Biomedical subjects

N Freytag

Publications and source records attributed to N Freytag.

4 recordsLinked to original sources

PubMed2002

NMR investigation of how free composite fermions are at nu=1 / 2.

NMR measurements of the electron spin polarization (P) have been performed on a 2D electron system at and around half-filled lowest Landau level. Comparing the magnetic field and the temperature dependence of P to models of free and interacting composite fermions (CF), the imbalance of spin-up and spin-down CF Fermi seas is mapped as a function of Zeeman energy. Independent measurements of the CF effective mass, g factor, and Fermi energy are obtained from the thermal activation of P in tilted fields. The filling factor dependence of the P for 2 / 5<nu<2 / 3 reveals a broken particle-hole symmetry for the partially polarized CF Fermi sea.

Journal Article↗

PubMed2001

New phase transition between partially and fully polarized quantum Hall states with charge and spin gaps at nu = 2/3.

The average electron spin polarization Rho of a two-dimensional electron gas confined in GaAs/GaAlAs multiple quantum wells was measured by NMR near the fractional quantum Hall state with filling factor nu = 2/3. Above this filling factor (2/3< or = nu < 0.85), a strong depolarization is observed corresponding to two spin flips per additional flux quantum. The most remarkable behavior of the polarization is observed at nu = 2/3, where a quantum phase transition from a partially polarized (Rho approximately 3/4) to a fully polarized (Rho = 1) state can be driven by increasing the ratio between the Zeeman and the Coulomb energy above a critical value eta(c) = Delta(Z)/Delta(C) = 0.0185.

Journal Article↗

PubMed2000

NMR determination of 2D electron spin polarization at nu = 1/2

Using a "standard" NMR spin-echo technique we determined the spin polarization P of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei located in the wells. Concentrating on the temperature ( 0.05 less, similarT less, similar10 K) and magnetic field ( 7 less, similarB less, similar17 T) dependencies of P at Landau level filling factor nu = 1/2, we find that the results are described well by a simple model of noninteracting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.

Journal Article↗

PubMed1996

[Not Available].

This article deals with theory and practice of animal magnetism in Prussia in the first half of the nineteenth century from a socio-historical point of view. A discussion of the disputes over mesmeric therapy elucidates the complex process of social change in medicine. Theoretical conflicts demonstrate that many scholars and physicians where not able to differentiate between "science" and "superstition". It was the proximity of animal magnetism to religious and magical cures that led to the disputes, stimulated by the fact that the reasons for the positive effects of this therapy could not be traced. The practice of animal magnetism supplies evidence for the reciprocation between the so-called two cultures of academic and popular medicine.

Germany↗