اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدPossible two-component pairings in electron-doped Bi$_{2}$Se$_{3}$ based on a tight-binding model
56
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Recent experiments show the spontaneous breaking of rotational symmetry in the superconducting topological insulators M$_{x}$Bi$_{2}$Se$_{3}$ (M represents Cu, Sr, or Nd), suggesting that the pairing belongs to a two-dimensional representation of the $D_{3d}$ symmetry group of the crystal. Motivated by these progresses, we construct an exhaustive list of possible two-component pairings of the M$_{x}$Bi$_{2}$Se$_{3}$ superconductors, both for the odd-parity $E_{u}$ representation and for the even-parity $E_{g}$ representation. Starting from a tight-binding model for the normal phase of Bi$_{2}$Se$_{3}$ and M$_{x}$Bi$_{2}$Se$_{3}$, we firstly construct the pairing channels in the spin-orbital basis, up to second-nearest-neighbor pairing correlations in the basal plane. We then infer the properties of these pairings by transforming them to the band (pseudospin) basis for the conduction band. A comparison with the key experimental consensuses on M$_{x}$Bi$_{2}$Se$_{3}$ superconductors shows that the true pairings should also be multichannel. Besides a nematic and time-reversal symmetric pairing combination, the other pairings that we have identified are chiral and nematic at the same time, which may be nonunitary and have a spontaneous magnetization. A complementary set of experiments are proposed to identify the true pairing symmetries of these superconductors and their evolution with the doping concentration $x$.
قيم البحث
اقرأ أيضاً
Recent experiments suggest a multi-component pairing function in Sr2RuO4, which appears to be inconsistent with the absence of an apparent cusp in the transition temperature (Tc) as a function of the uniaxial strain. We show, however, that the theore
tical cusp in Tc for a multi-component pairing can be easily smeared out by the spatial inhomogeneity of strain, and the experimental data can be reproduced qualitatively by a percolation model. This shed new light on multi-component pairings. We then perform a thorough group-theoretical classification of the pairing functions, taking the spin-orbit coupling into account. We list all 13 types of two-component spin-singlet pairing functions, with 8 of them belonging to the Eg representation. In particular, we find two types of intra-orbital pairings in the Eg representation ($k_xk_z$, $k_yk_z$) are favorable in view of most existing experiments.
We study the properties of two electrons with Coulomb interactions in a tight-binding model of La-based cuprate superconductors. This tight-binding model is characterized by long-range hopping obtained previously by advanced quantum chemistry computa
tions. We show analytically and numerically that the Coulomb repulsion leads to a formation of compact pairs propagating through the whole system. The mechanism of pair formation is related to the emergence of an effective narrow energy band for Coulomb electron pairs with conserved total pair energy and momentum. The dependence of the pair formation probability on an effective filling factor is obtained with a maximum around a filling factor of 20 (or 80) percent. The comparison with the case of the nearest neighbor tight-binding model shows that the long-range hopping provides an increase of the phase space volume with high pair formation probability. We conjecture that the Coulomb electron pairs discussed here may play a role in high temperature superconductivity.
Spontaneous rotational-symmetry breaking in the superconducting state of doped $mathrm{Bi}_2mathrm{Se}_3$ has attracted significant attention as an indicator for topological superconductivity. In this paper, high-resolution calorimetry of the single-
crystal $mathrm{Sr}_{0.1}mathrm{Bi}_2mathrm{Se}_3$ provides unequivocal evidence of a two-fold rotational symmetry in the superconducting gap by a emph{bulk thermodynamic} probe, a fingerprint of nematic superconductivity. The extremely small specific heat anomaly resolved with our high-sensitivity technique is consistent with the materials low carrier concentration proving bulk superconductivity. The large basal-plane anisotropy of $H_{c2}$ is attributed to a nematic phase of a two-component topological gap structure $vec{eta} = (eta_{1}, eta_{2})$ and caused by a symmetry-breaking energy term $delta (|eta_{1}|^{2} - |eta_{2}|^{2}) T_{c}$. A quantitative analysis of our data excludes more conventional sources of this two-fold anisotropy and provides the first estimate for the symmetry-breaking strength $delta approx 0.1$, a value that points to an onset transition of the second order parameter component below 2K.
We investigate Co nanostructures on Bi$_{2}$Se$_{3}$ by means of scanning tunneling microscopy and spectroscopy [STM/STS], X-ray absorption spectroscopy [XAS], X-ray magnetic dichroism [XMCD] and calculations using the density functional theory [DFT]
. In the single adatom regime we find two different adsorption sites by STM. Our calculations reveal these to be the fcc and hcp hollow sites of the substrate. STS shows a pronounced peak for only one species of the Co adatoms indicating different electronic properties of both types. These are explained on the basis of our DFT calculations by different hybridizations with the substrate. Using XMCD we find a coverage dependent spin reorientation transition from easy-plane toward out-of-plane. We suggest clustering to be the predominant cause for this observation.
The transmission of Cooper pairs between two weakly coupled superconductors produces a superfluid current and a phase difference; the celebrated Josephson effect. Because of time-reversal and parity symmetries, there is no Josephson current without a
phase difference between two superconductors. Reciprocally, when those two symmetries are broken, an anomalous supercurrent can exist in the absence of phase bias or, equivalently, an anomalous phase shift $varphi_0$ can exist in the absence of a superfluid current. We report on the observation of an anomalous phase shift $varphi_0$ in hybrid Josephson junctions fabricated with the topological insulator Bi$_2$Se$_3$ submitted to an in-plane magnetic field. This anomalous phase shift $varphi_0$ is observed directly through measurements of the current-phase relationship in a Josephson interferometer. This result provides a direct measurement of the spin-orbit coupling strength and open new possibilities for phase-controlled Josephson devices made from materials with strong spin-orbit coupling.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
