45 research outputs found
Demonstration of Rashba spin splitting in GaN-based heterostructures
The circular photogalvanic effect (CPGE), induced by infrared radiation, has
been observed in (0001)-oriented GaN quantum well (QW) structures. The
photocurrent changes sign upon reversing the radiation helicity demonstrating
the existence of spin-splitting of the conduction band in k-space in this type
of materials. The observation suggests the presence of a sizeable Rashba type
of spin-splitting, caused by the built-in asymmetry at the AlGaN/GaN interface.Comment: 7 pages, 3 figure
Spin-dependent tunnelling through a symmetric barrier
The problem of electron tunnelling through a symmetric semiconductor barrier
based on zinc-blende-structure material is studied. The Dresselhaus terms
in the effective Hamiltonian of bulk semiconductor of the barrier are shown to
result in a dependence of the tunnelling transmission on the spin orientation.
The difference of the transmission probabilities for opposite spin orientations
can achieve several percents for the reasonable width of the barriers.Comment: 3 pages, Submitted to Phys. Rev.
Magneto-Gyrotropic Photogalvanic Effects in Semiconductor Quantum Wells
We show that free-carrier (Drude) absorption of both polarized and
unpolarized terahertz radiation in quantum well (QW) structures causes an
electric photocurrent in the presence of an in-plane magnetic field.
Experimental and theoretical analysis evidences that the observed photocurrents
are spin-dependent and related to the gyrotropy of the QWs. Microscopic models
for the photogalvanic effects in QWs based on asymmetry of photoexcitation and
relaxation processes are proposed. In most of the investigated structures the
observed magneto-induced photocurrents are caused by spin-dependent relaxation
of non-equilibrium carriers
Isospin breaking corrections to low-energy pi-K scattering
We evaluate the matrix elements for the processes pi^0 K^0 -> pi^0 K^0 and
pi^- K^+ -> pi^0 K^0 in the presence of isospin breaking terms at leading and
next-to-leading order. As a direct application the releveant combination of the
S-wave scattering lengths involved in the pion-kaon atom lifetime is
determined. We discuss the sensitivity of the results with respect to the input
parameters.Comment: 33 pages, plain latex, 2 figure
The Strong Isospin-Breaking Correction for the Gluonic Penguin Contribution to epsilon'/epsilon at Next-to-Leading Order in the Chiral Expansion
The strong isospin-breaking correction, Omega_{st}, which appears in
estimates of the Standard Model value for the direct CP-violating ratio
epsilon'/epsilon, is evaluated to next-to-leading order (NLO) in the chiral
expansion using Chiral Perturbation Theory. The relevant linear combinations of
the unknown NLO CP-odd weak low-energy constants (LEC's) which, in combination
with 1-loop and strong LEC contributions, are required for a complete
determination at this order, are estimated using two different models. It is
found that, to NLO, Omega_{st}=0.08 +/- 0.05, significantly reduced from the
``standard'' value, 0.25 +/- 0.08, employed in recent analyses. The potentially
significant numerical impact of this decrease on Standard Model predictions for
epsilon'/epsilon, associated with the decreased cancellation between gluonic
penguin and electroweak penguin contributions, is also discussed.Comment: 12 pages, 1 figur
Rashba and Dresselhaus spin splittings in semiconductor quantum wells measured by spin photocurrents
Resonant inversion of circular photogalvanic effect in n-doped quantum wells,
We show that the sign of the circular photogalvanic effect can be changed by tuning the radiation frequency of circularly polarized light. Here resonant inversion of the photogalvanic effect has been observed for direct
intersubband transition in n-type GaAs quantum well structures. This inversion of the photon helicity driven
current is a direct consequence of the lifting of the spin degeneracy due to k-linear terms in the Hamiltonian in
combination with energy and momentum conservation and optical selection rules