We explore the atomistic mechanisms of thermal transport in solids, extending established formulations and developing the computational framework to solve them. Starting from a density-matrix formalism, we show how the phonon Boltzmann equation is missing a tunneling term that becomes pivotal in disordered or defective materials. Thus, we derive a unified ‘Wigner formulation’ that...
Twisted monolayer-bilayer graphene (TMBG) exhibits renormalized nearly flat bands harboring various exotic physical phenomena. Stacking an additional monolayer graphene on the TMBG paves a new way to extract single particle bandgap, the charge neutrality point (CNP) gap and bandwidth. The Dirac cone in the decoupled monolayer graphene serves as a perfect chemical potential sensor when the...
In most conductors, diffusive scattering from defects and lattice vibrations results in Ohmic transport. Alternatively, transport is ballistic, when the channel dimensions are the smallest length scale. However, when electron-electron interactions are sufficiently strong, charge transport can mimic the viscous flow of fluids. In the current work, we explore this analogy and observe that the...
Advances in the manipulation of van der Waals materials have shown that bilayers offer a unique platform for studying strongly correlated physics in two-dimensions (2D). Bilayers are importantly different from monolayers in that there exist long-range interactions between electrons in both the intra- and inter-layer channels, which differ only slightly. We show that the electronic charge...
Layered transition metal dichalcogenides exhibit numerous exotic electronic phases, which are known to be highly sensitive to minute changes in virtually any external parameter. We found that vanadium intercalation into the TaS$_2$ (V$_x$TaS$_2$) leads to intriguing changes in its properties. Upon increasing $x$, the electronic structure evolves from the pure 2H phase known for its charge...
Flat bands in twisted graphene systems offers plethora of strongly correlated states, among these, correlated insulator, superconductor and chern insulator are to name of few. Twisted trilayer graphene has shown robust superconductivity which drastically deviates from conventional weak-coupling BCS type superconductivity. In particular, twisted trilayer graphene may even host pragmatic example...
We perform tunnel spectroscopy on NbSe$_{2}$ by utilizing MoS$_{2}$ or hexagonal Boron Nitride (hBN) as a tunnel barrier. We observe subgap excitations and probe their origin by studying various heterostructure designs. We show that the edge of NbSe$_{2}$ hosts many defect states. By isolating the NbSe$_{2}$ edge and comparing MoS$_{2}$ and hBN tunnel barriers, we suggest defects in MoS$_{2}$...
In solid-state systems, strong correlations cause the emergence of quasiparticles that are immune to local environmental perturbations. An example of such a system is the Quantum Hall Effect, in which electrons confined in two dimensions and subjected to a high perpendicular magnetic field give rise to fractionally charged quasiparticles (anyons) that are topologically protected. The...
Scaling-up perovskite solar cells (PSCs) is a prerequisite to the adoption of perovskite photovoltaics. However, the performance and stability of perovskite solar modules (PSMs) have lagged behind those of lab-scale PSCs. The development o PSMs requires interfacial passivation, yet this is challenging for the buried interface, owing to the dissolution of passivation agents during perovskite...
Quantum matter is characterised by competing and intertwined orders. Here we will present our recent advances in using uniaxial pressure as a clean “surgical” tool to tune quantum phases while simultaneously obtaining microscopic insights via scattering experiments.
To achieve the fine-tuning, we have designed a new in-situ uniaxial device for large-scale facility research based on an...
The mechanism of the pseudogap observed in hole-doped cuprates remains one of the central puzzles in condensed matter physics. We analyze this phenomenon via a Feynman-diagrammatic inspection of the Hubbard model. Our approach captures the pivotal interplay between Mott localization and Fermi surface topology beyond weak-coupling spin fluctuations. Our analysis naturally explains puzzling...
