arXiv subjects

Benjamin Canals

Publications and source records attributed to Benjamin Canals.

29 records · Page 2Linked to original sources

arXiv2006

Spin liquid correlations in Nd-langasite anisotropic Kagomé antiferromagnet

Dynamical magnetic correlations in the geometrically frustrated Nd$\_3$Ga$\_5$SiO$\_{14}$ compound were probed by inelastic neutron scattering on a single crystal. A scattering signal with a ring shape distribution in reciprocal space and unprecedented dispersive features was discovered. Comparison with calculated static magnetic scattering from models of correlated spins suggests that the observed phase is a spin liquid inherent to an antiferromagnetic kagomé-like lattice of anisotropic Nd moments.

cond-mat.str-el↗

arXiv2006

Magnetic excitations in a new anisotropic Kagomé antiferromagnet

The Nd-langasite compound contains planes of magnetic Nd3+ ions on a lattice topologically equivalent to a kagomé net. The magnetic susceptibility does not reveal any signature of long-range ordering down to 2 K but rather a correlated paramagnetism with significant antiferromagnetic interactions between the Nd and a single-ion anisotropy due to crystal field effect. Inelastic neutron scattering on Nd-langasite powder and single-crystal allowed to probe its very peculiar low temperature dynamical magnetic correlations. They present unusual dispersive features and are broadly localized in wave-vector Q revealing a structure factor associated to characteristics short range-correlations between the magnetic atoms. From comparison with theoretical calculations, these results are interpreted as a possible experimental observation of a spin liquid state in an anisotropic kagomé antiferromagnet.

cond-mat.str-el↗

arXiv2006

Anomalous Hall Effect due to the spin chirality in the Kagomé lattice

We consider a model for a two dimensional electron gas moving on a kagomé lattice and locally coupled to a chiral magnetic texture. We show that the transverse conductivity $σ\_{xy}$ does not vanish even if spin-orbit coupling is not present and it may exhibit unusual behavior. Model parameters are the chirality, the number of conduction electrons and the amplitude of the local coupling. Upon varying these parameters, a topological transition characterized by change of the band Chern numbers occur. As a consequence, $σ\_{xy}$ can be quantized, proportional to the chirality or have a non monotonic behavior upon varying these parameters.

cond-mat.str-el↗

arXiv2002

Classical Spin Liquid Properties of the Infinite-Component Spin Vector Model on a Fully Frustrated Two Dimensional Lattice

Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are studied for the exactly solvable infinite-component spin-vector model, $D \to \infty$. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances smaller than the correlation length, $r \lesssim ξ_c \propto \exp(T^*/T)$, correlations in the checkerboard-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures, spin CFs decay as $<{\bf S}_0 {\bf S}_r > \propto 1/r^2$ in the range $a_0 \ll r \ll ξ_c \propto T^{-1/2}$, where $a_0$ is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are very similar with MC simulations, exact and analytical results for the classical Heisenberg model (D=3) on the pyrochlore lattice. This shows that the ground state of the infinite-component spin vector model on the checkerboard lattice is a classical spin liquid.

cond-mat.str-el↗

arXiv2002

From the Square Lattice to the Checkerboard Lattice : Spin Wave and Large-n Analysis

Within a spin wave analysis and a fermionic large-n limit, it is shown that the antiferromagnetic Heisenberg model on the checkerboard lattice may have different ground states, depending on the spin size $S$. Through an additional exchange interaction that corresponds to an inter-tetrahedra coupling, the stability of the Néel state has been explored for all cases from the square lattice to the isotropic checkerboard lattice. Away from the isotropic limit and within the linear spin wave approximation, it is shown that there exists a critical coupling for which the local magnetization of the Néel state vanishes for any value of the spin $S$. One the other hand, using the Dyson-Maleev approximation, this result is valid only in the case $S= \frac12$ and the limit between a stable and an unstable Néel state is at S=1. For $S= \frac12$, the fermionic large-n limit suggests that the ground state is a valence bond solid build with disconnected 4-spins singlets. This analysis indicates that for low spin and in the isotropic limit, the checkerboard antiferromagnet may be close to an instability between an ordered S=0 ground state and a magnetized ground state.

