919 research outputs found
Spectrum of Itinerant Fractional Excitations in Quantum Spin Ice
We study the quantum dynamics of fractional excitations in quantum spin ice. We focus on the density of states in the two-monopole sector, rho(omega), as this can be connected to the wave-vector-integrated dynamical structure factor accessible in neutron scattering experiments. We find that rho(omega) exhibits a strikingly characteristic singular and asymmetric structure that provides a useful fingerprint for comparison to experiment. rho(omega) obtained from the exact diagonalization of a finite cluster agrees well with that, from the analytical solution of a hopping problem on a Husimi cactus representing configuration space, but not with the corresponding result on a face-centered cubic lattice, on which the monopoles move in real space. The main difference between the latter two lies in the inclusion of the emergent gauge field degrees of freedom, under which the monopoles are charged. This underlines the importance of treating both sets of degrees of freedom together, and it presents a novel instance of dimensional transmutation
Topology and Interactions in a Frustrated Slab: Tuning from Weyl Semimetals to C > 1 Fractional Chern Insulators
We show that, quite generically, a [111] slab of spin-orbit coupled
pyrochlore lattice exhibits surface states whose constant energy curves take
the shape of Fermi arcs, localized to different surfaces depending on their
quasimomentum. Remarkably, these persist independently of the existence of Weyl
points in the bulk. Considering interacting electrons in slabs of finite
thickness, we find a plethora of known fractional Chern insulating phases, to
which we add the discovery of a new higher Chern number state which is likely a
generalization of the Moore-Read fermionic fractional quantum Hall state. By
contrast, in the three-dimensional limit, we argue for the absence of gapped
states of the flat surface band due to a topologically protected coupling of
the surface to gapless states in the bulk. We comment on generalizations as
well as experimental perspectives in thin slabs of pyrochlore iridates.Comment: Published. 6+4 page
Semi-classical Characters and Optical Model Description of Heavy Ion Scattering, Direct Reactions, and Fusion at Near-barrier Energies
An approach is proposed to calculate the direct reaction (DR) and fusion
probabilities for heavy ion collisions at near-Coulomb-barrier energies as
functions of the distance of closest approach D within the framework of the
optical model that introduces two types of imaginary potentials, DR and fusion.
The probabilities are calculated by using partial DR and fusion cross sections,
together with the classical relations associated with the Coulomb trajectory.
Such an approach makes it possible to analyze the data for angular
distributions of the inclusive DR cross section, facilitating the determination
of the radius parameters of the imaginary DR potential in a less ambiguous
manner. Simultaneous -analyses are performed of relevant data for the
O+Pb system near the Coulomb-barrier energy
Quantum melting of charge ice and non-Fermi-liquid behavior: An exact solution for the extended Falicov-Kimball model in the ice-rule limit
An exact solution is obtained for a model of itinerant electrons coupled to
ice-rule variables on the tetrahedron Husimi cactus, an analogue of the Bethe
lattice of corner-sharing tetrahedra. It reveals a quantum critical point with
the emergence of non-Fermi-liquid behavior in melting of the "charge ice"
insulator. The electronic structure is compared with the numerical results for
the pyrochlore-lattice model to elucidate the physics of electron systems
interacting with the tetrahedron ice rule.Comment: 5 pages, 4 figure
Field-Selective Anomaly and Chiral Mode Reversal in Type-II Weyl Materials
Three-dimensional condensed matter incarnations of Weyl fermions generically
have a tilted dispersionâin sharp contrast to their elusive high-energy
relatives where a tilt is forbidden by Lorentz invariance, and with the low-
energy excitations of two-dimensional graphene sheets where a tilt is
forbidden by either crystalline or particle-hole symmetry. Very recently, a
number of materials (MoTe2, LaAlGe, and WTe2) have been identified as hosts of
so-called type-II Weyl fermions whose dispersion is so strongly tilted that a
Fermi surface is formed, whereby the Weyl node becomes a singular point
connecting electron and hole pockets. We here predict that these systems have
remarkable properties in the presence of magnetic fields. Most saliently, we
show that the nature of the chiral anomaly depends crucially on the relative
angle between the applied field and the tilt, and that an inversion-asymmetric
overtilting creates an imbalance in the number of chiral modes with positive
and negative slopes. The field-selective anomaly gives a novel magneto-optical
resonance, providing an experimental way to detect concealed Weyl nodes
Cluster dynamical mean-field study of the Hubbard model on a 3D frustrated hyperkagome lattice
We study the Hubbard model on a geometrically-frustrated hyperkagome lattice
by a cluster extension of the dynamical mean field theory. We calculate the
temperature () dependences of the specific heat () and the spin-lattice
relaxation time () in correlated metallic region. shows a peak at
and rapidly decreases as . On the other hand, has a
peak at a higher temperature than , and largely decreases
below , followed by the Korringa law as . Both
peak temperatures are suppressed and the peaks become sharper as electron
correlation is increased. These behaviors originate from strong renormalization
of the energy scales in the peculiar electronic structure in this frustrated
system; a pseudo-gap like feature, the van-Hove singularity, and the flat band.
The results are discussed in comparison with the experimental data in the
hyperkagome material, NaIrO.Comment: 4 pages, 4 figures, Conference proceedings for Highly Frustrated
Magnetism 200
Trimer classical spin liquid from interacting fractional charges
We study a problem of interacting fractional charges with the J(1)-J(2)-J(3) Ising model on a checkerboard lattice under magnetic field. As a result of the interplay between repulsive interactions and particle density tuning by a magnetic field, the fractional charges form a classical spin liquid (CSL) phase. The CSL phase is composed of degenerate spin configurations, which can be mapped to the trimer covering of dual square lattice. The CSL state shows macroscopic ground-state entropy, implying the emergence of a novel quantum spin liquid phase when quantum fluctuations are turned on. In addition to the CSL phase, the system exhibits multiple magnetization plateaus, reflecting the fertile screening processes of dimer-monomer mixtures
Carrier doping to a partially disordered state in the periodic Anderson model on a triangular lattice
We investigate the effect of hole and electron doping to half-filling in the
periodic Anderson model on a triangular lattice by the Hartree-Fock
approximation at zero temperature. At half-filling, the system exhibits a
partially disordered insulating state, in which a collinear antiferromagnetic
order on an unfrustrated honeycomb subnetwork coexists with nonmagnetic state
at the remaining sites. We find that the carrier doping destabilizes the
partially disordered state, resulting in a phase separation to a doped metallic
state with different magnetic order. The partially disordered state is
restricted to the half-filled insulating case, while its metallic counterpart
is obtained as a metastable state in a narrow electron doped region.Comment: 4 pages, 2 figure
The future size and composition of the private rented sector: an LSE London project for Shelter
Current forecasts suggest that perhaps one in four households in England and maybe one in three in London might be living in the private rented sector by 2025. However, there has been little attempt to identify which household types are likely to be most affected. The brief for this study was both to fill this gap and to look somewhat further ahead. Shelter has asked LSE London to âproduce plausible modelling, forecasting how many privately renting households there will be in England in 2028, what their demographic composition will be and what proportion of each demographic group will be privately renting.â The findings would be used to provide an evidence base from which to discuss how policy towards the private rented sector might better serve the full range of households likely to be living in the sector
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