Found 18 papers in cond-mat
Date of feed: Mon, 29 Jan 2024 01:30:00 GMT

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Topological signatures of a p-wave superconducting wire through light. (arXiv:2401.14501v1 [cond-mat.supr-con])
Frederick Del Pozo, Karyn Le Hur

We show how the $\mathbb{Z}_{2}$ topological index of a one-dimensional topological p-wave superconductor can be revealed when driving with a classical vector potential i.e. an electromagnetic wave, through the quasiparticles inter-band transition rates. As a function of driving frequency $\omega$, it is possible to obtain a measure of this topological invariant from the resonance envelope classifying the two distinct topological phases of the short-range Kitaev wire. We also propose to probe the topological phase transition in the model through the responses of the global capacitance in the presence of the light field and also through the Josephson current between the wire and the proximity coupled bulk superconductor. The system may also be implemented on the Bloch sphere allowing alternative ways to measure the $\mathbb{Z}$ and $\mathbb{Z}_2$ topological invariants through circuit or cavity quantum electrodynamics.

Thermodynamics of vison crystals in an anisotropic quantum spin liquid. (arXiv:2401.14525v1 [cond-mat.str-el])
Ritwika Majumder, Onur Erten, Anamitra Mukherjee

Using unbiased Monte Carlo simulations and variational analysis, we present the ground state and finite temperature phase diagrams of an exactly solvable spin-orbital model with Kitaev-type interactions on a square lattice. We show that an array of new gapped and gapless vison crystals -- characterized by the periodic arrangement of $\mathbb{Z}_2$ flux excitations -- can be stabilized as a function of external magnetic field and exchange anisotropy. In particular, we discover a variety of `quarter phases' wherein new sixteen-site periodic patterns emerge, with only a quarter of the fluxes adopting 0-flux configurations. In contrast, the rest remain in $\pi$-flux configurations. Vison crystals break translational symmetry and undergo finite temperature phase transitions. We investigate the finite temperature properties of these phases and report the corresponding critical and crossover temperatures. Our results reveal an array of novel phases in exactly solvable extensions of the Kitaev model, wherein local and topological orders can coexist.

Discovery of a Topological Charge Density Wave. (arXiv:2401.14547v1 [cond-mat.str-el])
Maksim Litskevich, Md Shafayat Hossain, Songbo Zhang, Zi-Jia Cheng, Satya N. Guin, Nitesh Kumar, Chandra Shekhar, Zhiwei Wang, Yongkai Li, Guoqing Chang, Jia-Xin Yin, Qi Zhang, Guangming Cheng, Yu-Xiao Jiang, Tyler A. Cochran, Nana Shumiya, Xian P. Yang, Daniel Multer, Xiaoxiong Liu, Nan Yao, Yugui Yao, Claudia Felser, Titus Neupert, M. Zahid Hasan

Charge density waves (CDWs) appear in numerous condensed matter platforms, ranging from high-Tc superconductors to quantum Hall systems. Despite such ubiquity, there has been a lack of direct experimental study on boundary states that can uniquely stem from the charge order. Here, using scanning tunneling microscopy, we directly visualize the bulk and boundary phenomenology of CDW in a topological material, Ta2Se8I. Below the transition temperature (TCDW = 260 K), tunneling spectra on an atomically resolved lattice reveal a large insulating gap in the bulk and on the surface, exceeding 500 meV, surpassing predictions from standard weakly-coupled mean-field theory. Spectroscopic imaging confirms the presence of CDW, with LDOS maxima at the conduction band corresponding to the LDOS minima at the valence band, thus revealing a {\pi} phase difference in the respective CDW order. Concomitantly, at a monolayer step edge, we detect an in-gap boundary mode with modulations along the edge that match the CDW wavevector along the edge. Intriguingly, the phase of the edge state modulation shifts by {\pi} within the charge order gap, connecting the fully gapped bulk (and surface) conduction and valence bands via a smooth energy-phase relation. This bears similarity to the topological spectral flow of edge modes, where the boundary modes bridge the gapped bulk modes in energy and momentum magnitude but in Ta2Se8I, the connectivity distinctly occurs in energy and momentum phase. Notably, our temperature-dependent measurements indicate a vanishing of the insulating gap and the in-gap edge state above TCDW, suggesting their direct relation to CDW. The theoretical analysis also indicates that the observed boundary mode is topological and linked to CDW.

