arXiv subjects

Jeroen van den Brink

Publications and source records attributed to Jeroen van den Brink.

At least 55 records · Page 3Linked to original sources

arXiv2025

Electronic structure and hinge states of strained half-Heusler compounds LiSbZn and LiBiZn

Half-Heusler compounds are a class of materials with great potential for the study of distinct electronic states. In this work, we investigate, from first-principles, the possibility of hinge modes in closely related topological phases that are tunable by moderate uni-axial strain. We consider two compounds: LiSbZn and LiBiZn. While LiSbZn has a topologically trivial band structure, the larger spin-orbit coupling of Bi causes a band inversion in LiBiZn. We predict the existence of topologically trivial hinge states in both cases. The hinge modes are affected by both the crystal termination, and the bulk topological phase transitions, albeit indirectly: When present, topological surface modes hybridize with the hinge states and obscure their visibility. Thus, we find that the most visible hinge modes occur when no band inversions are present in the material. Our work highlights the interplay and competition between surface and hinge modes in half-Heuslers, and may help guide the experimental search for robust boundary signatures in these materials.

cond-mat.mtrl-sci↗

arXiv2025

Non-Hermitian topology of transport in the quantum Hall phases in graphene

It has recently been shown that signatures of non-Hermitian topology can be realized in a conventional quantum Hall device connected to multiple current sources. These signatures manifest as robust current-voltage characteristics, dictated by the presence of a nontrivial, non-Hermitian topological invariant of the conductance matrix. Chiral edge states are believed to be responsible for this non-Hermitian response, similar to how they lead to a quantized Hall conductivity in the presence of a single current source. Here, we go beyond this paradigm, showing that multi-terminal conductance matrices can exhibit non-Hermitian topological phase transitions that cannot be traced back to the presence and directionality of a boundary-localized chiral mode. By performing quantum transport simulations in the quantum Hall regime of monolayer graphene, we find that when the chemical potential is swept across the zeroth Landau level, unavoidable device imperfections cause the appearance of an additional non-Hermitian phase of the conductance matrix. This highlights graphene as an ideal platform for the study of non-Hermitian topological phase transitions, and is a first step towards exploring how the geometry of quantum devices can be harnessed to produce robust, topologically-protected transport characteristics.

cond-mat.mes-hall↗

arXiv2025

Self-consistent surface superconductivity in time-reversal symmetric Weyl semimetals

Weyl semimetals host topologically protected surface states, the so-called Fermi arcs, that have a penetration depth into the bulk that depends on surface-momentum, and diverges at the Weyl points. It has recently been observed in PtBi$_2$ that such Fermi arc states can become superconducting, with a critical temperature larger than that of the bulk. Here we introduce a general variational method that captures the interplay between surface and bulk superconductivity, for any bulk Hamiltonian that harbors (topological) surface states with varying penetration depth. From the self-consistent solutions we establish that the surface state localization length of Weyl semimetals leads to characteristic features in the surface superconductivity, with a gap depending on surface momentum and a penetration length for the order parameter that is temperature-dependent due to competition with the bulk superconductivity.

cond-mat.supr-con↗

arXiv2025

Antiferromagnetism and spin excitations in a two-dimensional non-Hermitian Hatano-Nelson flux model

The one-dimensional Hatano-Nelson model with non-reciprocal hoppings is a prominent example of a relatively simple non-Hermitian quantum-mechanical system, which allows to study various phenomena in open quantum systems without adding extra gain and loss terms. Here we propose to use it as a building block to construct a correlated non-Hermitian Hamiltonian in two dimensions. It has the characteristic form of a flux model with clock-anticlockwise non-reciprocal hopping on each plaquette. Adding the on-site Hubbard type interaction we analyze the formation of the longe-range antiferromagnetic order and its spin excitations. Such a model is non-Hermitian, but $\mathcal{PT}$-symmetric, which leads to the existence of two regions: a region of unbroken $\mathcal{PT}$ symmetry (real-valued spectrum) and a region of broken $\mathcal{PT}$ symmetry with exceptional lines and complex-valued energy spectrum. The transition from one region to another is controlled by the value of the on-site interaction parameter and coincides with the metal-insulator transition. We also analyze the spin wave spectrum, which is characterized by two diffusive d-wave type of modes corresponding to gain and loss.

