Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOrigin of the dome-shaped superconducting phase diagram in $mathrm{SrTiO}_3$-based interfaces
442
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A dome-shaped phase diagram of superconducting critical temperature upon doping is often considered as a hallmark of unconventional superconductors. This behavior, observed in two-dimensional electron gases in $mathrm{SrTiO}_3$-based interfaces whose electronic density is controlled by field effect, has not been explained unambiguously yet. Here, we elaborate a generic scenario for the superconducting phase diagram of these oxide interfaces based on Schrodinger-Poisson numerical simulations of the quantum well and transport experiments on a double-gate field-effect device. We propose that the optimal doping point of maximum $T_c$ marks the transition between a single-band and a fragile two-gap s$pm$-wave superconducting state involving $t_{2g}$ bands of different orbital character. At the optimal doping point, we predict and observe experimentally a bifurcation in the dependence of $T_c$ on the carrier density, which is controlled by the details of the doping execution. Where applying a back-gate voltage triggers the filling of a high-energy $d_mathrm{xy}$ subband and initiates the overdoped regime, doping with a top-gate delays the filling of the subband and maintains the 2-DEG in the single-band superconducting state of higher $T_c$.
rate research
Read More
We measure the gate voltage ($V_g$) dependence of the superconducting properties and the spin-orbit interaction in the (111)-oriented LaAlO$_3$/SrTiO$_3$ interface. Superconductivity is observed in a dome-shaped region in the carrier density-temperature phase diagram with the maxima of superconducting transition temperature $T_c$ and the upper critical fields lying at the same $V_g$. The spin-orbit interaction determined from the superconducting parameters and confirmed by weak-antilocalization measurements follows the same gate voltage dependence as $T_c$. The correlation between the superconductivity and spin-orbit interaction as well as the enhancement of the parallel upper critical field, well beyond the Chandrasekhar-Clogston limit suggest that superconductivity and the spin-orbit interaction are linked in a nontrivial fashion. We propose possible scenarios to explain this unconventional behavior.
Infinite-layer Nd1-xSrxNiO2 thin films with Sr doping level x from 0.08 to 0.3 were synthesized and investigated. We found a superconducting dome to be between 0.12 and 0.235 which is accompanied by a weakly insulating behaviour in both underdoped and overdoped regimes. The dome is akin to that in the electron-doped 214-type and infinite-layer cuprate superconductors. For x higher than 0.18, the normal state Hall coefficient ($R_{H}$) changes the sign from negative to positive as the temperature decreases. The temperature of the sign changes monotonically decreases with decreasing x from the overdoped side and approaches the superconducting dome at the mid-point, suggesting a reconstruction of the Fermi surface as the dopant concentration changes across the center of the dome.
Using muon spin spectroscopy we have found that, for both Na$_x$CoO$_2$ (0.6 $leq x leq$ 0.9) and 3- and 4-layer cobaltites, a common low temperature magnetic state (which in some cases is manifest as an incommensurate spin density wave) forms in the CoO$_2$ planes. Here we summarize those results and report a dome-shaped relation between the transition temperature into the low-$T$ magnetic state and the composition $x$ for Na$_x$CoO$_2$ and/or the high-temperature asymptotic limit of thermopower in the more complex 3- and 4-layer cobaltites. This behavior is explained using the Hubbard model on two-dimensional triangular lattice in the CoO$_2$ plane.
Multiple experiments have observed a sharp transition in the band structure of LaAlO$_3$/SrTiO$_3$ (001) interfaces as a function of applied gate voltage. This Lifshitz transition, between a single occupied band at low electron density and multiple occupied bands at high density, is remarkable for its abruptness. In this work, we propose a mechanism by which such a transition might happen. We show via numerical modeling that the simultaneous coupling of the dielectric polarization to the interfacial strain (electrostrictive coupling) and strain gradient (flexoelectric coupling) generates a thin polarized layer whose direction reverses at a critical density. The Lifshitz transition occurs concomitantly with the polarization reversal and is first-order at $T=0$. A secondary Lifshitz transition, in which electrons spread out into semiclassical tails, occurs at a higher density.
A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials such as the cuprate high temperature superconductors. Because of its unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping-and-temperature dependence ARPES study of spectral gaps in Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$ (Bi-2212), covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p$=$0.19 for the pseudogap phase and p$=$0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below T$_c$ and exists p$>$0.19 at higher temperatures. Our data imply a revised phase diagram which reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
