The effect of proton irradiation in Ba(Fe0.93Co0.07)2As2 single crystals is reported. We analyze temperature dependence of current density and normalized flux relaxation rate in the framework of collective creep model. Glassy exponent and barrier height for flux creep are directly determined by Maley's method. Our model functions for barrier height and critical current density in the absence of flux creep are explained by the superposition of \deltaTc- and \deltal-pinning. We also approach true critical current density by means of generalized inversion scheme, and the obtained result is in reasonable agreement with our model function. Proton irradiation effect on temperature dependence of current density and normalized relaxation rate can be summarized as doubling of barrier height at the beginning of flux creep.
In this report, we comprehensively study the effect of H$^+$ irradiation on the critical current density, $J_c$, and vortex pinning in FeSe single crystal. It is found that the value of $J_c$ for FeSe is enhanced more than twice after 3-MeV H$^+$ irradiation. The scaling analyses of the vortex pinning force based on the Dew-Hughes model reveal that the H$^+$ irradiation successfully introduce point pinning centers into the crystal. We also find that the vortex creep rates are strongly suppressed after irradiation. Detailed analyses of the critical current dependent pinning energy based on the …
Thermodynamics of the vortex liquid in heavy ion-irradiated superconductors
结果表明，重离子辐照对各向异性超导体$_{2}$ O $_{3}$的结晶性质的影响，在超导涨落区也有很大的扩展.诱导的非晶柱状缺陷的存在下转移的比热最大值在正常到超导转变。这种效应类似于最近在立方K $_{x}$ Ba $_{1-x}$ BioO $_{3}$（$x \simeq 0.35$）中证实的效应。在这两种化合物中，涡旋钉扎表现为\em平衡\rm扭矩的尖锐角度依赖性。在YBa $_{2}$ Cu $_{3}$ O $_{7-δ}$中，缺陷的钉扎出现在比热最大值的温度$T_{C_{p}}^{max}$，远高于磁不可逆线$T_{irr}(H)$。在各向同性K $_{x}$ Ba $_{1-x}$ Bi O $_{3}$中，与钉扎相关的扭矩异常的开始跟踪比热异常和不可逆线的开始。在$_{2}$ $_{3}$ O $_{7-δ}$中，顺序参数的振幅波动（而不是涡旋线漂移）最终导致钉扎消失。在K $_{x}$ Ba $_{1-x}$ Bi O $_{3}$中，涡旋钉扎仅在超导向正常转变时消失。结果表明，在这两种化合物中，在“玻色玻璃”转变的钉扎能相对于超导态的总自由能增益是大的。这意味着，后一种过渡的机制应该重新考虑。
Small-angle neutron scattering on high quality single crystalline Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ reveals the transition from a low--field vortex solid phase with orientational order to a vortex polycrystal at high magnetic field. The vortex order-disorder transition is correlated with the second-peak feature in isothermal hysteresis loops, and is interpreted in terms of the generation of supplementary vortex solid dislocations. The sharp drop of the structure factor above the second peak field is explained by the dynamics of freezing of the vortex ensemble in the high field phase.
Vortex states in hole-doped iron-pnictide superconductors
基于自旋密度波（SDW）竞争和扩展的$s-$波超导的唯象模型，通过求解Bogoliubov-de Gennes方程，研究了Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$中的涡旋态.我们的结果为最佳掺杂的化合物没有诱导SDW是在定性协议与最近的扫描隧道显微镜实验。我们还认为，SDW对涡旋态的主要作用是降低了局域态密度中的能隙内峰的强度，并转移了能谱权重，在能隙外形成了附加峰.
In a superconducting topological insulator, superconducting vortex line may trap 1-dimensional topological band with Majorana zero modes (MZMs) localized at its ends. In this work, we study the effect of hexagonal warping to the vortex phase transition. We carry out both analytical calculations based on a semiclassical formula and numerical calculations based on full quantum mechanics of Bogliubov de Gennes equation. We find that the hexagonal warping term enlarges the topological region of the vortex line as the chemical potential changes, and leads to the MZMs even in the absence of topologi…
Using small-angle neutron scattering we have studied the vortex lattice in superconducting MgB$_2$ with the magnetic field applied along the $c$-axis, doped with either manganese or carbon to achieve a similar suppression of the critical temperature. For Mn-doping, the vortex lattice phase diagram remains qualitatively similar to that of pure MgB$_2$, undergoing a field-and temperature-driven $30^{\circ}$ rotation transition, indicating only a modest effect on the vortex-vortex interaction. In contrast, the vortex lattice rotation transition is completely suppressed in the C-doped case, likely…
Fascination with glassy states has persisted since Fisher introduced the vortex-glass as a new thermodynamic phase that is a true superconductor that lacks conventional long-range order. Though Fisher's original model considered point disorder, it was later predicted that columnar defects (CDs) could also induce glassiness -- specifically, a Bose-glass phase. In YBa$_2$Cu$_3$O$_{7-x}$ (YBCO), glassy states can cause distinct behavior in the temperature ($T$) dependent rate of thermally activated vortex motion ($S$). The vortex-glass state produces a plateau in $S(T)$ whereas a Bose-glass can t…
The carrier transport and the motion of a vortex system in the electron-doped high-temperature superconductors Nd2-xCexCuO4 in underdoped and optimally doped (x = 0135, 0.145, 0.15) regions, in the area of the evolution from antiferromagnetic to superconducting order were investigated. To study the anisotropy of the transport properties of highly layered NdCeCuO system we have synthesized Nd2-xCexCuO4/SrTiO3 epitaxial films of three types with different orientations of the c-axis and conductive CuO2 layers relative to the substrate. Such a set of samples allowed us to study the processes of bo…