cond-mat.str-el↗

arXiv2025

Three prerequisites for high-temperature superconductivity in t-PtBi$_2$

Although the generic mechanism behind high-temperature superconductivity remains notoriously elusive, a set of favorable conditions for its occurrence in a given material has emerged: (i) the electronic structure should have a very high density of states near the Fermi level; (ii) electrons need to be susceptible to a sizable interaction with another degree of freedom to ensure pairing themselves; (iii) the ability to fine-tune some of the system properties significantly helps maximising the critical temperature. Here, by means of high-resolution ARPES, we show that all three criteria are remarkably fulfilled in trigonal platinum bismuthide (t-PtBi$_2$). Specifically, this happens on its surface, which hosts topological surface states known as Fermi arcs. Our findings pave the way for the stabilisation and optimisation of high-temperature superconductivity in this topological material.

cond-mat.supr-con↗

arXiv2025

Topological nodal $i$-wave superconductivity in PtBi$_2$

Most superconducting materials are well-understood and conventional in the sense that the pairs of electrons that cause the superconductivity by their condensation have the highest possible symmetry. Famous exceptions are the enigmatic high-$T_c$ cuprate superconductors. Nodes in their superconducting gap are the fingerprint of their unconventional character and imply superconducting pairing of $d$-wave symmetry. Here, using angle-resolved photoemission spectroscopy, we observe that the Weyl semimetal PtBi$_2$ harbors nodes in its superconducting gap, implying unconventional $i$-wave pairing symmetry. At temperatures below $10\,\mathrm{K}$, the superconductivity in PtBi$_2$ gaps out its topological surface states, the Fermi arcs, while its bulk states remain normal. The nodes in the superconducting gap that we observe are located exactly at the center of the Fermi arcs, and imply the presence of topologically protected Majorana cones around this locus in momentum space. From this, we infer theoretically that robust zero-energy Majorana flat bands emerge at surface step edges. This not only establishes PtBi$_2$ surfaces as unconventional, topological $i$-wave superconductors but also as a promising material platform in the ongoing effort to generate and manipulate Majorana bound states.

cond-mat.supr-con↗

arXiv2025

Exploring Topological Effects in Thin-Film X-Ray Cavities

Quantum control of single x-ray photons can be achieved using thin-film nanostructure cavities with embedded layers of resonant nuclei. Here, we design and theoretically investigate tailored cavity structures that implement a non-Hermitian version of the Su-Schrieffer-Heeger one-dimensional topological model. By tuning the geometry of the structure, different topological phases can be realized. We show that the presence of topological edge states can be identified in the reflectivity spectra of the thin-film cavities. Our findings pave the way for exploiting topological phases in x-ray quantum control.

quant-ph↗

arXiv2025

Chiral magnetic excitations and domain textures of g-wave altermagnets

Altermagnets (AMs) constitute a novel class of spin-compensated materials in which opposite-spin sublattices are connected by a crystal rotation, causing their electronic iso-energy surfaces to be spin-split. While cubic and tetragonal crystal symmetries tend to produce AMs in which the splitting of electronic iso-energy surfaces has $d$-wave symmetry, hexagonal AMs, such as CrSb and MnTe, are $g$-wave AMs. Here we investigate the purely magnetic modes and spin-textures of $g$-wave AMs and show that they are drastically different for easy-axial (CrSb) and easy-planar (MnTe) materials. We show that in CrSb the splitting of the chiral magnon branches possesses $g$-wave symmetry, with each branch carrying a fixed momentum-independent magnetic moment. The altermagnetic splitting is not affected by the easy-axial anisotropy and is the same as that in the nonrelativistic limit. The magnon splitting of MnTe, however, does not strictly possess $g$-wave symmetry due to its easy-planar anisotropy. Instead, the magnetic moment of each branch becomes momentum-dependent, with a distribution that is of $g$-wave symmetry. To generalize the concept of the altermagnetic splitting beyond the nonrelativistic limit, we introduce alternative, directly observable splitting parameter which comprises both the magnon eigenenergy and its magnetic moment and possesses the $g$-wave symmetry in both easy-axial and easy-planar cases. The associated altermagnetic domain walls in easy-axial CrSb possess a net magnetization with an amplitude that depends on their orientation.

