arXiv subjects

Patrick G. LaBarre

Publications and source records attributed to Patrick G. LaBarre.

3 recordsLinked to original sources

arXiv2020

Extremely Weakly Interacting $ΔS_z = 0$ and $ΔS_z = 1$ Excitations and Evidence for Fractional Quantization in a Magnetization Plateau: CeSb

The plateau at 1/3 of the saturation magnetization, $M_s$, in the metamagnet CeSb is accompanied by a state of ferromagnetic layers of spins in an up-up-down sequence. We measured $M$ and the specific heat, $C$, in the plateau, spin wave analyses of which reveal two distinct branches of excitations. Those with $ΔS_z = 1$ as measured by $M$, coexist with a much larger population of $ΔS_z = 0$ excitations measured by $C$ but invisible to $M$. The large density of $ΔS_z = 0$ excitations, their energy gap, and their seeming lack of interaction with $ΔS_z = 1$ excitations suggest an analogy with astrophysical dark matter. Additionally, in the middle of the plateau three sharp jumps in $M(H)$ are seen, the size of which, $0.15 $%$M_s$, is consistent with fractional quantization of magnetization-per-site in the down-spin layers.

cond-mat.str-el↗

arXiv2019

Probing the Electronic Structure of Graphene Near and Far from the Fermi Level via Planar Tunneling Spectroscopy

Scanning tunneling spectroscopy (STS) has yielded significant insight on the electronic structure of graphene and other two-dimensional (2D) materials. STS directly measures a fundamental and directly calculable quantity: the single particle density of states (SPDOS). Due to experimental setup limitations, however, STS has been unable to explore 2D materials in ultra-high magnetic fields where electron-electron interactions can drastically change the SPDOS. Recent developments in the assembly of heterostructures composed of graphene and hexagonal boron nitride have enabled a device-based alternative to potentially overcome these roadblocks. Thus far, however, these nascent efforts are incomplete in analyzing and understanding tunneling spectra and have yet to explore graphene at high magnetic fields. Here we report an experiment at magnetic fields up to 18 T that uses graphene tunneling field effect transistors (TFETs) to establish a clear benchmark for measurement and analysis of graphene planar tunneling spectroscopy. We acquire gate tunable tunneling spectra of graphene and then use these data and electrostatic arguments to develop a systematic analysis scheme. This analysis reveals that TFET devices directly probe electronic structure features near and far from the Fermi level. In particular, our study yields identification of the Dirac point and numerous Landau levels as they fill and empty with charge via application of a gate voltage. Our work demonstrates that TFET devices are a viable platform for directly probing the electronic structure of graphene and other 2D materials in high magnetic fields, where novel electronic states emerge.

cond-mat.mes-hall↗

arXiv2019

Mini Volume Collapse as Evidence for a 3-Body Magnetic Polaron in $Sm_{1-x}Eu_xS$

Samarium sulfide (SmS) is a non-magnetic narrow-gap (0.06 eV) semiconductor which undergoes a transition to a metallic intermediate valence state at 6.5 kbar. Europium sulfide (EuS) is a ferromagnetic semiconductor with a Curie temperature of 16K and a gap of 1.6 eV. Here we present a study of the lattice constant, magnetic susceptibility, and resistivity of the substitution series $Sm_{1-x}Eu_xS$ for 0 < x < 1. We observe a smooth interpolation of magnetic and transport behavior across the series, consistent with a virtual crystal scenario and Vegard's law. Surprisingly, however, the lattice constant deviates below Vegard's law in a manner that suggests parametric control of the Sm-Sm distance by the Eu moment in the manner of a magnetic polaron.

cond-mat.mes-hall↗