Advancing Scanning Probe Microscopy Simulations: A Decade of Development in Probe-Particle Models. (arXiv:2401.14564v1 [cond-mat.mes-hall])
Niko Oinonen, Aliaksandr V. Yakutovich, Aurelio Gallardo, Martin Ondracek, Prokop Hapala, Ondrej Krejci

The probe-particle model is an open-source package designed for simulation of scanning probe microscopy experiments, employing non-reactive, flexible tip apices (e.g., carbon monoxide, xenon, or hydrogen molecules) to achieve sub-molecular resolution. This abstract introduces the latest version of the probe-particle model, highlighting substantial advancements in accuracy, computational performance, and user-friendliness over previous versions. To demonstrate this we provide a comprehensive review of theories for simulating non-contact Atomic Force Microscopy (nc-AFM), spanning from the simple Lennard-Jones potential to the latest full density-based model. Implementation of these theories are systematically compared against ab initio calculated reference, showcasing their respective merits. All parts of the probe-particle model have undergone acceleration by 1-2 orders of magnitude through parallelization by OpenMP on CPU and OpenCL on GPU. The updated package includes an interactive graphical user interface (GUI) and seamless integration into the Python ecosystem via pip, facilitating advanced scripting and interoperability with other software. This adaptability positions the probe-particle model as an ideal tool for high-throughput applications, including the training of machine learning models for the automatic recovery of atomic structures from nc-AFM measurements. We envision significant potential for this application in future single-molecule analysis, synthesis, and advancements of surface science in general. Additionally, we discuss simulations of other sub-molecular scanning-probe imaging techniques, such as bond-resolved scanning tunneling microscopy and kelvin probe force microscopy, all built on the robust foundation of the probe-particle model. Altogether this demonstrates the broad impact of the model across diverse domains of surface science and molecular chemistry.

Topological Edge and Corner States in Biphenylene Network. (arXiv:2401.14731v1 [cond-mat.mtrl-sci])
Keiki Koizumi, Huyen Thanh Phan, Kento Nishigomi, Katsunori Wakabayashi

The electronic states and topological properties of the biphenylene network (BPN) are analyzed using a tight-binding model based on the $\pi$-electron network. It is shown that tuning the hopping parameters induces topological phase transitions, leading to the emergence of edge states owing to the nontrivial topological Zak phase of the bulk BPN. Elementary band analysis clearly gives the number of edge states, which are associated with the location of Wannier centers. In addition, we have presented the conditions for the emergence of corner states owing to the higher-order topological nature of BPN.

Anomalous electron-phonon coupling in kagome ferromagnetic Weyl semimetal Co$_3$Sn$_2$S$_2$. (arXiv:2401.14734v1 [cond-mat.str-el])
G. He, M. Kute, Z. C. Xu, L. Peis, R. Stumberger, A. Baum, D. Jost, E. M. Been, B. Moritz, Y. G. Shi, T. P. Devereaux, R. Hackl

We present results of a Raman scattering study of the Kagome ferromagnet Co$_3$Sn$_2$S$_2$, with a focus on electronic and phononic excitations and their interplay. In addition, the electronic band structure is analyzed theoretically, enabling a semi-quantitative explanation of the spectra. A prominent feature in the electronic spectra is a redistribution of spectral weight from low to high energies starting at the Curie temperature Tc. The Raman intensity is suppressed below approximately 1000cm$^{-1}$ and increases above to a peak at 2000 cm$^{-1}$ in all symmetries. Two Raman active phonon modes are identified in A$_{1g}$ and E$_g$ symmetry. The A$_{1g}$ phonon couples strongly to the electronic continuum as indicated by the asymmetric Fano-type line shape. The asymmetry depends non-monotonically on temperature and is maximal close to the magnetic transition. In the limit $T\to 0$ the phonon is nearly symmetric. The evolution of the coupling strength and the electronic continuum as a function of temperature is attributed to a band splitting induced by the ferromagnetic phase transition which substantially reduces the DOS towards $T=0$. The $3d_{z^2}$ electrons of the Co atoms in the crystal field modulated by the A$_{1g}$ phonon are implied to be a critical component contributing to the strong electron-phonon coupling of that phonon. These results allow a comprehensive understanding of the bulk band structure evolution as a function of temperature in Co$_3$Sn$_2$S$_2$, offering key insights for further studies of the driving force behind the long-range magnetic order and novel topological states in this compound.

