23 research outputs found
A comparison of the hidden order transition in URuSi to the -transition in He
The low-temperature states of ambient URuSi and superfluid He are
both characterized by momentum-dependent energy gaps between the ground and
excited states. This behavior weakly persists even above the transitions
temperatures but becomes over-damped because of the number of excitations
present at elevated temperature. We show that akin to the normal fluid to
superfluid transition in He, the hidden-order (HO) transition in
URuSi can be understood by a change of the gapped transitions to
elementary excitations (EE) of the unknown ordered state. These underdamped EEs
reflect the basic character and order parameters of the different phase
transitions. This view accounts for the full amount of entropy released in
these transitions, the jumps in the resistivity and thermal conductivity
directly below the transition, as well as the reduction of the Fermi surface.
We argue that the behavior in the HO phase is that of a gas of weakly
interacting excitations from charge density wave or crystal field states in a
similar manner to that of the phonon-roton excitations of the superfluid He
phase. We discuss the influence of applying pressure and magnetic fields within
this scenario and the role of the small moment antiferromagnetic clustering in
the hidden order phase.Comment: 14 pages, 12 figures, to be submitted to PR
Observing the origin of superconductivity in quantum critical metals
Despite intense efforts during the last 25 years, the physics of
unconventional superconductors, including the cuprates with a very high
transition temperature, is still a controversial subject. It is believed that
superconductivity in many of these strongly correlated metallic systems
originates in the physics of quantum phase transitions, but quite diverse
perspectives have emerged on the fundamentals of the electron-pairing physics,
ranging from Hertz style critical spin fluctuation glue to the holographic
superconductivity of string theory. Here we demonstrate that the gross energy
scaling differences that are behind these various pairing mechanisms are
directly encoded in the frequency and temperature dependence of the dynamical
pair susceptibility. This quantity can be measured directly via the second
order Josephson effect and it should be possible employing modern experimental
techniques to build a `pairing telescope' that gives a direct view on the
origin of quantum critical superconductivity.Comment: 19 pages, 9 figures; minor changes in the experimental part; added a
new appendix section calculating the pair susceptibility of marginal Fermi
liqui
Detection of electronic nematicity using scanning tunneling microscopy
Electronic nematic phases have been proposed to occur in various correlated
electron systems and were recently claimed to have been detected in scanning
tunneling microscopy (STM) conductance maps of the pseudogap states of the
cuprate high-temperature superconductor Bi2Sr2CaCu2O8+x (Bi-2212). We
investigate the influence of anisotropic STM tip structures on such
measurements and establish, with a model calculation, the presence of a
tunneling interference effect within an STM junction that induces
energy-dependent symmetry-breaking features in the conductance maps. We
experimentally confirm this phenomenon on different correlated electron
systems, including measurements in the pseudogap state of Bi-2212, showing that
the apparent nematic behavior of the imaged crystal lattice is likely not due
to nematic order but is related to how a realistic STM tip probes the band
structure of a material. We further establish that this interference effect can
be used as a sensitive probe of changes in the momentum structure of the
sample's quasiparticles as a function of energy.Comment: Accepted for publication (PRB - Rapid Communications). Main text (5
pages, 4 figures) + Supplemental Material (4 pages, 4 figures
Magnetic field effect on Fe-induced short-range magnetic correlation and electrical conductivity in BiPbSrCuFeO
We report electrical resistivity measurements and neutron diffraction studies
under magnetic fields of
BiPbSrCuFeO, in which hole
carriers are overdoped. This compound shows short-range incommensurate magnetic
correlation with incommensurability , whereas a Fe-free compound
shows no magnetic correlation. Resistivity shows an up turn at low temperature
in the form of and shows no superconductivity. We observe reduction
of resistivity by applying magnetic fields (i.e., a negative magnetoresistive
effect) at temperatures below the onset of short-range magnetic correlation.
Application of magnetic fields also suppresses the Fe induced incommensurate
magnetic correlation. We compare and contrast these observations with two
different models: 1) stripe order, and 2) dilute magnetic moments in a metallic
alloy, with associated Kondo behavior. The latter picture appears to be more
relevant to the present results.Comment: 7 pages, 5 figure
Spin and orbital hybridization at specifically nested Fermi surfaces in URuSi
The Fermi surface (FS) nesting properties of URuSi are analyzed with
particular focus on their implication for the mysterious hidden order phase. We
show that there exist two Fermi surfaces that exhibit a strong nesting at the
antiferromagnetic wavevector, =(0,\,0,\,1). The corresponding
energy dispersions fulfill the relation = at eight FS hotspot lines.
The spin-orbital characters of the involved states are {\it distinct}
(=5/2 {\it vs.} 3/2) and hence the degenerate Dirac crossings
are symmetry protected in the nonmagnetic normal state. Dynamical symmetry
breaking through an Ising-like spin and orbital excitation mode with =1 induces a hybridization of the two states, causing substantial FS
gapping. Concomitant spin and orbital currents in the uranium planes give rise
to a rotational symmetry breaking.Comment: 5 pages, 3 figure
The dual nature of magnetism in a uranium heavy fermion system
The duality between localized and itinerant nature of magnetism in
electron systems has been a longstanding puzzle. Here, we report
inelastic neutron scattering measurements, which reveal both local and
itinerant aspects of magnetism in a single crystalline system of
UPtSi. In the antiferromagnetic state, we observe broad continuum
of diffuse magnetic scattering with a resonance-like gap of 7 meV,
and surprising absence of coherent spin-waves, suggestive of itinerant
magnetism. While the gap closes above the Neel temperature, strong dynamic spin
correlations persist to high temperature. Nevertheless, the size and
temperature dependence of the total magnetic spectral weight can be well
described by local moment with . Furthermore, polarized neutron
measurements reveal that the magnetic fluctuations are mostly transverse, with
little or none of the longitudinal component expected for itinerant moments.
These results suggest that a dual description of local and itinerant magnetism
is required to understand UPtSi, and by extension, other 5
systems in general.Comment: see supplementary material for more detail