cond-mat.str-el↗

arXiv2001

Dzyaloshinski-Moriya interactions in the kagome lattice

The kagomé lattice exhibits peculiar magnetic properties due to its strongly frustated cristallographic structure, based on corner sharing triangles. For nearest neighbour antiferromagnetic Heisenberg interactions there is no Neel ordering at zero temperature both for quantum and classical s pins. We show that, due to the peculiar structure, antisymmetric Dzyaloshinsky-Moriya interactions (${\bf D} . ({\bf S}_i \times {\bf S}_j)$) are present in this latt ice. In order to derive microscopically this interaction we consider a set of localized d-electronic states. For classical spins systems, we then study the phase diagram (T, D/J) through mean field approximation and Monte-Carlo simulations and show that the antisymmetric interaction drives this system to ordered states as soon as this interaction is non zero. This mechanism could be involved to explain the magnetic structure of Fe-jarosites.

cond-mat.str-el↗

arXiv2001

Comparison of several tetrahedra-based lattices

A comparison of the quantum Heisenberg antiferromagnetic model (QHAM) on the pyrochlore lattice, the checkerboard lattice and the square lattice with crossing interactions is performed. The three lattices are constructed with the same tetrahedral unit cell and this property is used to describe the low energy spectrum by means of an effective hamiltonian restricted to the singlet sector. We analyze the structure of the effective hamiltonian and solve it within mean field approximation for the three lattices.

cond-mat.str-el↗

arXiv2001

Spin Liquid Phase in the Pyrochlore Antiferromagnet

Correlation functions (CFs) of the classical Heisenberg antiferromagnet on the pyrochlore lattice are studied by solving exactly the infinite-component spin-vector model. % As in many Fully Frustrated Lattices, the constraint due to the minimization of the energy and the particular structure based on corner sharing tetrahedra both contribute to the creation of local degrees of freedom. % The resulting degeneracy destroys any magnetic order at all temperature and we obtain no sign of criticality, even at $T = 0$. % Calculated neutron scattering cross sections have their maxima beyond the first Brillouin Zone and reproduce experimental results obtained on Y(Sc)Mn$_2$ and CsCrNiF$_6$ as well as theoretical predictions previously obtained by classical Monte Carlo simulations. % Evidences for thermal and spatial decoupling of the magnetic modes are found so that the magnetic fluctuations in this system can be approximated by $S(q,T) \approx f(q) h(T)$.

cond-mat.str-el↗

arXiv1999

Classical Spin Liquid: Exact Solution for the Infinite-Component Antiferromagnetic Model on the Kagomé Lattice

Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the kagomé lattice are studied for the exactly solvable infinite-component spin-vector model, D \to \infty. In this limit, the critical coupling of fluctuations dies out and the critical behavior simplifies, but the effect of would be Goldstone modes preventing ordering at any nonzero temperature is properly accounted for. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances smaller than the correlation length, r < ξ_c \propto \exp(T^*/T), correlations in the kagomé-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures, spin CFs decay as <{\bf S}_0 {\bf S}_r> \propto 1/r^2 in the range a_0 << r << ξ_c \propto T^{-1/2}, where a_0 is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are in fairly good quantitative agreement with the MC simulations for the classical Heisenberg model, D=3. The neutron scattering cross section has its maxima beyond the first Brillouin zone; at T\to 0 it becomes nonanalytic but does not diverge at any q.

cond-mat.stat-mech↗

arXiv1998

Kondo Screening and Magnetic Ordering in Frustrated UNi4B

UNi4B exhibits unusual properties and, in particular, a unique antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the low temperature behavior of this compound, we propose that the remaining 1/3 U sites are nonmagnetic due to the Kondo effect. We derive a model in which the coexistence of magnetic and nonmagnetic U sites is the consequence of the competition between frustration of the crystallographic structure and instability of the 5f moments.

cond-mat.str-el↗

arXiv1998

Pyrochlore Antiferromagnet: A Three-Dimensional Quantum Spin Liquid

The quantum pyrochlore antiferromagnet is studied by perturbative expansions and exact diagonalization of small clusters. We find that the ground state is a spin-liquid state: The spin-spin correlation functions decay exponentially with distance and the correlation length never exceeds the interatomic distance. The calculated magnetic neutron diffraction cross section is in very good agreement with experiments performed on Y(Sc)Mn2. The low energy excitations are singlet-singlet ones, with a finite spin gap.

cond-mat.str-el↗