E-Beam Induced Micropattern Generation and Amorphization of L-Cysteine-Functionalized Graphene Oxide Nano-composites. (arXiv:2401.14783v1 [cond-mat.mtrl-sci])
Y.Melikyan, H.Gharagulyan, A.Vasilev, V.Hayrapetyan, M.Zhezhu, A.Simonyan, D.A.Ghazaryan, M.S.Torosyan, A.Kharatyan, J.Michalicka, M.Yeranosyan

The evolution of dynamic processes in graphene-family materials are of great interest for both scientific purposes and technical applications. Scanning electron microscopy and transmission electron microscopy outstand among the techniques that allow both observing and controlling such dynamic processes in real time. On the other hand, functionalized graphene oxide emerges as a favorable candidate from graphene-family materials for such an investigation due to its distinctive properties, that encompass a large surface area, robust thermal stability, and noteworthy electrical and mechanical properties after its reduction. Here, we report on studies of surface structure and adsorption dynamics of L-Cysteine on electrochemically exfoliated graphene oxides basal plane. We show that electron beam irradiation prompts an amorphization of functionalized graphene oxide along with the formation of micropatterns of controlled geometry composed of L-Cysteine-Graphene oxide nanostructures. The controlled growth and predetermined arrangement of micropatterns as well as controlled structure disorder induced by e beam amorphization, in its turn potentially offering tailored properties and functionalities paving the way for potential applications in nanotechnology, sensor development, and surface engineering. Our findings demonstrate that graphene oxide can cover L-Cysteine in such a way to provide a control on the positioning of emerging microstructures about 10-20 um in diameter. Besides, Raman and SAED measurement analyses yield above 50% amorphization in a material. The results of our studies demonstrate that such a technique enables the direct creation of micropatterns of L-Cysteine-Graphene oxide eliminating the need for complicated mask patterning procedures.

Higher-order topology in Fibonacci quasicrystals. (arXiv:2401.14896v1 [cond-mat.supr-con])
Chaozhi Ouyang, Qinghua He, Dong-Hui Xu, Feng Liu

In crystalline systems, higher-order topology, characterized by topological states of codimension greater than one, typically arises from the mismatch between Wannier centers and atomic sites, leading to filling anomalies. However, this phenomenon is less understood in aperiodic systems, such as quasicrystals, where Wannier centers are not well defined. In this study, we examine Fibonacci chains and squares, a quintessential type of quasicrystal, to investigate their higher-order topological properties. We discover that topological interfacial states, including corner states, can be inherited from their higher-dimensional periodic counterparts, such as the two-dimensional Su-Schrieffer-Heeger model. This finding is validated through numerical simulations of both phononic and photonic Fibonacci quasicrystals by the finite element method, revealing the emergence of topological edge and corner states at interfaces between Fibonacci quasicrystals with differing topologies inherited from their parent systems. Our results not only provide insight into the higher-order topology of quasicrystals but also open avenues for exploring novel topological phases in aperiodic structures.

