31 research outputs found
Intertwined Orders in Heavy-Fermion Superconductor CeCoIn
The appearance of spin-density-wave (SDW) magnetic order in the
low-temperature and high-field corner of the superconducting phase diagram of
CeCoIn is unique among unconventional superconductors. The nature of this
magnetic phase is a matter of current debate. Here, we present the thermal
conductivity of CeCoIn in a rotating magnetic field, which reveals the
presence of an additional order inside the phase that is intimately
intertwined with the superconducting -wave and SDW orders. A discontinuous
change of the thermal conductivity within the phase, when the magnetic
field is rotated about antinodes of the superconducting -wave order
parameter, demands that the additional order must change abruptly together with
the recently observed switching of the SDW. A combination of interactions,
where spin-orbit coupling orients the SDW, which then selects the secondary
-wave pair-density-wave component (with an average amplitude of 20\% of the
primary -wave order parameter), accounts for the observed behavior
Signatures of a Majorana-Fermi surface in the Kitaev magnet AgLiIrO
Detecting Majorana fermions in experimental realizations of the Kitaev
honeycomb model is often complicated by non-trivial interactions inherent to
potential spin liquid candidates. In this work, we identify several distinct
thermodynamic signatures of massive, itinerant Majorana fermions within the
well-established analytical paradigm of Landau-Fermi liquid theory. We find a
qualitative and quantitative agreement between the salient features of our
Landau-Majorana liquid theory and the Kitaev spin liquid candidate
AgLiIrO. Our study presents strong evidence for a Fermi liquid-like
ground state in the fundamental excitations of a honeycomb iridate, and opens
new experimental avenues to detect itinerant Majorana fermions in condensed
matter systems.Comment: 40 pages, 7 figure
Direct observation of magnetic phase coexistence and magnetization reversal in a GdCaMnO thin film
We have investigated the ferrimagnetic domain structure in a
GdCaMnO thin film using magnetic force microscopy. We
observe clear signs of phase separation, with magnetic islands embedded in a
non-magnetic matrix. We also directly visualize the reversal of magnetization
of ferrimagnetic domains as a function of temperature and attribute it to a
change in the balance of magnetization of anti-aligned Mn and Gd sublattices.Comment: 4 pages, 3 figure
Thermal and magnetic properties of a low-temperature antiferromagnet CePtSn
We report specific heat () and magnetization () of single crystalline
CePtSn at temperature down to 50mK and in fields up to
3T. exhibits a sharp anomaly at 180mK, with a large 30J/molK-Ce, which, together with the corresponding cusp-like
magnetization anomaly, indicates an antiferromagnetic (AFM) ground state with a
N\'eel temperature =180mK. Numerical calculations based on a Heisenberg
model reproduce both zero-field and data, thus placing
CePtSn in the weak exchange coupling limit of the
Doniach diagram, with a very small Kondo scale . Magnetic field
suppresses the AFM state at 0.7T, much more effectively than
expected from the Heisenberg model, indicating additional effects possibly due
to frustration or residual Kondo screening.Comment: 8 pages, 7 figures, accepted for publication in Phys. Rev.
Bose glass and Mott glass of quasiparticles in a doped quantum magnet
The low-temperature states of bosonic fluids exhibit fundamental quantum
effects at the macroscopic scale: the best-known examples are Bose-Einstein
condensation (BEC) and superfluidity, which have been tested experimentally in
a variety of different systems. When bosons are interacting, disorder can
destroy condensation leading to a so-called Bose glass. This phase has been
very elusive to experiments due to the absence of any broken symmetry and of a
finite energy gap in the spectrum. Here we report the observation of a Bose
glass of field-induced magnetic quasiparticles in a doped quantum magnet
(Br-doped dichloro-tetrakis-thiourea-Nickel, DTN). The physics of DTN in a
magnetic field is equivalent to that of a lattice gas of bosons in the
grand-canonical ensemble; Br-doping introduces disorder in the hoppings and
interaction strengths, leading to localization of the bosons into a Bose glass
down to zero field, where it acquires the nature of an incompressible Mott
glass. The transition from the Bose glass (corresponding to a gapless spin
liquid) to the BEC (corresponding to a magnetically ordered phase) is marked by
a novel, universal exponent governing the scaling on the critical temperature
with the applied field, in excellent agreement with theoretical predictions.
Our study represents the first, quantitative account of the universal features
of disordered bosons in the grand-canonical ensemble.Comment: 13+6 pages, 5+6 figures; v2: Fig. 5 update
Electronic and magnetic phase diagrams of Kitaev quantum spin liquid candidate NaCoTeO
The 3 Co-based insulating magnet \NCTO{} has recently been
reported to have strong Kitaev interactions on a honeycomb lattice, and is thus
being considered as a Kitaev quantum spin liquid candidate. However, due to the
existence of other types of interactions, a spontaneous long-range magnetic
order occurs. This order is suppressed by applied magnetic fields leading to a
succession of phases and ultimately saturation of the magnetic moments. The
precise phase diagram, the nature of the phases, and the possibility that one
of the field-induced phases is a Kitaev quantum spin liquid phase are still a
matter of debate. Here we measured an extensive set of physical properties to
build the complete temperature-field phase diagrams to magnetic saturation at
10 T for magnetic fields along the - and -axes, and a partial phase
diagram up to 60 T along . We probe the phases using magnetization, specific
heat, magnetocaloric effect, magnetostriction, dielectric constant, and
electric polarization, which is a symmetry-sensitive probe. With these
measurements we identify all the previously incomplete phase boundaries and
find new high-field phase boundaries. We find strong magnetoelectric coupling
in the dielectric constant and moderate magnetostrictive coupling at several
phase boundaries. Furthermore, we detect the symmetry of the magnetic order
using electrical polarization measurements under magnetic fields. Based on our
analysis, the absence of electric polarization under zero or finite magnetic
field in any of the phases or after...Comment: LA-UR-22-3257
Switching of magnetic domains reveals evidence for spatially inhomogeneous superconductivity
The interplay of magnetic and charge fluctuations can lead to quantum phases
with exceptional electronic properties. A case in point is magnetically-driven
superconductivity, where magnetic correlations fundamentally affect the
underlying symmetry and generate new physical properties. The superconducting
wave-function in most known magnetic superconductors does not break
translational symmetry. However, it has been predicted that modulated triplet
p-wave superconductivity occurs in singlet d-wave superconductors with
spin-density wave (SDW) order. Here we report evidence for the presence of a
spatially inhomogeneous p-wave Cooper pair-density wave (PDW) in CeCoIn5. We
show that the SDW domains can be switched completely by a tiny change of the
magnetic field direction, which is naturally explained by the presence of
triplet superconductivity. Further, the Q-phase emerges in a common
magneto-superconducting quantum critical point. The Q-phase of CeCoIn5 thus
represents an example where spatially modulated superconductivity is associated
with SDW order
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Localized ferromagnetic resonance force microscopy of permalloy-cobalt films
We report the Ferromagnetic Resonance Force Microscopy (FMRFM) experiments on a combined permalloy-cobalt continuous film. Our studies demonstrate the capability of FMRFM to perform local spectroscopy of different ferromagnetic materials. Theoretical analysis of the uniform resonance mode at the edge of the film provides good quantitative agreement with the experimental data. Our experiments demonstrate the micron scale lateral resolution and allow to extract local magnetic properties in continuous ferromagnetic samples