Dirac semimetals (DSMs), characterized by linear dispersion relations in their electronic band structure, have gained prominence due to their unique topological features and potential applications in electronic devices. Through systematic calculation, we explore the electronic structure evolution of KCdP under varying negative pressure conditions. Our findings reveal a compelling transition from a normal semiconductor to a triple point semimetal when spin-orbit coupling (SOC) is not introduced, whereas in the SOC case, it converts into a Dirac semimetallic state in KCdP under negative triaxial pressure. The electronic band structure exhibits distinct Dirac cones at the Fermi level, indicating the presence of massless Dirac fermions. Moreover, the negative pressure-induced Dirac semimetallic phase in this compound is found to be robust and is protected by crystal symmetry. We provide a symmetry analysis of the bandgap, Fermi surface, Fermi velocity, and other relevant electronic properties, offering insights into the pressure-driven phase transition in KCdP. The tunability of this material under external pressure suggests the potential utility in next-generation electronic devices and quantum technologies.

Nodal line semimetals represent precursor states for various topological phases, exhibiting intrinsic topological characteristics and intriguing properties. These materials host rare and distinctive topological features, which can give rise to exotic phenomena, thereby garnering significant attention in both fundamental research and technological applications. In this study, we conduct ab-initio calculations to explore the properties of SrCaX (X = Bi, Sb, As, P), identifying these as multiple Dirac nodal line semimetals protected by Z2 quantized Berry phases and manifesting multiple drum-head-like surface states. The nodal lines in these compounds are situated at the M point when kz = 0 and at the A point when kz = π. Notably, SrCaX family exhibits a unique characteristic wherein they host both type II Dirac point and topological nodal line semimetal within a single crystal structure, hence providing an excellent platform for studying the interplay between different topological properties. Additionally, in SrCaP topological Dirac semimetal, Type II Dirac point and topological nodal line semimetal features coexist in a single crystal. These special features in this series of materials make them ideal candidates for further investigation by experimental means.

A quest for phenomenological footprints of quantum gravity is among the central scientific tasks in the rising era of gravitational wave astronomy. We study gravitational wave dynamics within the noncommutative geometry framework, based on a Drinfeld twist and newly proposed noncommutative Einstein equation, and obtain the leading quantum correction to Regge-Wheeler potential up to first order in the noncommutativity parameter. By calculating the quasinormal mode frequencies we show that the noncommutative Schwarzschild black hole remains stable under axial gravitational perturbations.

Abstract We study the noncommutative corrections to the entropy of the Reissner-Nordström black hole using a κ-deformed scalar probe within the brick-wall framework. The noncommutativity is encoded in an Abelian Drinfeld twist constructed from the Killing vector fields of the Reissner-Nordström black hole. We show that the noncommutative effects naturally lead to a logarithmic correction to the Bekenstein-Hawking entropy even at the lowest order of the WKB approximation. In contrast, such logarithmic corrections in the commutative setup appear only after the quantum effects are included through higher order WKB corrections or through higher loop effects. Our analysis thus provides further evidence towards the hypothesis that the noncommutative framework is capable of encoding at least some quantum effects in curved spacetime, although additional contributions will appear when the NC effects are fully incorporated in a gravity theory.

Using DFT-based first-principles calculations, we demonstrate the tuning of the electronic structure of Weyl semimetal SrSi2 via external uniaxial strain. The uniaxial strain facilitates the opening of bandgap along Γ-X direction and subsequent band inversion between Si p and Sr d orbitals. Z2 invariants and surface states reveal conclusively that SrSi2 under uniaxial strain is a strong topological insulator. Hence, uniaxial strain drives the semimetallic SrSi2 into fully gapped topological insulating state depicting a semimetal to topological insulator phase transition. Our results highlight the suitability of uniaxial strain to gain control over the topological phase transitions and topological states in SrSi2.