In this work, we will discuss our latest investigations of the Bi$_2$Sr$_2$Ca$_1$Cu$_2$O$_8$$_+$$_\delta$ cuprate superconductor using Scanning Tunneling Microscopy (STM). We focus on the atomic scale periodic charge modulations as a function of doping and magnetic field. Specifically, we try to address the nature and origin of the 4a$_0$×4a$_0$ and (4/3)a$_0$×(4/3)a$_0$ modulations (a$_0$:...
Based on now well-established universal transport and optical conductivity properties, we show that the phenomenology of cuprates across the phase diagram is fully captured by the charge conservation relation:
1 + p = n_loc + n_eff
with the superfluid density that simply corresponds to:
ρ_S = n_eff ⋅ (O_S ⋅ n_loc)
where p is doping, n_eff is the carrier density,...
Exploring novel materials as the candidates for unconventional superconductors can help to understand the mechanism of this exotic phenomenon but also lead to synthesis of compounds with important technological applications. The main compound of interest is murunskite, a material isostructural to iron-based superconductors with iron and copper occupying the same crystal site. I will discuss...
We investigate the magnetic response on transport properties in cuprates. Firstly, we show that the Hall coefficient in the low-field/high-temperature regime is accurately described by Boltzmann transport equations. Secondly, we validate Kohler's rule for the magnetoresistance across the phase diagram. Thirdly, we determine that field promoted charge density wave correlations at $p\sim0.12$...
Extensive experimental evidence indicates that the mobile carriers in the normal state of high-Tc superconducting cuprates are a Fermi liquid with practically the same transport parameters for all compounds and dopings. A comprehensive theoretical framework is laid out to explain such an outcome, despite the large Coulomb scales affecting the mobile carriers, and despite the superconducting...
Bifacial photovoltaic (PV) systems have shown great promise in generating higher annual energy yields compared to conventional monofacial-based PV systems. They offer advantages in building-integrated PVs, vertically mounted bifacial PVs, and agrivoltaics, with low-carbon emissions and a cost-effective levelized cost of electricity.
However, bifacial thin-film solar cells, specifically...
Heat dissipation has become a critical problem in the performance of electronic devices, thus, reducing their lifespans. Therefore, to manipulate and control heat, thermal circuit elements analogous to electronic ones like thermal diodes, transistors, and thermal logic gates are needed. In our current research, we have experimentally studied telescopic nanowires for their thermal rectification...
Tannin-furanic foams are green lightweight materials, presenting quite good compression resistance and thermal insulation, and being suitable as a wastewater treatment agent, therefore getting more attention as alternatives to oil-based lightweight materials. Within the Interreg V-A Italy-Austria project ITAT1059 InCIMa4, and within the CERIC proposal 20217081, mechanically and structurally...
The ultrafast dynamics in the quantum many-body systems introduces the novel photoinduced phase transition (PIPT) to the family of quantum phase transitions. In the VO2, although the thermal-induced metal-to-insulator transition due to the lattice distortion has been explained with cluster DMFT since 2005, it was verified only a few years ago in the experiment that the photoexcitation is also...
Magnonics is a rapidly developing domain of nanomagnetism, with application potential in information processing systems. Realisation of this potential and miniaturisation of magnonic circuits requires their extension into the third dimension. However, so far, magnonic conduits are largely limited to thin films and 2D structures. Here, we introduce 3D magnonic nanoconduits fabricated by the...
Superconductivity in laser-excited correlated electron systems has attracted considerable interest due to reports of light-induced superconducting-like states. We explore the possibility of non-thermal superconducting order in strongly interacting multi-orbital Hubbard systems, using non-equilibrium dynamical mean field theory. We find that a staggered $\eta$-type superconducting phase can be...
Superconductivity in nickelates was discovered only four years ago, and sparked great interest in this family of superconductors. Although the underlying mechanism for superconductivity is still under debate, D$\Gamma$A could successfully predict the occurrence of a superconducting dome. In short, the T$_c$ is inversely proportional to the ratio between the Hubbard interaction U and the...