Scanning Tunneling Microscopy for Molecules: Effects of Electron Propagation into Vacuum. (arXiv:2401.14937v1 [cond-mat.mes-hall])
Abhishek Grewal, Christopher C. Leon, Klaus Kuhnke, Klaus Kern, Olle Gunnarsson

Using scanning tunneling microscopy (STM), we experimentally and theoretically investigate isolated platinum phthalocyanine (PtPc) molecules adsorbed on atomically thin NaCl(100) vapor deposited on Au(111). We obtain good agreement between theory and constant-height STM topography. We examine why strong distortions of STM images occur as a function of distance between molecule and STM tip. The images of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) exhibit, for increasing distance, significant radial expansion due to electron propagation in the vacuum. Additionally, the imaged angular dependence is substantially distorted. The LUMO image has substantial intensity along the molecular diagonals where PtPc has no atoms. In the electronic transport gap the image differs drastically from HOMO and LUMO, even at energies very close to these orbitals. As the tunneling becomes increasingly off-resonant, the eight angular lobes of the HOMO or of the degenerate LUMOs diminish and reveal four lobes with maxima along the molecular axes, where both, HOMO and LUMO have little or no weight. These images are strongly influenced by low-lying PtPc orbitals that have simple angular structures.

pyMBE: the Python-based Molecule Builder for ESPResSo. (arXiv:2401.14954v1 [cond-mat.soft])
David Beyer, Paola B. Torres, Sebastian P. Pineda, Claudio F. Narambuena, Jean-Noël Grad, Peter Košovan, Pablo M. Blanco

We present the Python-based Molecule Builder for ESPResSo (pyMBE), an open source software designed to build coarse-grained models of polyelectrolytes, peptides and globular proteins of arbitrary topology into the Extensible Simulation Package for Research on Soft Matter (ESPResSo). ESPResSo features the constant pH (cpH) and grand-reaction (G-RxMC) methods, which are powerful tools to study macromolecular systems with many reactive groups, permitting to efficiently sample systems with multiple coupled chemical equilibria. However, setting up these methods for macromolecules with many different reactive groups is a non-trivial and error-prone task, especially for beginners. pyMBE enables the automatic setup of cpH and G-RxMC simulations in ESPResSo, lowering the barrier for newcomers and opening the door to investigate complex systems not yet studied with these methods. To demonstrate some of the applications of pyMBE, we showcase several study cases where pyMBE successfully reproduces previous simulations in the literature done with ESPResSo and other software, including various simulations of different peptides in bulk solution, simulations of weak polyelectrolytes in dialysis and simulations of globular proteins in bulk solution. pyMBE is publicly available as a GitLab repository ( which includes its source code and various sample and test scripts, including the ones that we used to generated the data presented in this article.

Fermi-arcs mediated transport in surface Josephson junctions of Weyl semimetal. (arXiv:2401.14956v1 [cond-mat.mes-hall])
Rekha Kumari, Dibya Kanti Mukherjee, Arijit Kundu

This study presents Fermi-arcs mediated transport in a Weyl semimetal thin slab, interfacing two $s$-wave superconductors. We present detailed study with both time-reversal and inversion symmetry broken Weyl semimetals under grounding, orbital magnetic fields, and Zeeman fields. An orbital magnetic field induces energy level oscillations, while a Zeeman field give rise to the periodic anomalous oscillations in the Josephson current. These anomalous oscillations correlate with the separation of Weyl nodes in momentum space, junction length, and system symmetries. Additionally, we present an explanation by scattering theory modeling the Fermi-arcs as a network model.

Intrinsic and extrinsic photogalvanic effects in twisted bilayer graphene. (arXiv:2401.15005v1 [cond-mat.mes-hall])
Fernando Peñaranda, Hector Ochoa, Fernando de Juan

The chiral lattice structure of twisted bilayer graphene with D6 symmetry allows for intrinsic photogalvanic effects only at off-normal incidence, while additional extrinsic effects are known to be induced by a substrate or a gate potential. In this work, we first compute the intrinsic effects and show they reverse sign at the magic angle, revealing a band inversion at the {\Gamma} point. We next consider different extrinsic effects, showing how they can be used to track the strengths of the substrate coupling or displacement field. We also show that the approximate particle-hole symmetry implies stringent constraints on the chemical potential dependence of all photocurrents. A detailed comparison of intrinsic vs. extrinsic photocurrents therefore reveals a wealth of information about the band structure and can also serve as a benchmark to constrain the symmetry breaking patterns of correlated states.

