6 research outputs found
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
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
Study of Intrinsic Spin Hall Effect and Orbital Hall Effect in 4d- and 5d- Transition Metals
We study the intrinsic spin Hall conductivity (SHC) in various
-transition metals (Ta, W, Re, Os, Ir, Pt, and Au) and 4d-transition metals
(Nb, Mo, Tc, Ru, Rh, Pd, and Ag) based on the Naval Research Laboratory
tight-binding model, which enables us to perform quantitatively reliable
analysis. In each metal, the obtained intrinsic SHC is independent of
resistivity in the low resistive regime ()
whereas it decreases in proportion to in the high resistive regime.
In the low resistive regime, the SHC takes a large positive value in Pt and Pd,
both of which have approximately nine -electrons per ion (). On the
other hand, the SHC takes a large negative value in Ta, Nb, W, and Mo where
. In transition metals, a conduction electron acquires the
trajectory-dependent phase factor that originates from the atomic wavefunction.
This phase factor, which is reminiscent of the Aharonov-Bohm phase, is the
origin of the SHC in paramagnetic metals and that of the anomalous Hall
conductivity in ferromagnetic metals. Furthermore, each transition metal shows
huge and positive -orbital Hall conductivity (OHC), independently of the
strength of the spin-orbit interaction (SOI). Since the OHC is much larger than
the SHC, it will be possible to realize a {\it orbitronics device} made of
transition metals.Comment: 17 pages, 12 figures, 3 tables, resubmitted to Physical Review
Anomalous Transport Phenomena in Fermi Liquids with Strong Magnetic Fluctuations
In many strongly correlated electron systems, remarkable violation of the
relaxation time approximation (RTA) is observed. The most famous example would
be high-Tc superconductors (HTSCs), and similar anomalous transport phenomena
have been observed in metals near their antiferromagnetic (AF) quantum critical
point (QCP). Here, we develop a transport theory involving resistivity and Hall
coefficient on the basis of the microscopic Fermi liquid theory, by considering
the current vertex correction (CVC). In nearly AF Fermi liquids, the CVC
accounts for the significant enhancements in the Hall coefficient,
magnetoresistance, thermoelectric power, and Nernst coefficient in nearly AF
metals. According to the numerical study, aspects of anomalous transport
phenomena in HTSC are explained in a unified way by considering the CVC,
without introducing any fitting parameters; this strongly supports the idea
that HTSCs are Fermi liquids with strong AF fluctuations. In addition, the
striking \omega-dependence of the AC Hall coefficient and the remarkable
effects of impurities on the transport coefficients in HTSCs appear to fit
naturally into the present theory. The present theory also explains very
similar anomalous transport phenomena occurring in CeCoIn5 and CeRhIn5, which
is a heavy-fermion system near the AF QCP, and in the organic superconductor
\kappa-(BEDT-TTF).Comment: 100 pages, Rep. Prog. Phys. 71, 026501 (2008