Vanadium dioxide (VO$_2$) is a prototypical metal-insulator transition (MIT) material, hosting both intriguing physical phenomena and industrial application potential. The VO$_2$ MIT originates from a complex interplay between Peierls-like dimerization and Hubbard-Mott correlations that is difficult to capture with standard theoretical models or computational techniques. Here, we present...
One of the central tasks in condensed matter physics is the characterization of phase diagrams. Traditionally, this is done by a physicist who identifies a small set of characteristic quantities, like response functions or order parameters, guided by his human intuition. This process can be automated by casting the problem of mapping out a phase diagram as a classification task. We show that...
$BaTiO_3$-relaxors are promising materials for energy storage applications in microelectronics. These lead-free dielectrics are thermally stable and suitable for high-temperature operation due to their broad and high permittivity response and low electric coercivity. Relaxor behaviour is induced by homo- or heterovalent substitution of the central $Ti^{4+}$ ions, which disrupts the long-range...
Co$_3$Sn$_2$S$_2$ is a Weyl ferromagnet (T$_c$ ~ 177 K) with kagome layers stacked along its c-axis. A recent resonant inelastic X-ray scattering (RIXS) study with linear polarized X-rays reported correlation driven near-flat band Stoner excitations. However, our RIXS measurements employing a magnetic circular dichroism (MCD) analysis suggests that the reported “near-flat band” is dispersive...
The finite temperature behavior of the Kagome Ising Antiferromagnet with farther neighbor interactions $(J_1,J_2,J_3)$ is investigated with the Corner Transfer Matrix Renormalization Group (CTMRG) algorithm. In the parameter region $J_1>J_3>J_2>0$, the system breaks a $\mathbb{Z}_3$ rotation symmetry and a $\mathbb{Z}_2$ translation symmetry in the ground state. These symmetries are restored...
Magnetic van der Waals (vdW) materials offer exciting opportunities to study exotic magnetic phases and collective behavior in two-dimensional limits. FePS$_{3}$ is an S = 2 zig-zag quasi-two-dimensional antiferromagnetic insulator with a honeycomb lattice, making it an ideal candidate for investigating dimensionality and interlayer coupling on magnetic behavior. In this talk, Resonant...
We introduce a non-equilibrium dynamical mean-field theory (DMFT) for studying an inhomogeneous Anderson-Hubbard lattice that contains both electron-electron interactions and chemical disorders, which are treated on an equal footing. The theory reduces to conventional DMFT in the presence of only electron interactions and to coherent potential approximation (CPA) with only disorders.
An...
Floquet engineering has attracted significant interest given the recent developments in experimental techniques such as ultrafast spectroscopy and the potential to enhance the stability of phases of matter such as superconductivity. Here we explore how an external drive and intrinsic dissipation jointly affect superconductivity. Inspired by the fitness criterion for static superconductors, we...
At low magnetic fields, the approach to deduce the energy relaxation times from current-voltage curves fails. The problem arises given the fact that the number of vortices, deduced from the applied magnetic field only, is in fact larger. Here, we provide a method to count the number of vortices in samples at zero magnetic field. Experiments were performed on MoSi samples with focused ion beam...
The nature of the experimentally-measured fractional conductance plateau at filling 5/2 in Quantum Hall states remains an open question. After a decade of debate, the theoretical consensus settled on the non-Abelian Antipfaffian while recent experimental results measured an incompatible quantized thermal conductance of 5/2.
We revisit previous theoretical approaches with a more careful...
While the topological classification of non-interacting spin excitation band structures has successfully been applied to understand many magnetic insulators, intrinsic magnon-magnon interactions can modify the topological properties significantly. Using a coupled wire approach, we show that the system of weakly coupled spin chains with modulated Dzyaloshinskii-Moriya coupling strengths can be...
The simulation of strongly-correlated quantum many-body systems is a long-standing numerical challenge. Although the ground-state properties of one-dimensional systems may be efficiently distilled using the density matrix renormalization group, now understood in the framework of matrix product states, generalizing this procedure to higher dimensions is problematic, since the exact evaluation...
