644 research outputs found
The Magnetic Ordering of the 3d Wigner Crystal
Using Path Integral Monte Carlo, we have calculated exchange frequencies as
electrons undergo ring exchanges of 2, 3 and 4 electrons in a ``clean'' 3d
Wigner crystal (bcc lattice) as a function of density. We find pair exchange
dominates and estimate the critical temperature for the transition to
antiferromagnetic ordering to be roughly Ry at melting. In
contrast to the situation in 2d, the 3d Wigner crystal is different from the
solid bcc 3He in that the pair exchange dominates because of the softer
interparticle potential. We discuss implications for the magnetic phase diagram
of the electron gas
Giant Intrinsic Spin and Orbital Hall Effects in Sr2MO4 (M=Ru,Rh,Mo)
We investigate the intrinsic spin Hall conductivity (SHC) and the d-orbital
Hall conductivity (OHC) in metallic d-electron systems, by focusing on the
t_{2g}-orbital tight-binding model for Sr2MO4 (M=Ru,Rh,Mo). The conductivities
obtained are one or two orders of magnitude larger than predicted values for
p-type semiconductors with 5% hole doping. The origin of these giant Hall
effects is the ``effective Aharonov-Bohm phase'' that is induced by the
d-atomic angular momentum in connection with the spin-orbit interaction and the
inter-orbital hopping integrals. The huge SHC and OHC generated by this
mechanism are expected to be ubiquitous in multiorbital transition metal
complexes, which pens the possibility of realizing spintronics as well as
orbitronics devices.Comment: 5 pages, accepted for publication in PR
Leading Temperature Corrections to Fermi Liquid Theory in Two Dimensions
We calculate the basic parameters of the Fermi Liquid: the scattering vertex,
the Landau interaction function, the effective mass, and physical
susceptibilities for a model of two-dimensional (2D) fermions with a short
ranged interaction at non-zero temperature. The leading temperature dependences
of the spin components of the scattering vertex, the Landau function, and the
spin susceptibility are found to be linear. T-linear terms in the effective
mass and in the ``charge-sector''- quantities are found to cancel to second
order in the interaction, but the cancellation is argued not to be generic. The
connection with previous studies of the 2D Fermi-Liquid parameters is
discussed.Comment: 4 pages, 1 figur
Pengaruh Metode Pemisahan Pelarut Dalam Gel Terhadap Sifat Fisik Titania-alumina Sebagai Penyangga Katalis
PENGARUH METODE PEMISAHAN PELARUT DALAM GEL TERHADAP SIFAT FISIK TITANIA-ALUMINA SEBAGAI PENYANGGA KATALIS. TiO2-Al2O3 gel monolitik dalam nisbah mol 0,2 untuk TiO2 dan 0,8 untuk Al2O3 telah dibuat dengan cara hidrolisis dari aluminium sec-butoksida, Al (OC4H9sec)3 dan titanium isopropoksida Ti(OC3H7iso)4 dalam larutan n-propanol dengan katalis asam. Pemisahan pelarut dalam gel dilakukan dengan dua cara, pertama pengeringan pada tekanan atmosfer hingga terbentuk xerogel. Kedua, pemisahan pelarut pada kondisi CO2 superkritik, hingga terbentuk aerogel. Terbentuknya gugus Ti-O, salah satu dari titanium dioksida atau jaringan polimer –Ti-O-Ti-O-Al-O- ditunjukkan dengan adanya puncak antara 500 dan 900 cm-1 yang tajam tetapi lebar pada spektrum infra merah. Puncak yang kuat pada 1635 cm-1 menandakan adanya gugus –OH uluran yang merupakan derajat yang tinggi dari permukaan hidroksilasi. Volume kumulatif pori-pori dari xerogel sangat kecil jika dibandingkan dengan aerogel hasil pemisahan pelarut pada kondisi CO2 superkritik. Fase anatase TiO2 tidak terbentuk selama proses kristalisasi hingga kalsinasi sampai suhu 1000oC. Pengkristalan alumina terjadi secara langsung dari fasa amorf Al2O3 ke fasa α-Al2O3 dan fasa-fasa antara θ- dan γ-Al2O3 tidak teramati. Dari hasil tersebut dapat diperkirakan bahwa selama kalsinasi partikel TiO2 terpisah dari partikel Al2O3 membentuk inti atom rutil sebelum terbentuknya kristal α-Al2O3. Karena itu pembentukan fasa rutile TiO2 akan mempercepat terbentuknya fasa α-Al2O3. Keasaman campuran titania alumina setelah dikalsinasi pada suhu 500 oC lebih tinggi daripada oksidanya masing-masing, yaitu TiO2 dan Al2O3. Hal ini disebabkan oleh terbentuknya asam Lewis dari campuran titania-alumina