cond-mat.str-el↗

arXiv2025

Polarization-Driven Charge Frustration and Emergent Phases in the One-Dimensional Extended Hubbard Model

Frustration is a key driver of exotic quantum phases, yet its role in charge dynamics remains largely unexplored. We show that charge frustration - induced by electronic polarization effects - stabilizes unconventional insulating states in the one-dimensional extended Hubbard model. Using exact diagonalization and density-matrix renormalization group, we uncover a charge-disordered phase that remains insulating despite lacking long-range order and possessing an effectively attractive on-site interaction - a behavior reminiscent of gapful spin liquids in frustrated spin systems. We also identify a fragile ferroelectric phase and a charge-density-wave state with emergent eight-site periodicity. These findings establish charge frustration, driven by charge-dipole interactions, as a robust mechanism for realizing exotic phases in low-dimensional correlated systems, with implications for organic conductors, transition-metal oxides, and ultracold polar molecules.

cond-mat.str-el↗

arXiv2025

Emergent heavy-fermion physics in a new family of topological insulators RAsS (R = Y, La, and Sm)

Realizing topological phases in strongly correlated materials has become a major impetus in condensed matter physics. Although many compounds are now classified as topological insulators, $f$-electron systems (with their strong electron correlations) provide an especially fertile platform for emergent heavy-fermion phenomena driven by the interplay of topology and many-body effects. In this study, we examine the crystalline topology of a new RAsS series (R = Y, La, Sm), revealing a structural variant from previous reports. We demonstrate that YAsS and SmAsS host hourglass fermions protected by glide symmetry. SmAsS notably exhibits a strong effective-mass enhancement, placing it alongside SmB${}_6$ and YbB${}_{12}$ as a material that couples topological surface states with emergent Kondo physics, yet distinguished by its crystalline symmetry constraints and $f$-$p$ orbital hybridization. To capture these features, we construct a minimal model incorporating $f$-electron degrees of freedom, which reproduces the observed topological properties and predicts that the surface states survive in the correlated regime, albeit shifted in energy. Our work thus introduces a new family of correlated topological materials and forecasts the robustness of their surface states under Kondo correlations.

cond-mat.mtrl-sci↗

arXiv2025

One-dimensional conduction channels in the correlated Mott NiS2 arising from obstructed Wannier charges

NiS2, a compound characterized by its pyrite structure, uniquely bridges the realms of strong correlation physics and topology. While bulk NiS2 is known to be a Mott or charge-transfer insulator, its surface displays anomalous metallic behavior and finite conductivity. Using high-resolution neutron scattering data and symmetry analysis, we propose a refined description of NiS2's magnetic phases by introducing a novel model for its ground state. Combined with high-resolution scanning tunneling microscopy and spectroscopy (STM/STS), we unveil the presence of edge states in both Ni- and S-terminated surfaces, which exhibit remarkable resilience to external magnetic fields. Although both types of edge states exhibit similar properties, only the edge states at the Ni termination populate the vicinity of the Fermi level and, therefore contribute to the surface conductivity. Utilizing ab initio methods combined with a topological quantum chemistry analysis, we attribute these edge states to obstructed atomic charges originating from bulk topology. Overall, this work not only deepens our understanding of NiS2 but also lays a robust experimental and theoretical foundation for further exploration of the interplay between one-dimensional step-edge states and the Wannier obstruction in correlated materials.

cond-mat.str-el↗

arXiv2025

Controlling photo-excited electron-spin by light-polarization in ultrafast-pumped altermagnets

Altermagnets (AMs) constitute a novel class of spin-compensated materials in which the symmetry connecting opposite-spin sublattices involves a spatial rotation. Here, we uncover a set of unique non-linear, light-driven properties that set AMs apart from traditional ferro- and antiferromagnets. We demonstrate theoretically that the polarization of an electromagnetic pulse that photo-excites electrons and holes in an AM, controls the spin orientation of these non-equilibrium charge carriers. For a d-wave AM model and a prototype material, we show that very large post-pump spin polarizations may be attained by exploiting resonances. We show that this protocol also allows, in an AM, to directly probe the spin splitting of the electronic states in energy and momentum space. Thus, it can be used to identify and characterize altermagnetic materials via ultrafast pump-probe Kerr/Faraday spectroscopy or spin- and time-resolved ARPES. This opens up the possibility of devising ultrafast optical switches of non-equilibrium spin-polarization, finely tunable by adjusting the pump-pulse characteristics.

