arXiv subjects

Sabrina J. Li

Publications and source records attributed to Sabrina J. Li.

3 recordsLinked to original sources

arXiv2026

Magnetic order, magnons, and crystal fields in van der Waals CeSiI

We report neutron, X-ray absorption, and resonant X-ray spectroscopy of magnetic excitations in the new heavy-fermion van-der-Waals superconductor CeSiI. We determined effective Hamiltonians and ground states of crystal electric fields and magnons. Isotropic Heisenberg interactions on a quasi two dimensional lattice, including ferromagnetic nearest-neighbor exchange as the dominant interaction, provide an excellent account to the low-energy measured dynamics and stabilize a co-rotating spin cycloid. Our study provides the basis to model CeSiI from first principles, thereby laying the ground for microscopic understanding of heavy-fermion physics, their unconventional superconductivity, and quantum criticality.

cond-mat.str-el↗

arXiv2025

Explaining the extra crystal field mode in ACeX2

A growing list of Ce-based magnets have shown an extra and heretofore unexplained crystal electric field (CEF) mode at high energies. We describe a process whereby an optical phonon can produce a split CEF mode well above the phonon energy. We use density functional theory and point-charge model calculations to estimate the phonon distortions and coupling to model this effect in KCeO$_2$, showing that it accounts for the extra CEF mode observed. This mechanism is generic, and may explain the extra modes observed on a variety of Ce$^{3+}$ compounds.

cond-mat.str-el↗

arXiv2019

Thermal Expansion in Insulating Solids From First Principles

In this Tutorial, we describe the use of the quasiharmonic approximation and first-principles density functional theory (DFT) to calculate and analyze the thermal expansion of insulating solids. We discuss the theory underlying the quasiharmonic approximation, and demonstrate its practical use within two common frameworks for calculating thermal expansion: the Helmholtz free energy framework and Grüneisen theory. Using the example of silicon, we provide a guide for predicting how the lattice parameter changes as a function of temperature using DFT, including the calculation of phonon modes and phonon density of states, elastic constants, and specific heat. We also describe the calculation and interpretation of Grüneisen parameters, as well as how they relate to coefficients of thermal expansion. The limitations of the quasiharmonic approximation are briefly touched on, as well as the comparison of theoretical results with experimental data. Finally, we use the example of ferroelectric PbTiO$_3$ to illustrate how the methods used can be adapted to study anisotropic systems.

cond-mat.mtrl-sci↗