We consider different effects that arise when time-reversal symmetry breaking superconductors are subjected to an external magnetic field, thus rendering the superconductor to be in the mixed state. We focus in particular on two time-reversal symmetry breaking order parameters which are believed to be realized in actual materials: $p+ıp'$-wave and $d+ıs$- or $d+ıd'$-wave. The first order parameter is relevant for Sr$_2$RuO$_4$, while the latter order parameters have been suggested to exist near surfaces in some of the high-$T_c$ cuprates. We investigate the interplay between surface states and vortex states in the presence of an external magnetic field and their influence on both the tunneling conductance and the local density of states. Our findings may be helpful to experimentally identify the symmetry of unconventional time-reversal symmetry breaking superconducting states.
Surface adatom conductance filtering in scanning tunneling spectroscopy of Co-doped BaFe2As2 iron pnictide superconductors
我们建立在从头算理论和实验相结合,在扫描隧道显微镜/光谱的A-122铁pnictide超导体的隧穿过程-在这种情况下BaFe $_{2-x}$ Co $_x$ As $_2$ -涉及一个强大的吸附原子过滤的微分电导从近EF Fe 3d状态,这反过来又源于最顶部的子表面Fe层的晶体。计算结果表明,表面Ba相关的隧穿途径的主导地位留下的指纹中发现的实验微分电导数据,包括大粒子空穴不对称性和能量依赖的对比度反转。
Charge density waves as the origin of dip-hump structures in differential tunneling conductance of cuprates: the case of $d$-wave superconductivity
计算了具有电荷密度波(CDW)的$d$波超导体与正常金属之间的非对称隧道结的电导-电压特性(CVC)。结果表明,它们在小电压$V$下具有V状形式,并且由于在其中一个$V$ -分支中存在CDW峰而在较大的$V$下是不对称的。电介质(CDW)序参量的空间散射将CDW峰涂抹成一个驼峰,并诱导出在这种结中观察到的典型CVC的峰-谷-驼峰结构(PDHS)。当温度高于超导临界温度时,PDHS演变为赝能隙凹陷。结果与Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8+δ}$和YBa $_{2}% $ Cu $_{3}$ O $_{7-δ}$的扫描隧道显微镜数据一致。
Tunneling conductance of normal metal / $d_{x^{2}-y^{2}}$-wave superconductor junctions in the presence of broken time reversal symmetry states near interfaces
We study the differential conductance of a time-reversal symmetric Weyl semimetal-superconductor (N-S) junction with an s-wave superconducting state. We find that there exists an extended regime where the zero-bias differential conductance acquires the universal value $e^{2}/h$ per unit channel, independent of the pairing and chemical potentials on each side of the junction, due to a perfect cancellation of Andreev and normal reflection contributions. This universal conductance can be attributed to the interplay of the unique spin/orbital-momentum locking and s-wave pairing that couples Weyl n…
Quasi-classical theory of tunneling spectroscopy in superconducting topological insulator
本文发展了超导拓扑绝缘体(STI)的隧穿谱理论,即载流子掺杂拓扑绝缘体的超导态。基于准经典近似,我们得到了表面Andreev束缚态(ABS)的能量色散的解析表达式和正常金属/STI结隧穿电导的简洁公式.所得到的隧穿电导的简洁公式使实验数据的分析变得容易。作为我们理论的应用,我们研究了Cu $_x$ Bi $_2$ Se $_3$的隧穿电导。我们揭示了我们的理论再现了Yamakage { \it et al} [Phys. Rev. B 85,180509(R)(2012)]的先前结果。我们进一步研究了在外加磁场中准粒子的能量由于多普勒效应而移动的磁隧道谱。通过旋转基面上的磁场,我们可以在磁隧穿谱中区分两种不同的拓扑超导态,即有和没有点节点。
A one-dimensional semiconductor nanowire proximitized by a nearby superconductor may become a topological superconductor hosting localized Majorana zero modes at the two wire ends in the presence of spin-orbit coupling and Zeeman spin splitting (arising from an external magnetic field). The hallmark of the presence of such Majorana zero modes is the appearance of a zero-temperature quantized zero-bias conductance peak in the tunneling spectroscopy of the Majorana nanowire. We theoretically study the temperature and the tunnel coupling dependence of the tunneling conductance in such nanowires t…
We study the differential conductance for charge tunneling into a semiconductor wire--superconductor hybrid structure, which is actively investigated as a possible scheme for realizing topological superconductivity and Majorana zero modes. The calculations are done based on a tight-binding model of the heterostructure using both a Blonder-Tinkham-Klapwijk approach and a Keldysh non-equilibrium Green's function method. The dependence of various tunneling conductance features on the coupling strength between the semiconductor and the superconductor, the tunnel barrier height, and temperature is …
Conductance measurements cannot distinguish crossed Andreev reflection from elastic co-tunneling in normal--superconductor--normal junctions
Osipyan Institute of Solid State Physics, Russian Academy of Sciences(俄罗斯科学院奥西皮扬固体物理研究所);Condensed-Matter Physics Laboratory, HSE University(国立高等经济学院凝聚态物理实验室);National Research University Higher School of Economics(国立高等经济大学)
Universal fractionalization of quantum transport characteristics in Majorana quantum dot devices is expected to emerge for well separated Majorana bound states. We show that the Majorana universality of the differential shot noise $\partial S^>/\partial V$ and conductance $\partial I/\partial V$ at low bias voltages $V$ arises only in ideal setups with only one Majorana mode entangled with the quantum dot. In realistic devices, where both Majorana modes are entangled with the quantum dot, $\partial S^>/\partial V$ and $\partial I/\partial V$ become very sensitive to tunneling phases and their …
We present a theory for the differential shot noise, $dS/dV$, as measured via shot-noise scanning tunneling spectroscopy, and the differential conductance, $dI/dV$, for tunneling into Majorana zero modes (MZMs) in the putative topological superconductor FeSe$_{0.45}$Te$_{0.55}$. We demonstrate that for tunneling into chiral Majorana edge modes near domain walls, as well as MZMs localized in vortex cores and at the end of defect lines, $dS/dV$ vanishes whenever $dI/dV$ reaches a quantized value proportional to the quantum of conductance. These results are independent of the particular orbital t…