Most proposals to realize topological superconductivity rely on exploiting the properties of a topologically trivial superconductor through the proximity effect. An alternate route is to search for systems where the pairing interaction directly gives rise to topologically non-trivial superconductivity. We show that magnon-mediated superconductivity in heterostructures of transition metal...
We utilized pressure-tuned and ultra-low-temperature muon-spin spectroscopy to uncover the unconventional nature of superconductivity in kagome metals (Rb,K)V$_{3}$Sb$_{5}$[1,2]. At ambient pressure, the superconducting state displays a nodal energy gap and a reduced superfluid density, which is attributed to the competition with the charge order. Upon applying pressure, the charge-order is...
The rich interplay of unconventional superconductivity and symmetry-breaking states lies at the frontier of physics and materials science. Here we report muon spin rotation (${\mu}$SR) experiments of the magnetic impurity effect on the superconducting and normal state properties in the prototypical kagome superconductor LaRu$_{3}$Si$_{2}$. In the normal state, zero-field ${\mu}$SR experiments...
Localized or propagating Majorana boundary modes are the key feature of topological superconductors. Lattices of Yu-Shiba-Rusinov bound states – Shiba lattices – that arise when magnetic adatoms are placed on the surface of a conventional superconductor can be used to create topological bands within the superconducting gap of the substrate. I will discuss results using scanning tunnelling...
The Little-Parks effect, the periodic change in the critical temperature upon threading magnetic flux through a superconducting cylinder, exhibits a maximum or a minimum at zero flux in the presence of time-reversal symmetry. The latter situation, referred to as $\pi$ rings, is only expected for polycrystalline rings of an unconventional superconductor. Interestingly, recent measurements of...
Some aspects concerning coherence in open quantum systems remain poorly understood. On the one hand, coherence leads to entanglement and nonlocality. On the other, it leads to a suppression of fluctuations, causing violations of classical thermo-kinetic uncertainty relations. These represent its different manifestations, one depending only on the state of the system and one depending on...
We show how data can be denoised via a deep convolutional neural network such that weak signals appear with quantitative accuracy. In particular, we study X-ray diffraction on crystalline materials. We demonstrate that weak signals stemming from charge ordering, insignificant in the noisy data, become visible and accurate in the denoised data. This success is enabled by supervised training of...
Ultrasound techniques offer a simple and efficient method for studying quantum matter as they are able to detect subtle changes to symmetry and are also sensitive to lattice-spin/charge coupling. There are two distinct measurement paradigms used for ultrasonic studies: Whereas RUS provides a comprehensive view of the elastic tensor of solids, PEUS measures changes in sound wave attenuation and...
We report an infrared ellipsometry study of the charge carrier dynamics in polycrystalline Kxp-terphenyl samples with nominal x = 3, for which signatures of high-temperature superconductivity were previously reported. A dc resistivity of about 0.3 Ω·cm at 300 K is deduced from the IR data, comparable to values measured by electrical resistivity on a twin sample. Our data might still be...
Transition metal dichalcogenides like molybdenum disulphide (MoS2) have been studied on metal surfaces, but little is known about twist angle-dependent electronic properties of these simple heterostructures, which indeed offers tremendous opportunities to design functional quantum materials. In this talk, we present a detailed scanning tunnelling microscopy and spectroscopy investigation of...
High-field Inelastic Neutron Scattering experiments have been conducted on SrCu$_2$(BO$_3$)$_2$ up to 25.9T and we find a rich set of excitations whose energies and spectral intensities have been measured as a function of magnetic field. Using cylinder matrix-product-states calculations on the Shastry-Sutherland model with Dzyaloshinskii–Moriya interactions, we reproduce experimental spectra. ...
Electron ptychography has demonstrated the world-record highest resolution in imaging two-dimensional materials such as transition metal dichalcogenides (TMD). We are investigating the possibility of applying electron ptychography-related techniques for three-dimensional reconstruction of atomic positions and the associated resolution limits.
