arXiv subjects

Eric Thewalt

Publications and source records attributed to Eric Thewalt.

3 recordsLinked to original sources

arXiv2018

Field evolution of magnons in $α$-RuCl$_3$ by high-resolution polarized terahertz spectroscopy

The Kitaev quantum spin liquid (KSL) is a theoretically predicted state of matter whose fractionalized quasiparticles are distinct from bosonic magnons, the fundamental excitation in ordered magnets. The layered honeycomb antiferromagnet $α$-RuCl$_3$ is a KSL candidate material, as it can be driven to a magnetically disordered phase by application of an in-plane magnetic field, with $H_c \sim 7$ T. Here we report a detailed characterization of the magnetic excitation spectrum of this material by high-resolution time-domain terahertz (THz) spectroscopy. We observe two sharp magnon resonances whose frequencies and amplitudes exhibit a discontinuity as a function of applied magnetic field, as well as two broader peaks at higher energy. Below the Néel temperature, we find that linear spin wave theory can account for all of these essential features of the spectra when a $C_3$-breaking distortion of the honeycomb lattice and the presence of structural domains are taken into account.

cond-mat.str-el↗

arXiv2017

Imaging anomalous nematic order and strain in optimally doped BaFe$_2$(As,P)$_2$

We present the strain and temperature dependence of an anomalous nematic phase in optimally doped BaFe$_2$(As,P)$_2$. Polarized ultrafast optical measurements reveal broken 4-fold rotational symmetry in a temperature range above $T_c$ in which bulk probes do not detect a phase transition. Using ultrafast microscopy, we find that the magnitude and sign of this nematicity vary on a ${50{-}100}~μ$m length scale, and the temperature at which it onsets ranges from 40 K near a domain boundary to 60 K deep within a domain. Scanning Laue microdiffraction maps of local strain at room temperature indicate that the nematic order appears most strongly in regions of weak, isotropic strain. These results indicate that nematic order arises in a genuine phase transition rather than by enhancement of local anisotropy by a strong nematic susceptibility. We interpret our results in the context of a proposed surface nematic phase.

cond-mat.supr-con↗

arXiv2015

Optical evidence of broken C$_4$ symmetry across optimal doping in BaFe$_{2}$(As$_{1-x}$P$_x$)$_2$

The isovalently doped high-$T_{\text{c}}$ superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$ is characterized by a rich temperature-doping phase diagram, which includes structural, antiferromagnetic, and superconducting phase transitions. In this work, we use photomodulated reflectance at 1.5 eV to detect the onset of linear birefringence in the normal state, and by inference, the breaking of four-fold rotational (C$_4$) symmetry. We find that C$_4$ breaking takes place in the normal state over a range of $x$ that spans the optimal P concentration, unlike the line of orthorhombic-tetragonal and magnetic phase transitions, which terminates at, or just below, the optimal value of $x$.

cond-mat.supr-con↗