The carrier transport and the motion of a vortex system in a mixed state of an electron-doped high-temperature superconductors Nd2-xCexCuO4 were investigated. To study the anisotropy of galvanomagnetic effects of highly layered NdCeCuO system we have synthesized Nd2-xCexCuO4/SrTiO3 epitaxial films with non-standart orientations of the c-axis and conductive CuO2 layers relative to the substrate. The variation ofe the angle of inclination of the magnetic field B, relative to the current J, reveals that the behavior of both the in-plane r_xx(B) and the out-plane r_xy(B) resistivities in the mixed…
We study the vortex bound states in three dimensional (3D) superconducting Dirac semimetals with time reversal symmetry. Assuming two Dirac points on the kz-axis and bulk s-wave superconductivity, with a quantum vortex line parallel to the z-direction, we find that the superconducting vortex line has a robust quasi-1D nodal phase. The nodal phase stems from the symmetry protected Dirac points in the normal state bands, and it can be characterized by a topological index (ν; n) at kz = 0 and kz = π, where νis the Z2 topological invariant for a 0D class-D system and n is the Z topological invaria…
The occurrence of the Berezinskii-Kosterlitz-Thouless (BKT) transition is investigated in heavily boron-doped nanocrystalline diamond films through a combination of current-voltage and resistance measurements. We observe a robust BKT transition in the nanocrystalline diamond films with smaller grain size along with transport features related to vortex pinning. The vortex core energy determined through analysis of the resistance temperature curves was found to be anti-correlated to the BKT transition temperatures. It is also observed that the higher BKT temperature is related to an increased vo…
Using Ginzburg-Landau approach we show that the strain of the nematic superconductor can generate a specific (nematic) vorticity. In the case of doped topological insulators that vorticity forms a spin vortex. We find two types of topologically different spin vortices that either enhance (type I) or suppress (type II) superconductivity far from the vortex core. We apply Bogoliubov-de Geunnes equations to study electronic states in the nematic superconductor with spin vortices. We find that in the case of the vortex of type I, zero-energy states are localized near the vortex core. These states …
Measurements on magnetization and relaxation have been carried out on an optimally doped Ba$_{0.59}$K$_{0.47}$BiO$_{3+δ}$ single crystal with $T_c$ = 31.3 K. Detailed analysis is undertaken on the data. Both the dynamical relaxation and conventional relaxation have been measured leading to the self-consistent determination of the magnetization relaxation rate. It is found that the data are well described by the collective pinning model leading to the glassy exponent of about $μ\approx$ 1.64 to 1.68 with the magnetic fields of 1 and 3 T. The analysis based on Maley's method combining with the c…
We report on the critical current density Jc and the vortex dynamics of pristine and 3 MeV proton irradiated (cumulative dose equal to 2x10^16 cm^-2) $β$-FeSe single crystals. We also analyze a remarkable dependence of the superconducting critical temperature Tc, Jc and the flux creep rate S on the sample mounting method. Free-standing crystals present Tc =8.4(1)K, which increases to 10.5(1)K when they are fixed to the sample holder by embedding them with GE-7031 varnish. On the other hand, the irradiation has a marginal effect on Tc. The pinning scenario can be ascribed to twin boundaries and…
Charge doping-induced quasiparticle scattering in iron-pnictide superconductors as probed by vortex pinning
铁磷属元素化物超导体的电荷掺杂导致磁通涡旋的集体钉扎，而等价掺杂则不会。此外，磁通钉扎在电荷掺杂的化合物是一贯的平均自由程波动所引入的掺杂剂原子，允许提取的弹性准粒子散射率。等价掺杂的BaFe $_{2}$（As $_{1-x}$ P $_{x}$）$_{2}$中不存在掺杂剂原子的散射与该材料中低温渗透深度的线性温度依赖性的观察结果一致。
Second magnetization peak (SMP) in hole-doped cuprates and iron pnictide superconductors has been widely explored. However, similar feature in the family of electron-doped cuprates is not common. Here, we report the vortex dynamics study in the single crystal of an electron-doped cuprate Pr$_{0.87}$LaCe$_{0.13}$CuO$_4$ superconductor using dc magnetization measurements. A SMP feature in the isothermal $M(H)$ was observed for $H$$\parallel$$ab$-planes. On the other hand, no such feature was observed for $H$$\parallel$$c$-axis in the crystal. Using magnetic relaxation data, a detailed analysis o…
Majorana modes at the ends of superconductor vortices in doped topological insulators
最近的实验已经在掺杂的拓扑绝缘体中观察到了体超导性。在这里，我们问是否涡马约拉纳零模式，以前预测发生时，超导性诱导的表面上的拓扑绝缘体，生存，即使在这些掺杂系统与金属正常状态。假设反转对称，我们发现，马约拉纳零模式确实出现，但只有低于临界掺杂。临界掺杂与涡线的拓扑相变相关，在那里它支持沿其长度的无间隙激发。临界点仅取决于涡旋线的取向和Berry相的性质，即金属正常态费米面的SU（2）Berry相。通过计算可用能带结构的该相位，我们确定了诸如$p$掺杂的Bi $_{2}$ Te $_{3}$的材料候选物在压力下支持涡旋端Majorana模式。令人惊讶的是，即使是从拓扑上平凡的能带结构衍生的超导体也可以支持马约拉纳模式，这为实现它们提供了一条有前途的途径。
Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors. Consequently, three different types of magnetic order are possible. Of theses, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of …
