, which we attribute to a combination of cooperative polaronic effects and scattering by defects. First-principles calculations support the presence of dipolar Fröhlich interaction via non-zero Born effective charges. Our findings provide insights into the physics of color centers in diamonds.
RESUMO
23Na-MRI provides information on Na+ content, and its application in the medical field has been highly anticipated. However, for existing clinical 1H-MRI systems, its implementation requires an additional broadband RF transmitter, dedicated transceivers, and RF coils for Na+ imaging. However, a standard medical MRI system cannot often be modified to perform 23Na imaging. We have developed an add-on crossband RF repeater system that enables 23Na-MRI simply by inserting it into the magnet bore of an existing 1H MRI. The three axis gradient fields controlled by the 1H-MRI system were directly used for 23Na imaging without any deformation. A crossband repeater is a common technique used for amateur radio. This concept was proven by a saline solution phantom and in vivo mouse experiments. This add-on RF platform is applicable to medical 1H MRI systems and can enhance the application of 23Na-MRI in clinical usage.