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Polarization-resolved electronic Raman spectroscopy is an important experimental tool to investigate collective excitations in superconductors. In this work, we present a general theory that allows us to study the evolution of all Raman active collective modes in multiple symmetry channels across a time-reversal symmetry (TRS) breaking superconducting transition. This comprehensive approach reveals that multiple modes belonging to different symmetry channels show a tendency to soften, even when the interactions in the subleading channel are held constant. This indicates an increased competition induced by the proximity to the TRS breaking transition. The entry into the TRS broken phase is marked by the introduction of an additional mode into the gap in multiple symmetry channels. These new modes have a phase character complementary to the ones that are already present. Even though all the modes in the TRS broken phase acquire an amplitude character, we explicitly demonstrate that the coupling to the Raman probe is exclusively through the phase sector. We demonstrate that the Raman spectrum collected in lower symmetry channels shows a selective sensitivity to the sign of the ground state order parameters and the sign of the interband interactions. Finally, we demonstrate the applicability of an interaction induced selection rule that clearly explains the spectral weights of various modes in various irreps, including the possible of $``$dark$"$ Leggett and Bardasis-Schrieffer modes.

Electronic Raman scattering in the fully symmetric channel couples to the charge excitations in the system, including the plasmons. However, the plasmon response has a spectral weight of $\sim q^2$, where $q$, the momentum transferred by light, is small. In this work, we show that in inversion symmetry broken systems where Rashba type spin-orbit coupling affects the states at the Fermi energy (which is a known low energy effect) as well as the transition elements to other states (a high energy effect), there is an additional coupling of the plasmons to the Raman vertex, even at zero momentum transfer, that results in a spectral weight that is proportional to the spin-orbit coupling. The high energy effect is due to the breaking of SU(2) spin invariance in the spin-flip transitions to the intermediate state. We present a theory for this coupling near the resonant regime of Raman scattering and show that in giant Rashba systems it can dominate over the conventional $q^2$ weighted coupling. We also provide experimental support along with a symmetry based justification for this spin-mediated coupling by identifying a prominent c-axis plasmon peak in the fully symmetric channel of the resonant Raman spectrum of the giant Rashba material BiTeI. This new coupling could lead to novel ways of manipulating coherent charge excitations in inversion-broken systems. This process is also relevant for spectroscopic studies in ultrafast spectroscopies, certain driven Floquet systems and topologically non-trivial phases of matter where strong inversion-breaking spin-orbit coupling plays a role., Comment: 22p with 9 figures, replaced with journal version

We study the transport properties of a tight-binding model of non-interacting fermions with random hopping on the honeycomb lattice. At the particle-hole symmetric chemical potential, the absence of diagonal disorder (random onsite potentials) places the system in the well-studied chiral orthogonal universality class of disordered fermion problems, which are known to exhibit both a critical metallic phase and a dimerization-induced localized phase. Here, our focus is the behavior of the two-terminal conductance and the Lyapunov spectrum in quasi-1D geometry near the dimerization-driven transition from the metallic to the localized phase. For a staggered dimerization pattern on the square and honeycomb lattices, we find that the renormalized localization length $\xi/M$ ($M$ denotes the width of the sample) and the typical conductance display scaling behavior controlled by a crossover length-scale that diverges with exponent $\nu \approx 1.05(5)$ as the critical point is approached. However, for the plaquette dimerization pattern, we observe a relatively large exponent $\nu \approx 1.55(5)$ revealing an apparent non-universality of the delocalization-localization transition in the BDI symmetry class., Comment: 8+3 pages, 7 figures

Bipolar resistive switching using organic molecule is very promising for memory application owing to their advantages like simple device structure, low manufacturing cost, their stability and flexibility etc. Herein we report Langmuir-Blodgett and spin-coated film based bipolar resistive switching devices using organic material indole derivative. Pressure - area per molecule isotherm, Brewster Angle Microscopy, Atomic Force Microscopy and Scanning Electron Microscopy were used to have an idea about organization and morphology of the organic material onto thin film. Based on device structure and measurement protocol it is observed that the device made up of 1 shows non-volatile Resistive Random Access Memory behaviour with very high memory window, data sustainability and repeatability.Oxidation-reduction process as well as electric field driven conduction are the key behind such switching behaviour.Due to very good data retention, repeatability, stability and high device yield the switching device designed using compound 1may be a potential candidate for memory applications., Comment: 18 pages, 9 figures, 1 table

Organic electronics is very promising due to the flexibility, modifiability as well as variety of the available organic molecules. Efforts are going on to use organic materials for the realization of memory devices. In this regard resistive switching devices surely will play a key role. In this paper an effort has been made to illustrate the general information about resistive switching devices as well as switching mechanisms involving organic materials. As a whole a general overview of the emerging topic resistive switching has been given., Comment: 8 pages, 3 figures

