arXiv subjects

Carmen J. Calzado

Publications and source records attributed to Carmen J. Calzado.

3 recordsLinked to original sources

arXiv2026

Electrical Probing of Sub-Néel Spin Dynamics in Two-Dimensional Antiferromagnets Using Graphene Heterostructures

Low-dimensional antiferromagnetic van der Waals materials have emerged as a versatile platform for exploring exotic spin dynamics and magnetic phases, yet electrically accessing these phenomena remains a major challenge because of their vanishing net magnetization and highly insulating nature. Here, we demonstrate that graphene can act as an ultrasensitive electrical transducer of hidden spin dynamics in two-dimensional antiferromagnets. By integrating graphene with the van der Waals antiferromagnet FePS$_3$, low-temperature transport measurements combined with magnetic-field and gate-voltage control reveal multiple resistance anomalies well below the Néel temperature. Their distinct temperature, magnetic-field, and carrier-density dependences enable us to associate these anomalies with magnon excitations and with a low-temperature magnetic reconfiguration of the antiferromagnetic state, both of which remain largely inaccessible to conventional magnetometry. Density functional theory calculations further show that competing antiferromagnetic spin configurations in FePS$_3$ are nearly degenerate in energy while producing markedly different electronic responses in the adjacent graphene layer. The pronounced electrostatic tunability of these signatures demonstrates that graphene directly transduces interfacial magnetic dynamics into an electrical signal. Our work establishes graphene/antiferromagnetic van der Waals heterostructures as a versatile platform for the electrical readout of spin dynamics in two-dimensional magnets.

cond-mat.mtrl-sci↗

arXiv2000

Ab initio determination of an extended Heisenberg Hamiltonian in CuO2 layers

Accurate ab initio calculations on embedded Cu_4O_{12} square clusters, fragments of the La_2CuO_4 lattice, confirm a value of the nearest neighbor antiferromagnetic coupling (J=124 meV) previously obtained from ab initio calculations on bicentric clusters and in good agreement with experiment. These calculations predict non negligible antiferromagnetic second-neighbor interaction (J'=6.5 meV) and four-spin cyclic exchange (K=14 meV), which may affect the thermodynamic and spectroscopic properties of these materials. The dependence of the magnetic coupling on local lattice distortions has also been investigated. Among them the best candidate to induce a spin-phonon effect seems to be the movement of the Cu atoms, changing the Cu-Cu distance, for which the variation of the nearest neighbor magnetic coupling with the Cu-O distance is {ΔJ}/{Δd_{Cu-O}}\sim 1700 cm^{-1} A^{-1}.

cond-mat.str-el↗

arXiv2000

Proposal of an extended t-J Hamiltonian for high-Tc cuprates from ab initio calculations on embedded clusters

A series of accurate ab initio calculations on Cu_pO-q finite clusters, properly embedded on the Madelung potential of the infinite lattice, have been performed in order to determine the local effective interactions in the CuO_2 planes of La_{2-x}Sr_xCuO_4 compounds. The values of the first-neighbor interactions, magnetic coupling (J_{NN}=125 meV) and hopping integral (t_{NN}=-555 meV), have been confirmed. Important additional effects are evidenced, concerning essentially the second-neighbor hopping integral t_{NNN}=+110meV, the displacement of a singlet toward an adjacent colinear hole, h_{SD}^{abc}=-80 meV, a non-negligible hole-hole repulsion V_{NN}-V_{NNN}=0.8 eV and a strong anisotropic effect of the presence of an adjacent hole on the values of the first-neighbor interactions. The dependence of J_{NN} and t_{NN} on the position of neighbor hole(s) has been rationalized from the two-band model and checked from a series of additional ab initio calculations. An extended t-J model Hamiltonian has been proposed on the basis of these results. It is argued that the here-proposed three-body effects may play a role in the charge/spin separation observed in these compounds, that is, in the formation and dynamic of stripes.

cond-mat.str-el↗