Recently, interest in developing efficient, low-cost, nontoxic, and stable metal halide emitters that can be incorporated into solid-state lighting technologies has taken hold. Here we report nontoxic, stable, and highly efficient blue-light-emitting Cs3Cu2Br5–x I x (0 ≤ x ≤ 5). Room-temperature photoluminescence measurements show bright blue emission in the 456 to 443 nm range with near-unity quantum yield for Cs3Cu2I5. Density functional theory calculations and power-dependent PL measurements suggest that the emission results from self-trapped excitons induced by strong charge localization within the zero-dimensional cluster structure of Cs3Cu2Br5–x I x .

Slow intrinsic fluctuations of resistance, also known as the flicker noise or 1/f-noise, in the surface transport of strong topological insulators (TIs) is a poorly understood phenomenon. Here, we have systematically explored the 1/f-noise in field-effect transistors (FET) of mechanically exfoliated Bi1.6Sb0.4Te2Se TI films when transport occurs predominantly via the surface states. We find that the slow kinetics of the charge disorder within the bulk of the TI induces mobility fluctuations at the surface, providing a new source of intrinsic 1/f-noise that is unique to bulk TI systems. At small channel thickness, the noise magnitude can be extremely small, corresponding to the phenomenological Hooge parameter γH as low as ≈10(-4), but it increases rapidly when channel thickness exceeds ∼1 μm. From the temperature (T)-dependence of noise, which displayed sharp peaks at characteristic values of T, we identified generation-recombination processes from interband transitions within the TI bulk as the dominant source of the mobility fluctuations in surface transport. Our experiment not only establishes an intrinsic microscopic origin of noise in TI surface channels, but also reveals a unique spectroscopic information on the impurity bands that can be useful in bulk TI systems in general.

Magnetic and dielectric properties of the double perovskite HoNiMnO are reported. The compound is synthesized by nitrate route and is found to crystallize in monoclinic P2/n space group. Lattice parameters obtained by refining powder x-ray diffraction data are; a  =  5.218(2) Å, b  =  5.543(2) Å, c  =  7.480(3) Å and the monoclinic angle is [Formula: see text](4). A phase transition is observed at [Formula: see text] K in the temperature-dependent magnetization curve, M(T). The inverse magnetic susceptibility, (1/[Formula: see text]) fits reasonably well with modified Curie-Weiss law by incorporating the paramagnetic response of Ho. 1/[Formula: see text] manifests as an upward deviation from ideal Curie-Weiss behaviour well above the ferromagnetic transition. Signs of inherent Griffiths phase pertaining to the Ni/Mn subsystem are visible when one subtracts the Ho paramagnetic contribution from total susceptibility and does the power-law analysis. The magnetic hysteresis at 2 K gives the maximum value of magnetization [Formula: see text] [Formula: see text]/f.u. at 50 kOe. Field-derivative of magnetization at 2 K shows discontinuities which indicates the existence of metamagnetic transitions in this compound. This needs to be probed further. Out of the two dielectric relaxations observed, the one at low temperature may be attributed to phononic frequencies and that at higher temperature may be due to Maxwell-Wagner relaxation. A correlation between magnetic and lattice degrees of freedom is plausible since the anomaly in dielectric constant coincides with T .

A mechanically robust, novel sandwich architecture with intriguing electrical properties and tunable dielectric properties as a function of MgTiO3 loading within the PVDF matrix was fabricated.

