arXiv subjects

A. Ribak

Publications and source records attributed to A. Ribak.

6 recordsLinked to original sources

arXiv2022

Two-fluid dynamics in driven YBa$_2$Cu$_3$O$_{6.48}$

Coherent optical excitation of certain phonon modes in YBa$_2$Cu$_3$O$_{6+x}$ has been shown to induce superconducting-like interlayer coherence at temperatures higher than $T_c$. Recent work has associated these phenomena to a parametric excitation and amplification of Josephson plasma polaritons, which are overdamped above $T_c$ but are made coherent by the phonon drive. However, the dissipative response of uncondensed quasiparticles, which do not couple in the same way to the phonon drive, has not been addressed. Here, we investigate both the enhancement of the superfluid density, $ωσ_2(ω)$, and the dissipative response of quasiparticles, $σ_1(ω)$, by systematically tuning the duration and energy of the mid-infrared pulse while keeping the peak field fixed. We find that the photo-induced superfluid density saturates to the zero-temperature equilibrium value for pulses made longer than the phonon dephasing time, whilst the dissipative component continues to grow with increasing pulse duration. We show that superfluid and dissipation remain uncoupled as long as the drive is on, and identify an optimal regime of pump pulse durations for which the superconducting response is maximum and dissipation is minimized.

cond-mat.supr-con↗

arXiv2020

Link between superconductivity and a Lifshitz transition in intercalated Bi$_2$Se$_3$

Topological superconductivity is an exotic phase of matter in which the fully gapped superconducting bulk hosts gapless Majorana surface states protected by topology. Intercalation of copper, strontium or niobium between the quintuple layers of the topological insulator Bi$_2$Se$_3$ increases the carrier density and leads to superconductivity that is suggested to be topological. Here we study the electronic structure of strontium-intercalated Bi$_2$Se$_3$ using angle resolved photoemission spectroscopy (ARPES) and Shubnikov-de Haas (SdH) oscillations. Despite the apparent low Hall number of $\sim2 \times 10 ^{19}$cm$^{-3}$, we show that the Fermi surface is shaped as an open cylinder with a larger carrier density of $\sim 10 ^{20}$cm$^{-3}$. We suggest that superconductivity in intercalated Bi$_2$Se$_3$ emerges with the appearance of a quasi-2D open Fermi surface.

cond-mat.supr-con↗

arXiv2019

Parametrically amplified phase-incoherent superconductivity in YBa$_2$Cu$_3$O$_{6+x}$

The possibility of enhancing desirable functional properties of complex materials by optical driving is motivating a series of studies of their nonlinear terahertz response. In high-Tc cuprates, large amplitude excitation of certain infrared-active lattice vibrations has been shown to induce transient features in the reflectivity suggestive of non-equilibrium superconductivity. Yet, a microscopic mechanism for these observations is still lacking. Here, we report measurements of time- and scattering-angle-dependent second-harmonic generation in YBa$_2$Cu$_3$O$_{6+x}$, taken under the same excitation conditions that result in superconductor-like terahertz reflectivity. We discover a three-order-of-magnitude amplification of a 2.5-terahertz electronic mode, which is unique because of its symmetry, momentum, and temperature dependence. A theory for parametric three-wave amplification of Josephson plasmons, which are assumed to be well-formed below T$_c$ but overdamped throughout the pseudogap phase, explains all these observations and provides a mechanism for non-equilibrium superconductivity. More broadly, our work underscores the role of parametric mode mixing to stabilize fluctuating orders in quantum materials.

cond-mat.supr-con↗

arXiv2019

Chiral superconductivity in the alternate stacking compound 4Hb-TaS$_2$

Layered van der Waals (vdW) materials are emerging as one of the most versatile directions in the field of quantum condensed matter physics. They allow an unprecedented control of electronic properties via stacking of different types of two-dimensional (2D) materials. A fascinating frontier, largely unexplored, is the stacking of strongly-correlated phases of matter in vdW materials. Here, we study 4Hb-TaS$_2$, which naturally realizes an alternating stacking of a Mott insulator, recently reported as a gapless spin-liquid candidate(1T-TaS$_2$), and a 2D superconductor (1H-TaS$_2$). This raises the question of how these two components affect each other. We find a superconducting ground state with a transition temperature of 2.7K, which is significantly elevated compared to the 2H polytype (Tc=0.7K). Strikingly, the superconducting state exhibits signatures of time-reversal-symmetry breaking abruptly appearing at the superconducting transition, which can be naturally explained by a chiral superconducting state.

cond-mat.supr-con↗

arXiv2017

Gapless excitations in the ground state of 1T-TaS$_2$

1T-TaS$_2$ is a layered transition metal dichalgeonide with a very rich phase diagram. At T=180K it undergoes a metal to Mott insulator transition. Mott insulators usually display anti-ferromagnetic ordering in the insulating phase but 1T-TaS$_2$ was never shown to order magnetically. In this letter we show that 1T-TaS$_2$ has a large paramagnetic contribution to the magnetic susceptibility but it does not show any sign of magnetic ordering or freezing down to 20mK, as probed by $μ$SR, possibly indicating a quantum spin liquid ground state. Although 1T-TaS$_2$ exhibits a strong resistive behavior both in and out-of plane at low temperatures we find a linear term in the heat capacity suggesting the existence of a Fermi-surface, which has an anomalously strong magnetic field dependence.

cond-mat.str-el↗

arXiv2013

Evolution of the fermi surface of a doped topological insulator with carrier concentration

In an ideal bulk topological-insulator (TI) conducting surface states protected by time reversal symmetry enfold an insulating crystal. However, the archetypical TI, Bi2Se3, is actually never insulating; it is in fact a relatively good metal. Nevertheless, it is the most studied system among all the TIs, mainly due to its simple band-structure and large spin-orbit gap. Recently it was shown that copper intercalated Bi2Se3 becomes superconducting and it was suggested as a realization of a topological superconductor (TSC). Here we use a combination of techniques that are sensitive to the shape of the Fermi surface (FS): the Shubnikov-de Haas (SdH) effect and angle resolved photoemission spectroscopy (ARPES) to study the evolution of the FS shape with carrier concentration, n. We find that as n increases, the FS becomes 2D-like. These results are of crucial importance for understanding the superconducting properties of CuxBi2Se3.

cond-mat.mes-hall↗