Spin-½

About: Spin-½ is a research topic. Over the lifetime, 40423 publications have been published within this topic receiving 796639 citations.

Phase diagram of a two-component Fermi gas with resonant interactions

Abstract: A major controversy has surrounded the stability of superfluidity in spin-polarized Fermi gas systems with resonant interactions when the 'up' and 'down' spin components are imbalanced. This problem is explored for a Fermi gas of 6Li atoms, using tomographic techniques to map out the superfluid phases as the temperature and density imbalance are varied. Evidence is found for various types of phase transitions, enabling quantitative tests of theoretical calculations on the stability of resonant superfluidity. The pairing of fermions lies at the heart of superconductivity and superfluidity. The stability of these pairs determines the robustness of the superfluid state, and the quest for superconductors with high critical temperature equates to a search for systems with strong pairing mechanisms. Ultracold atomic Fermi gases present a highly controllable model system for studying strongly interacting fermions1. Tunable interactions (through Feshbach collisional resonances) and the control of population or mass imbalance among the spin components provide unique opportunities to investigate the stability of pairing2,3,4—and possibly to search for exotic forms of superfluidity5,6. A major controversy has surrounded the stability of superfluidity against an imbalance between the two spin components when the fermions interact resonantly (that is, at unitarity). Here we present the phase diagram of a spin-polarized Fermi gas of 6Li atoms at unitarity, experimentally mapping out the superfluid phases versus temperature and density imbalance. Using tomographic techniques, we reveal spatial discontinuities in the spin polarization; this is the signature of a first-order superfluid-to-normal phase transition, and disappears at a tricritical point where the nature of the phase transition changes from first-order to second-order. At zero temperature, there is a quantum phase transition from a fully paired superfluid to a partially polarized normal gas. These observations and the implementation of an in situ ideal gas thermometer provide quantitative tests of theoretical calculations on the stability of resonant superfluidity.

Skyrmions and anomalous Hall effect in a Dzyaloshinskii-Moriya spiral magnet

Abstract: Monte Carlo simulation study of a classical spin model with Dzyalosinskii-Moriya interaction and the spin anisotropy under the magnetic field is presented. We found a rich phase diagram containing the multiple spin spiral (or Skyrme crystal) phases of square, rectangular, and hexagonal symmetries in addition to the spiral spin state. The Skyrme crystal states are stabilized by a spin anisotropy or a magnetic field. The Hall conductivity ${\ensuremath{\sigma}}_{xy}$ is calculated within the $sd$ model for each of the phases. Applying a magnetic field induces nonzero uniform chirality and the anomalous Hall conductivity simultaneously. The field dependence of ${\ensuremath{\sigma}}_{xy}$ is shown to be a sensitive probe of the underlying magnetic structure. Relevance of the present results to several recent experiments on MnSi is discussed.

Multi-component quantum gases in spin-dependent hexagonal lattices

Abstract: Ultracold quantum gases in optical lattices have been used to study a wide range of many-body effects. Nearly all experiments so far, however, have been performed in cubic optical lattice structures. Now a ‘honeycomb’ lattice structure has been realized. The approach promises insight into materials with hexagonal crystal symmetries, such as graphene or carbon nanotubes.

All-optical initialization, readout, and coherent preparation of single silicon-vacancy spins in diamond.

Abstract: The spin on a silicon defect in diamond can be prepared in a coherent quantum state, a promising sign that it could encode information in a quantum internet.

Spin injection and spin accumulation in all-metal mesoscopic spin valves

Abstract: We study the electrical injection and detection of spin accumulation in lateral ferromagnetic-metal--nonmagnetic-metal--ferromagnetic-metal (F/N/F) spin valve devices with transparent interfaces. Different ferromagnetic metals, Permalloy (Py), cobalt (Co), and nickel (Ni), are used as electrical spin injectors and detectors. For the nonmagnetic metal both aluminum (Al) and copper (Cu) are used. Our multiterminal geometry allows us to experimentally separate the spin valve effect from other magnetoresistance signals such as the anisotropic magnetoresistance and Hall effects. In a ``nonlocal'' spin valve measurement we are able to completely isolate the spin valve signal and observe clear spin accumulation signals at $T=4.2\mathrm{K}$ as well as at room temperature (RT). For aluminum we obtain spin relaxation lengths $({\ensuremath{\lambda}}_{\mathrm{sf}})$ of $1.2\ensuremath{\mu}\mathrm{m}$ and $600\mathrm{nm}$ at $T=4.2\mathrm{K}$ and RT, respectively, whereas for copper we obtain $1.0\ensuremath{\mu}\mathrm{m}$ and 350 nm. At RT these spin relaxation lengths are within a factor of 2 of the maximal obtainable spin relaxation length, being limited by electron-phonon scattering. The spin relaxation times ${\ensuremath{\tau}}_{\mathrm{sf}}$ in the Al and Cu thin films are compared with theory and results obtained from giant magnetoresistance (GMR), conduction electron spin resonance, antiweak localization, and superconducting tunneling experiments. The magnitudes of the spin valve signals generated by the Py and Co electrodes are compared to the results obtained from GMR experiments. For the Ni electrodes no spin signal could be observed beyond experimental accuracy.