Low dimensional materials (1D and 2D) are promising candidates as building blocks of future electronics and optoelectronics. Controllable bandgap, strong light-matter interaction, sub-nanometer thickness, and high carrier mobility are among their favorable properties for electronic and optical applications. Comprehensive characterization of these materials is a crucial learning step toward...
Fiber-reinforced silicon carbide composite materials are promising candidates for applications in the aerospace industries as well as future energy sources (fusion and fission). They have structural as well as functional applications. These composites were previously analyzed by methods of neutron scattering and neutron tomography. Recently synchrotron X-ray phase contrast micro-tomography has...
Chemical synthesis of colloidal nanocrystals (NCs) can produce particles with controlled sizes and complex shapes, which influence their physical properties. For controlling the NCs’ morphology, the 3D shape analysis of NCs is a key issue. Small angle X-ray scattering (SAXS) is a leading technique for analyzing NCs in sub-nanometer resolution. From SAXS data the 3D mean shape can be retrieved...
Designing materials with tailormade thermal properties is crucial in developing energy-efficient devices. [1] Superlattices (SLs), which are artificially layered superstructures with periodic repetition of two or more materials, offer a promising approach for controlling thermal properties through the modification of the phonon spectrum. To control heat flow, we must manipulate the phonons at...
Squaraines are a class of organic chromophores which are particularly well-suited as molecular aggregates. Their structure-functionality relashipship allowes one to manipulate optical properties through the adjustment of side chains. SQIB is investigated via femtosecond transient absorption microscopy in an amorphous PMMA matrix and in its orthorhombic molecular crystal form with four...
The equilibrium tunning of doping generates substantial changes in the electronic states of cuprates. They undergo a gradual transition from Mott insulator to Fermi liquid, crossing d-wave superconductivity. Usually, these changes are accompanied by an abrupt transformation in Fermi surface topology, the so-called Lifshitz transition. Here in this work, we address the effect of ultrashort...
Blue Bronze ($K_{0.3}MoO_3$) is a quasi 1D material exhibiting a charge density wave with a periodic lattice distortion (PLD). In a time resolved x-ray experiment at SwissFEL, we study the dynamics of the PLD by pumping $K_{0.3}MoO_3$ with short laser pulses and probing it using x-ray diffraction. We construct reciprocal space maps (RSM) of superlattice reflections at different delays. The RSM...
None zero Berry curvature in condensed matter is the fundamental concept behind the unique responses topological materials exhibit. We report intrinsic spin fluctuations to be enough to realise anomalous hall effect (AHE) in PrGeAl. PrGeAl is a topological ferromagnet and is stabilised in a none centosymmetric structure. Based on muon spin relaxation, transport, angle resolved photo emission...
We conducted a resonant inelastic X-ray scattering (RIXS) experiment at the O-K edge on $\mathrm{La_{1.675}Eu_{0.2}Sr_{0.125}CuO_{4}}$, leveraging RIXS's high resolution to study charge density wave (CDW) and its interaction with phonons in cuprate superconductor. Three phonon modes are detected in the RIXS spectra, which are assigned to the bond-stretching, bond-buckling, and an acoustic...
We studied the d-d excitations in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ by Cu L$_3$-edge Resonant Inelastic X-ray Scattering with azimuthal rotation of the polarizations in the sample space, and analyzed the experimental response with a single cluster model. Utilizing group theory classification to incorporate two-hole Coulomb interactions via a Green's function approach, the calculations suggest that...
Layered two-dimensional (2D) semiconductors such as the transition metal dichalcogenides molybdenum disulfide (MoS$_2$) or tungsten disulfide (WS$_2$) offer promising properties for being used as a channel in electronic devices. For example, their atomic thinness and their sizable mobilities allow to fabricate highly scaled field-effect transistors (FETs) with excellent gate control or their...