Intrinsic Spin Hall Effect in s-wave Superconducting State: Analysis of Rashba Model
A general expression for the spin Hall conductivity (SHC) in the s-wave
superconducting state at finite temperatures is derived. Based on the
expression, we study the SHC in a two-dimensional electron gas model in the
presence of Rashba spin-orbit interaction (SOI). The SHC is zero in the normal
state, whereas it takes a large negative value as soon as the superconductivity
occurs, due to the change in the quasiparticle contributions. Since this
remarkable behavior is independent of the strength of the SOI, it will be
widely observed in thin films of superconductors with surface-induced Rashba
SOI, or in various non-centrosymmetric superconductors.Comment: 4 pages, to be published in Phys. Rev. Let
Electronic susceptibilities in systems with anisotropic Fermi surfaces
The low temperature dependence of the spin and charge susceptibilities of an
anisotropic electron system in two dimensions is analyzed. It is shown that the
presence of inflection points at the Fermi surface leads, generically, to a dependence, and a more singular behavior, ,
is also possible. Applications to quasi two-dimensional materials are
discussed.Comment: 8 pages, 5 figures, revtex 4 styl
Giant Orbital Hall Effect in Transition Metals: Origin of Large Spin and Anomalous Hall Effects
In transition metals and their compounds, the orbital degrees of freedom
gives rise to an orbital current, in addition to the ordinary spin and charge
currents. We reveal that considerably large spin and anomalous Hall effects
(SHE and AHE) observed in transition metals originate from an orbital Hall
effect (OHE). To elucidate the origin of these novel Hall effects, a simple
periodic s-d hybridization model is proposed as a generic model. The giant
positive OHE originates from the orbital Aharonov-Bohm phase factor, and
induces spin Hall conductivity that is proportional to the spin-orbit
polarization at the Fermi level, which is positive (negative) in metals with
more than (less than) half-filling.Comment: 5 pages, to be published in Phys. Rev. Let
Giant Extrinsic Spin Hall Effect due to Rare-Earth Impurities
We investigate the extrinsic spin Hall effect in the electron gas model due
to magnetic impurities, by focusing on Ce- and Yb-impurities. In the dilute
limit, the skew scattering term dominates the side jump term. For
Ce-impurities, the spin Hall angle due to skew scattering is
given by , where is the phase shift
for partial wave. Since reaches if
\delta_2 \simge 0.03, the spin Hall effect is anticipated to be considerable
in metals with rare-earth impurities. The giant extrinsic SHE originates from
the large orbital angular momentum, which is also significant for the intrinsic
SHE.Comment: 5 pages, 3 figures, to be published in New Journal of Physic
Weak-coupling expansions for the attractive Holstein and Hubbard models
Weak-coupling expansions (conserving approximations) are carried out for the
attractive Holstein and Hubbard models (on an infinite-dimensional hypercubic
lattice) that include all bandstructure and vertex correction effects. Quantum
fluctuations are found to renormalize transition temperatures by factors of
order unity, but may be incorporated into the superconducting channel of
Migdal-Eliashberg theory by renormalizing the phonon frequency and the
interaction strength.Comment: 10 pages, (five figures available from the author by request) typeset
with ReVTeX, preprint NSF-ITP-93-10
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