89 research outputs found
Balanced electron-hole transport in spin-orbit semimetal SrIrO3 heterostructures
Relating the band structure of correlated semimetals to their transport
properties is a complex and often open issue. The partial occupation of
numerous electron and hole bands can result in properties that are seemingly in
contrast with one another, complicating the extraction of the transport
coefficients of different bands. The 5d oxide SrIrO3 hosts parabolic bands of
heavy holes and light electrons in gapped Dirac cones due to the interplay
between electron-electron interactions and spin-orbit coupling. We present a
multifold approach relying on different experimental techniques and theoretical
calculations to disentangle its complex electronic properties. By combining
magnetotransport and thermoelectric measurements in a field-effect geometry
with first-principles calculations, we quantitatively determine the transport
coefficients of different conduction channels. Despite their different
dispersion relationships, electrons and holes are found to have strikingly
similar transport coefficients, yielding a holelike response under field-effect
and thermoelectric measurements and a linear, electronlike Hall effect up to 33
T.Comment: 5 pages, 4 figure
Characterization of fast magnetosonic waves driven by interaction between magnetic fields and compact toroids
Magnetosonic waves are low-frequency, linearly polarized magnetohydrodynamic
(MHD) waves that can be excited in any electrically conducting fluid permeated
by a magnetic field. They are commonly found in space, responsible for many
well-known features, such as heating of the solar corona and acceleration of
energetic electrons in Earth's inner magnetosphere. In this work, we present
observations of magnetosonic waves driven by injecting compact toroid (CT)
plasmas into a static Helmholtz magnetic field at the Big Red Ball (BRB)
Facility at Wisconsin Plasma Physics Laboratory (WiPPL). We first identify the
wave modes by comparing the experimental results with the MHD theory, and then
study how factors such as the background magnetic field affect the wave
properties. Since this experiment is part of an ongoing effort of forming a
target plasma with tangled magnetic fields as a novel fusion fuel for
magneto-inertial fusion (MIF, aka magnetized target fusion), we also discuss a
future possible path of forming the target plasma based on our current results
Emergence of the nematic electronic state in FeSe
We present a comprehensive study of the evolution of the nematic electronic
structure of FeSe using high resolution angle-resolved photoemission
spectroscopy (ARPES), quantum oscillations in the normal state and
elastoresistance measurements. Our high resolution ARPES allows us to track the
Fermi surface deformation from four-fold to two-fold symmetry across the
structural transition at ~87 K which is stabilized as a result of the dramatic
splitting of bands associated with dxz and dyz character. The low temperature
Fermi surface is that a compensated metal consisting of one hole and two
electron bands and is fully determined by combining the knowledge from ARPES
and quantum oscillations. A manifestation of the nematic state is the
significant increase in the nematic susceptibility as approaching the
structural transition that we detect from our elastoresistance measurements on
FeSe. The dramatic changes in electronic structure cannot be explained by the
small lattice effects and, in the absence of magnetic fluctuations above the
structural transition, points clearly towards an electronically driven
transition in FeSe stabilized by orbital-charge ordering.Comment: Latex, 8 pages, 4 figure
Unusual phase boundary of the magnetic-field-tuned valence transition in CeOs4Sb12
The phase diagram of the filled skutterudite has been mapped in fields
H of up to and temperatures T down to using resistivity, magnetostriction, and MHz conductivity. The valence transition separating the semimetallic low-H, low-T L phase from the metallic high-H, high-T H phase exhibits a very unusual, wedge-shaped phase boundary, with a non-monotonic gradient alternating between positive and negative. The expected "elliptical" behavior of the phase boundary of a valence transition with H2∝T2 originates in the H
and T dependence of the free energy of the f~multiplet. Here, quantum oscillation measurements suggest that additional energy scales associated with a quantum critical point are responsible for the deviation of the phase boundary of from this text-book behavior at high H and low T. The distortion of the low-H, high-T portion of the phase boundary may be associated with the proximity of to a topological semimetal phase induced by uniaxial stress
Spin-Dependent Mass Enhancement under Magnetic Field in the Periodic Anderson Model
In order to study the mechanism of the mass enhancement in heavy fermion
compounds in the presence of magnetic field, we study the periodic Anderson
model using the fluctuation exchange approximation. The resulting value of the
mass enhancement factor z^{-1} can become up to 10, which is significantly
larger than that in the single-band Hubbard model. We show that the difference
between the magnitude of the mass enhancement factor of up spin (minority spin)
electrons z^{-1}_up and that of down spin (majority spin) electrons z^{-1}_down
increases by the applied magnetic field B//z, which is consistent with de
Haas-van Alphen measurements for CeCoIn_5, CeRu_2Si_2 and CePd_2Si_2. We
predict that z^{-1}_up >z^{-1}_down in many Ce compounds, whereas z^{-1}_up <
z^{-1}_down in Yb compounds.Comment: 5 pages, 4 figure
Phase separation and suppression of critical dynamics at quantum transitions of itinerant magnets: MnSi and (SrCa)RuO
Quantum phase transitions (QPTs) have been studied extensively in correlated
electron systems. Characterization of magnetism at QPTs has, however, been
limited by the volume-integrated feature of neutron and magnetization
measurements and by pressure uncertainties in NMR studies using powderized
specimens. Overcoming these limitations, we performed muon spin relaxation
(SR) measurements which have a unique sensitivity to volume fractions of
magnetically ordered and paramagnetic regions, and studied QPTs from itinerant
heli/ferro magnet to paramagnet in MnSi (single-crystal; varying pressure) and
(SrCa)RuO (ceramic specimens; varying ). Our results
provide the first clear evidence that both cases are associated with
spontaneous phase separation and suppression of dynamic critical behavior,
revealed a slow but dynamic character of the ``partial order'' diffuse spin
correlations in MnSi above the critical pressure, and, combined with other
known results in heavy-fermion and cuprate systems, suggest a possibility that
a majority of QPTs involve first-order transitions and/or phase separation.Comment: 11 pages, 4 figures, 21 authors, to appear in Nature Physic
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