arXiv subjects

Lior Verbitsky

Publications and source records attributed to Lior Verbitsky.

3 recordsLinked to original sources

arXiv2026

New Superconductors in the PtPb$_3$Bi Structure Type

The quest for new superconductors is of both fundamental and technological importance. Recently, an artificial intelligence method correctly predicted PtPb$_3$Bi to be a superconductor. In this work, we find superconductivity in the newly synthesized $M$Pb$_{4-x}$Bi$_x$ ($M$ = Au, Pd, and Rh), of which PtPb$_3$Bi is a member. When $M$ = Ni, whose radius is considerably smaller, the structure instead collapses into the different, Pb-substituted NiBi$_3$ type. Interestingly, the stoichiometric parameter $x$ shifts across the three compounds to keep the total valence electron count close to 20 per formula unit. The superconducting transitions occur at 4.9, 4.2, and 3.4 K, for $M$ = Au, Pd, and Rh, respectively. Using electrical resistivity, magnetization, and specific heat measurements, we establish the bulk nature of the superconducting state and determine the critical fields, characteristic length scales, and anisotropy ratios. All three compounds are moderately anisotropic type-II superconductors, with modest upper critical field anisotropies of $H_{c2}^{\parallel c}/H_{c2}^{\perp c} \approx 1.2$ to $1.5$. These results establish $M$Pb$_{4-x}$Bi$_x$ as a family of anisotropic superconductors and a platform for studying how site disorder and Pb-Bi mixing govern superconductivity in heavy-element intermetallics.

cond-mat.supr-con↗

arXiv2026

From interface-limited to Auger-dominated carrier dynamics in $\pi$-SnS

Metastable cubic tin(II) sulfide ($\pi$-SnS) is an earth-abundant semiconductor whose three-dimensionally bonded chiral lattice may overcome the short minority-carrier lifetime of orthorhombic SnS while maintaining a near-ideal bandgap for tandem photovoltaics. Despite its promise, ultrafast carrier cooling and recombination mechanisms over illumination density remain poorly constrained. We use core-level extreme-ultraviolet attosecond transient absorption spectroscopy at the Sn $4d$ edge to track carrier injection, cooling, and recombination in $\pi$-SnS with element- and orbital-specific sensitivity. Following femtosecond near-infrared excitation, the Sn $4d\rightarrow$CB onset exhibits conduction-band state filling and a carrier-induced edge shift, enabling extraction of density-dependent kinetics. The transient response follows a biexponential decay with a fast hot-carrier cooling component and a slower recombination component. At low carrier densities, recombination is consistent with interface-limited processes, whereas above $\sim1\times10^{20}$ cm$^{-3}$ both cooling and recombination accelerate, indicating a crossover to carrier-carrier interaction-dominated dynamics. Coherent phonon oscillations with a period of $\sim188$ fs reveal coupling between electronic excitation and lattice motion. These results provide a comprehensive picture of nonequilibrium carrier and phonon dynamics in cubic SnS, reveal a change of mechanisms over a range of carrier densities, and establish the value of using attosecond transient absorption spectroscopy to study ultrafast processes in complex semiconductors that have optoelectronic and energy-conversion applications.

cond-mat.mtrl-sci↗

arXiv2023

Photon Correlations in Colloidal Quantum Dot Molecules Controlled by the Neck Barrier

We investigate the charge re-distribution upon optical excitation of various necked homodimer CQDMs using single particle emission spectroscopy. By tuning the hybridization of the electron wavefunction at a fixed center-to-center distance through controlling the neck girth, we reveal two coupling limits. On one hand a connected-but-confined situation where neighbouring CQDs are weakly fused to each other manifesting a weak coupling regime, and on the other hand, a connected-and-delocalized situation, where the neck is filled beyond the facet size leading to a rod-like architecture manifesting strong-coupling. Either coupling regimes entrust distinct optical signatures clearly resolved at room temperature in terms of photoluminescence quantum yield, intensity time traces, lifetimes, and spectra of the neutral-exciton, charged-exciton, and biexciton states. The interplay between the radiative and non-radiative Auger decays of these states, turns emitted photons from the CQDMs in the weak-coupling regime highly bunched unlike CQD monomers, while the antibunching is regained at the strong-coupling regime. This behavior correlates with the hybridization energy being smaller than the thermal energy (kT approx. 25meV) at the weak-coupling limit (delta E approax.5-10meV), leading to exciton localization suppressing Auger decay. In the neck-filled architectures, the larger hybridization energy (delta E approx.20-30meV) leads to exciton delocalization while activating the fast charged and multi-exciton Auger decay processes. This work sets an analogy for the artificial molecule CQDMs with regular molecules, where the two distinct regimes of weak- and strong-coupling correspond to ionic- or covalent- type bonding, respectively.

cond-mat.mes-hall↗