We study the dynamics of a non-magnetic impurity interacting with the surface states of a 3D and 2D topological insulator. Employing the linked cluster technique we develop a formalism for obtaining the Greens function of the mobile impurity interacting with the low-energy Dirac fermions. We show that for the non-recoil case in 2D, similar to the case involving the parabolic spectrum, the Greens function in the long-time limit has a power-law decay in time implying the breakdown of the quasiparticle description of the impurity. The spectral function, in turn, exhibits a weak power-law singularity. In the recoil case, however, the reduced phase-space for scattering processes implies a non-zero quasiparticle weight and the presence of a coherent part in the spectral function. Performing a weak coupling analysis we find that the mobility of the impurity reveals a divergence at low temperatures. In addition, we show that the Greens function of an impurity interacting with the helical edge modes (surface states of 2D TI), exhibit power-law decay in the long-time limit for both the non-recoil and recoil case (with low impurity momentum), indicating the break down of the quasiparticle picture. However, for impurity with high momentum, the quasiparticle picture is restored. Using the Boltzmann approach we show that the presence of the magnetic field results in a power-law divergence of the impurity mobility at low-temperatures., Comment: 14 pages, 6 figures

We present a detailed study of the imaginary and real parts of the spin-susceptibility of silicene which can be generalized to other buckled honeycomb structure. We find that while the off-diagonal components are non-zero in individual valleys, they add up to zero upon including contributions from both the valleys. We investigate the interplay of the spin-orbit interaction and an external electric field applied perpendicular to the substrate and find that although the xx and yy components of the susceptibility are identical, they differ from the zz-component. The external electric field plays an important role in modifying the allowed inter-subband regions. In the dynamic limit, the real part of the susceptibility exhibits log-divergence, position of which can be tuned by the electric field and therefore has implications for spin-collective excitations. The effect of the electric field on the static part of the susceptibility and its consequence for the long distance decay of the spin-susceptibility have been explored.

We theoretically investigate the transport properties of a normal-insulator-superconductor (NIS) junction of silicene in the thin barrier limit. Similar to graphene the tunneling conductance in such NIS structure exhibits an oscillatory behavior as a function of the strength of the barrier in the insulating region. However, unlike in graphene, the tunneling conductance in silicene can be controlled by an external electric field owing to its buckled structure. We also demonstrate the change in behavior of the tunneling conductance across the NIS junction as we change the chemical potential in the normal silicene region. In addition, at high doping levels in the normal region, the period of oscillation of the tunneling conductance as a function of the barrier strength changes from $\pi/2$ to $\pi$ with the variation of doping in the superconducting region of silicene., Comment: 7 pages, 7 figures

We theoretically study the properties of thermal conductance in a normal-insulator-superconductor junction of silicene for both thin and thick barrier limit. We show that while thermal conductance displays the conventional exponential dependence on temperature, it manifests a nontrivial oscillatory dependence on the strength of the barrier region. The tunability of the thermal conductance by an external electric field is also investigated. Moreover, we explore the effect of doping concentration on thermal conductance. In the thin barrier limit, the period of oscillations of the thermal conductance as a function of the barrier strength comes out be $\pi/2$ when doping concentration in the normal silicene region is small. On the other hand, the period gradually converts to $\pi$ with the enhancement of the doping concentration. Such change of periodicity of the thermal response with doping can be a possible probe to identify the crossover from specular to retro Andreev reflection in Dirac materials. In the thick barrier limit, thermal conductance exhibits oscillatory behavior as a function of barrier thickness $d$ and barrier height $V_0$ while the period of oscillation becomes $V_0$ dependent. However, amplitude of the oscillations, unlike in tunneling conductance, gradually decays with the increase of barrier thickness for arbitrary height $V_0$ in the highly doped regime. We discuss experimental relevance of our results., Comment: This is the published vesion

We present a combined experimental-theoretical study demonstrating the role of site disorder, off-stoichiometry and strain on the optical behavior of magnetoelectric gallium ferrite. Optical properties such as band-gap, refractive indices and dielectric constants were experimentally obtained by performing ellipsometric studies over the energy range 0.8 eV to 4.2 eV on pulsed laser deposited epitaxial thin films of stoichiometric gallium ferrite with b-axis orientation and the data was compared with theoretical results. Calculations on the ground state structure show that the optical activity in GaFeO3 arises primarily from O2p-Fe3d transitions. Further, inclusion of site disorder and epitaxial strain in the ground state structure significantly improves the agreement between the theory and the room temperature experimental data substantiating the presence of site-disorder in the experimentally derived strained GaFeO3 films at room temperature. We attribute the modification of the ground state optical behavior upon inclusion of site disorder to the corresponding changes in the electronic band structure, especially in Fe3d states leading to a lowered band-gap of the material., Comment: 18 Pages, 6 figures