55 research outputs found
Hall coefficient anomaly in the low-temperature high-field phase of Sr3Ru2O7
We report a study of the Hall effect of high-purity Sr3Ru2O7 single crystals. We establish an empirical
correlation between the onset of its unusual low-temperature, high-field phase and a pronounced dip in the fielddependent Hall coefficient. Unlike the order parameter obtained from measurements of anisotropic resistivity,
which is affected by the formation of domains, the Hall effect feature seems to reflect the nature of the ordering
within a single domain. We checked for violations of the Onsager relations for the off-diagonal components
of the resistivity tensor but do not detect any. We compare our observations to those on materials that have
long-wavelength spin structures, and discuss them in relation to a growing body of theoretical work on the nature
of the low-temperature phase in Sr3Ru2O7
Quantum oscillations in the anomalous phase in Sr3Ru2O7
This is the final version. Available from American Physical Society via the DOI in this recordWe report measurements of quantum oscillations detected in the putative nematic phase of Sr3Ru2O7. Improvements in sample purity enabled the resolution of small amplitude de Haas-van Alphen (dHvA) oscillations between two first order metamagnetic transitions delimiting the phase. Two distinct frequencies were observed, whose amplitudes follow the normal Lifshitz-Kosevich profile. Variations of the dHvA frequencies are explained in terms of a chemical potential shift produced by reaching a peak in the density of states, and an anomalous field dependence of the oscillatory amplitude provides information on domains. © 2009 The American Physical Society.Engineering and Physical Sciences Research Council (EPSRC
Quantum oscillations near the metamagnetic transition in Sr3Ru2O7
This is the final version. Available from American Physical Society via the DOI in this recordWe report a detailed investigation of quantum oscillations in Sr 3 Ru2 O7, observed inductively (the de Haas-van Alphen effect) and thermally (the magnetocaloric effect). Working at fields from 3 to 18 T allowed us to straddle the metamagnetic transition region and probe the low- and high-field Fermi liquids. The observed frequencies are strongly field dependent in the vicinity of the metamagnetic transition, and there is evidence for magnetic breakdown. We also present the results of a comprehensive rotation study. The most surprising result concerns the field dependence of the measured quasiparticle masses. Contrary to conclusions previously drawn by some of us as a result of a study performed with a much poorer signal-to-noise ratio, none of the five Fermi-surface branches for which we have good field-dependent data gives evidence for a strong-field dependence of the mass. The implications of these experimental findings are discussed. © 2010 The American Physical Society.Engineering and Physical Sciences Research Council (EPSRC
Field-induced polarisation of Dirac valleys in bismuth
Electrons are offered a valley degree of freedom in presence of particular
lattice structures. Manipulating valley degeneracy is the subject matter of an
emerging field of investigation, mostly focused on charge transport in
graphene. In bulk bismuth, electrons are known to present a threefold valley
degeneracy and a Dirac dispersion in each valley. Here we show that because of
their huge in-plane mass anisotropy, a flow of Dirac electrons along the
trigonal axis is extremely sensitive to the orientation of in-plane magnetic
field. Thus, a rotatable magnetic field can be used as a valley valve to tune
the contribution of each valley to the total conductivity. According to our
measurements, charge conductivity by carriers of a single valley can exceed
four-fifth of the total conductivity in a wide range of temperature and
magnetic field. At high temperature and low magnetic field, the three valleys
are interchangeable and the three-fold symmetry of the underlying lattice is
respected. As the temperature lowers and/or the magnetic field increases, this
symmetry is spontaneously lost. The latter may be an experimental manifestation
of the recently proposed valley-nematic Fermi liquid state.Comment: 14 pages + 5 pages of supplementary information; a slightly modified
version will appear as an article in Nature physic
Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides
The in-plane anisotropy of the electrical resistivity across the coupled
orthorhombic and magnetic transitions of the iron pnictides has been
extensively studied in the parent and electron-doped compounds. All these
studies universally show that the resistivity across the long
orthorhombic axis - along which the spins couple antiferromagnetically
below the magnetic transition temperature - is smaller than the resistivity
of the short orthorhombic axis , i. e. .
