Spin excitations of the spin-polarized electron gas in semimagnetic quantum wells

Spin-Orbit Twisted Spin Waves: Group Velocity Control

We present a theoretical and experimental study of the interplay between spin-orbit coupling (SOC), Coulomb interaction, and motion of conduction electrons in a magnetized two-dimensional electron gas. Via a transformation of the many-body Hamiltonian we introduce the concept of spin-orbit twisted spin waves, whose energy dispersions and damping rates are obtained by a simple wave-vector shift of the spin waves without SOC. These theoretical predictions are validated by Raman scattering measurements. With optical gating of the density, we vary the strength of the SOC to alter the group velocity of the spin wave. The findings presented here differ from that of spin systems subject to the Dzyaloshinskii-Moriya interaction. Our results pave the way for novel applications in spin-wave routing devices and for the realization of lenses for spin waves.

Terahertz radiation from magnetic excitations in diluted magnetic semiconductors

We probed, in the time domain, the THz electromagnetic radiation originating from spins in CdMnTe diluted magnetic semiconductor quantum wells containing high-mobility electron gas. Taking advantage of the efficient Raman generation process, the spin precession was induced by low power near-infrared pulses. We provide a full theoretical first-principles description of spin-wave generation, spin precession, and of emission of THz radiation. Our results open new perspectives for improved control of the direct coupling between spin and an electromagnetic field, e.g., by using semiconductor technology to insert the THz sources in cavities or pillars.

From spin flip excitations to the spin susceptibility enhancement of a two-dimensional electron gas

The g-factor enhancement of the spin-polarized two-dimensional electron gas was measured directly over a wide range of spin polarizations, using spin flip resonant Raman scattering spectroscopy on two-dimensional electron gases embedded in Cd(1-x)Mn(x)Te semimagnetic quantum wells. At zero Raman transferred momentum, the single-particle spin flip excitation, energy Z*, coexists in the Raman spectrum with the spin flip wave of energy Z, the bare giant Zeeman splitting. We compare the measured g-factor enhancement with recent spin-susceptibility enhancement theories and deduce the spin-polarization dependence of the mass renormalization.