arXiv subjects

Wei-En Tseng

Publications and source records attributed to Wei-En Tseng.

4 recordsLinked to original sources

arXiv2026

Fingerprinting fractons with pump-probe spectroscopy

We demonstrate how pump-probe techniques enable specific spectroscopic diagnostics of fracton phases of matter by studying lineon-planon braiding in the paradigmatic X-cube model. Our discussion builds on previous works probing anyonic exchange statistics in conventional spin liquids, but the extension to fracton phases reveals qualitatively new phenomena due to the restricted mobility of fractionalized excitations. A key feature is that nearby planons can form an emergent bound state by accessing different planes via alternative pairing configurations. We show that this bound state qualitatively modifies the long-time linear and nonlinear responses, leading to an asymptotic linear-in-$t$ behavior for the pump-probe signal $χ_\mathit{ZZX}$. By contrast, swapping the pump and probe polarizations produces a nonlinear response $χ_\mathit{XXZ}$ that is asymptotically $t$-independent. This asymmetry reflects the fact that the two species of fractionalized excitations live in different spatial dimensions. Thus, the pump-probe signals studied here are sensitive to (i) nontrivial braiding statistics in three dimensions, (ii) the existence of bound states among fractionalized excitations, and (iii) the one-dimensional mobility of lineons. Our results therefore provide spectroscopic signatures that distinguish fracton phases from conventional topologically ordered spin liquids.

cond-mat.str-el↗

arXiv2026

Measuring intrinsic relaxation rates in superconductors using nonlinear response

We discuss intrinsic relaxation rates in superconductors, and how they may be measured using non-linear optical (terahertz) response. We consider both $s$ and $d$-wave superconductors, both with and without a phenomenological (energy dependent) damping. Intrinsic relaxation rates of interest include the Higgs mode decay rate, the quasiparticle redistribution rate ($1/T_1$) and the quasiparticle dephasing rate ($1/T_2$), where the latter two rates are zero in the pure BCS model, but non-zero in the presence of damping. Using the Anderson pseudospin formalism, we illustrate how these intrinsic relaxation rates are related to measurable quantities such as the time-dependent gap function and the non-linear current (a.k.a. third harmonic generation). Hence, we show how intrinsic relaxation rates may be experimentally extracted and discuss what one may thereby learn about the underlying damping. We also discuss the effects of polarization control (viz. non-linear response to light polarized in different directions), which offers a useful experimental knob, especially for $d$-wave superconductors, enabling selective excitation of modes in different irreducible representations (and readout of their corresponding relaxation rates).

cond-mat.supr-con↗

arXiv2025

Competing interlayer interactions in twisted monolayer-bilayer graphene: From spontaneous electric polarization to quasi-magic angle

The family of moiré materials provides a powerful platform for tuning interlayer couplings via the twist angle in systems with large spatial periodicity. In trilayer graphene systems, interlayer couplings at the two interfaces can possibly be tuned separately, and the competition between these interactions can therefore influence the electronic structure in a significant way. In this study, we investigate the electronic properties of twisted monolayer-bilayer graphene (aAB) beyond the continuum model, using first-principles calculations combined with an accurate tight-binding model. We find that at large twist angles, the electronic features of aAB are well described by the interaction between the parabolic bands of the Bernal AB-bilayer and the Dirac bands of the twisted monolayer, resulting in a spontaneous electric polarization in the former that splits the parabolic bands. As the twist angle decreases, the coupling between adjacent layers at the twisted interface becomes dominant, which makes aAB look like twisted bilayer graphene (TBG) interacting with the outer Bernal layer. A moiré potential emerges in the TBG-like layers, leading to charge localization, while the outer Bernal layer exhibits charge delocalization with substantial sublattice polarization at the atomic scale. Furthermore, we identify narrow bands with a minimum width at a quasi-magic angle of 1.16 degrees, closely matching the magic angle of TBG. The enhanced electron correlation expected in these narrow bands suggests that aAB is a promising platform for exploring correlated electronic phenomena.

cond-mat.mes-hall↗

arXiv2023

BN-embedded monolayer graphene with tunable electronic and topological properties

Finding an effective and controllable way to create a sizable energy gap in graphene-based systems has been a challenging topic of intensive research. We propose that the hybrid of boron nitride and graphene (h-BNC) at low BN doping serves as an ideal platform for band-gap engineering and valleytronic applications. We report a systematic first-principles study of the atomic configurations and band gap opening for energetically favorable BN patches embedded in graphene. Based on first-principles calculations, we construct a tight-binding model to simulate general doping configurations in large supercells. Unexpectedly, the calculations find a linear dependence of the band gap on the effective BN concentration at low doping, arising from an induced effective on-site energy difference at the two C sublattices as they are substituted by B and N dopants alternately. The significant and tunable band gap of a few hundred meVs, with preserved topological properties of graphene and feasible sample preparation in the laboratory, presents great opportunities to realize valley physics applications in graphene systems at room temperature.

cond-mat.mes-hall↗