58 research outputs found
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-Independent Ultrasonic Dispersions in the Magnetically Robust Heavy Fermion System SmOs4Sb12
Elastic properties of the filled skutterudite compound SmOsSb have
been investigated by ultrasonic measurements. The elastic constant
shows two ultrasonic dispersions at 15 K and 53 K
for frequencies between 33 and 316 MHz, which follow a Debye-type
formula with Arrhenius-type temperature-dependent relaxation times, and remain
unchanged even with applied magnetic fields up to 10 T. The corresponding
activation energies were estimated to be = 105 K and = 409 K,
respectively. The latter, , is the highest value reported so far in the
Sb-based filled skutterudites. The presence of magnetically robust ultrasonic
dispersions in SmOsSb implies a possibility that an emergence of a
magnetically insensitive heavy fermion state in this system is associated with
a novel local charge degree of freedom which causes the ultrasonic dispersion.Comment: 5 pages, 4 figure
Observation of odd-parity superconductivity in UTe2
Symmetry properties of the order parameter are among the most fundamental
characteristics of a superconductor. The pairing symmetry of recently
discovered heavy fermion superconductor UTe2 featuring an exceedingly large
upper critical field has attracted a great deal of attention. Even though it is
widely believed that UTe2 possesses an odd-parity, spin-triplet pairing
symmetry, direct evidence for it is lacking, especially at zero or low magnetic
fields. We report here the selection-rule results of Josephson coupling between
In, an s-wave superconductor, and UTe2. The orientation dependence of the
Josephson coupling suggests very strongly that UTe2 possess an odd-parity
pairing state of B_1u in zero magnetic fields. We also report the formation of
Andreev surface bound states on the (1-10) surface of UTe2.Comment: 16 pages, 4 figures, 2 table
Visualizing heavy fermions emerging in a quantum critical Kondo lattice
In solids containing elements with f orbitals, the interaction between
f-electron spins and those of itinerant electrons leads to the development of
low-energy fermionic excitations with a heavy effective mass. These excitations
are fundamental to the appearance of unconventional superconductivity and
non-Fermi-liquid behaviour observed in actinide- and lanthanide-based
compounds. Here we use spectroscopic mapping with the scanning tunnelling
microscope to detect the emergence of heavy excitations with lowering of
temperature in a prototypical family of cerium-based heavy-fermion compounds.
We demonstrate the sensitivity of the tunnelling process to the composite
nature of these heavy quasiparticles, which arises from quantum entanglement of
itinerant conduction and f electrons. Scattering and interference of the
composite quasiparticles is used to resolve their energy-momentum structure and
to extract their mass enhancement, which develops with decreasing temperature.
The lifetime of the emergent heavy quasiparticles reveals signatures of
enhanced scattering and their spectral lineshape shows evidence of
energy-temperature scaling. These findings demonstrate that proximity to a
quantum critical point results in critical damping of the emergent heavy
excitation of our Kondo lattice system.Comment: preprint version, 26 pages, 6 figures. Supplementary: 15 pages, 14
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