Protocol for certifying entanglement in surface spin systems using a scanning tunneling microscope. (arXiv:2401.15017v1 [cond-mat.mes-hall])
Rik Broekhoven, Curie Lee, Soo-hyon Phark, Sander Otte, Christoph Wolf

Certifying quantum entanglement is a critical step towards realizing quantum-coherent applications of surface spin systems. In this work, we show that entanglement can be unambiguously shown in a scanning tunneling microscope (STM) with electron spin resonance by exploiting the fact that entangled states undergo a free time evolution with a distinct characteristic time constant that clearly distinguishes it from any other time evolution in the system. By implementing a suitable phase control scheme, the phase of this time evolution can be mapped back onto the population of one entangled spin in a pair, which can then be read out reliably using a weakly coupled sensor spin in the junction of the scanning tunneling microscope. We demonstrate through open quantum system simulations with realistic spin systems, which are currently available with spin coherence times of $T_2\approx$ 300 ns, that a signal directly correlated with the degree of entanglement can be measured at a temperature range of 100$-$400 mK accessible in sub-Kelvin cryogenic STM systems.

Higher-Order Network Interactions through Phase Reduction for Oscillators with Phase-Dependent Amplitude. (arXiv:2305.04277v2 [math.DS] UPDATED)
Christian Bick, Tobias Böhle, Christian Kuehn

Coupled oscillator networks provide mathematical models for interacting periodic processes. If the coupling is weak, phase reduction -- the reduction of the dynamics onto an invariant torus -- captures the emergence of collective dynamical phenomena, such as synchronization. While a first-order approximation of the dynamics on the torus may be appropriate in some situations, higher-order phase reductions become necessary, for example, when the coupling strength increases. However, these are generally hard to compute and thus they have only been derived in special cases: This includes globally coupled Stuart--Landau oscillators, where the limit cycle of the uncoupled nonlinear oscillator is circular as the amplitude is independent of the phase. We go beyond this restriction and derive second-order phase reductions for coupled oscillators for arbitrary networks of coupled nonlinear oscillators with phase-dependent amplitude, a scenario more reminiscent of real-world oscillations. We analyze how the deformation of the limit cycle affects the stability of important dynamical states, such as full synchrony and splay states. By identifying higher-order phase interaction terms with hyperedges of a hypergraph, we obtain natural classes of coupled phase oscillator dynamics on hypergraphs that adequately capture the dynamics of coupled limit cycle oscillators.

Lieb-Schultz-Mattis anomalies and web of dualities induced by gauging in quantum spin chains. (arXiv:2308.00743v2 [cond-mat.str-el] UPDATED)
Ömer M. Aksoy, Christopher Mudry, Akira Furusaki, Apoorv Tiwari

Lieb-Schultz-Mattis (LSM) theorems impose non-perturbative constraints on the zero-temperature phase diagrams of quantum lattice Hamiltonians (always assumed to be local in this paper). LSM theorems have recently been interpreted as the lattice counterparts to mixed 't Hooft anomalies in quantum field theories that arise from a combination of crystalline and global internal symmetry groups. Accordingly, LSM theorems have been reinterpreted as LSM anomalies. In this work, we provide a systematic diagnostic for LSM anomalies in one spatial dimension. We show that gauging subgroups of the global internal symmetry group of a quantum lattice model obeying an LSM anomaly delivers a dual quantum lattice Hamiltonian such that its internal and crystalline symmetries mix non-trivially through a group extension. This mixing of crystalline and internal symmetries after gauging is a direct consequence of the LSM anomaly, i.e., it can be used as a diagnostic of an LSM anomaly. We exemplify this procedure for a quantum spin-1/2 chain obeying an LSM anomaly resulting from combining a global internal $\mathbb{Z}^{\,}_{2}\times\mathbb{Z}^{\,}_{2}$ symmetry with translation or reflection symmetry. We establish a triality of models by gauging a $\mathbb{Z}^{\,}_{2}\subset\mathbb{Z}^{\,}_{2}\times\mathbb{Z}^{\,}_{2}$ symmetry in two ways, one of which amounts to performing a Kramers-Wannier duality, while the other implements a Jordan-Wigner duality. We discuss the mapping of the phase diagram of the quantum spin-1/2 $XYZ$ chains under such a triality. We show that the deconfined quantum critical transitions between Neel and dimer orders are mapped to either topological or conventional Landau-Ginzburg transitions. Finally, we extend our results to $\mathbb{Z}^{\,}_{n}$ clock models and provide a reinterpretation of the dual internal symmetries in terms of $\mathbb{Z}^{\,}_{n}$ charge and dipole symmetries.