cond-mat.mtrl-sci↗

arXiv2025

Finite temperature fermion Monte Carlo simulations of frustrated spin-Peierls systems

The Abrikosov fermion representation of the spin-1/2 degree of freedom allows for auxiliary-field quantum Monte Carlo simulations of frustrated spin systems. This approach provides a manifold of equivalent actions over which the negative sign problem can be optimised. As a result, we can reach temperature scales well below the magnetic scale. Here, we show how to generalise this algorithm to spin-Peierls systems. In contrast to exact diagonalisation approaches, Monte Carlo methods are not Hilbert space bound such that the computational effort per sweep remains invariant when adding phonons. However, the computational effort required to generate independent configurations increases in the presence of phonons. We also show that, for the specific case of the Kitaev-Heisenberg model, the inclusion of phonons does not render the negative sign problem more severe. This new algorithm hence allows us to investigate the interplay between phonon degrees of freedom and magnetic frustration. We present results for frustrated and non-frustrated spin systems.

cond-mat.str-el↗

arXiv2025

Photo-induced Dynamics and Momentum Distribution of Chiral Charge Density Waves in 1T-TiSe$_{2}$

Exploring the photoinduced dynamics of chiral states offers promising avenues for advanced control of condensed matter systems. Photoinduced or photoenhanced chirality in 1T-TiSe$_{2}$ has been suggested as a fascinating platform for optical manipulation of chiral states. However, the mechanisms underlying chirality training and its interplay with the charge density wave (CDW) phase remain elusive. Here, we use time-resolved X-ray diffraction (tr-XRD) with circularly polarized pump lasers to probe the photoinduced dynamics of chirality in 1T-TiSe$_{2}$. We observe a notable ($\sim$20%) difference in CDW intensity suppression between left- and right-circularly polarized pumps. Additionally, we reveal momentum-resolved circular dichroism arising from domains of different chirality, providing a direct link between CDW and chirality. An immediate increase in CDW correlation length upon laser pumping is detected, suggesting the photoinduced expansion of chiral domains. These results both advance the potential of light-driven chirality by elucidating the mechanism driving chirality manipulation in TiSe$_2$, and they demonstrate that tr-XRD with circularly polarized pumps is an effective tool for chirality detection in condensed matter systems.

cond-mat.str-el↗

arXiv2025

Influence of pressure on properties of multi-gap type-I superconductor BeAu

We report on studies of the superconducting and normal state properties of the noncentrosymmetric superconductor BeAu under hydrostatic pressure conditions. The room-temperature equation of state (EOS) reveals the values of the bulk modulus ($B_0$) and its first derivative ($B^\prime_0$) at ambient pressure to be $B_0 \simeq 132$~GPa and $B^\prime_0 \simeq 30$, respectively. Up to the highest pressures studied ($p \simeq 2.2$~GPa), BeAu remains a multi-gap type-I superconductor. The analysis of $B_{\rm c}(T, p)$ data within the self-consistent two-gap approach suggests the presence of two superconducting energy gaps, with the gap-to-$T_{\rm c}$ ratios $Δ_1/k_{\rm B}T_{\rm c} \sim 2.3$ and $Δ_2/k_{\rm B}T_{\rm c} \sim 1.1$ for the larger and smaller gaps, respectively [$Δ= Δ(0)$ is the zero-temperature value of the gap and $k_{\rm B}$ is the Boltzmann constant]. With increasing pressure, $Δ_1/k_{\rm B}T_{\rm c}$ increases while $Δ_2/k_{\rm B}T_{\rm c}$ decreases, suggesting that pressure enhances (weakens) the coupling strength between the superconducting carriers within the bands where the larger (smaller) superconducting energy gap has opened. The superconducting transition temperature $T_{\rm c}$, \textcolor{black}{the zero-temperature values of the superconducting gaps $Δ_1$ and $Δ_2$} and the zero-temperature value of the thermodynamic critical field $B_{\rm c}(0)$ decrease with increasing pressure, with the rates of ${\rm d}T_{\rm c}/{\rm d}p \simeq -0.195$~K/GPa, \textcolor{black}{${\rm d}Δ_1/{\rm d}p \simeq -0.034$~meV/GPa, ${\rm d}Δ_2/{\rm d}p \simeq -0.029$~meV/GPa,} and ${\rm d}B_{\rm c}(0)/{\rm d}p = -2.65(1)$~mT/GPa, respectively. The measured $B_{\rm c}(0)$ values plotted as a function of $T_{\rm c}$ follow an empirical scaling relation established for conventional type-I superconductors.

