arXiv subjects

U. Sivan

Publications and source records attributed to U. Sivan.

6 recordsLinked to original sources

arXiv2004

Comment on "Critical behavior of the Pauli spin susceptibility..." by A. A. Shashkin et. al

The paper by A. A. Shashkin et al. [cond-mat/0409100] reports measurements of the thermodynamic magnetization of two-dimensional electrons in silicon. Although the experimental data is very similar to that reported by us more then two years ago, the authors arrive at an opposite conclusion regarding the spin susceptibility "critical behavior" and spin instability in the vicinity of the metal-insulator transition. We show that this interpretation is based on a flawed analysis of the experimental data.

cond-mat.str-el↗

arXiv2003

Optimal rotations of deformable bodies and orbits in magnetic fields

Deformations can induce rotation with zero angular momentum where dissipation is a natural ``cost function''. This gives rise to an optimization problem of finding the most effective rotation with zero angular momentum. For certain plastic and viscous media in two dimensions the optimal path is the orbit of a charged particle on a surface of constant negative curvature with magnetic field whose total flux is half a quantum unit.

physics.class-ph↗

arXiv2003

The thermodynamic spin magnetization of strongly correlated 2d electrons in a silicon inversion layer

A novel method invented to measure the minute thermodynamic spin magnetization of dilute two dimensional fermions is applied to electrons in a silicon inversion layer. Interplay between the ferromagnetic interaction and disorder enhances the low temperature susceptibility up to 7.5 folds compared with the Pauli susceptibility of non-interacting electrons. The magnetization peaks in the vicinity of the density where transition to strong localization takes place. At the same density, the susceptibility becomes extremely close to that of free spins (Curie susceptibility), indicating an almost perfect compensation of the kinetic energy toll associated with spin polarization by the energy gained from the ferromagnetic correlation. Yet, the balance favors a paramagnetic phase over spontaneous magnetization.

cond-mat.mes-hall↗

arXiv2001

On the Cooling of Electrons in a Silicon Inversion Layer

The cooling of two-dimensional electrons in silicon-metal-oxide semiconductor field effect transistors is studied experimentally. Cooling to the lattice is found to be more effective than expected from the bulk electron-phonon coupling in silicon. Unexpectedly, the extracted heat transfer rate to phonons at low temperatures depends cubically on electron temperature, suggesting that piezoelectric coupling (absent in bulk silicon) dominates over deformation potential. According to our findings, at 100 mK, electrons farther than 0.1 mm from the contacts are mostly cooled by phonons. Using long devices and low excitation voltage we measure electron resistivity down to 100 mK and find that some of the "metallic" curves, reported earlier, turn insulating below about 300 mK. This finding renders the definition of the claimed 2D metal-insulator transition questionable. Previous low temperature measurements in silicon devices are analyzed and thumb rules for evaluating their electron temperatures are provided.

cond-mat.mes-hall↗

arXiv1998

Transmission through a n interacting quantum dot in the Coulomb blockade regime

The influence of electron-electron (e-e) interactions on the transmission through a quantum dot is investigated numerically for the Coulomb blockade regime. For vanishing magnetic fields, the conductance peak height statistics is found to be independent of the interactions strength. It is identical to the statistics predicted by constant interaction single electron random matrix theory and agrees well with recent experiments. However, in contrast to these random matrix theories, our calculations reproduces the reduced sensitivity to magnetic flux observed in many experiments. The relevant physics is traced to the short range Coulomb correlations providing thus a unified explanation for the transmission statistics as well as for the large conductance peak spacing fluctuations observed in other experiments.

cond-mat.mes-hall↗

arXiv1996

Even-odd correlations in capacitance fluctuations of quantum dots

We investigate effects of short range interactions on the addition spectra of quantum dots using a disordered Hubbard model. A correlation function \cS(q) is defined on the inverse compressibility versus filling data, and computed numerically for small lattices. Two regimes of interaction strength are identified: the even/odd fluctuations regime typical of Fermi liquid ground states, and a regime of structureless $\cS(q)$ at strong interactions. We propose to understand the latter regime in terms of magnetically correlated localized spins.

cond-mat↗