49 research outputs found
Anisotropic determined up to 92 T and the signature of multi-band superconductivity in Ca(PtAs)((FePt)As) superconductor
The upper critical fields, (), of single crystals of the
superconductor
Ca(PtAs)((FePt)As)
( 0.246) are determined over a wide range of temperatures
down to = 1.42 K and magnetic fields of up to 92 T. The
measurements of anisotropic () curves are performed in pulsed
magnetic fields using radio-frequency contactless penetration depth
measurements for magnetic field applied both parallel and perpendicular to the
\textbf{ab}-plane. Whereas a clear upward curvature in
() along \textbf{H}\textbf{c} is
observed with decreasing temperature, the ()
along \textbf{H}\textbf{ab} shows a flattening at low temperatures.
The rapid increase of the () at low
temperatures suggests that the superconductivity can be described by two
dominating bands. The anisotropy parameter,
, is 7 close
to and decreases considerably to 1 with decreasing temperature,
showing rather weak anisotropy at low temperatures.Comment: 4pages, 3figures, accepted PRB Rapid Communicatio
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
Low temperature thermodynamic properties near the field-induced quantum critical point in DTN
We present a comprehensive experimental and theoretical investigation of the
thermodynamic properties: specific heat, magnetization and thermal expansion in
the vicinity of the field-induced quantum critical point (QCP) around the lower
critical field \,T in DTN . A behavior in the
specific heat and magnetization is observed at very low temperatures at
that is consistent with the universality class of Bose-Einstein
condensation of magnons. The temperature dependence of the thermal expansion
coefficient at shows minor deviations from the expected
behavior. Our experimental study is complemented by analytical calculations and
Quantum Monte Carlo simulations, which reproduce nicely the measured
quantities. We analyze the thermal and the magnetic Gr\"{u}neisen parameters
that are ideal quantities to identify QCPs. Both parameters diverge at
with the expected power law. By using the Ehrenfest relations at the
second order phase transition, we are able to estimate the pressure
dependencies of the characteristic temperature and field scales.Comment: 11 paged, 10 figures, submitted to PR
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
Continuous spin excitations in the three-dimensional frustrated magnet K2Ni2(SO4)3
Continuous spin excitations are widely recognized as one of the hallmarks of
novel spin states in quantum magnets, such as quantum spin liquids (QSLs).
Here, we report the observation of such kind of excitations in K2Ni2(SO4)3,
which consists of two sets of intersected spin-1 Ni2+ trillium lattices. Our
inelastic neutron scattering measurement on single crystals clearly shows a
dominant excitation continuum, which exhibits a distinct temperature-dependent
behavior from that of spin waves, and is rooted in strong quantum spin
fluctuations. Further using the self-consistent-gaussian-approximation method,
we determined the fourth- and fifth-nearest neighbor exchange interactions are
dominant. These two bonds together form a unique three-dimensional network of
corner-sharing tetrahedra, which we name as ''hyper-trillium'' lattice. Our
results provide direct evidence for the existence of QSL features in
K2Ni2(SO4)3 and highlight the potential for the hyper-trillium lattice to host
frustrated quantum magnetism.Comment: 6 pages and 5 figures, plus several pages of supplemental material,
comments are welcom