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A key feature of disordered topological insulators (TI) is symplectic symmetry of the Hamiltonian which changes to unitary when time reversal symmetry is lifted and the topological phase transition occurs. However, such a crossover has never been explicitly observed, by directly probing the symmetry class of the Hamiltonian. In this report, we have probed the symmetry class of topological insulators by measuring the mesoscopic conductance fluctuations in the TI Bi1.6Sb0.4Te2Se, which shows an exact factor of two reduction on application of a magnetic field due to crossover from symplectic to unitary symmetry classes. The reduction provides an unambiguous proof that the fluctuations arise from the universal conductance fluctuations (UCF), due to quantum interference and persists from T ∼ 22 mK to 4.2 K. We have also compared the phase breaking length l φ extracted from both magneto-conductivity and UCF which agree well within a factor of two in the entire temperature and gate voltage range. Our experiment confirms UCF as the major source of fluctuations in mesoscopic disordered topological insulators, and the intrinsic preservation of time reversal symmetry in these systems.Topological insulators [1-4] at zero magnetic field are time reversal invariant systems characterized by surface states with a linear band structure. The Hamiltonian for such surface states is described by H = v F − → σ · − → k which belongs to the AII/symplectic universality class, where v F , σ, and k are the Fermi velocity, spin matrices, and momentum respectively. This is also known as the Anderson universality class for non-relativistic particles in the presence of a random spin-orbit coupling where time reversal symmetry (TRS) is preserved [5]. The addition of an external magnetic field or ferromagnetic impurities introduce a Zeeman/orbital term in the Hamiltonian and breaks the TRS which results in a topological to trivial phase transition in the bulk states and manifests as a gap opening in the linear surface states [3]. In terms of random matrix theory, this crossover at the surface states is well described by a crossover from AII/symplectic to A/unitary class in the system. Experimentally, the sensitivity of transport to magnetic impurities [6,7] or the saturation of the phase breaking length at low temperatures are directly connected to the TRS in TI systems [8,9]. This makes an explicit demonstration of the symplectic to unitary crossover an important task, which has however, not been achieved yet.One direct method to probe such crossover of symmetry classes is universal conductance fluctuations (UCF) [10][11][12], which is observed in mesoscopic devices, when the length of the sample L becomes comparable to l φ , the phase breaking length. UCF is an effect which results from quantum interference of all possible electron paths traversed between two points in a sample making the electrical conduction sensitive to the Fermi energy, magnetic field and impurity configuration. These fluctuations are * isaurav@iisc.ac.in independent of th...

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*Implementing topological insulators as elementary units in quantum technologies requires a comprehensive understanding of the dephasing mechanisms governing the surface carriers in these materials, which impose a practical limit to the applicability of these materials in such technologies requiring phase coherent transport. To investigate this, we have performed magneto-resistance (MR) and conductance fluctuations (CF) measurements in both exfoliated and molecular beam epitaxy grown samples. The phase breaking length (l φ ) obtained from MR shows a saturation below sample dependent characteristic temperatures, consistent with that obtained from CF measurements. We have systematically eliminated several factors that may lead to such behavior of l φ in the context of TIs, such as finite size effect, thermalization, spin-orbit coupling length, spin-flip scattering, and surface-bulk coupling. Our work indicates the need to identify an alternative source of dephasing that dominates at low T in topological insulators, causing saturation in the phase breaking length and time./h) B (T) -60 0 60 120 6 8 10 6 8 10 V G (V) R EXF (K:) R MBE (K:) 10 …m (b) (a) Figure 1. Quantum transport in topological insulator FETs. (a) Typical R -VG for exfoliated TI (R EXF ) TBN11 and epitaxially grown TI (R M BE ) M10 at 20mK. Inset: optical micrograph of a typical exfoliated TI FET (b) Weak-antilocalisation behavior observed in different samples at T = 300 mK. The solid black lines are fits to the data using Eq. 1.Topological insulators (TIs) [1-4] are a new class of materials characterized by the presence of gapless and linearly dispersing metallic surface states present in the bulk band gap due to non-trivial topology of the bulk band structure. The surface carriers are prohibited from back-scattering against non-magnetic impurities and exhibit a plethora of fundamentally important effects such as spin-momentum locking, hosting Majorana fermions in the presence of a superconductor, topological magnetoelectric effect, and quantum anomalous Hall effect [1,5]. The topological protection of these surface states makes these materials a strong contender for the building blocks of qubits, which require long phase coherence length (l φ ) * isaurav@iisc.ac.in; SI and SB contributed equally for error tolerant quantum computation. Hence, it is critical to understand the mechanisms responsible for dephasing or decoherence, which is equivalent to loss of information, in the surface states of TIs. The most common dephasing mechanism in TIs at low temperature (T ) has been known to be electron-electron interaction [6][7][8][9][10], and the coupling of the surface states to localized charged puddles in the bulk [11]. Li et al. have demonstrated that electron-phonon interaction is also required to explain the dependence of l φ on T [12]. Although theoretically, all these mechanisms lead to a diverging l φ with decreasing T [6,7,13,14], experimentally, the increase of l φ with reducing T is often followed by its saturation for T ≤ 2 − 5 K [11,12,15,16...