cond-mat.supr-con↗

arXiv2024

Curvature induced magnetization of altermagnetic films

We consider a thin film of $d$-wave altermagnet bent in a stretching-free manner and demonstrate that gradients of the film curvature induce a local magnetization which is approximately tangential to the film. The magnetization amplitude directly reflects the altermagnetic symmetry and depends on the direction of bending. It is maximal for the bending along directions of the maximal altermagnetic splitting of the magnon bands. A periodically bent film of sinusoidal shape possesses a total magnetic moment per period $\propto\mathscr{A}^2q^4$ where $\mathscr{A}$ and $q$ are the bending amplitude and wave vector, respectively. The total magnetic moment is perpendicular to the plane of the unbent film and its direction (up or down) is determined by the bending direction. A film roll up to a nanotube possesses a toroidal moment directed along the tube $\propto δ_r/r^2$ per one coil, where $r$ and $δ_r$ are the coil radius and the pitch between coils. All these analytical predictions agree with numerical spin-lattice simulations.

cond-mat.str-el↗

arXiv2024

Walking behavior induced by $\mathcal{PT}$ symmetry breaking in a non-Hermitian $\rm XY$ model with clock anisotropy

A quantum system governed by a non-Hermitian Hamiltonian may exhibit zero temperature phase transitions that are driven by interactions, just as its Hermitian counterpart, raising the fundamental question how non-Hermiticity affects quantum criticality. In this context we consider a non-Hermitian system consisting of an $\rm XY$ model with a complex-valued four-state clock interaction that may or may not have parity-time-reversal ($\mathcal{PT}$) symmetry. When the $\mathcal{PT}$ symmetry is broken, and time-evolution becomes non-unitary, a scaling behavior similar to the Berezinskii-Kosterlitz-Thouless phase transition ensues, but in a highly unconventional way, as the line of fixed points is absent. From the analysis of the $d$-dimensional RG equations, we obtain that the unconventional behavior in the $\mathcal{PT}$ broken regime follows from the collision of two fixed points in the $d\to 2$ limit, leading to walking behavior or pseudocriticality. For $d=2+1$ the near critical behavior is characterized by a correlation length exponent $ν=3/8$, a value smaller than the mean-field one. These results are in sharp contrast with the $\mathcal{PT}$-symmetric case where only one fixed point arises for $2<d<4$ and in $d=1+1$ three lines of fixed points occur with a continuously varying critical exponent $ν$.

quant-ph↗

arXiv2024

Spin Hall and Edelstein Effects in Novel Chiral Noncollinear Altermagnets

Altermagnets are a newly discovered class of magnetic phases that combine the spin polarization behavior of ferromagnetic band structures with the vanishing net magnetization characteristic of antiferromagnets. Initially proposed for collinear magnets, the concept has since been extended to include certain non-collinear structures. A recent development in Landau theory for collinear altermagnets incorporates spin-space symmetries, providing a robust framework for identifying this class of materials. Here we expand on that theory to identify altermagnetic multipolar order parameters in non-collinear chiral materials. We demonstrate that the interplay between non-collinear altermagnetism and chirality allows for spatially odd multipole components, leading to non-trivial spin textures on Fermi surfaces and unexpected transport phenomena, even in the absence of SOC. This makes such chiral altermagnets fundamentally different from the well-known SOC-driven Rashba-Edelstein and spin Hall effects used for 2D spintronics. Choosing the chiral topological magnetic material Mn$_3$IrSi as a case study, we apply toy models and first-principles calculations to predict experimental signatures, such as large spin-Hall and Edelstein effects, that have not been previously observed in altermagnets. These findings pave the way for a new realm of spintronics applications based on spin-transport properties of chiral altermagnets.

cond-mat.mtrl-sci↗