199 research outputs found
The thermal Hall effect of spin excitations in a Kagome magnet
At low temperatures, the thermal conductivity of spin excitations in a
magnetic insulator can exceed that of phonons. However, because they are charge
neutral, the spin waves are not expected to display a thermal Hall effect in a
magnetic field. Recently, this semiclassical notion has been upended in quantum
magnets in which the spin texture has a finite chirality. In the Kagome
lattice, the chiral term generates a Berry curvature. This results in a thermal
Hall conductivity that is topological in origin. Here we report
observation of a large in the Kagome magnet Cu(1-3, bdc) which
orders magnetically at 1.8 K. The observed undergoes a remarkable
sign-reversal with changes in temperature or magnetic field, associated with
sign alternation of the Chern flux between magnon bands. We show that thermal
Hall experiments probe incisively the effect of Berry curvature on heat
transport.Comment: 6 pages, 3 figure
Combination toceranib and lomustine shows frequent high grade toxicities when used for treatment of non-resectable or recurrent mast cell tumours in dogs: A European multicentre study
The magnetic phase diagram of underdoped YBa2Cu3Oy inferred from torque magnetization and thermal conductivity
Strong evidence for charge-density correlation in the underdoped phase of the
cuprate YBa2Cu3Oy was obtained by nuclear magnetic resonance (NMR) and resonant
x-ray scatter- ing. The fluctuations were found to be enhanced in strong
magnetic fields. Recently, 3D (three dimensional) charge-density wave (CDW)
formation with long-range order (LRO) was observed by x-ray diffraction in H
>15 T. To elucidate how the CDW transition impacts the pair condensate, we have
used torque magnetization to 45 T and thermal conductivity to
construct the magnetic phase diagram in untwinned crystals with hole density p
= 0.11. We show that the 3D CDW transitions appear as sharp features in the
susceptibility and at the fields HK and Hp, which define phase
boundaries in agreement with spectroscopic techniques. From measurements of the
melting field Hm(T) of the vortex solid, we obtain evidence for two vortex
solid states below 8 K. At 0.5 K, the pair condensate appears to adjust to the
3D CDW by a sharp transition at 24 T between two vortex solids with very
different shear moduli. At even higher H (42 T) the second vortex solid melts
to a vortex liquid which survives to fields well above 45 T. de Haas-van Alphen
oscillations appear at fields 24-28 T, below the lower bound for the upper
critical field Hc2.Comment: 7 pages, 8 figures; New version of previous posting, reporting torque
measurements to 45 Tesla and final magnetic phase diagra
Z topology and superconductivity from symmetry lowering of a 3D Dirac Metal AuPb
3D Dirac semi-metals (DSMs) are materials that have massless Dirac electrons
and exhibit exotic physical properties It has been suggested that structurally
distorting a DSM can create a Topological Insulator (TI), but this has not yet
been experimentally verified. Furthermore, quasiparticle excitations known as
Majorana Fermions have been theoretically proposed to exist in materials that
exhibit superconductivity and topological surface states. Here we show that the
cubic Laves phase AuPb has a bulk Dirac cone above 100 K that gaps out upon
cooling at a structural phase transition to create a topologically non trivial
phase that superconducts below 1.2 K. The nontrivial Z = -1 invariant in
the low temperature phase indicates that AuPb in its superconducting state
must have topological surface states. These characteristics make AuPb a
unique platform for studying the transition between bulk Dirac electrons and
topological surface states as well as studying the interaction of
superconductivity with topological surface states
Quantum Tricritical Points in NbFe
Quantum critical points (QCPs) emerge when a 2nd order phase transition is
suppressed to zero temperature. In metals the quantum fluctuations at such a
QCP can give rise to new phases including unconventional superconductivity.
Whereas antiferromagnetic QCPs have been studied in considerable detail
ferromagnetic (FM) QCPs are much harder to access. In almost all metals FM QCPs
are avoided through either a change to 1st order transitions or through an
intervening spin-density-wave (SDW) phase. Here, we study the prototype of the
second case, NbFe. We demonstrate that the phase diagram can be modelled
using a two-order-parameter theory in which the putative FM QCP is buried
within a SDW phase. We establish the presence of quantum tricritical points
(QTCPs) at which both the uniform and finite susceptibility diverge. The
universal nature of our model suggests that such QTCPs arise naturally from the
interplay between SDW and FM order and exist generally near a buried FM QCP of
this type. Our results promote NbFe as the first example of a QTCP, which
has been proposed as a key concept in a range of narrow-band metals, including
the prominent heavy-fermion compound YbRhSi.Comment: 21 pages including S
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