Here we report that in the hole-doped compounds
BaKFeAs, as the doping level increases, the
resistivity anisotropy initially becomes vanishingly small, and eventually
changes sign for sufficiently large doping, i. e. . This
observation is in agreement with a recent theoretical prediction that considers
the anisotropic scattering of electrons by spin-fluctuations in the
orthorhombic/nematic state.Comment: This paper has been replaced by the new version offering new
explanation of the experimental results first reported her
Tunable Emergent Heterostructures in a Prototypical Correlated Metal
At the interface between two distinct materials desirable properties, such as
superconductivity, can be greatly enhanced, or entirely new functionalities may
emerge. Similar to in artificially engineered heterostructures, clean
functional interfaces alternatively exist in electronically textured bulk
materials. Electronic textures emerge spontaneously due to competing
atomic-scale interactions, the control of which, would enable a top-down
approach for designing tunable intrinsic heterostructures. This is particularly
attractive for correlated electron materials, where spontaneous
heterostructures strongly affect the interplay between charge and spin degrees
of freedom. Here we report high-resolution neutron spectroscopy on the
prototypical strongly-correlated metal CeRhIn5, revealing competition between
magnetic frustration and easy-axis anisotropy -- a well-established mechanism
for generating spontaneous superstructures. Because the observed easy-axis
anisotropy is field-induced and anomalously large, it can be controlled
efficiently with small magnetic fields. The resulting field-controlled magnetic
superstructure is closely tied to the formation of superconducting and
electronic nematic textures in CeRhIn5, suggesting that in-situ tunable
heterostructures can be realized in correlated electron materials
Broken rotational symmetry in the pseudogap phase of a high-Tc superconductor
The nature of the pseudogap phase is a central problem in the quest to
understand high-Tc cuprate superconductors. A fundamental question is what
symmetries are broken when that phase sets in below a temperature T*. There is
evidence from both polarized neutron diffraction and polar Kerr effect
measurements that time- reversal symmetry is broken, but at temperatures that
differ significantly. Broken rotational symmetry was detected by both
resistivity and inelastic neutron scattering at low doping and by scanning
tunnelling spectroscopy at low temperature, but with no clear connection to T*.
Here we report the observation of a large in-plane anisotropy of the Nernst
effect in YBa2Cu3Oy that sets in precisely at T*, throughout the doping phase
diagram. We show that the CuO chains of the orthorhombic lattice are not
responsible for this anisotropy, which is therefore an intrinsic property of
the CuO2 planes. We conclude that the pseudogap phase is an electronic state
which strongly breaks four-fold rotational symmetry. This narrows the range of
possible states considerably, pointing to stripe or nematic orders.Comment: Published version. Journal reference and DOI adde
Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states
In the high-transition-temperature (high-Tc) superconductors the pseudogap
phase becomes predominant when the density of doped holes is reduced1. Within
this phase it has been unclear which electronic symmetries (if any) are broken,
what the identity of any associated order parameter might be, and which
microscopic electronic degrees of freedom are active. Here we report the
determination of a quantitative order parameter representing intra-unit-cell
nematicity: the breaking of rotational symmetry by the electronic structure
within CuO2 unit cell. We analyze spectroscopic-imaging scanning tunneling
microscope images of the intra-unit-cell states in underdoped
Bi2Sr2CaCu2O8+{\delta} and, using two independent evaluation techniques, find
evidence for electronic nematicity of the states close to the pseudogap energy.
Moreover, we demonstrate directly that these phenomena arise from electronic
differences at the two oxygen sites within each unit cell. If the
characteristics of the pseudogap seen here and by other techniques all have the
same microscopic origin, this phase involves weak magnetic states at the O
sites that break 90o -rotational symmetry within every CuO2 unit cell.Comment: See the Nature website for the published version. High-resolution
version of figures, supplementary information and supplementary movies are
available at http://eunahkim.ccmr.cornell.edu/KimGroup/highlights.htm
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