arXiv subjects

Marcin Mucha-Kruczyński

Publications and source records attributed to Marcin Mucha-Kruczyński.

6 recordsLinked to original sources

arXiv2026

Observation of dodecagonal replica bands in 30$^{\circ}$-twisted bilayer WSe$_2$

Twisted bilayers of two-dimensional (2D) transition metal dichalcogenides are promising systems for achieving tunable quasicrystalline orders with emergent properties. The underpinning electronic structure and scattering processes in 2D quasicrystals with multiorbital dodecagonal replica bands have so far not been determined. Here, we utilize angle-resolved photoemission spectroscopy (ARPES) with micrometer spatial resolution to directly observe replica bands in 30$^{\circ}$-twisted bilayer WSe$_2$. The symmetry and intensity distribution of the observed replicas are explained by interlayer Umklapp scattering from bottom to top WSe$_2$ layers. Our spectral function measurements are consistent with the presence of a van Hove singularity adjacent to the $\mathrm{K}$-valleys, which underlines the possibility of inducing electronic reconstructions in bilayers with a large interlayer twist angle.

cond-mat.mes-hall↗

arXiv2026

Change in charge density wave order beyond the Lifshitz transition in 2H-Ta\textsubscript{1$\pmδ$}S\textsubscript{2}

We investigate electronic instabilities in 2H-TaS\textsubscript{2} and a self-intercalated variant, 2H$^\dagger$-Ta\textsubscript{1+$δ$}S\textsubscript{2}. In conventional samples, which we determine to be slightly hole-doped, spectral gaps and backfolded features are found as fingerprints of the $3\times3$ charge density wave (CDW). Notably, the backfolded features emerge only at a temperatures below $T\approx$~65~K, substantially lower than the established CDW temperature of 78~K, suggesting an incommensurate-commensurate lock-in transition analogous to the phenomenology of the 2H-TaSe\textsubscript{2}. In contrast, the self-intercalated 2H$^\dagger$ sample exhibits substantial electron doping and signatures of a novel \tworootthree CDW. Using \textit{ab initio} calculations of the phonon spectrum, we demonstrate that the \threebythree instability ($\mathbf{q}=\sfrac{2}{3}\mathbf{ΓM}$) is highly sensitive to band filling. Furthermore, with increased interlayer spacing, a competing soft phonon mode emerges near $\mathbf{q}=\sfrac{1}{2}\mathbf{ΓK}$, corresponding to the superstructure observed in the 2H$^\dagger$ phase, although in our calculations this instability arises under hole doping rather than the electron doping inferred experimentally. These results establish band filling and interlayer spacing as key control parameters for CDW ordering vectors in 2H-TaS\textsubscript{2}, and highlight a route to engineering electronic instabilities in a prototypical layered material.

cond-mat.str-el↗

arXiv2017

Emergence of Frohlich polaron from interlayer electron-phonon coupling in van der Waals heterostructure

Van der Waals heterostructures, vertical stacks of layered materials, offer newopportunities for novel quantum phenomena which are absent in their constituent components. Here we report the emergence of polaron quasiparticles at the interface of graphene/hexagonal boron nitride (h-BN) heterostructures. Using nanospot angle-resolved photoemission spectroscopy, we observe zone-corner replicas of h-BN valence band maxima, with energy spacing coincident with the highest phonon energy of the heterostructure|an indication of Frohlich polaron formation due to forward scattering electron-phonon coupling. Parabolic fitting of the h-BN bands yields an effective mass enhancement of ~ 2.3, suggesting an intermediate coupling strength. Our theoretical simulations based on Migdal-Eliashberg theory corroborate the experimental results, allowing the extraction of microscopic physical parameters. Moreover,renormalisation of graphene $π$ band is observed due to the hybridisation with the h-BN band. Our work generalises the polaron study from transition metal oxides to Van derWaals heterostructures with higher material exibility, highlighting interlayer coupling as an extra degree of freedom to explore emergent phenomena.

cond-mat.mes-hall↗

arXiv2017

Moiré band model and band gaps of graphene on hexagonal boron nitride

Nearly aligned graphene on hexagonal boron nitride (G/BN) can be accurately modeled by a Dirac Hamiltonian perturbed by smoothly varying moiré pattern pseudospin fields. Here, we present the moiré-band model of G/BN for arbitrary small twist angles under a framework that combines symmetry considerations with input from ab-initio calculations. Our analysis of the band gaps at the primary and secondary Dirac points highlights the role of inversion symmetry breaking contributions of the moiré patterns, leading to primary Dirac point gaps when the moiré strains give rise to a finite average mass, and to secondary gaps when the moiré pseudospin components are mixed appropriately. The pseudomagnetic strain fields which can reach values of up to $\sim$40 Tesla near symmetry points in the moiré cell stem almost entirely from virtual hopping and dominate over the contributions arising from bond length distortions due to the moiré strains.

cond-mat.mes-hall↗

arXiv2015

Tunable Fermi surface topology and Lifshitz transition in bilayer graphene

Bilayer graphene is a highly tunable material: not only can one tune the Fermi energy using standard gates, as in single-layer graphene, but the band structure can also be modified by external perturbations such as transverse electric fields or strain. We review the theoretical basics of the band structure of bilayer graphene and study the evolution of the band structure under the influence of these two external parameters. We highlight their key role concerning the ease to experimentally probe the presence of a Lifshitz transition, which consists in a change of Fermi contour topology as a function of energy close to the edges of the conduction and valence bands. Using a device geometry that allows the application of exceptionally high displacement fields, we then illustrate in detail the way to probe the topology changes experimentally using quantum Hall effect measurements in a gapped bilayer graphene system.

cond-mat.mes-hall↗

arXiv2013

Transport signatures of pseudo-magnetic Landau levels in strained graphene ribbons

In inhomogeneously strained graphene, low-energy electrons experience a valley-antisymmetric pseudo-magnetic field which leads to the formation of localized states at the edge between the valence and conduction bands, understood in terms of peculiar n=0 pseudo-magnetic Landau levels. Here we show that such states can manifest themselves as an isolated quadruplet of low-energy conductance resonances in a suspended stretched graphene ribbon, where clamping by the metallic contacts results in a strong inhomogeneity of strain near the ribbon ends.

cond-mat.mes-hall↗