Composite quantum compounds (CQCs) have emerged as a key tool for examining the interactions between two different physical phenomena. Some of these CQCs that have lately received a lot of community attention are topological superconductors and axion insulators, among others. Despite being two distinct quantum phenomena, Rashba spin physics and topological nontriviality can coexist in a CQC platform. In this work, we have performed ab initio calculations to discover materials that inherit both giant Rashba splitting and topological nontrivial states in a single crystalline system, coined as intrinsic CQCs. In this regard, we have investigated two materials, RbSnBi and CsSnBi, that are found to be strong topological insulators along with giant Rashba splitting energy in valence bands (133 and 228 meV, respectively) with Rashba coefficient alpha R to be 4.26 and 6.4 eV angstrom, respectively. These values of alpha R are quite large, and the Rashba coefficient of CsSnBi is the largest, corresponding to valance bands, among previously reported topological materials. Coexisting characteristics of Rashba spin physics and topological nontriviality have the potential to unveil new physical phenomena. For both RbSnBi and CsSnBi, the topological insulating state is found to be associated with coexisting multiple band inversion and multiple Dirac surface states.

The topological semimetals (TSMs) are the electronic gap-less phases with topological band crossing near the Fermi-level and have attracted a lot of attention from researchers in recent years. In this work, we have identified topological Dirac semimetallic phase in hexagonal NaHgAs and NaHgBi via first-principles DFT calculations. We have studied structural, electronic, elastic, mechanical, thermodynamic and topological properties of NaHgX (X = As, Sb and Bi) without and with application of external uniaxial strain. Our findings reveal that NaHgAs is a Dirac semi metal (DSM) in its ground state as well as in strained state, while NaHgBi is DSM only in its strained state. The elastic constants and mechanical properties of NaHgX (X = As, Sb and Bi) were also calculated and it was found that only NaHgAs and NaHgBi are mechanically and thermodynamically stable.

The quantum dynamics of isolated systems under quench condition exhibits a variety of interesting features depending on the integrable/chaotic nature of system. We study the exact dynamics of trivially integrable system of harmonic chains under a multiple quench protocol. Out of time ordered correlator of two Hermitian operators at large time displays scrambling in the thermodynamic limit. In this limit, the entanglement entropy and the central component of momentum distribution both saturate to a steady-state value. We also show that reduced density matrix assumes the diagonal form long after multiple quenches for large system size. These exact results involving infinite-dimensional Hilbert space are indicative of dynamical equilibration for a trivially integrable harmonic chain.

Some observable consequences that follow from a fiber bundle description of a tight binding condensed matter system on a lattice are described. The geometrical picture can be extended to describe non-periodic lattice structures, where a single Brillouin zone is predicted.

We show that a noncommutative massless scalar probe can dress a naked singularity in AdS3 spacetime, consistent with the weak cosmic censorship. The dressing occurs at high energies, which is typical at the Planck scale. Using a noncommutative duality, we show that the dressed singularity has the geometry of a rotating BTZ black hole which satisfies all the laws of black hole thermodynamics. We calculate the entropy and the quasi-normal modes of the dressed singularity and show that the corresponding spacetime can be quantum mechanically complete. The noncommutative duality also gives rise to a light scalar, which can be relevant for early universe cosmology.

We show that the N-particle Sutherland model with inverse-square and harmonic interactions exhibits orthogonality catastrophe. For a fixed value of the harmonic coupling, the overlap of the N-body ground state wave functions with two different values of the inverse-square interaction term goes to zero in the thermodynamic limit. When the two values of the inverse-square coupling differ by an infinitesimal amount, the wave function overlap shows an exponential suppression. This is qualitatively different from the usual power law suppression observed in the Anderson's orthogonality catastrophe. We also obtain an analytic expression for the wave function overlaps for an arbitrary set of couplings, whose properties are analyzed numerically. The quasiparticles constituting the ground state wave functions of the Sutherland model are known to obey fractional exclusion statistics. Our analysis indicates that the orthogonality catastrophe may be valid in systems with more general kinds of statistics than just the fermionic type.

Recently unusual properties of water in single-walled carbon nanotubes (CNT) with diameters ranging from 1.05 nm to 1.52 nm were observed. It was found that water in the CNT remains in an ice-like phase even when the temperature ranges between 105 - 151 C and 87 - 117 C for CNTs with diameters 1.05 nm and 1.06 nm respectively. Apart from the high freezing points, the solid-liquid phase transition temperature was found to be strongly sensitive to the CNT diameter. In this paper we show that water in such CNT's can admit coherent nanoscale structures provided certain conditions are met. The formation of such coherent structures allows for high values of solid-liquid phase transition temperatures that are in qualitative agreement with the empirical data. The model also predicts that the phase transition temperature scales inversely with the square of the effective radius available for the water flow within the CNT. This is consistent with the observed sensitive dependence of the solid-liquid phase transition temperature on the CNT diameter.

