Fragile state

Physics 2, s28
Optical measurements in electron gases at low temperatures and high magnetic fields show the electron spins are, as predicted, polarized, but that this state is surprisingly delicate.

In the presence of a magnetic field, the physics of a two-dimensional electron gas such as GaAs at very low temperatures is often determined by electron-electron interactions rather than single-electron effects alone. In the lowest Landau level, i.e., for states with the least cyclotron energy, the physics is particularly interesting near the case where the number of electrons exactly equals the number of available states (often referred to as a “filling factor ν=1”). Here the ground state is expected to form a so-called quantum Hall ferromagnet, with fully polarized spins, even for the small Zeeman coupling typical in GaAs.

Writing in Physical Review Letters, Paulina Plochocka and co-workers at the CNRS in Grenoble, France, and colleagues in Israel and the US report detailed optical absorption measurements, which are often more reliable than transport measurements near integral filling factors, confirming that a full spin alignment does occur at ν=1 in a quantum Hall ferromagnet. Though predicted by theory, the polarized state could not be concluded from earlier experiments. More significantly, the authors find that the spin polarization is very fragile and the spins depolarize rapidly as either the filling factor or the temperature changes even slightly. This depolarization appears to be consistent with the presence of spin textures, known as skyrmions, that have been predicted in quantum Hall ferromagnets. – Sami Mitra

Subject Areas


Related Articles

Close Passes Give Atoms Tiny Quantum Kicks  
Atomic and Molecular Physics

Close Passes Give Atoms Tiny Quantum Kicks  

A new technique in which atoms move slowly through a diffraction grating lets researchers measure the tiny Casimir-Polder interaction, a force that arises from quantum vacuum fluctuations. Read More »

Long-Range Spin Currents with Chiral Crystals
Condensed Matter Physics

Long-Range Spin Currents with Chiral Crystals

Chiral crystals can produce spin-polarized currents that propagate over tens of micrometers—a promising feature for application in spintronics devices. Read More »

Fine Structure Constant Goes Big in Spin Ices

Fine Structure Constant Goes Big in Spin Ices

Inside a quantum spin ice, the constant that defines electromagnetic interactions is 10 times larger than normal, according to calculations. Read More »

More Articles