arXiv subjects

V. F. Sapega

Publications and source records attributed to V. F. Sapega.

22 records · Page 2Linked to original sources

arXiv2010

Coherent magnetization precession in ferromagnetic (Ga,Mn)As induced by picosecond acoustic pulses

We show that the magnetization of a thin ferromagnetic (Ga,Mn)As layer can be modulated by picosecond acoustic pulses. In this approach a picosecond strain pulse injected into the structure induces a tilt of the magnetization vector M, followed by the precession of M around its equilibrium orientation. This effect can be understood in terms of changes in magneto-crystalline anisotropy induced by the pulse. A model where only one anisotropy constant is affected by the strain pulse provides a good description of the observed time-dependent response.

cond-mat.mes-hall↗

arXiv2006

Electrical control of optical orientation of neutral and negatively charged excitons in n-type semiconductor quantum well

We report a giant electric field induced increase of spin orientation of excitons in n-type GaAs/AlGaAs quantum well. It correlates strongly with the formation of negatively charged excitons (trions) in the photoluminescence spectra. Under resonant excitation of neutral heavy-hole excitons, the polarization of excitons and trions increases dramatically with electrical injection of electrons within the narrow exciton-trion bias transition in the PL spectra, implying a polarization sensitivity of 200 % per Volt. This effect results from a very efficient trapping of neutral excitons by the quantum well interfacial fluctuations (so-called "natural" quantum dots) containing resident electrons.

cond-mat.mes-hall↗

arXiv2005

Large spin splitting of GaN electronic states induced by Gd doping

We present a detailed study of the magnetic-field and temperature-dependent polarization of the near-band-gap photoluminescence in Gd-doped GaN layers. Our study reveals an extraordinarily strong influence of Gd doping on the electronic states in the GaN matrix. We observe that the spin splitting of the valence band reverses its sign for Gd concentrations as low as 1.6 x 10^{16} cm^{-3}. This remarkable result can be understood only in terms of a long range induction of magnetic moments in the surrounding GaN matrix by the Gd ions.

cond-mat.mtrl-sci↗

arXiv2005

GaN:Gd: A superdilute ferromagnetic semiconductor with a Curie temperature above 300 K

We investigate the magnetic and magneto-optic properties of epitaxial GaN:Gd layers as a function of the external magnetic field and temperature. An unprecedented magnetic moment is observed in this diluted magnetic semiconductor. The average value of the moment per Gd atom is found to be as high as 4000 \mub as compared to its atomic moment of 8 \mub. The long-range spin-polarization of the GaN matrix by Gd is also reflected in the circular polarization of magneto-photoluminescence measurements. Moreover, the materials system is found to be ferromagnetic above room temperature in the entire concentration range under investigation (7$\times10^{15}$ to 2$\times10^{19}$ cm$^{-3}$). We propose a phenomenological model to understand the macroscopic magnetic behavior of the system. Our study reveals a close connection between the observed ferromagnetism and the colossal magnetic moment of Gd.

cond-mat.mtrl-sci↗