We analyze the fermionic quasinormal modes of the BTZ black hole in the presence of space-time noncommutativity. Our analysis exploits a duality between a spinless and spinning BTZ black hole, the spin being proportional to the noncommutative deformation parameter. Using the AdS/CFT correspondence we show that the horizon temperatures in the dual CFT are modified due to noncommutative contributions. We demonstrate the equivalence between the quasinormal and non-quasinormal modes for the noncommutative fermionic probes, which provides further evidence of holography in the noncommutative setting. Finally we present an analysis of the emission of Dirac fermions and the corresponding tunneling amplitude within this noncommutative framework.

We present an exact and fully analytical treatment of the entanglement dynamics for an isolated system of N coupled oscillators following a sudden quench of the system parameters. The system is analyzed using the solutions of the time dependent Schrodinger's equation, which are obtained by solving the corresponding nonlinear Ermakov equations. The entanglement entropies exhibit a multi-oscillatory behaviour, where the number of dynamically generated time scales increases with N. The harmonic chains exhibit entanglement revival and for larger values of N (> 10), we find near-critical logarithmic scaling for the entanglement entropy, which is modulated by a time dependent factor. The N=2 case is equivalent to the two site Bose-Hubbard model in the tunneling regime, which is amenable to empirical realization in cold atom systems.

Spectral line widths, the Lamb shift and the Casimir effect are generally accepted to be observable consequences of the zero-point electromagnetic (ZPEM) fields. A new class of observable consequences of ZPEM field at the mesoscopic scale were recently proposed and observed. Here, we extend this class of observable effects and predict that mesoscopic water layers should have a high value for its solid–liquid phase transition temperature, as illustrated by water inside a single-walled carbon nanotube (CNT). For this case, our analysis predicts that the phase transition temperature scales inversely with the square of the effective radius available for the water flow within the CNT.

We show that the realizations of noncommutative coordinates that are linear in the Lorentz generators form a closed Lie algebra under certain conditions. The star product and the coproduct for the momentum generators are obtained for these Lie algebras and the corresponding twist satisfies the cocycle and normalization conditions. We also obtain the twisted flip operator and the R-matrix that define the statistics of particles or quantum fields propagating in these noncommutative spacetimes. The Lie algebra obtained in this work contains a special case which has been used in the literature to put bounds on noncommutative parameters from the experimental limits on Pauli forbidden transitions. The general covariant framework presented here is suitable for analyzing the properties of particles or quantum fields at the Planck scale.

We analyze the effects of noncommutativity in conformal quantum mechanics (CQM) using the κ-deformed space–time as a prototype. Up to the first order in the deformation parameter, the symmetry structure of the CQM algebra is preserved but the coupling in a canonical model of the CQM gets deformed. We show that the boundary conditions that ensure a unitary time evolution in the noncommutative CQM can break the scale invariance, leading to a quantum mechanical scaling anomaly. We calculate the scaling dimensions of the two and three point functions in the noncommutative CQM which are shown to be deformed. The AdS2/CFT1 duality for the CQM suggests that the corresponding correlation functions in the holographic duals are modified. In addition, the Breitenlohner–Freedman bound also picks up a noncommutative correction. The strongly attractive regime of a canonical model of the CQM exhibit quantum instability. We show that the noncommutativity softens this singular behaviour and its implications for the corresponding holographic duals are discussed.

An observable influence of zero-point fluctuations of the vacuum electromagnetic field on bound electrons is well known in the hydrogen atom, where it produces the Lamb shift. Here, we adapt an approach used to explain the Lamb shift in terms of a slight expansion of the orbits due to interaction with the zero-point field and apply it to assemblies of N electrons that are modeled as independent atomically bound two-level systems. The effect is to stabilize a collective ground-state energy, which leads to a prediction of novel effects at room temperature for quasi-two-dimensional systems over a range of parameters in the model, namely, N, the two-level excitation energy (h) over bar omega and the ionization energy (h) over bar omega + epsilon. Some mesoscopic systems where these effects may be observable include water sheaths on protein or DNA, surfaces of gaseous nanobubbles, and themagnetic response of inhomogeneous, electronically dilute oxides. No such effects are envisaged for uniform three-dimensional systems.