Non-Hermitian extended midgap states and bound states in the continuum. (arXiv:2310.18270v2 [physics.optics] UPDATED)
Maria Zelenayova, Emil J. Bergholtz

We investigate anomalous localization phenomena in non-Hermitian systems by solving a class of generalized Su-Schrieffer-Heeger/Rice-Mele models and by relating their provenance to fundamental notions of topology, symmetry-breaking and biorthogonality. We find two flavours of bound states in the continuum, both stable even in the absence of chiral symmetry. The first being skin bulk states which are protected by the spectral winding number. The second flavour is constituted by boundary modes associated with a quantized biorthogonal polarization. Furthermore, we find the extended state stemming from the boundary state that delocalizes while remaining in the gap at bulk critical points. This state may also delocalize within a continuum of localized (skin) states. These results clarify fundamental aspects of topology, and symmetry in the light of different approaches to the anomalous non-Hermitan bulk-boundary correspondence -- and are of direct experimental relevance for mechanical, electrical and photonic systems.

From noise on the sites to noise on the links: discretizing the conserved Kardar-Parisi-Zhang equation in real space. (arXiv:2312.13065v2 [cond-mat.stat-mech] UPDATED)
Andrea Cavagna, Javier Cristín, Irene Giardina, Mario Veca

Numerical analysis of conserved field dynamics has been generally performed with pseudo spectral methods. Finite differences integration, the common procedure for non-conserved field dynamics, indeed struggles to implement a conservative noise in the discrete spatial domain. In this work, we present a novel method to generate a conservative noise in the finite differences framework, which works for any discrete topology and boundary conditions. We apply it to numerically solve the conserved Kardar-Parisi-Zhang (cKPZ) equation, widely used to describe surface roughening when the number of particles is conserved. Our numerical simulations recover the correct scaling exponents $\alpha$, $\beta$, and $z$ in $d=1$ and in $d=2$. To illustrate the potentiality of the method, we further consider the cKPZ equation on different kinds of non-standard lattices and on the random Euclidean graph. This is the first numerical study of conserved field dynamics on an irregular topology, paving the way to a broad spectrum of possible applications.

Electrodynamics of superconductors: from Lorentz to Galilei at zero temperature. (arXiv:2401.04493v2 [cond-mat.supr-con] UPDATED)
Luca Salasnich

We discuss the derivation of the electrodynamics of superconductors coupled to the electromagnetic field from a Lorentz-invariant bosonic model of Cooper pairs. Our results are obtained at zero temperature where, according to the third law of thermodynamics, the entropy of the system is zero. In the nonrelativistic limit we obtain a Galilei-invariant superconducting system which differs with respect to the familiar Schr\"odinger-like one. From this point of view, there are similarities with the Pauli equation of fermions which is derived from the Dirac equation in the nonrelativistic limit and has a spin-magnetic field term in contrast with the Schr\"odinger equation. One of the peculiar effects of our model is the decay of a static electric field inside a superconductor exactly with the London penetration length. In addition, our theory predicts a modified D'Alembert equation for the massive electromagnetic field also in the case of nonrelativistic superconducting matter. We emphasize the role of the Nambu-Goldstone phase field which is crucial to obtain the collective modes of the superconducting matter field. In the special case of a nonrelativistic neutral superfluid we find a gapless Bogoliubov-like spectrum, while for the charged superfluid we obtain a dispersion relation that is gapped by the plasma frequency.